Characterisation of polymers by thermal analysis by Caio Lopes

CHARACTERISATION OF POLYMERS BY THERMAL ANALYSIS

This Page Intentionally Left Blank

CHARACTERISATION OF POLYMERS BY THERMAL ANALYSIS

W.M. GROENEWOUD Eerste Hervendreef 32, 5232 JK 's Hertogenbosch The Netherlands

ELSEVIER Amsterdam. Boston 9London 9New Y o r k - O x f o r d 9Paris San Diego. San Francisco. Singapore- Sydney- Tokyo

E L S E V I E R S C I E N C E B.V. Sara Burgerhartstraat 25 P.O. Box 211, 1000 A E Amsterdam, The Netherlands 9 2001 Elsevier Science B.V. All rights reserved. This work is protected under copyright by Elsevier Science, and the following terms and conditions apply to its use: Photocopying Single photocopies of single chapters may be made for personal use as allowed by national copyright laws. Permission of the Publisher and payment of a fee is required for all other photocopying, including multiple or systematic copying, copying for advertising or promotional purposes, resale, and all forms of document delivery. Special rates are available for educational institutions that wish to make photocopies for non-profit educational classroom use. Permissions may be sought directly from Elsevier's Science & Technology Rights Department in Oxford, UK: phone: (+44) 1865 843830, fax: (+44) 1865 853333, e-mail: permissions@elsevier.com. You may also complete your request on-line via the Elsevier Science homepage (http:llwww.elsevier.com), by selecting 'Customer Support' and then 'Obtaining Permissions'. In the USA, users may clear permissions and make payments through the Copyright Clearance Center, Inc., 222 Rosewood Drive, Danvers, MA 01923, USA; phone: (+!) (978) 7508400, fax: (+1) (978) 7504744, and in the UK through the Copyright Licensing Agency Rapid Clearance Service (CLARCS), 90 Tottenham Court Road, London WIP 0LP, UK; phone: (+44) 207 631 5555; fax: (+44) 207 631 5500. Other countries may have a local repmgraphic rights agency for payments. Derivative Works Tables of contents may be reproduced for internal circulation, but permission of Elsevier Science is required for external resale or distribution of such material. Permission of the Publisher is required for all other derivative works, including compilations and translations. Electronic Storage or Usage Permission of the Publisher is required to store or use electronically any material contained in this work, including any chapter or part of a chapter. Except as outlined above, no part of this work may be reproduced, stored in a retrieval system or transmitted in any form or by any means, electronic, mechanical, photocopying, recording or otherwise, without prior written permission of the Publisher. Address permissions requests to: Elsevier's Science & Technology Rights Department, at the phone, fax and e-mail addresses noted above. Notice No responsibility is assumed by the Publisher for any injury and/or damage to persons or property as a matter of products liability, negligence or otherwise, or from any use or operation of any ~ , products, imtn~ons or ideas contained in the material herein. Because of rapid advances in the medical sciences,in particular,independent verificationof diagnoses and drug dosages should be made. First edition 2001 Second impression 2003 Library of Congress Cataloging in Publication Data A catalog record from the Library of Congress has been applied for.

ISBN:

0-444-50604-7

T r a n s f e r r e d to digital p r i n t i n g 2 0 0 5

To Vera for 36 years of love, support and continuous inspiration.

This Page Intentionally Left Blank

PREFACE The development of the Linear Variable Displacement Transducer (LVDT) was a first order technological break-through after centuries in optical length-difference measurments. The first LVDT's became commercially available in Holland in 1959. Our research team (I was a junior member) bought one LVDT for the development of a length dilatometer to measure the change in length of a polymer sample during a heating or cooling procedure. The LVDT signal and (sample temperature) thermocouple signal were recorded on an XY-recorder. Indeed, we were very proud of our first 'automated' measuring system. We did not yet call our system a Thermal Mechanical Analyser (TMA) nor described our activities as 'Thermal Analysis'. Nowadays, computer controlled dynamic and static TMA systems are supplied by several manufacturers and perform completely automated the measuring and data handling procedures required. This story illustrates the huge technological development during the last forty years. Thermal Analysis (TA) has become an indispensable family of analytical techniques in polymer research. This increased importance of these techniques can be seen as the result of three more or less parallel developments: a tempestuous development of TA measuring techniques in combination with a high degree of automation, - the strongly increased understanding of the underlying theory, published by authors like Wunderlich, Hohne, Richardson and Mathot [1,2] and - the increasing knowledge of the relation between the polymers' chemical structure and their physical properties. These developments still continue and a lot of work has yet to be done in the second and especially the third area. Increasing knowledge of the dependence of physical properties on chemical structure form the added value of accurate thermoanalytical measurements and this knowledge is very important for the development of new polymeric systems. -

The table below lists the various TA techniques following the notation of the ICTA (International Committee for Thermal Analysis) nomenclature committee. The three "classic" TA techniques are DSC, TGA and TMA of which DSC is still the "workhorse". TA is also covering, however, a substantial number of other techniques and applications and several of these techniques are described in this book. This book is not a comprehensive textbook about TA but more a survey of the author's work during many years, at the Koninklijke Shell Laboratorium in Amsterdam. It describes in six chapters the use of the various TA techniques (printed in bold in the table) for specific problems, illustrating the versatility of TA. A technical description is only given for equipment of own design.

Thermal Analysis techniques Differential Scanning Calorimetry - high pressure DSC - photo-DSC - modulated DSC Thermogravimetric Analysis Thermodilatometry length dilatometry volume dilatometry -

(DSC)

(TGA)

(TMA)

Dynamic Mechanical Analysis (DMA) (low frequency) DMA - u l t r a s o n i c (high frequency) analysis -

Thermo-electrometry dielectric analysis (DETA) volume resistivity analysis thermally stimulated discharge analysis -

Simultaneous Techniques - thermally stimulated discharge analysis/thermomechanical analysis (TSD/TMA) - thermogravimetric analysis/fourier transform infra red/mass spectroscopy (TGA/FTIR/MS) - thermogravimetric analysis/differential thermal analysis/ mass spectroscopy (TGA/DTA/MS) - thermomechanical analysis/dielectric analysis (TMA/DETA) Thermoluminosence Thermomagnet ome try Thermo-optometry Thermosonimetry Over the years, quantitative structure/property relationships have been developed by various workers in the polymer research field. Well known are for example the important contributions made by D.W. van Krevelen in 'Properties of polymers' [3] and by J. Bicerano in 'Prediction of Polymer Properties' [4]. An endeavour is made in chapter seven (and eight) to improve some of such correlations by using consistently measured, reproducible TA data. Chapter nine shows the contribution of TA to the characterisation effort necessary for the technical and commercial development of a new polymer system. Chapter ten finally, provides information about different polymers obtained during special case studies. This book illustrates in this way, applications of a wide variety of thermal analysis techniques. The author hopes that this monograph will be useful especially to those who are going to work in the thermal analysis area in the context of polymer research. Wire Groenewoud

ACKNOWLEDGMENTS The results described in this book could only be obtained by the expertise and the cooperation of many members of the different skillgroups at the Koninklijke Shell Laboratorium in Amsterdam (KSLA). The still unique possibilities of this laboratory are mentioned with pleasure. Without pretending to be complete, I have to mention a number of colleagues: For stimulating discussions and valuable insight provided by Roel Jongepier, Bram Ghijsels, Toni Cervenka, John Wintraecken and Piet Kooijmans. An important part of the experimental work was performed by: Arie van der Zwan, Nico Groesbeek, Ton Jakobs, Wouter de Jong, Bob Oudhaarlem, Leo Sman and Karin Orzessek. Bob van Wingerden read and discussed with me many of the internal reports which formed the basic data source of this book resulting in many, always improving, suggestions. Regretting any unintentional omissions I finally thank the management of KSLA for the permission to publish results of our polymer research.

This Page Intentionally Left Blank

CONTENTS Preface

Acknowledgments Chapter 1. Differential Scanning Calorimetry I. 1 Introduction I.I.I DSC calibration and stability 1.1.2 The Tg-value determination 1.1.2 Melting/recrystallisation determinations 1.2 Tg-values of car-tyre rubber systems 1.2.1 Introduction 1.2.2 The Tg-value of BR and SSBR rubbers 1.2.3 The Tg-value after blending and oil-extension of BR and SBR rubbers

10 Ii 14 17 17

1.3 Recrystallisation and fusion of polypropylene 1.3.1 Introduction 1.3.2 Additives acting as nucleating agents for PP 1.3.3 Annealing experiments with i-PP

26 26 28

1.4 Side-chain crystallisation in poly(1-olefine) s 1.4.1 Introduction 1.4.2 Crystallisation in poly(l-olefin)s

36 36

1.5 Chemical reactions monitored by DSC I. 5.1 Introduction 1.5.2 The determination of the cure conditions of a powder coating system 1..5.3 Reactions of model compounds studied by DSC 1.6 Determination of the heat of vaporisation by DSC 1.6.1 Introduction 1.6.2 DSC modification for the AHvap.25 determination 1.6.3 Results of AHvap.25 determinations by DSC Chapter 2. Thermogravimetrical 2.1 Introduction

Analysis

2.2 01igomers c o n t e n t and thermal stability of polypropylene 2.2.1 The non-isothermal thermal stability determination 2.2.2 The isothermal thermal stability determination 2.3 The TG analysis of a PP catalyst system 2.3.1 A 'plastic wrapped' TGA 2.3.2 TG analysis of a MgCl2-supported, TiCI4/DIBP catalyst

40 43 43 52 52 54 61

63 65 70 72

Chapter 3. Thermodilatometry 3.1 Length dilatometry (TMA) 3. i. 1 Introduction 3.1.2 The l.e.c, determination of filled polymers 3.1.3 Shrinkage of PK terpolymer and nylon 6.6 due to moisture loss 3.2 Volume 3.2.1 3.2.2 3.2.3 3.2.4

dilatometry Introduction The volume dilatometer The measuring procedure Isothermal crystallisation of IR rubbers

Chapter 4. Dynamic Mechanical Analysis 4.1 The standard DMA technique 4.1.1 Introduction 4.1.2 DMA analysis of PP/C2C3 rubber blends 4.1.3 Tg-value determination of aged, rigid PU foams by DMA 4.2 Mechanical measurements at ultra-sonic frequencies 4.2.1 Introduction 4.2.2 The ultra-sonic measuring equipment 4.2.3 Results of ultra-sonic measurements on car- tyre rubbers Chapter 5. Thermo-electrometry 5.1 The DC and AC properties of polymers 5.1.i Introduction 5.1.2 DC properties of polymers 5. i. 3 AC properties of polymers 5.1.4 The AC and DC measuring system 5.1.5 AC and DC properties of a cured resin system 5. i. 6 Time/temperature superposition of dielectric results 5.1.7 The dielectric constant of rigid PU foam 5.2 Effect of moisture on the electrical properties of polymers 5.2.1 Introduction 5.2.2 Influence of moisture on the dielectric properties of resin castings and laminates 5.2.3 Effect of seawater and cargo on the electrical properties of a tankcoating system 5.2.4 The determination of the Ki-value of PVC cable insulation 5.3 Conduction improvement of epoxy resins by carbon black addition 5.3.1 Electrostatic safety criteria 5.3.2 DC properties of experimental epoxy resin/ carbon black systems 5.3.3 DC properties of anti-static epoxy GFR pipes

77 77 81 85 85 89 91

94 99 105 109 112 114

123 124 128 132 134 140 145

151 153 158 163

171 172 177

5.4 Thermally Stimulated Discharge analysis 5.4.1 The TSD technique 5.4.2 Bucci's TSD theory 5.4.3 Results of TSD experiments

181 181 184

Chapter 6. Coupled thermal analysis techniques 6.1 Introduction

188

6.2 Simultaneous TSD/TMA measurements 6.2.1 The TSD/TMA system 6.2.2 TSD/TMA results

191 192

6.3 The TGA - coupled - FTIR/MS technique 6.3.1 Introduction 6.3.2 The TGA/FTIR and TGA/MS coupling 6.3.3 The heated capillaries tip temperatures 6.3.4 Single component calibration 6.3.5 Investigation of the thermal decomposition of Cobaltphthalocyanine by TGA - coupled FTIR/MS 6.3.6 Investigation of the released vapours during the cure of epoxy resin system by TGA coupled - FTIR/MS

222

Chapter 7. Chemical structure/physical correlations 7.1 Introduction

230

195 196 200 201 209

properties

7.2 The Tg-value estimation 7.2.1 Introduction 7.2.2 The 'modified cohesion energy' method 7.2.3 The Tg-value of crosslinked polymeric systems

232 233 245

7.3 The Tm-value estimation 7.3.1 Introduction 7.3.2 The reduced Tg/Tm correlations

253 254

7.4 The Hf-value estimation

264

7.5 The thermal stability estimation 7.5.1 Introduction 7.5.2 The semi-static Td, o-value determination 7.5.3 Thermal stability estimation based on Td, o-values

268 269 269

7.6 The moisture sensitivity estimation

274

7.7 Estimation of the key-properties

277

of a new polymer

Chapter 8. Tg-values of polymers with double bonds in the main chain and Tg-values of non-polar polymers with side chains 8.1 Introduction

282

8.2 Experimental BR systems 8.2.1 BR with a high 1,4 trans content 8.2.2 BR with a high syndiotactic 1,2 BR content

282 286

8.3 Experimental

288

IR systems

8.4 A Tg/structure correlation systems with side-chains

for non-polar polymer

293

Chapter 9. Characterisation of polyketone polymer systems by Thermal Analysis Techniques 9.1 Introduction 9.2 Investigation of the crystalline phase of PK co- and terpolymers 9.2.1 PK copolymer and PK terpolymer 9.2.2 The Tm(o)- and Hf(max.)-values of PK copolymer 9.2.3 Alpha- and beta-crystallinity in PK copolymer 9.2.4 Alpha- and beta-crystallinity in PK copolymer after a common processing procedure 9.2.5 Alpha- and beta-crystallinity in PK terpolymers

297

297 299 302 308 310

9.3 Investigation of the amorphous phase of PK terpolymer by DMA/DSC 9.3.1 Amorphous phase transition effects 312 9.3.2 Ageing and moisture absorption effects 312 9.3.3 Determination of the Tg-value of PK terpolymer by DSC 318 9.4 TMA measurements on PK terpolymer systems 9.4.1 The linear thermal expansion coefficient of long glassfibre reinforced PK terpolymers 9.4.2 The repeatability of the l.e.c, determination on PK terpolymer systems

322 325

9.5 Determination of electrical properties of PK terpolymers 9.5.1 The influence of moisture on the dielectric properties 9.5.2 The frequency dependency of the dielectric properties 9.5.3 The specific volume resistivity determination of PK terpolymer

334

9.6 Survey of PK terpolymer thermal analytical characterisation results

337

327 331

9 Chapter i0. Thermo-analytical case studies i0.i Introduction

339

10.2 The effect of the presence of a solvent during the cure of a thermoharding system

339

10.3 The thermal transitions of a liquid crystalline polymer

342

10.4 The optimal crystallisation temperature of diphenylolmethane

345

10.5 The dynamic stiffness of ultra-high molecular weight polypropylene in its melt

350

10.6 The effect of an anti-static additive on the electrical resistivity of a polystyrene foam

354

10.7 The dielectric constant of polyethylene foil

356

10.8 The volume resistivity of epoxy based moulding powder systems during immersion in hot water

359

10.9 The determination of the composition of a cartyre rubber

364

I0.I0 The thermal stability of ASB

366

I0.ii The thermo-analytical characterisation of a maize based, 'green' polymer

371

Index

377

DIFFERENTIAL S CANNING CALORIMETRY

CHAPTER 1

I0 CHAPTER i: D I F F E R E N T I A L SCANNING C A L O R I M E T R Y i. 1 Introduction

1 , 1 , 1 The D$C Differential scanning calorimetry is, according to the ICTA I n o m e n c l a t u r e committee, a technique in which the heat flux (power) to the sample is monitored against time or temperature while the temperature of the sample, in a specified atmosphere, is programmed. In practice, the difference in heat flux to a pan containing the sample and an empty pan is monitored. The instrument used is a differential scanning calorimeter or DSC. The DSC is commercially available as a p o w e r - c o m p e n s a t i n g DSC or as a heat-flux DSC. The p o w e r - c o m p e n s a t i n g DSC has two nearly identical (in terms of heat losses) measuring cells, one for the sample and one reference holder. Both cells are heated with separate heaters, their temperatures are measured with separate sensors. The temperature of both cells can be linearly varied as a function of time being controlled by an average-temperature control loop. A second-differential-control loop adjusts the power input as soon as a temperature difference starts to occur due to some exothermic or endothermic process in the sample. The differential power signal is recorded as a function of the actual sample temperature. One single heater is used in the heat-flux DSC to increase the temperature of both the sample cell and the reference cell. Small temperature differences occurring due to exothermic/ endothermic effects in the sample are recorded as a function of the programmed temperature. Both systems are extensively described in the literature, more recently by Wunderlich [i]. The DSC is used (after proper calibration, see 1.1.2) in polymer research for mainly three different types of experiments. a) glass-rubber transition temperature (Tg-value) determinations, see 1.1.3, b) m e l t i n g / r e c r y s t a l l i s a t i o n temperature and heat (Tm/Tcvalue and Hf/Hc-value) determinations, see 1.1.4, c) measurements on reacting systems (cure measurements). An example of m o n i t o r i n g chemical reactions by DSC is given in 1.5. Besides, the use of the DSC for a specific non-standard application is described in 1.6. 1.1.2 DSC calibration and stability The DSC measurements reported in this book are performed with the p o w e r - c o m p e n s a t i n g DSC-2 and DSC-7 systems from Perkin Elmer. The block surrounding the DSC sample holders is kept at -150~ â&#x20AC;˘ I~ with the aid of a controlled liquid nitrogen supply, both cells are purged with helium (60 ml/minute). The standard temperature calibration is performed at a heating rate of 20~ using the melting effects of cyclohexane ~ICTA,

International

Committee for Thermal Analysis

Ii (-87.06~ and 6.3~ indium (156.60~ and tin (231.88~ The computer controlled two point calibration p r o c e d u r e is performed using the cyclohexane -87.06~ value and the indium 156.60~ value. The heat of fusion of indium (Hf-value = 28.45 J/g) is introduced to p e r f o r m the energy calibration. A tin sample fusion measurement is, subsequently, p e r f o r m e d to check the possible deviation in the u p p e r part of the temperature region. This deviation proved always to be less than 0.5~ If the temperature region of interest is ranging from about 100~ up to 350~ the two-point calibration p r o c e d u r e is performed using indium and tin. The m e l t i n g effect of lead (327.4~ is used in that case as the high temperature check. The temperature and energy calibrations of the DSC-2 and DSC-7 are surprisingly stable as shown by a series of fusion measurements on the same indium sample placed in the F~_~_~DSC7 apparatus, see Table I.I. The average indium T(onset) value proved to be 156.6~ â&#x20AC;˘ 0.1~ whereas the average Hf-value proved to be 28.5 J/g â&#x20AC;˘ 0.3 J/g measured over a p e r i o d of about three month while the system was in use five days a week. Table i.I Results of a temperature calibration stability test of a Perkin Elmer DSC-7 ,, ~,J

time, days

,,~

deviation, ~

Hf-value, J/g

deviation

28.10

-0.35

28.63

+0.18

28.86

+0.41

156.59

156.54

156.75

+0.15

156.47

-0.13

28.40

156.47 156.53

-0.13 -0.07

28.40 28.40

a. b. c. d.

,j,,

T (onset), oc

-0.01

-0.06 .

:,,,,

, t,,

. . . .

I',I,

....

,', . . . .

......

-0.O5

-0.05 -O.O5

........ ~ , ,

.......

DSC cell base at -150~ Helium purge gas, 60 ml/minute, Indium sample 5.81 mg. Indium T(onset) and Hf-values m e a s u r e d at 20~ second heating scan values after a first heating/ cooling scan between 120oc and 160~

1.1.3 T u , v a l u e d e t e r m i n a t i o n The DSC is widely used to measure the g l a s s - r u b b e r t r a n s i t i o n temperature (Tg-value), which is an important p a r a m e t e r for polymer characterisation. The T g - v a l u e represents the temperature region at w h i c h the (amorphous phase) of a p o l y m e r is transformed from a brittle, glassy material into a tough rubberlike liquid. This effect is accompanied by a 'step-wise' increase of the DSC heat flow/temperature or specific heat/ temperature curve. Enthalpy relaxation effects can hamper the

12 ( ) = COOLING RATE, ~ THROUGH Tg AFTER PREHEATING AT 150~ [ ] = AGEING TIME, DAYS AGEING AT ROOM TEMPERATURE FOLLOWING QUICK COOLING (320~ FROM 150~

HEAT FLUX

OLAS'~'

(3ZO)

[03 I

(40)

(10)

1:23

. ~~s t

(2.5) I

u I! 1r ILl z I,,o K W ~

-~0

(0.62)

Figure 1.1 The Tg(onset)-value

50 TEMP[RATURE,

Figure 1.2 Effects of cooling rate and ageing time (heating rate 20~

gO ~

13 DSC Tg-value determination. A s t a n d a r d i s e d procedure is therefore necessary, to arrive at reproducible results. In general two types of DSC thermograms can be obtained for the glass transition of a rigid polymer. Figure I.I shows these two types for a linear epoxy resin. The u p p e r t h e r m o g r a m was obtained by scanning a sample of this resin at a rate of 20~ without pretreatment. The lower thermogram was obtained on the same sample, which was preheated at 150oc for one minute, then q u i c k l y cooled (320~ to room temperature before scanning it under the same conditions. In the lower curve the glass t r a n s i t i o n is visible as the expected 'step-wise' heat flow shift. In the upper curve, however, a strong endothermic effect is superimposed on the heat flow shift. The temperature at the intersection of the e x t r a p o l a t e d heat flow curve at the low temperature end and the tangent of the ascending curve at the inflection point is defined as Tg-value often indicated as DSC Tg(onset)-value. It is evident from Figure i.I the this Tg definition leads to different results for both thermograms. This is caused by the different thermal histories of the samples, which results in a d i f f e r e n c e in the extent of the so-called enthalpy relaxation effect [2]. Figure 1.2 illustrates, u s i n g the same sample, how the rate of cooling through Tg and storage at room temperature bring into evidence the presence of the e n t h a l p h y relaxation effect as a superposition on the heat flow curve shift. Figure 1.2 also shows the extent of the T g ( o n s e t ) - v a l u e differences due to the presence of these endothermic peaks. It will be clear that a standardised Tg-value d e t e r m i n a t i o n procedure is n e c e s s a r y to obtain reproducible resultsthe sample (I0 to 15 mg.) is p l a c e d in the DSC sample holder, - the sample is heated at a rate of 20~ through the possible present enthalphy r e l a x a t i o n maximum, the sample temperature is decreased, subsequently, at m a x i m u m cooling speed to a temperature of at least 50~ below the measured Tg effect, - the sample is heated a second time through its Tg region at a rate of 20~ and this second scan result is used to calculate the Tg(onset)-value, the sample weight is checked to see if any weight loss occurred due to the thermal treatment of the sample (for instance due to loss of moisture). -

The Tg-values reported in this book are m e a s u r e d a c c o r d i n g to this procedure. A series of T g ( o n s e t ) - v a l u e d e t e r m i n a t i o n s on rubber samples (i.e. 100% amorphous samples, p r o v i d i n g a good sample/sample holder contact) resulted in a T g ( o n s e t ) - v a l u e precision of â&#x20AC;˘ 0.5~ and a r e p e a t a b i l i t y of â&#x20AC;˘ l~ for this method. The reproducibility of this method was d e t e r m i n e d as â&#x20AC;˘ 4~ during a round robin test with seven samples, m e a s u r e d in twenty-three laboratories [5]. These values might increase,

14 however, for Tg-value determinations on semi-crystalline and crosslinked polymers. The sample/sample holder contact is less good for the more brittle semi-crystalline polymers while crosslinked polymers show a clearly smaller 'step-wise' heat flow increase effect compared with rubbery samples. The disadvantages of using the Tg(onset)-value as Tg-value are discussed by Richardson [2]. Determination of the Tg-value using the enthalpy/temperature curve results in a theoretically better defined Tg-value. Software to follow this procedure is commercially available at present. In the (european) industry, however, the Tg(onset)-value method is used almost exclusively because it is not only convenient, but also yields an indication for the maximum application temperature of a polymer. 1.1.4 Meltina/recrvstallisation temperature determinations Semi-crystalline polymers generally-melt over a wide temperature range. This behaviour is related to imperfections in the crystallites and non-uniformity in their size- the smaller and/or less perfectly formed crystallites will melt at lower temperatures. The endothermic fusion effect as measured by the DSC is in many cases indicated by the temperature of the maximum heat flow (the Tm-value) and by the total heat involved in the fusion process (the Hf-value). Often reported is also the Te-value i.e. the temperature at which the last crystallite has fused. Figure 1.3 illustrates the sensitivity of the measured Tmvalue for the sample weight. The maximum sample weights possible to measure a sample weight independent Tm-value are, of course, heating rate dependent. 20 ~ sample weight & 4 mg., i0 ~ sample weight & 6 mg., 5 ~ sample weight & 8 mg., (Perkin Elmer DSC-2/DSC-7, standard aluminum sample pans). The Tm-values reported in this book have been measured on 4 mg. samples at a heating rate of 20~ unless other conditions are mentioned. A fused sample is often subsequently cooled, to follow the recrystallisation from the melt. The resulting exothermic recrystallisation effect is usually described by the temperature of the minimum heat flow (the Tc-value) and by the total heat effect involved (Hc-value). Some advance knowledge is necessary, however, to arrive at reproducible data. Incompletely fused crystal residues remain present when the temperature of the fused sample has been too low. These residues cause the nucleation process to start at higher temperatures than would normally be the case, resulting in higher Tc-values. Samples of a commercial polypropylene (PP) grade were heated at a rate of 20~ up to a temperature Tmax. Subsequently, the samples were cooled and reheated again. The resulting melting/recrystallisation/melting values are listed

6.0

3.1 mg

5.5

5.2

4.2 mg

s. o fl

!11

4.5"~ 4.0-

5.5

I~ \ e . l

5.0

\'t 12.4 mg

4.5

o~ 3.5-

.,,.,,.

~ 3.o~

2.5-

4,0 ,

1 i

2.5

2.0

1.5

1.0

0.5 o.

o t~~--------r---------r-------T-------

200. 0

210. 0

Figure 1.3

220. 0

2~0. 0

240. 0

250. 0

260. 0

270. 0

Temperature (~

The influence of the sample size on the Tm-value of a linear polymeric system during heating in the DSC at a rate of 20~

0.0

16 in Table 1.2. These data show that heating up to at least 210~ is necessary to avoid the so-called self-seeding effect. Therefore, PP samples are heated up to 220~ as a standard procedure, before recrystallisation measurements are performed. Table 1.2 Melting/recrystallisation data of PP samples after heating the samples up to different temperatures ,,

',"l

i, heating Tml, Hfl, ~ J/g

2, cool ing Tc, Hc, ~ J/g

"l~ax.

3, heating Tm2, Hf2, ~ J/g

162.5

I00

230

108.6

i01

160.9

162.1

102

220

108.7

160.5

162.5

210

108.7

161.0

162.5

2OO

109.2

102

161.0

162.4

190

109.3

161.0

180

110.0

161.2

162.2

. . . .

........

,,,

a. 4 mg. powder samples b. heating/cooling rates 20~

A series of heating, cooling and heating scans is the general approach to get an impression of the melting/recrystallisation behaviour of a semi-crystalline polymer. The Tml/Hfl-values are influenced by the thermal history of the sample. The Tc/Hc-values are characteristic for the recrystallisation of the polymer under standard (thermal) conditions. Finally, the Tm2/Hf2-values can be used to compare different samples recrystallised under identical conditions. The Tml/Hfl values listed in Table 1.2 are giving an impression of the repeatability of these measurements: Tml-value, 162.4~ • 0.2oc Hfl-value, 97 J/g • 5 J/g The base-line drawing procedure is the main reason for the relative low repeatability of the Hf-value determination. The self-seeding effect, clearly influencing the Tc-value, makes calculation of an average Tc-value meaningless. The Hc-, Tm2and Hf2-values are hardly influenced, thusHc -value, 99 J/g • 2 J/g Tm2-value, 160.9~ • 0.2~ Hf2-value, 95 J/g • 3 J/g The slightly improved repeatability of the Hc- and Hf2-values in comparison with that of the Hfl-value might be caused by the improved thermal contact between sample and sample holder after the fusion process. Nakamura [5] reports a reproducibility of • 3~ for the Tm/Tc determination. The difference between the repeatability and the reproducibility values of the Tm/Tc determinations is thus considerably higher than those found for the Tg(onset)-value determination.

17 1.2 Tg-values of car-tyre rubber systems 1.2.1 Introduction The Tg-value is an important p r o p e r t y for tyre tread rubbers [6]. It determines to a large extent the a b r a s i o n resistance, the road holding behaviour on wet roads (wet grip), the rolling resistance and the low t e m p e r a t u r e performance. A rubber with a relative high Tg-value (about -40~ generally results in a high wet grip but also in a reduced abrasion resistance and winter performance. Moreover, the rolling resistance is high! A rubber with a relative low Tg-value (about -90"C) is giving a high a b r a s i o n resistance, a good winter performance and a low rolling r e s i s t a n c e but a reduced wet grip. Hence, the tyre tread rubber used is often a b l e n d of different rubbers (and sometimes oil) to obtain a compromise between the properties m e n t i o n e d and, of course, the cost of the tyre. The synthetic rubbers most frequently used for car tyres are emulsion and solution s t y r e e n / b u t a d i e n e r a n d o m copolymers (ESBR and SSBR) and butadiene rubber (BR). Truck tyres, however, often contain a certain amount of natural rubber (NR) or its synthetic version isoprene rubber (IR). The Tg-value of BR rubber as such can vary, d e p e n d i n g on its chemical structure between -100~ and -20~ the T g - v a l u e of SBR can, in principle, vary between -100~ and 100~ 1.2.2 The Ta-value of BR and SSBR rubbers B u t y l l i t h i u m - i n i t i a t e d h o m o p o l y m e r i s a t i o n of butadiene results in a BR polymer containing random d i s t r i b u t e d cis-l,4, trans1,4 and 1,2-BR or vinyl-BR units. The c o n c e n t r a t i o n of the catalyst m o d i f i e r and the p o l y m e r i s a t i o n temperature (between 40~ and 75~ determine the c o n c e n t r a t i o n s of the three different components. Thus, BR rubber is in fact nearly always a terpolymer and its Tg-value can be d e s c r i b e d by means of the G o r d o n - T a y l o r relation [7]. This relation is w r i t t e n in its general form as: Wi.Ai. (Tg - Tg, i) - 0 where: Wi Ai Tg Tg, i

= = =

(1.1)

the weight fraction of m o n o m e r i, a constant c h a r a c t e r i s t i c for m o n o m e r i, the Tg-value of the co- or terpolymer, the Tg-value of the h o m o p o l y m e r of m o n o m e r i; by convention Tg, i+l > Tg, i.

Constant Ai represents the difference in the specific thermal expansivities, AEi, above and b e l o w the Tg of the h o m o p o l y m e r of monomer i. This equation can be w r i t t e n for BR in the following form which is explicit for TgTg(BR)

= Wc.Tg.c + W~.Ki,Tg.t + W v , K 2 . T g , v Wc + Wt.KI + Wv.K2

(1.2)

where-

Tg(BR) Wc,t,v Tg,c,t,v Kn

= the T g - v a l u e (Kelvin) of BR t e r p o l y m e r , - the w e i g h t f r a c t i o n of cis-l,4, t r a n s - l , 4 and v i n y l BR (I,2-BR), - the T g - v a l u e (Kelvin) of the 100% cis-BR, trans-BR and vinyl-BR homopolymers, = AK(n+I)/A~I.

T h e e x p e r i m e n t a l v a l u e s a v a i l a b l e for the c o n s t a n t Kn, in general, do not a g r e e w i t h t h o s e p r e d i c t e d b y the c o n s i d e r a t i o n s of G o r d o n a n d Taylor. W o o d [7] s u g g e s t e d , t h e r e f o r e , to c o n s i d e r Kn as a c h a r a c t e r i s t i c p a r a m e t e r for the p a r t i c u l a r c o p o l y m e r i c system, not n e c e s s a r i l y r e l a t e d to the A ~ v a l u e s of the h o m o p o l y m e r s . G h y s e l s et al. [8] u s e d ten l i t h i u m c a t a l y s e d BR s a m p l e s w i d e l y d i f f e r i n g c o m p o s i t i o n s , to c a l c u l a t e the (DSC) h o m o p o l y m e r T g - v a l u e s a n d the c o n s t a n t s K1 and K2Tg, c = 164 K Tg, t = 179 K T g , v -- 257 K Introducing

(-I09~ (- 94~ (- 16~ these

K1 = 0.75 K2 = 0.50

values

in e q u a t i o n

Tg(BR)

= 164.Wc + 134,W~ + 129,Wy wc + 0 . 7 5 w t + 0 . 5 0 w v

where-

+ Wt

with

1.2

is giving" (1.3)

+ Wv = 1.0

The d i f f e r e n c e b e t w e e n the m e a s u r e d and c a l c u l a t e d T g - v a l u e s of the ten BR s a m p l e s p r o v e d to be <_ 0.5~ This d i f f e r e n c e i n c r e a s e d to m a x i m a l l y 2~ b y i n c l u d i n g the T g - v a l u e s of five c o m m e r c i a l (Co-, Ni- a n d T i - c a t a l y s t based) BR s y s t e m s . To c a l c u l a t e to: Tg(SSBR) where:

the T g - v a l u e

= 164.Wc WC

of SSBR,

+ 134.Wt + 0.75Wt

+ 129.Wv + 0.50Wv

equation

1.2 was

extended

+ K3.Ws.Tu.s + K3.Ws

(1.4)

Tg, s = the T g - v a l u e of p o l y s t y r e n e i.e. 378 K, Ws = the w e i g h t f r a c t i o n of s t y r e n e m o n o m e r .

The T g - v a l u e s of six S S B R s a m p l e s m e a s u r e d w e r e u s e d to c a l c u l a t e an a v e r a g e v a l u e for K3. The o b t a i n e d v a l u e of 0.6 was s u b s e q u e n t l y s u b s t i t u t e d into e q u a t i o n 1.4 r e s u l t i n g intoTg(SSBR) where-

= 164.Wc Wc + Wt

+ 134.Wt + 0.75Wt

+ Wv + Ws

+ 129,Wv + 0.50Wv

+ 227.W~ + 0.60Ws

(1.5)

- 1.0

T h e m e a s u r e d a n d the c a l c u l a t e d T g - v a l u e s are l i s t e d in T a b l e 1.3. The a v e r a g e v a l u e of T g ( e x p e r i m e n t a l ) - T g ( c a l c u l a t e d ) is -2~ + 4~

19 Table 1.3 Composition and Tg-values of SSBR samples sample composition cis trans vinyl styrene

sample code

Tg(c)

Tg(e)

Tg(e) Tg(c)

196.0

-4.0

193

196.5

-3.5

0.240

242

240.1

+1.9

0.147 0.272 0.377

0.204

229

234.9

-5.9

B 4193

0.099 0.112 0.534

0.255

266

262.0

+4.0

SSBRI

0.297 0.465 0.085 0.135 0.270 0.405 0.970 0.020 0.010

0.153 0.190 0.000

197 232 163

202.0 235.0 164.7

-5.0

B 473

0.364 0.427 0.073

0.136

192

B 476

0.341 0.450 0.073

0.136

B 475

0.183 0.202 0.375

EI66AC

SSBR2 BRI ,

a. b. c. d.

....

,,,

-3.0 -1.7 ,

IR composition data, B473 to B4193 experimental systems, SSBRI and SSBR2 are commercial SSBR grades, BRI is a commercial BR rubber grade.

Equation 1.5 permits us to give an impression of the Tg-value of SSBR, as a function of the vinyl/styrene content, assuming Wt = 2Wc, see Figure 1.4. The vinyl content is usually expressed as the fraction of the BR part whereas the styrene content is expressed as the percentage on the total (SSBR) polymer. This notation is also used in Figure 1.4. 1.2.3 Th~ Tg-value after blending and o i l - ~ t e n t i o n of BR and SBR rubbers The vulcanisate properties of SSBR car tyre rubbers are often adjusted by blending with other rubbers e.g. natural rubber, BR rubbers or high styrene ESBR rubber. Usually, these rubbers are not compatible [9]. Figure 1.5 shows, for example, the DSC thermograms of SSBR/BR (75/25) samples mechanically blended in an internal mixer at 50~ and solution (cyclo-hexane) blended. The Tg-value of the BR phase (-II0~ is unaffected; however, the glass-rubber transition of the SSBR phase is influenced on the low temperature side. The two transition effects clearly present are an indication for the non-compatibility of these two polymers. Blends of low (8.5 %wt) vinyl SSBR and high vinyl (40.5 %wt) SSBR, in spite of their relatively large difference in vinyl content, almost fully miscible at room temperature. This is indicated by the occurrence of only one glass-rubber transition temperature effect for both the mechanical and the solution blended systems, see Figure 1.6. Only the temperature shift of the Tg-value and the increased transition width (30/40oC in comparison with about 20~ for both pure polymers) are an indication that this system is a blend of two polymers. The slightly different curves might reflect the different blending techniques used. Figure 1.7 shows the DSC Tg-values

Figure 1.4 Tg/1.2 BR-styrene relation 20

(78)

.......

(SSBR rubber)

~/~(88) /-+ (50)

C) - 1 0 40)

d~ r -20 -1:3 6 -30

I -40 I/)

c -50

I- - 6 0 (B)

0 u) - 7 0 d:] -80

(

-90 -100

) ~ wt. =f, y r e n e (on total polymer) (N o f t h e t o t a l . BR p a r '

I )

!~ , 0.00

0.20

0.40

0.60

1.2 BR

fraction

0.80

1.00

21 O. '=JO

-0. 3o

O. 2S O)

internal mixer (50~ ~--~.~epared sample

/"/ / "

0.20

3= 0

~ ,/~~~/~

0.15

-0, 25

-0. 20

cyclohexane solution

0.9 IS

0. I0

-0. tO

O. OS

-0.05

O. O 0

-120. 0

--[ tO. 0

" -tO0.0

.......

"gO. 0

-BO. 0

i ' " -70. 0

I -60.0

O. O0

I -SO.O

-40.0

Figure 1.5 Temperature (~ Tg effects of SSBN/BR (75/25) blends

0.24

sample prepared from a_

O. 22 O. 20

,00 0 . | 4 LL

"0. I8

.,// / /

~ " O. 16

intemal mixer (50~ " ~" "0. 16 prepared sample -0. ia

"~ 0.12 O)

-0. IZ

o. lo

"0. 22 -0.

O) O. 18

-0.2a

"0. I0

-0. 08

O. 06

-0.06

O. Oa

-0. O,t

0.02 -

"0. 02

O. O 0

-90.0

--3~. 3

-70.0

......

-50.0

' I ~'

-~0. 0

. . . . . .

--~'0.0

-30.0

"0. O0

Figure 1.6 Temperature (~ Tg effects of low vinyl content SSBR / high vinyl content SSBR (75125) blends

22 of two solution blended low vinyl content SSBR/high vinyl content samples plotted as a function of the high vinyl content SSBR weight fraction. This figure also demonstrates that the Tg-values of these blends can be calculated with the aid of the G o r d o n - T a y l o r relationTg(blend) where:

= Wl~Tgl + W2.KI.Tg2 Wl + K1 . W 2

Tgl Tg2 WI,W2 K1

= = =

(1.6)

the Tg-value low vinyl content SSBR (197 K), the Tg-value high vinyl content SSBR (232 K), weight fraction of both SSBR samples, system constant.

Introducing the measured Tg-values of 200.5 K for the low vinyl content SSBR/high vinyl content SSBR 75/25 (solution) b l e n d and 217.5 K for the 25/75 (solution) blend of the same p o l y m e r s resulted in an average K1 value of 0.41. Using this value for KI, equation 1.6 can be written as: Tg(low/high where"

vinyl

SSBR blend,

= 1 9 7 . W I + 95.W2 W1 + 0.41W2

(1.7)

W1 = weight fraction low vinyl content SSBR, W2 = weight fraction high vinyl content SSBR, W1 + W2 - 1.0

The good agreement in figure 1.7 between the calculated Tgvalues and measured Tg-values (within 1.5"C), indicates the u s e f u l n e s s of equation 1.7. Oil is also often a component of the car tyre rubber compound. It is blended with the pure rubber forming the so-called oile x t e n d e d rubber phase. Usually an aromatic oil is used; such an oil showed a Tg(onset)-value at 232K (-41~ But also naphtenic oil with a T g ( o n s e t ) - v a l u e of 208 K (-65~ is used. A few experimental data were available based on SSBR (Tg-value = 197 K, three systems) and on ESBR (Tg-value = 215 K, two systems) both extended with an aromatic oil. The Tg-value of the rubber phase is in both cases lower than that of the oil phase i.e. the SSBR/ESBR rubber phases are for Tg-rubber < temperatures < Tg-oil, 'filled' with glassy oil 'particles', r e s u l t i n g in an increased Tg-value of the rubber after the oil addition. The experimental values could be fitted again satisfactorily using the G o r d o n - T a y l o r relationsTg-value

(SSBR/aromatic

oil,

= 197.W1 + 123.W2 W1 + 0.53W2

(~.8)

Tg-value

(ESBR/aromatic

oil,

= 215,WI + 91.W2 W1 + 0 . 3 9 W 2

(1.9)

Figure 1.7 Tg value of high and low vinyl content SSBR blends (solution blended SSBR systems) A measured

+ calculated

-40 -45 -50

= -55 r

I:1::

m -60

Or~ @

e, - 6 5

I--

-70 -75 -80

0.0 0.1

,,,I

......

,,,

0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 high vinyl content SSBR weight fraction

1.O

24 where-

W1 = w e i g h t fraction SSBR or ESBR rubber, W2 = weight fraction of a r o m a t i c oil. W1 + W2 = 1.0

One e x p e r i m e n t a l value was a v a i l a b l e for a SSBR sample (Tgvalue = 232 K) e x t e n d e d with a n a p h t e n i c (Tg-value = 208 K). The T g - v a l u e of the rubber phase is now h i g h e r than that of the oil phase i.e. the oil will act as a p l a s t i c i s e r in the t e m p e r a t u r e region b e t w e e n Tg-oil and T g - r u b b e r and the Tgv a l u e of the r u b b e r is ~ e c r e a s e ~ after the oil addition. A s s u m i n g that also in this case the e x p e r i m e n t a l v a l u e s are d e s c r i b e d by the G o r d o n - T a y l o r relation, the e q u a t i o n might hold: Tg-value where-

(SSBR/naphtenic

oil,

= 208.WI + 362.W2 W1 + 1.56W2

W1 w e i g h t fraction n a p h t e n i c W2 w e i g h t fraction SSBR. W1 + W2 = 1.0

(1.10)

oil,

Figure 1.8 shows that the agreement b e t w e e n the e x p e r i m e n t a l data a n d the c a l c u l a t e d values is satisfactory.

Tg-value of oil-extended SSBR and E S B R s y s t e m s &

mess. ~ / ~ $

-40

;BR

aromatic oil

--45 C3 ,: - 5 0 @ D -a r -a

-55

~9 - 6 0

ESBR

X r

o....

o -65

naphtenic

oil

. . . . .

I -70

F-

-75 -80

SSBR _ _J_

0.0 0.1

Figure 1.8

0.2 0 . 3 Oil,

I,,

0.4

0,5

weight

! ..............

0.6

0.7

fraction

0.8 0.9

1.0

26 1.3 R e c r y s t a l l i s a t i o n and fusion of p o l y p r o p y l e n e 1.3.1 IntroductiQn Three different p o l y p r o p y l e n e (PP) m o d i f i c a t i o n s can be distinguished- the atactic, the syndiotactic and the isotactic modification. The atactic m o d i f i c a t i o n is an amorphous polymer with a Tg(onset)-value of -21~ The syndiotactic modification, made with a stereospecific homogeneous metallocene catalyst, is a s e m i - c r y s t a l l i n e polymer (crystallinity about 25 %wt.) with a Tm-value of about 133~ [I0]. The isotactic modification, made with a stereospecific heterogeneous Ziegler Natta catalyst is also a semicrystalline polymer (crystallinity about 50 %wt.) with a Tmvalue of about 160~ and contains nearly always 2 %wt. - 5 %wt. of atactic material. At present, isotactic p o l y p r o p y l e n e (i-PP) is commercially by far the most important system of the three m o d i f i c a t i o n s mentioned above. During crystallisation from the melt, i-PP is u s u a l l y in the u form, which has a monoclinic crystal lattice with a Tm-value of about 160~ The occurrence of a ~ form (with a hexagonal lattice and a Tm-value of about 152~ is also possible during c r y s t a l l i s a t i o n under stress. Besides, a third (gamma) form with a triclinic crystal lattice is possible under exceptional circumstances [II]. 1.3.2 Additives acting as nucleating agents for PP The recrystallisation from the melt of standard, commercial iPP grades, is characterised by a Tc-value (see 1.1.4) of about II0~ i.e. about 50~ u n d e r c o o l i n g is necessary for spontaneous recrystallisation. Such an amount of undercooling causes relative long duty cycles during injection moulding processing. N u c l e a t i n g additives are, therefore, often used in the industrial practice to decrease the injection moulding cycle times or to improve optical/mechanical properties by reducing spherulite sizes. The most efficient n u c l e a t i n g additives for PP, like 4-Biphenyl carboxylic acid and 2Naphtoic acid are able to increase the Tc-value from about ll0~ to about 130~ [12]. Talc is often used as nucleating agent but also carbon black or glass fibres, added for other reasons, can act as nucleating agents. This is shown by the results of a series of Tc-values m e a s u r e d on PP samples with talc, carbon black and talc + carbon black, listed in Table 1.4. The same Tc-values are plotted as a function of the total additive content in Figure 1.9. These data indicate that the Tc increasing effect of both additives seems to be the same i.e. their contributions can be added up. The Tc-value of 125~ seems to be the maximum value reached due to the addition of about 1 %wt. of talc, carbon black or a combination of these two additives. The obtained effect nearly disappears however, if a considerable higher amount (i0 %wt.) of talc is added. The increase in Tc-value of 15~ is accompanied by a Tm2-value

Figure 1.9 PP Tc-value/additive content relation (additives: talc/carbon black)

128 126 ,,, A

124 122

Tm2-value/Tc-value additives: talc/carbon black

166

120

~1~

165 154

I 118

~i~

F-

&116

163

161

I--160 n n 159

el.

ororo ~

114

15e 157

112

156

9, - . . . . . . . 112 11(~ 120 124

t08

12"

Tc-value, ~

110 108 !

0.2

0.4

0.6

0.8

1.0

Additive

content,

1.2

J ....

%wt.

1.6

1,8

28 increase of 6~ i.e. the amount of u n d e r c o o l i n g necessary for recrystallisation decreases from 48~ to 39~ Table 1.4 ~,

,', ,

talc

o.o5

0.19

, I

0.00

l ,

0.00

.....

0.00

......

0.00

0.05

0.19 ,

0.47

, ,,

content, i % wt.

o.oo

additive

. . . . . .

0.53 .

total

% wt.

0.00 .

PP.

content,

0.00

black

% wt.

,,,

i carbon

content,

Effect of talc and carbon black addition on the Tc-

value

. . . . .

1.37

0.85

J/~

I .

ii0 ,,

118

,=,

158

9.57

a commercial

PP g r a d e ,

c. d.

carbon black the talc and

a d d e d v i a a 4 0 %wt. m a s t e r b a t c h , carbon black concentrations measured

1.02 .

i0.59 .

. .

163

: .

163

114

~25 .

95 L,

, .

162 161

0.76

9.5

i,,

125

~.6~

161

124.

0.00

value, .

120

Tm2-

value,

118

,,,,,,

Hc-

0..,38,'

.....

0.97

0.59,.

0.53

value, ~

0.47

Tc-

. ,

~64

160

....

b. talc added via a I0 %wt. masterbatch, analysis on the 4 mg. DSC samples.

TGA

The equilibrium m e l t i n g temperature for the ~ form of i-PP is still uncertain; values in the range between 185.2~ and 208.2~ are reported [13]. Whichever of these two extreme values might be the right one, the rather big difference between the melting temperature and the crystallisation temperature means that the crystalline phase of PP is very sensitive for its thermal history i.e. for annealing processes. 1.3.3 Annealinu experiments with i-PP. A series of annealing experiments was performed using an experimental, PP powder sample. This high isotactic content (96 â&#x20AC;˘ 1 % w t . isotactic triads) i-PP had a m o l e c u l a r weight (Mw-value) of about 300.000 and a Mw/Mn value of 5.0, it was coded HH-SB-35. The DSC samples (4 mg.) were heated up to the annealing temperature T(a) and stored there during a certain time t(a). Subsequently, the samples were cooled down to 20~ and

29 reheated up to 220~ minute.

The h e a t i n g / c o o l i n g

rate was 20~

Fillon et al. [14] showed already that the upper side of the endothermic fusion m a x i m u m forms the temperature region in which PP is most sensitive for annealing. A few scouting experiments resulted indeed in a strong Tm- and Hf-value increase for T(a) = 163~ A series of experiments with t(a) values b e t w e e n 5 and 60 minutes at T(a) = 163~ learnt that a t (a) value of at least 30 minutes is necessary to reach an e q u i l i b r i u m situation, see Figure i.i0. The curves in this figure clearly illustrate that this time is necessary to convert the less perfect crystalline fraction o r i g i n a l l y present (standard Tm-value about 162~ into a more perfect state as shown by the increase of the Tm-value from 162~ to about 175~ Subsequently, a series of experiments was p e r f o r m e d with T(a) values ranging from 146~ up to 167~ while t(a) was kept constant at 30 minutes. The Tm-value of this PP sample p r o v e d to increase from 161~ to 176~ due to annealing b e t w e e n 146~ and 163~ see Table 1.5. The shape of the fusion curve starts to change considerably for annealing temperatures > 163~ see Figure I.Ii. The perfection of the whole crystalline fraction improves due to annealing at temperatures up to 163~ At T(a) values of 164~ or higher a lesser part of the crystalline fraction can improve still further. This 'high Tm-value fraction' disappeared at a T(a) of 167~ While this 'high Tmvalue fraction disappeared, the crystal fraction with the 'standard' Tm-value of about 162~ increased again, see Figure 1.12. In v i e w of the results shown in Table 1.5 and Figure I.ii, four d i f f e r e n t annealing regions can be d i s t i n g u i s h e d in the 'standard' fusion curve of this i-PP sample r e p r e s e n t e d in Figure i. 13 :

Annealing region I, T(a)

< 150oC The fusion curve becomes asymmetrical on the low temperature side; slightly higher Tm- and Hf-values.

Annealing region II, 150"C _< T(a) _< 163oC

The fusion curve is more or less symmetrical, the Tm-values increase with T(a) and the Hf-values are going through a maximum. Annealing region III, 163"C < T(a) < 167oC Fusion curve with two maxima, the Tin-value reaches its maximum value (179.5~ the Hf-value becomes zero, this is a c c o m p a n i e d byan increase of the Hf'-value up to 100 J/g, while Tm' constant (about 164oc), see Figure 1.12. A n n e a l i n g region IV, T (a} > 167 "C More or less symmetrical fusion curve, Tm'- and Hf'-values decrease to the 'standard' values with increasing T(a) values.

7.0-'

6.5-

Rnnealed at, 163~ during"

6.0-

-'~

5.5Re~eerence

5.0~

HH-SB-35

po~der' mample (end samp] e)

4.5-

15 mln.

4.0o ~

3.5-

3.0-

5 mtn.

2.5-

2.0-

t.51.0-

" 130.0

0.5-

140.0

t50.0

160.0

Temperature

170.0

t80.0

t90.0

Figure 1.10 DSC fusion endotherms of reference sample HH-SB-35 measured after annealing at 163~ using different annealing times

.06.5-

5.05,5-

...~ 5 . 0 o'J

Re~e Pence p o w d e r s amp I e HH-SB-35 ( e n d 8amp 1e )

~.. 4 . 5 I,I, ~ ~)

"I"

4.0-

/ /

30 m! nul;es anneal ed at. z 163"C

164 *C

3 5 -9

3,0-

2.5

2o-1

_~~ -~ -

t.5

IG5~

~~~J j

Im~mll~P

1.0 0.5 - ~ t30.0

[

i40.0

i50.0

i60.0

Temperature (~

t70.0

180.0

Figure 1.11 DSC fusion endotherms of reference sample HH-SB-35 measured after 30 minutes annealing at different temperatures

[90.0

32 T h e s e results were s u c c e s s f u l l y a p p l i e d to e s t i m a t e the m a x i m u m t e m p e r a t u r e s 'seen' by the product at d i f f e r e n t l o c a t i o n s in a PP r e a c t o r s y s t e m d u r i n g a series of reactor trials.

Table

1.5 R e s u l t s samples

of a n n e a l i n g e x p e r i m e n t s 30 m i n u t e s at T(a)

on i-PP,

Tm value, oc

Hf' value, J/g

T(a) value, oc

Tc value, oc

Hf value, J/g

Tm' value, ~

146

161.0

150

163.4

152

165.1

156

168.7

159

172.0

161

174.4

109

162

175.8

Ii0

163

175.8

107

164

141.4

178.3

161.3

164.5

140.8

178.7

163.5

165

140.9

179.2

164.2

166

138.9

179.2

164.2

138.3

179.5

164.6

163.6

i00

.,,

166.5 167

135.8 ,

,,,

,.!

0, I

L I L

, i

* s t a n d a r d p r o c e d u r e i.e. h e a t i n g to 220~ followed c o o l i n g to 20~ and r e h e a t i n g at a rate of 2 0 ~ r e s u l t e d inTc-value = I13~ T m ' - v a l u e = 159~ H f ' - v a l u e = 85 J/g.

--4

0"I 0

._~

-~ 0 -1~

PO 0

O~ i~

~ 0

O~ -I~

@ 0

CD 0

"q 0

0 0

Hf-value, J/g

Tm-value, ~ "q PO

Po 0

"q .1~

~ 0

"q ~

O~ 0

".q ~

Oo 0

CD 0

0 -.g -g

- 9, . . ~

I= L,,

AE'ro

.L. r

241 22

2.0 -I 1.8

PP a n n e a ! ! n g d u r i n g 3(] mlnut, e8 a t Ta ( d e g .

region region region region

t58 C t63 C 187 C t67

t. 2. 3. 4.

Ta < tS;] C .< Ta .< 163 C < Ta < Ta I

~i.6 v

o J.4 u. =i i . E (D -Ii.O 0.8 0.6 0.4

0.~ 1

..~,o, ,..__,o,,~, o~ ~._~

~' _t'- ~176 r 9

0.0 too. o

t20. o

t4o. o

t6o. o

Figure 1.13 Temperature (~ The "standard" melting endotherm of reference sample HH-SB-35 with the four different annealing regions indicated

teo. o

35 F i l l o n et al. [12] p r o p o s e d an e f f i c i e n c y factor e v a l u a t i o n of n u c l e a t i n g a d d i t i v e s for polymersnucleating whereTc,na Tcl Tc2,max.

efficiency

for the

(1.11)

(NE) = I00. (Tc.na -Tcl) (Tc2,max. - Tcl)

= T c - v a l u e of the s y s t e m with the n u c l e a t i n g a d d i t i v e i.e. 125@C for the PP s y s t e m w i t h 1.05 %wt. talc and c a r b o n b l a c k (Table 1.4), = T c - v a l u e of the r e f e r e n c e s y s t e m i.e. II0~ for the s y s t e m in Table 1.4, = T c - v a l u e of the s y s t e m s e l f - n u c l e a t e d to s a t u r a t i o n [12].

Tc2,max. was not m e a s u r e d for the s y s t e m in T a b l e 1.4. The Tcv a l u e of 141.4~ g i v e n in T a b l e 1.5 can be used, however, as a r e a s o n a b l e a p p r o x i m a t i o n (both PP systems are m a d e w i t h c o m p a r a b l e catalyst systems). U s i n g this Tc2,max. v a l u e results in a N E - v a l u e ofNE = I00. (125 - 1 1 0 ) / ( 1 4 1 . 4

- ii0)

- 47.7

i.e.

48%

F i l l o n et al. [12] report a N E - v a l u e of 32% for PP w i t h 1 % w t . of talc as n u c l e a t i n g additive. The d i f f e r e n c e b e t w e e n b o t h NE v a l u e s is not too bad c o n s i d e r i n g the T c 2 , m a x a p p r o x i m a t i o n , the d i f f e r e n c e s in the u s e d e x p e r i m e n t a l m e t h o d s and the d i f f e r e n t PP systems i n v e s t i g a t e d .

36 1.4 S i d e - c h a i n

crystallisation

in poly(l-olefin) s

1,4,1 Introduction The presence of long (linear) side chains in b r a n c h e d polymers can cause side chain crystallisation. It is important to d i s t i n g u i s h main chain from side chain c r y s t a l l i s a t i o n for the effect of this difference on the product properties can be considerable. The Tm- and Tc-values of a polymeric system increase in general as a function of the chainlength i.e. the system's m o l e c u l a r weight. Both values become constant at h i g h e r m o l e c u l a r weights or go through a kind of m a x i m u m value [2]. This makes d i s c r i m i n a t i o n b e t w e e n main chain and side chain c r y s t a l l i s a t i o n on basis of the side chain length easy" - Side chains are in comparison with the main chains usually short and the Tm- and Tc-values of side chain crystallisation effects will, therefore, in general increase with increasing side chain length. - The presence of side chains hampers usually the main chain crystallisation. Increasing side chain length will result, in general, in decreasing main chain c r y s t a l l i s a t i o n Tm- and Tc-values. A series of poly(l-olefin) s was analysed by DSC, offering the p o s s i b i l i t y to map the differences between side and main chain crystallisation. 1.4.2 C r y s t a l l i s a t i o n in p o l y ( l - o l e f i n ) s A series of C6 up to C18 ~-olefin fractions prepared by the so-called SHOP process were p o l y m e r i s e d with a Ziegler-Natta catalyst system. The purity of these fractions was > 98 %wt. The (peak) m o l e c u l a r weights of the polymers proved to be > 200.000; NMR analysis showed atactic material and some stereoregularity. The results of the fusion/recrystallisation measurements (see 1.1.4) are listed in Table 1.6. Table

1.6

Results

of DSC analysis ,

fraction

.~ I ~,

-47

-73

C10

-75

1212

s-C

cl,4

s-C

i c16 L

Tgvalue oc

i,.

system A. or s-C.

* A.

Tcvalue oc ,

= amorphous;

Tm2 value ~

I !

. . . . .

Hc value J/g

of poly(l-olefin) s w

s-C s-C

s-C.

-67

-22

.,,

= semi-crystalline

i i

9. . .

4.00

- = .......................................................................................................

3.50

3 . O0 -

- .............

RECRYSTRLLISRTION FROM THE MELT OF SHOP LINERR RLPHR-OLEFINE BRSED POLYMERS

..............

--..-.C~.I~,~SHOP

C 12-SHOP

"-~.,..

2.50-

"~.

C ! 4-SHOP ~

C I (]-SHOP

.9o

,-,9

2.00

::E 1.50

L~ ,.J -

1. O0

0.50

O. O0 -100.0

...............

~............................. t . . . . . . . . . . . . . . . -75.0 -50.0

Figure 1.14

1 ................................. I . . . . . . . . . . . . . . . . -25.0 O. 0

Temperature (~

I ..........

25.0

I-

50.0

75.0

38 The C6 based polymers (side-chain: -[CH2]n-CH3, n=3) and the C8 based polymers are amorphous systems which did not crystallise even at low temperatures. The CI0 based system is 'as received' amorphous but crystallises at low temperatures. The C12 to C18 based polymers are s e m i - c r y s t a l l i n e systems. Figure 1.14 shows the r e c r y s t a l l i s a t i o n exotherms of the CI0 to C18 systems. These curves show a strong increase of the extent of the crystalline phases with the chain length. This increase is somewhat distorted by expressing it in J/g. But, if e x p r e s s e d in J/mol, the difference in Hc-value between the Cl0 based polymer (Hc = 0.ii J/mol) and the C18 based polymer (Hc = 0.38 J/mol) is still clearly present! The Tc- and Figure 1.15 side-chain. crystalline butene (PIB)

Tm2-values of these p o l y ( l - o l e f i n ) s are plotted in as a function of the number of C-atoms in the Besides, Tm- and Tc-values of the m a i n - c h a i n phases as present in p o l y p r o p y l e n e (PP), poly land poly l-pentene (PIP):

PP : Tm = 162~ PIB: Tm = 124~ PIP: Tm = 70~

Tc = II0~ Tc = 67~

[3],

are also p l o t t e d as a function of the number of C-atoms in the side-chains. The differences earlier decribed between the two types of crystalline phases are clearly present.

Figure 1.15 T m / T c - v a l u e s of p o l y ( 1 - o l e f i n s )

s.c.

m.c.

/T/. C.

S.C.

240 Hc-value poly(1 -olefin)s

,oo

200

8O 70

160

> r

120 00 d

310

0 10 0

I:::: E

F-

\\ \\

Number of C-atoms in side chain

.,1,.

.-I..9j

-40

..i_ ~

I "l " j

-'l-"

... ,,.....,

f"l" " ""

4" I "

-80

..I

...I

I .....

Number of C-atoms in side chain

~ ....

40 1.5 Chemical reactions m o n i t o r e d by DSC 1,5,1 ~ntroduc~ion The cure reaction of thermosetting resin systems is the subject of m a n y p u b l i c a t i o n s about m o n i t o r i n g chemical reactions by DSC. In much of this work is tried to derive kinetic information from the heat of reaction measured during both scanning and isother~al experiments [2, 15]. However, the results reported by Wisanrakkit and G i l l h a m [16] illustrate the insensitivity of the DSC technique for small (residual) cure exotherms. They show that the development of the Tg-value during isothermal DSC experiments is offering a much more sensitive measure for the conversion of a curing system. Besides, the heat of reaction measurement can not be used for all thermosetting resin systems. There are thermosetting resin systems which give no exothermic effect at all during their cure. This p r o b l e m is illustrated by the results of four experiments p e r f o r m e d with a Perkin Elmer DSC-2, using a heating rate of 20~ Figure 1.16A shows the cure e x o t h e r m of an epoxy powder coating system cured with an amine based curing agent. The exothermic effect is strong, the begin and end temperatures for a (partial) integration procedure can be defined easily. Figure 1.16B shows the cure exotherm of an epoxy powder coating system cured with a p h e n o l i c - O H based curing agent. This cure exotherm, although clearly smaller than the p r o c e e d i n g one, can still be treated with the same calculation techniques. Figure 1.16C shows the exothermic effect of an epoxy powder coating system cured with an anhydride based curing agent. A certain exothermic effect seems to be present but a (partial) integration procedure is with this result impossible. Figure 1.17, finally, shows the DSC thermograms of an epoxy powder coating system also cured with an anhydride based curing agent, which shows no cure exotherm at all. The cure process of these resins consists of a number of both exothermic and endothermic reactions; the DSC measures the totall amount of heat released which thus even can be nearly zero! The Tg-value increase seen in the second scan is the only indication for the occurance of a cure reaction during the first DSC scan. These examples comfirm the conclusion of Wisanrakkit and G i l l h a m [16] that the Tg-value development offers in many cases the best p o s s i b i l i t y to characterise the cure process of a certain t h e r m o s e t t i n g resin system. An example of such a procedure is given below (see 1.5.2). This conclusion holds especially for the examples of relative complex cure processes shown above. Less complex reactions with pure, low m o l e c u l a r weight components can often succesfully be studied using the exothermic reaction effect. An example of such a procedure is also given below (see

~.5.3).

,12 5=.,0

T~ ~ ~ ~ K

~-40

con0scao

Figure 1 . 1 7 The first and second DSC heating scans on an epoxy resin based powder coating system

, / ~ ~

S.T~Lp..~~~A~,'o.e~-.~-~-_3~,'K

z.4~O

~oo =zo

3,,O

| .~ | |

"t'E"PKRA'ruRE, KI First scan

s~rr,~= T~.s.tm" ~

43 1.5.2 The d e t e r m i n @ ~ i o n of the cure conditions of a powder coatina system The Tg[vaiue development of an epoxy p o w d e r coating system was used to determine the cure time (at 180~ as a function of the curing agent concentration, n e c e s s a r y to reach a Tg-value of at least 100~ The Tg-value of the system before cure [Tg(o)], the Tg-values after different cure times at 180~ [Tg(t)] and the m a x i m u m Tg-value due to cure at 180~ [Tg(e)] were m e a s u r e d using four curing agent concentrations i.e. 13.5 phr., 17 phr., 20.5 phr. and 24 phr. A typical result of such a series of m e a s u r e m e n t s is shown in the inserted figure of Figure 1.18. The results of the Tg(o)- and Tg(e)-value d e t e r m i n a t i o n s were averaged: Tg before cure: Tg(o) Tg(maximum) : Tg(e)

= 60.5~ = I08.5~

+ I~ _+ 1.5~

The conversion of the cure reaction can, based on the Tg(t)values and using these Tg(o)- and Tg(e)-values, be expressed as : conversion x(t)

= Tg(t) Tg(e)

- Tq(o) - Tg(o)

(1.12)

The conversion data of the i n v e s t i g a t e d system with four different curing agent c o n c e n t r a t i o n s are plotted as a function of the log(cure time) at 180~ in Figure 1.18. The drawn straight lines have R v a l . - v a l u e s > 0.993; the slopes of these curves increase slightly from 0.49 for the system with 13.5 phr curing agent to 0.55 for the system with 24 phr of the anhydride based curing agent. The conversion of this system has to be 0.82 or more to reach a Tg-value of at least 100~ according to equation 1.12. Using Figure 1.18, Figure 1.19 can be c o n s t r u c t e d containing the information asked by the customer about this system. !.5.~ Reactions of model compounds studied by DSC The development of acid b a s e d curing agents, to cure a new generation of UV resistant epoxy resins, required a study of the epoxy/acid reaction w i t h model compounds. A monofunctional, liquid epoxy resin (CARDURA E5) was used as model resin; the selected model acids are listed in Table 1.7. The reaction of a stoichiometric with the epoxy resin was m e a s u r e d isothermal DSC experiments. These with a Perkin Elmer DSC-2C u s i n g minute. Each experiment c o n s i s t e d

amount of these twelve acids d u r i n g a series of nonm e a s u r e m e n t s were p e r f o r m e d a scanning rate of 10~ of three heating scans:

Figure 1.18 (Tg-Tgo)/(Tge-Tgo) of a powder coating system versus the cure time at 180~ -}-

1.00

13.5 phr

17 phr

20.5 pit

curing agent cone.

phr

0.90 +

0.80 0.70 0 o) F10.60 E~

E--

0 E~ F-

0.50

12o

1 lO

lOO

+ / +

ยง

10.40

F-

!4+

0.30

Tg development during cure at 180~

0.20

60 1000

2ooo

3ooo

40oo

Cure time at 180~

0.10 0.00 I/ 30

, ,I f l

.,,I

time

180 ~

10000

1000

100 Cure

e,o o o

Epoxy resin based powdercoating system (cure temperature 180~ .

1000

,,,,, 0

0 'T"

E L__

Figur Time/curing agent concentration relation necessary to reach a Tg-value of the cured product of at least 100~

2O0 10

......

Curing agent concentration, phr.

"~. ~ .

46 Table

1.7 Survey of the used model

,,,,

Acid

chemical

hexane acid Ii

acid

, ,

CH2OH

cyclohexane i carboxylic acid

l-methyl-cyclo hexanecarboxylic acid benzoic acid

ml ,,

COOH

/-COOH ~COOH

2 -methyl -

benzoic

CH3 -COOH

acid

3 -methoxybenzoic acid 4 -methoxybenzoic acid 2 -ethoxybenzoic acid ~l

~H3 CH3 -C-COOH ~H3

hydroxy-pival ic acid

sol. in liquid epoxy , res in

CH3-CH-COOH ~H3

pivalic acid

structure

CH3 -CH2 -CH2 -CH2 -CH2 -COOH

i isobutyric I

compounds

. . . . . . . . . . . .

4 -ethoxybenzoic acid

liquid epoxy resin-

CH3 -~

COOH

o O coo.

-CH2 -CH3

COOH L

CH3 -CH2 -0 O

COOH

~H3 ~,O

cH3-c-c-o-

CH3

c.2

4 '/

- the first scan from 20~ up to 250~ to d e t e r m i n e the extent and temperature location of the reaction exotherm, the second scan from -120~ up to 250~ to m e a s u r e the Tgvalue of the reaction product and a p o s s i b l e residual exothermic effect, - the third scan from -120~ up to 20~ to check if the Tgvalue still increased after a second thermal treatment. -

The m e a s u r e m e n t s were p e r f o r m e d with the samples in high pressure capsules (internal pressure m a x i m a l l y 150 bar) to avoid sample loss due to evaporation. A possible mixing p r o b l e m had to be solved first. Six of these twelve acids are soluble in the liquid epoxy r e s i n at room temperature and the DSC samples were made using a standard m a s t e r b a t c h procedure. The other six acids, however, proved to be insoluble in the liquid epoxy resin. W e i g h t i n g the insoluble acids d i r e c t l y into the DSC high p r e s s u r e capsules upon the liquid epoxy phase was the first option. S u b s e q u e n t l y two epoxy/acid systems, with one in the resin soluble acid and one insoluble acid, were m e a s u r e d four times to detect possible differences in the r e p e a t a b i l i t y of these measurements: soluble acid liq. epoxy resin /hexane acid,

Tmax. (exotherm) dH(heat of reaction)

= 161 _+ 2~ = 87 _+ 1.5 kJ/mol

insoluble acid liq. epoxy resin 2-m.benzoic acid,

Tmax. (exotherm) dH(heat of reaction)

= 152 _+ 2~ = 79 + 2 kJ/mol

These results confirmed that the experimental p r o c e d u r e followed worked satisfactory. Figure 1.20 shows a t y p i c a l result. The reaction e x o t h e r m of the e p o x y / b e n z o i c acid system is m e a s u r e d during the first scan. This effect is characterised by a T m a x . - v a l u e of 139~ and a dH-value of 87 kJ/mol. No sign of a residual reaction e x o t h e r m is m e a s u r e d during the second scan. The Tg-value increased from -I09~ for the liquid epoxy as such to -48~ after the reaction with benzoic acid. A Tg-value of -48~ was also m e a s u r e d during the third scan, indicating that no (detectable) further progress of the reaction occurred after the first scan. The results of the m e a s u r e m e n t s p e r f o r m e d in this way are listed in Table 1.8. The first six systems listed in Table 1.8 show that the T m a x . ( e x o t h e r m ) - v a l u e of the e p o x y / a l i f a t i c acid systems is related with the strength (pKa-value) of the acid used. The inductive action of the h y d r o x y l - g r o u p in h y d r o x y p i v a l i c acid, for example, causes a p K a - v a l u e decrease from 5.03 (pivalic acid) to 4.50 (hydroxypivalic acid). This d i f f e r e n c e results in a T m a x . ( e x o t h e r m ) - v a l u e decrease of 24~ Subsequently, a still stronger acid, d i - e t h y l m a l l o n i c acid (DEMA), was tried.

~. 51~

Figure 1.20 The reaction of liquid epoxy resin / benzoic acid as measured by DSC

_,j~i

. . . , , ' w

O El Or)

< o

8. 25

jr="

_f r ~"

.,,

2nd

scan

TEMPERATURE B.eB

see.ca

2a.ee

2=.=

3=. ~

34~. ~

~ e . ~8

. . . . . .

(K) .

42~. 00

468. ~0

s~. ~

Table 1.8 The results of DSC model experiments with liquid epoxy r e s i n / a c i d reactions 9 ....

~,,

..,

Acid

pKa value

1 -methyl- cyclo hexanecarboxyl ic acid pivalic acid | 9

,,,

5.03

[

dH value, kJ/mol

176

171

167

4.86 ,

.....

76 63

-66 (-66) -62

(,-62) -85

-79

(-80)

. . . . . . .

147

-52

(-52)

4 -ethoxybenzoic acid

4.80

181

-34 (-3.4)

2 -ethoxybenzoic acid

4.21

174

-41 (-41)

4 -methoxybenzoic acid

4.47

173

3.91

2-methylbenzoic acid

,,,

................

benzoic acid ,

~,,,,,,,

4 09

I !

.... -

....

3-methoxy~benzoic acid ~,,,,,

4.19

152 141 |

, '

.....

139

99 m

[ (-85)

160

4.50

87 ,

hydroxy,.pivalic acid

161 .

....

Tgl (Tg2) ~ -60 (-60)

4.88

acid

isobutyric acid

,,,

4.90 .

cycl ohexane carboxylic acid hexane

Tmax. value, ~

-36 (-36) ......

-52 (-52) . . . . . .

-42

-48

87 ,

(-48)

50 Figure 1.21 The Tmax.-value versus the pKa-value (liquid epoxy resin/acid model series) +

a l/fa tic

aroma tic

acids

185.00 176.50

168.00 159.50 .A

151.00

.....,

142.50

I,,-

134.00 125.50 117.00 108.50

pKa-value 100.OO

2.80

3.20

3.60

4.00

~..

4.40

4.80

5.20

53. di-ethylmallonic

acid

~2H5 9H O O C - C - C 0 0 H

~2H5

The epoxy/DEMA system resulted in a T m a x . ( e x o t h e r m ) - v a l u e of I03~ and a dH-value of 74 kJ/mol. The p K a - v a l u e of DEMA is about 2.9. All the m e a s u r e d T m a x . ( e x o t h e r m ) - v a l u e s are p l o t t e d as a function of the p K a - v a l u e in Figure 1.21. it illustrates clearly that a relation b e t w e e n Tmax.(exotherm) and the pKavalue which is found for the alifatic systems does not hold for the aromatic systems. The aromatic acid systems show other effects. The Tmax. (exotherm)-values of three of the aromatic acids show, for example, a clear steric h i n d r a n c e effect. The T m a x . ( e x o t h e r m ) values for benzoic acid, for 2 - m e t h y l - b e n z o i c acid and for 2ethoxy-benzoic acid increase from 139~ to r e s p e c t i v e l y 152~ and 174~ The effect of a p a r a - a l k o x y substitution of benzoic acid is also clear; the pKa-values and T m a x . ( e x o t h e r m ) - v a l u e s are increasing going from benzoic acid, to 4 - m e t h o x y - b e n z o i c acid and to 4-ethoxy-benzoic acid. Besides, the dH-values of the last two mentioned acids are clearly lower than all the other dH-values. Such a d i f f e r e n c e in T m a x . ( e x o t h e r m ) - v a l u e is not present between benzoic acid and 3 - m e t h o x y - b e n z o i c acid (metaalkoxy substitution). The reason for the d e c r e a s e d epoxide reactivity due to p a r a - a l k o x y substitution might be the conjugated mesomeric structure which causes an extra negative charge on the carbonyl-group. The dH-values of eight of these systems seem to be more or less constant i.e. 80 â&#x20AC;˘ 5 kJ/mol. The dH-values of the paraalkoxy substituted benzoic acid systems and that of hydroxypivalic acid are s i g n i f i c a n t l y lower. The dH-value of the m e t a - a l k o x y substituted benzoic acid system is s i g n i f i c a n t l y higher (99 kJ/mol). The reasons for these d i f f e r e n c e s are not clear. The Tgl- and Tg2-values of all systems are equal indicating that all systems reacted only during the first h e a t i n g scans. This does not mean, however, that the conversion was I00 % for all systems. The Tg-values are no indication for the conversion, in this case, due to the strong sensitivity of these Tg-values for small structural differences. The Tg-value can only be used in this situation to check if some residual reaction effect occurred.

52 1.6 Determination of the heat of vaporisation by DSC i. 6.1 I~t.roductiQn The heat of vaporisation at 25~ (AHvap.25) of a solvent is used to calculate the Hildebrand Solubility Parameter (HSP) assuming that the evaporating solvent behaves like an ideal gas. The HSP, subsequently, is one of the three parameters used in the Nelson, Hernwall and Edwards system to describe and predict the solvent power [17]. The heat of vaporisation is usually measured with a completely closed calorimetric system permitting vaporisation experiments under controlled vacuum or pressure. The equipment developed for these measurements is rather complicated and scarcely available [18]. Farritor and Tao [19] used the convenient, wide-spread DSC technique for this purpose, accepting that this choice permitted heat of vaporisation measurements under atmospheric pressure only. Their Perkin Elmer DSC-IB was equipped with an open measuring cell system and could be used as such for vaporisation experiments. The DSC-2, -4 and -7 systems used at present, are equipped with semi-closed cell systems and have to be modified to perform vaporisation experiments. The DSC modification and the results of a series of heat of vaporisation measurements at 25~ are reported in this chapter. 1.6.2 DSC modification for th~ AHvaD.25 determination The DSC vaporisation determination is based on measuring the amount of heat necessary to vaporise a known amount of the substance. This substance is placed in the DSC measuring cell in a closed container and about I0 minutes is waited then to restore the equilibrium in the DSC cell. The heat of vaporisation determination is started, subsequently, by opening the sample container in the DSC cell and measuring the amount of heat necessary to evaporate the whole sample. Stainless steel high pressure capsules (Perkin Elmer) provided with holes in the upper side of respectively 0.5 mm., 3.0 mm. and 4.0 mm. in diameter, are used as sample containers. The sample containers are closed by covering these holes with mild steel lids which can be removed magnetically. Both the sample container surfaces and the mild steel lid surfaces are polished to obtain an optimal closing action of the lids. The aluminium cover of a DSC-2 system was replaced by a polycarbonate cover (see Figure 1.22) provided with a spring loaded, moveable magnetic system to remove the mild steel lids from the sample containers, while the DSC cell is closed. Two experimental parameters can be varied to vaporise samples with boiling temperatures ranging from 50~ to 200~ within maximal 30 minutes i.e. the sample container hole diameter and the sample weight. Besides, the DSC sensitivity can be varied.

Figure 1.22 Modified DSC-2 sample cell for vaporization experiments (shown schematically)

j n fill!I' .

. . . . . .

i !

il I i ........

i ~

i= =i

stopp!ng

spr!ng loaded magnet== h o ! d e r

i I i ! ! il I j i I i I ! il I i

"/,'

////zl,~

magnet~ mi Id s t e e l

A: DSC cell base B: polycarbonate cell cover

block

rubber

I id

0-r|ng

54 A series of p r e l i m i n a r y experiments set of experimental conditions. solvent boiling point range, ~

sample cup hole diameter, mm.

55 - 80 80 - 170 170 - 200

0.5 3.0 4.0

resulted

in the following

sample weight, mg. 1 - i0 1 - 2 0.i - 0.5

DSC sensitivity, mcal/s i0 I0 0.I

The sample holder environment was purged with h e l i u m during these experiments, at the relative high flow-rate of 200 ml/minute. Such a flow-rate proved to be necessary to obtain flow-rate independent results. Apparently, the formation of a the vapour 'cloud' above the sample container is prevented in this way. The standard DSC h e a t - f l o w calibration procedure with indium is not longer accurate enough, due to the change from a closed to an open cell system (the standard p l a t i n u m cell lids are removed). D e m i n e r a l i s e d water is used, therefore, as calibration substance for the v a p o r i s a t i o n experiments. The heat of v a p o r i s a t i o n of demineralised water was m e a s u r e d six times which each of the sample cups. The average heat of v a p o r i s a t i o n m e a s u r e d was compared with the known heat of v a p o r i s a t i o n of water (43.9 kJ/mol., [20]) to calculate a correction factor for each sample cupsample cup hole diam.,

average AHvap.25 measured, kJ/mol,

correction factor

0.5 n~n. 3.0 mm. 4.0 mm.

38.4 _+ 0.4 39.5 + 0.2 39.0 +_ 0.2

1.14 I.Ii 1.13

The isothermal (25~ experiments thus give a heat-flow versus time signal, see Figure 1.23. The time at which the mild steel lids are removed is indicated by (A) while the time that all the solvent is evaporated, is indicated by (B). Integration of this signal provides the total amount of energy necessary to vaporise the investigated sample. The base-line used for the heat of v a p o r i s a t i o n integration is indicated by (C). The shift of the DSC base-line shown in Figure 1.23, is mainly caused by the removal of the mild steel lids. The total amount of energy m e a s u r e d is used then to calculate the AHvap.25 after m u l t i p l i c a t i o n with one of the above given correction factors. 1.6.3 Results of AHvaD.25 d e t e r m i n a t i o n s by DSC The AHvap.25 of a series of samples with known AHvap.25 values [18] and boiling temperatures ranging from 57~ to 214~ was m e a s u r e d to determine the accuracy of this 'DSC' method. The results are listed in Table 1.9. Figure 1.24 shows the measured curve of n-dodecane. In spite of the (too) long

2.5

I ......

til. I~

TIME

(minutes)

Figure 1.23 DSC curve of the vaporization of ethyl propionate

56 Table 1.9 The DSC AHvap.25 d e t e r m i n a t i o n accuracy i

solvent

boiling tempera ture, ~

AHvap. 25 exper. kJ/mol

AHvap. 25 literat. kJ/mol

ยง

30.8

30.5

+I.0

methanol

38.0

37.4

+1.4

ethanol

42 .i

42.3

-0.5

4-methyl-2 9p e n t a n o n e

116

40.6

0.0

2heptanone

147

47.3

47.2

+0.2

61.3

+2 .I

acetone .

n-dodecane ~,

214

62.6 T.

m e a s u r i n g time, a reasonable baseline can still be constructed. The results listed in Table 1.9 are the average values of triplicate measurements. These data show that an accuracy of + 2 % is possible with this method. The AHvap.25 values of a series of propionate esters prepared with a new catalyst system was measured, subsequently, using this DSC method. Besides, a series of acetate esters was m e a s u r e d as references. The average values of the triplicate measurements are listed, together with the available literature values, in Table i. I0. The ~Hvap.25 values of a homologous series of organic solvents increase with their m o l e c u l a r weight. Figure 1.25 shows that the measured values of the linear p r o p i o n a t e samples and that of the linear acetate samples form in fact two different, linear relations (only the AHvap.25 value m e a s u r e d for npentyl acetate deviates clearly). The difference in heat of v a p o r i s a t i o n between linear propionate and linear acetate samples with equal m o l e c u l a r weights seems to be disappeared for the branched systems. The influence of the structure on the heat of v a p o r i s a t i o n is illustrated by the results of the following samples (mol. weight = 102). n-propyl

acetate

ethyl propionate i-propyl acetate

0 CH3-CH2-CH2-O-~-CH3 0

AHvap. 25 39.7 kJ/mol.

CH3-CH2-O-'~-CH2-CH3

38.1 kJ/mol.

CH3-~H-O-~-CH3 Ctt3

35.7 kJ/mol.

The more asymmetrical location of the -CO0- group in the acetate sample seems to increase the heat of vaporisation. Branching, however, clearly overrules this effect.

0.30

0.15 0 I.U r

0.00 ~. 0

TIME (minutes) Figure

1.24

DSC CURVE OF THE V R P O R I Z R T I O N N-DODECRNE RT 25 DEG. C.

58 Table I.I0

AHvap.25 values of propionate and acetate esters .......

solvent 9.

AHvap. 25 experim. kJ/mol .

........

AHvap. 25 literat. kJ /mo 1 9

methyl ,p r o p i o n a t e

32.5

35.85

ethyl

38.1

39.21

43.8 41 .i

43.45

propionate

n-propyl propionate i-propyl propionate

n-butyl propionate ..s - b u t y l P r o p i o n a t e

50.0 46.7

..n-Pentyl pr~pionate

55.9

30.0

32.29

34.6

35.60

n-propyl acetate ,.~i-propyl a~etate

39.7 35.7

39.72 37.20

n-butyl a c e t a t e s-butyl acetate ,I i-butyl acetate

45.1 41.5 42.4

43.86

,methyl

acetate.

ethyl

acetate

n-penny I acetat e

....

53.0

. . . . . . . .

~..,u.~

....

i -,

Figure 1.25 The heat of vaporisation at 25~ as a function of the molecular weight -t-

n-propio nares

n-ace rates

branched propion,

'4"

branched acetate

E +

50 -d

1,0 0

,.,,,

c 0

9==,.,

.,a,,.

0 CI.

> t4==,

41 I

38 35 +

32 Molecular weight

100

110

120

130

140

150

60 References I. B. Wunderlich. Thermal Analysis, Academic Press Inc., New York, 1990. 2. V.B.F. Mathot" Calorimetry and Thermal Analysis of Polymers, Hanser Publishers, Munich, 1994. 3. D.W. van Krevelen- Properties of Polymers, Third edition, Elsevier, Amsterdam, 1990. 4. J. Bicerano- Prediction of Polymer Properties, Marcel D e k k e r Inc., 1993. 5. H. Nakamura, Thermochimica Acta, 136, (1988) , p. 163 178. 6. K.H. Nordsiek, Kautsch. Gummi Kunstst., 3~, (1985), p. 1 7 8 - 185. 7. L.A. Wood, J. Polymer Sc., 28, (1958), p. 319. 8. A. GHijsels, Internal Shell Report, DTRS.0011.74. 9. J.E. Stamhuis, W.M. Groenewoud and J. Raadsen, Plastics & Rubber, Processing and Application, ii, (1989) . i0. M. A n t b e r g et.al., Macromol. Chemie, Macromol. Symp., 48/49, (1991), p. 333 - 347. ii. E. Devaux and B. Chabert, Pol. Comm., 32, 15, (1991), p. 464. 12. B. Fillon et.al., J. of Pol. Sc.- Part B, Polymer Physics, 31, (1993), p.1395 -1405. 13. J. Janimak et.al., Polymer, 3/, 4, (1992), p. 728. 14. See reference 12, p.1383 - 1393. 15. J.M. Barton, Adv. Polym. Sci., 72, (1985), p. Iii. 16. G. Wisanrakkit and J.K. Gillham, J. Appl. Pol. Sc., 41, (1990), p. 2885 - 2929. 17. R.C. Nelson et al., J. Paint Techn., 42, (1970), p.636. 18. V. Majer and V. Svoboda" Enthalpies of v a p o r i s a t i o n of organic compounds, Blackwell Scientific Publications, Oxford, 1985. 19. R.E. Farritor and L.C. Tao, Thermochim. Acta, i, (1970), p. 297. 20. Handbook of Chemistry and Physics, 41 st edition, Cleveland, 1959.

THERMOGRAVIMETRICAL ANALYSIS CHAPTER 2

CHAPTER

2" T H E R M O G R A V I M E T R Y

2.1 Introduction T h e r m o g r a v i m e t r y (TG), the technique in which the mass of a sample is m o n i t o r e d against time or temperature, is p e r f o r m e d with a T h e r m o G r a v i m e t r i c A n a l y s e r (TGA) or thermobalance. Recently, a survey of this technique and the available commercial equipment was given by W u n d e r l i c h [i]. Important differences b e t w e e n the balances are- the type of balance, vertical or horizontal furnace systems (the horizontal furnace TGA needs a correction for the influence of the thermal e x p a n s i o n on the length of the balance-arm), - the sensitivity in c o m b i n a t i o n with the m a x i m u m sample weight (a typical example is the Perkin Elmer TGA-7 with a sensitivity of 0.0001 mg and a m a x i m u m sample weight of 200 milligramme. - the temperature range and the temperature accuracy. The sample mass d e t e r m i n a t i o n and the sample temperature measurement of the TGA has to be calibrated using calibrated weights and the ferromagnetic transition (Curie) temperatures of calibration metals. A Perkin Elmer TGA-7 (vertical furnace) system is used for the TGA experiments d e s c r i b e d in this chapter. The balance is purged with 40 ml/minute of nitrogen. A second n i t r o g e n purge gas stream of 20 m l / m i n u t e is entering the system via the sample purge entrance, see Figure 6.5. Both gas streams purge the furnace part of the TGA. The sample purge can be switched from nitrogen to air w i t h the aid of a software c o n t r o l l e d gas-selector. The automated two-point t e m p e r a t u r e c a l i b r a t i o n p r o c e d u r e is performed with the c a l i b r a t i o n standards alumel and perkalloy. Subsequently, the Curie temperatures of four c a l i b r a t i o n standards are measured to check the whole TGA temperature range of interest. A typical c a l i b r a t i o n result m e n t i o n e d below shows that a t r a n s i t i o n temperature accuracy of about â&#x20AC;˘ I~ can be obtained u s i n g the standard temperature c a l i b r a t i o n procedure" alumel nickel : perkailoy: iron :

163oc, 356~ 597oc, 787~

Curie " " "

temperature " " "

= = -

163~ 354~ 597~ 787~

The TG technique is (just like the DSC) very p o p u l a r in polymer reseach, in p a r t i c u l a r to study the thermal stability of polymeric systems u n d e r a p p l i c a t i o n conditions. An example of the straightforward use of this technique for p o l y p r o p y l e n e (PP) is given in chapter 2.2. A series of TG experiments on PP catalyst systems under special conditions (an oxygen- and moisture-free sample l o a d i n g procedure) is d e s c r i b e d in

62 chapter 2.3. A number of TGA applications in combination with FTIR and MS analysis of the released purge gas is, finally, mentioned in chapter 6. 2.20ligomers

content and thermal stability of polypropylene

2.2,1 The non-isothermal thermal stability d e t e r m i n a t i o n A quick impression of the thermal stability of a polymer is obtained by m e a s u r i n g its mass with a TGA as a function of the temperature at a constant heating rate. Figure 2.1 shows the results of four TGA scans on ~'P samples using a heating rate of l~ These results illustrate that" - the thermal stability of PP considerably decreases if oxygen is present and, - that the added stabilisation system only works under inert conditions. These non-isothermal TG experiments offer a simple and relative quick analytical p o s s i b i l i t y to compare the thermal stability of different polymers or different polymer batches. A polymer is thermally stable untill the d e c o m p o s i t i o n process starts. Two (main) types of thermal d e c o m p o s i t i o n processes are usually recognised for polymers, chain d e p o l y m e r i s a t i o n and random decomposition. Chain d e p o l y m e r i s a t i o n is the release of m o n o m e r units from a chain end or at a weak link and is essentially the reverse process of polymerisation. It is often called d e p r o p a g a t i o n or unzipping. Random degradation occurs by chain rupture at random points along the chain, giving a disperse mixture of fragments. These two different processes may occur separately or in combination; the latter case is rather normal [2]. Both processes cause sample mass losses which can be measured with a TGA. The thermal stability of a p o l y m e r is often expressed by its Td(0.5)-value. This is the temperature at which the loss of mass during p y r o l y s i s (at a constant heating rate) reaches 50 % of its final value. This Td(0.5)-value is measured in an inert atmosphere and is, according to Van Krevelen [2], determined by the polymer's chemical structure. It is important to realise, however, that the physical properties of a polymer are c h a n g e d / d e c r e a s e d significantly at the moment that the Td(0.5) temperature is reached. We prefer, therefore, to characterise the thermal stability of a polymer by the Td(o)-value i.e. the temperature at which a loss of mass during heating just starts. The d e t e r m i n a t i o n of the Td(o)value can be hampered, however, by mass loss effects due to a low molecular weight fraction (oligomers) and/or residual monomer/solvent in the polymer sample. Commercial PP grades, for example, always contain a small (0.I %wt. - 0.3 %wt.) oligomer fraction (C6 - C39). A series of isothermal TG experiments was used to determine the oligomer content of a commercial PP grade. In addition, the Td(o) -value of pure i.e. n o n - s t a b i l i s e d PP was determined.

I--

e,i~-

/ !

./"

= ......

,.,

0 7

"r r ~ _ Q.W m

W nN ~1 ~ m -i

Zr W 0 Z

w "r

0 I--

- -

- . . . . . . . . .

IHrdl3M %

i .

ILl F-

" "

o~ Q~

_-J

o ,--

o .....

c56

i;i

64 2.2,2 The isQ~hermal thermal stability determination. Isothermal mass/time curves of n o n - s t a b i l i s e d PP powder samples were measured during I000 minutes at temperatures b e t w e e n 160~ and 280~ The PP TGA samples (about I0 mg.) were flushed with nitrogen during one hour at 30~ before the experiment was started. Oligomers and polymer are separated, during these TGA experiments, on basis of the boiling temperature (and thus the m o l e c u l a r weight) of the different oligomer fractions. The total amount of oligomers determined during these isothermal TGA experiments will increase, therefore, with increasing m e a s u r i n g temperatures. The mass/time curve measured at T(isothermal) = 160~ shows a non-linear mass loss effect during the first 250 minutes, see Figure 2.2. No further mass losses were detected during the remaining 750 minutes of this experiment. This mass loss effect of about 0.3 %wt. is assumed to be caused by the evaporation of an oligomeric fraction. The TGA experiments at T(isothermal) ~ 190~ show a continuous, nearly linear with the time, d e c r e a s i n g sample mass after the first (non-linear) mass losses due to evaporation of the oligomers fraction. The slopes of the linear part of these curves increase with isothermal measuring temperatures. This effect is thought to be caused by the thermal degradation of the polymer matrix. The mass/time curves were extrapolated, subsequently, as indicated in Figure 2.2 to determine the oligomers fractions [wl, w2, w(n)]. The curves in Figure 2.2 clearly illustrate that the extent of the oligomers fraction increases with increasing m e a s u r i n g temperatures. The oligomer content values and slopes of the curves which are thought to represent the rate of the' thermal degradation process of the PP matrix are listed in Table 2.1. Nib samples (i.e. the extruded and stabilised material) were investigated, subsequently, in the same way. The results of this series of experiments is listed in Table 2.2. The oligomer contents m e a s u r e d for both the powder and the nib samples are plotted as a function of the isothermal measuring temperature in Figure 2.3. The oligomer content of the nonstabilised powder sample increases nearly linearly with the temperature. The oligomer contents measured on the (stabilised) nib samples are lower and scatter considerably more than the powder sample values. These values have to be lower due to e v a p o r a t i o n losses during the nib extrusion process. Differences in the cooling rates of single nibs after the extrusion process might be the reason for the considerable amount of scatter. The broken line indicates thus a kind of m a x i m u m oligomer content for nib samples. The loss rates due to thermal degradation of the PP matrix are p l o t t e d in Figure 2.4 as a function of the reciprocal absolute temperature. The first detectable loss rate value was measured for the non-stabilised PP sample at T(isothermal) = 191~

I00.099. 9 I

-100.0 ................ - 99.9

g9. 8

. . . . . l ~z .

T(lsot, h.) .

o~" 99,

_ _

99. 8

t68~

99. 7

T ( t soth. ) -

198 ~

99. 6

"" 99,5

99. 5

---~

~: 99,4

9g.

3 -

T(t=oth.)

99. 3

, %

99. ~ 4 99.

99. 4

- 228~

- 99.2

]

99.0

" 99.0

98, 9 -

I 0.0

100. 0

I ......

200. 0

300. 0

400. 0

500. 0

600. 0

700. 0

800. 0

900. 0

Time (minutes)

Figure 2.2 Isothermal TGA mass/temperature curves of a PP powder sample (non-stabilised)

99.1

- 98.9 1000. 0

o~ v

66 Table

2.1 R e s u l t s of i s o t h e r m a l T G A e x p e r i m e n t s n o n - s t a b i l i s e d PP p o w d e r s a m p l e s

~,..~[_

oligomer fraction w (n) , %wt.

T (isoth. ) oC

% wt./s

0.288

0.0

171

0.353

0.0

181

0.278

0.0

191

0.413

6.9E-7

201

0.467

1.4E-6

211

0.463

1.4E-6

221

0.585

2 .IE-6

232

0.675

4.9E-6

251

0.783

1.0E-5

2.2

w(n), ...... ,

182

192

202

% wt.

0.282

0.0

0.350

0.0

7.4E-7 ,,

....

242

0.534

7.8E-7

250

0.425

1.5E-6

262

0.568

4.7E-6

270

0.496

1.6E-5

0.412

3.3E-5

277

0.0

0.423 =

% wt./s

0.261

--7

222 ,

thermal degradation lOSS rate,

0.286

isothermal TGA experiments PP nib s a m p l e s

oligomers fraction

171

R e s u l t s of stabilised

T (isoth. )

thermal degradation loss rate,

161

Table

9.0E-7

67 Figure 2.3 Oligomer content/temperature relation (nonstabilised powder/stabilised nibs) +

nonstab.

stab. mibs

0.80

-I-

0.70 +

0.60 A

0.50 c 0 o

-I-

0.40

-t-

J A

J _r

0.30

0.20 I 160

180

2OO

220

T(isothermal), ~

240

26O

28O

::::I

o0 o

Ix,)

C)'l

...l.

...t.

0 IX)

IX.)

LO 0

_,.l,

CO -

-q

T '"

O"l

(1)

cl)

i t

loss rate, % w t . / s

I::>"

. II

o) ::3

0 0

.,.,...

"13

.-~

(I}

...,..

_,~,.. 0

~ (tO

""II

(i} ! ~

-~ (1) ""

--I'T1 (Ii (::

O'i

(30

69 Hence, the Td(o)-value of pure (non-stabilised) PP is about 190~ It is also clear that the small amounts of oligomers presen t in these samples do not hamper a proper Td(o)-value determination. This Td(o)-value of 190~ increases to about 240~ due to the addition of the stabiliser system (ionol and irganox). The activity of this stabiliser system is not only temperature but also in time limited. Figure 2.5 shows that this stabiliser system stays active (at 250~ for about I000 minutes i.e. long enough to withstand the thermal treatments during all different PP processing procedures. Usually, non-isothermal TGA experiments are used to determine the 'standard' Td(0.5)- and Td(o)-values. The non-stabilised PP sample was measured, therefore, at different heating rates in order to match a non-isothermally determined Td(o)-value with the isothermally determined Td(o)-value of 190~ This match was obtained, see Figure 2.6, for a heating rate of 0.1~ The slope of this mass/temperature curve increases due to the evaporation of oligomers between 75~ and 184~ and clearly decreases then in the temperature region between 184oC and 204~ The presence of the latter temperature region indicates that there is sufficient separation between the oligomer evaporation process and the start of the polymer matrix degradation. The Td(o)-value of PP determined in this way is estimated at 194~ and is called the semi-static Td(o)-value.

2.3 The TG analysis of a PP catalyst system 2,3.1 A 'plastic w r a p p e d ' TGA TIC14, the active component of a Ziegler-Natta PP catalyst system, has to be coordinated on the MgCI2 carrier material together with an internal electron donor like di-isobutyl phthalate (DIBP). The close presence of TiCl4 and DIBP might also result, however, in the formation of a TiCI4.DIBP complex, which would influence directly the catalyst activity. Different analytical techniques like NMR and IR have been used to study these catalyst systems, but they did not resolve the doubts about the state of the TIC14, the DIBP and possibly the TiCI4.DIBP complex in these catalysts. Terano et.al, used TG experiments to investigate a TiCl4/ethyl benzoate system (EB) [3]. Their results suggested that the TiCl4 and EB exist seperately on the MgCI2 surface. Based on these results, a series of non-isothermal TGA measurements was performed to study the TiCI4/DIBP system in the same way. A 5~ heating rate was used (Terano used 17oC/minute) to improve the resolving power of this technique. Besides, the TGA sample loading procedure had to be optimised. These types of catalysts have to be handled in an moisture and oxygen free atmosphere and are stored in a dry-box. Special precautionary measures are, therefore, necessary for the TGA

100.0 -

lO0. 0

gg. 5 -

99. 5 PP N I B S A M P L E stabilised

gg. 0 -

99. 0

98.5 -

98. 5

98.0 -

g8. 0

e.. . = . .

97.5 -

gT. 5

PP P O W D E R S A M P L E non.stabilised

97.0

97.0 T i m e (minutes)

96.5 0.0

500. 0

1000. 0

1500. 0

2000. 0

g6. 5

2500. 0

3000. 0

3500. 0

4000. 0

Figure 2.5 The mass/time curves of a non-stabilised and a stabilised PP sample during isothermal TGA experiments at 250~ (nitrogen atm.)

PERKIN-ELMER

100.0

i,i -

,,,,,,,/,,

,,,

,,,,,,

,',

7 Series Thermal Analysis System ,

'. . . . .

99.8 9g. 6 -

9g. 4

TCA F i l e Nome: Somple We19ht: Sun H o t

t2472 10.714 m 9

14.49:23

Unstob~lIsed

lggl

PP powder" ex P e r n l s

CPO

o~ 9 9 . 2 9g.o.,m, QI

9a.a98.6 -

,,,3

nitrogenatmosphere

TEMP 1: 30.0~ TEMP 2: 450.0~

TIME 1: 0 . 0 m i n

RATE 1: 0.1~

98.4 -

184[~ 2@41~

98. 2 -

98.0 -

50.0

75. o

, . . . . .

~oo. o

t . . . .

~25. o

~5o. o

I ....

~ ' '

~75. o

2oo. o

Figure 2.6 PP TGA experiment. Heating rate 0.1~

/ -I

225.o

............

250. o

27~.o

Temperature(~

3oo. o

72 sample loading operation. The TGA sample pan was filled with about I0 mg. of catalyst sample and placed in a closed, n i t r o g e n flushed, small bottle. This happened in the dry-box used to store the catalyst. The TGA sample pan was transported in this bottle to the TGA sample loading table. The whole TGA balance system was packed, subsequently, in a big p o l y e t h y l e n e bag (Sigma A3533 Atmosbag 36" x 51" x 58", provided with two gloves) This bag was closed as good as possible around the electrical cables and blown up with an excess of nitrogen. The relative humidity in the bag decreased in about one hour from 50 - 70 % to less than 5 % due to this nitrogen purge. The catalyst sample was then, using the gloves of the Atmosbag, taken out of the bottle and placed in the TGA hang-up wire. Subsequently, the TGA furnace was closed and the m e a s u r e m e n t was started. 2.3.2 TG analysis of a MaCl2-suppor~ed. TiCI4/DIBP catalyst Figure 2.7 shows the TG m a s s / t e m p e r a t u r e curves of the reference systems MgCI2, DIBP and a mixture of MgCI2/DIBP. The d e c o m p o s i t i o n of MgCI2 starts at temperatures > 400~ The total mass loss between 420~ and 730~ was 17.7 %wt. The DIBP as such evaporated completely b e t w e e n II0~ and 250~ The MgCI2/DIBP mixture m a s s / t e m p e r a t u r e curve clearly shows a twostep mass loss effect due to e v a p o r a t i o n of the DIBP as such and due to evaporation or possibly d e c o m p o s i t i o n of DIBP absorped on the MgCI2 surface. A mass loss effect of 25 %wt. is measured between II0~ and 300~ (evaporation) while 11.3 %wt. weight loss is measured between 510~ and 584~ (evaporation or decomposition). The total weight loss due to DIBP release (after correction for the MgCI2 weight losses) is thus 36.3 %wt. This value fairly agrees with the DIBP content of 34.7 %wt. reported for this system. _

Two other reference systems, M g C l 2 - s u p p o r t e d TIC14 and TiCI4.DIBP complex were measured in the same way. The TIC14 decomposes in two steps with DTGA minima at I19~ and 221~ The total weight loss at 420~ (the starting temperature of the MgCI2 mass loss process) was 18.5 %wt. The calculated weight loss due to a conversion of the TIC14 to Ti is 20.0 %wt. The main mass loss effects of the T i C I 4 . D I B P complex occur between 128~ and 288~ with at least t w o DTGA minima at about 184~ and about 220~ The main evaporation process of DIBP both from T i C I 4 . D I B P complex and from the MgCI2/DIBP mixture thus occurs in the same temperature region which was disappointing. On the other hand, the TiCI4.DIBP complex shows a small but clearly present effect at about 400~ which is not present in the M g C I 2 / D I B P mixture results. Besides, the MgCl2/ DIBP mixture shows a strong effect between 510~ and 584~ (Figure 2.7) which is hardly present in the TiCI4.DIBP complex results.

100. 0

~ :

"L1e

~'C',-"c"---~ ~ ' :

':L=-i

~"-----~ ""-'-~-~

go. 0 85.0 ~ ..; ~

BO. 0

-I

mixture

HgCl 2 / D I B P _1[

75. o

3 ~8 " 75.8

70. 0 -

Commercial M g C 1 2 ~ 1?.7 ~ = t , , loss between 4 2 B - 7 3 0 C

65.0 60. 0 DIBP,

55. 0 -

I B 8 ~'.=t.

betueen

50. 0 ,1~ ..................

1oo. o

Figure 2.7

200. o

300. o

1o==

se4 c 55.9

t 1(]-25(] C.

.....

1. . . . . . . . .

400. o

5oo. o

Temperature (~

''l

. . . .

son. o

I I--

~oo. o

Non-isothermal TGA mass/temperature curves of DIBP, MgC12 and a mixture of MgC12/DIBP measured in a nitrogen atmosphere

74 Figure 2.8 shows the TG m a s s / t e m p e r a t u r e curves and the corresponding DTGA curves of the MgCl2-supported, TiCI4/DIBP catalyst in duplo. This catalyst contained 15.8 %wt. of TIC14 and 20.8 %wt. of DIBP. These two m a s s / t e m p e r a t u r e curves have roughly the same shape as the M g C I 2 / D I B P mixture mass/ temperature curve shown in Figure 2.7. This is an indication that an important part of the DIBP in this catalyst sample is present as DIBP and not as TiCI4.DIBP complex. The "blown-up" DTGA curves in Figure 2.9 illustrate that the TiCI4.DIBP complex DTGA m i n i m u m at 390~ is not present in the catalyst samples. These results are, therefore, suggesting strongly that the DIBP is present as DIBP in this catalyst system and not as T i C I 4 . D I B P complex. References

i. B. Wunderlich. Thermal Analysis, A c a d e m i c Press Inc., New York, 1990. 2. D.W. van Krevelen- Properties of Polymers, Third edition, Elsevier, Amsterdam, 1990. 3. M. Terano and T. Kataoka, Makromol. Chemie, i__~, (1987), p. 1477 - 1487.

100. 0 95, 0

-0, 9 I

go. 0

"-0. 2

85. 0 A

J::

8o.o

75.0-

"-0. 3

"-0. 4

"-0. 5

.,,..

// / I

7o.o-

-0.

-0~ 7

65, 0 k

60. 0 55, 0 50, 0

-0. 8

-0. 9

528~

........

~. . . . . . . . . . . . I00. 0

Figure 2.8

I 200.0

234~ ......... I ..... 300. 0

400. 0

. . . . . .

500. 0

i .......

600, 0

700, 0

Temperature (~ Results of two non-isothermal TGA measurements on PP catalyst BR900718 in a nitrogen atmosphere

-1.0

.,,1 U1

-0. 1

-0. 2 -0, 3

-0. 1

\ |

.c_ -0. 4 E

"-~ -0. 5

/ I

~ -0. 6 .~_

E3 - 0 . 7

-0. 2

I |

' / .J

-0. 3

\.,

;

-0. 5

[

390~

15.BY. T I C I 4

-1.0 -1.1

4.BX T t C I 4 9 2 2 . 5 ~ DIBP

2oo. o 9

-0. g .0

~o0. o

-0. B

i i

-0. 9

-0. 7

28. B~. DIBP

-0.8

-0, 6

-1.1

5aeoc

a~o. o

,od. o

Temperature (~

sod. o

coo. o

7od. o

Figure 2.9 DTGA minima of two PP catalyst samples and a TiC14.DIBP complex sample measured at 5~ in a nitrogen atmosphere

,..3

THERMODILATOMETRY

CHAPTER 3

Chapter 3- THERMODILATOMETRY 3.1 Length dilatometry

(TMA)

3,1.~ Introduction Thermodilatometry, the technique in which the dimensions of a sample are monitored against time or temperature, is performed as length dilatometry or as volume dilatometry. Length d i l a t o m e t r y uses a thermomechanical analyser ~TMA) which measures the sample length as a function of the temperature or time while the sample is held under a small, constant compression force. Volume dilatometry, performed with the classical dilatometer, uses a liquid (for example mercury) to measure the volume change of a sample as a function of the t ~ m p e r ~ t a ~ e o r time. Due to its simple, easy to operate, technique is length dilatometry far more popular in polymer research applications than the complicated, time-consumin~ volume dilatometry. TMA equipment is, nowadays, available from several manufacturers. Recently, also dynamic load thermomechanical analysers (DLTMA) became commercially available. A survey of the TMA/DLTMA techniques was given by Wunderlich

[i].

The TMA technique can be used for Tg-value determinations, resin cure studies, penetration experiments or orientation effect determinations. The most important application is thought to be the linear thermal expansion coefficient (l.e.c.) determination of engineering polymers. An example of this application is given in chapter 3.1.2. The results of a polymer shrinkage experiment monitored by TMA are described in chapter 3.1.3. The TMA used for the l.e.c, determinations described in this chapter is a Perkin Elmer TMA-7. This TMA is purged with 60 ml/minute of nitrogen. The system is operated at a heating rate of 2~ while a small (I0 mN) compression force is put on the sample. The length measurement is calibrated using (calibration) standards; the automated two-point temperature calibration program is performed using indium (156.6~ a S1215 rubber sample [Tg(midpoint)-value = -36oC]. 3.1.2 The linear thermal expansion coefficien~ determin@tion o f filled polyketone systems Engineering polymers are often filled with glass fibres or other filler types to improve certain mechanical properties, like stiffness and thermal expansion. The thermal expansion of polyketone* samples filled with different filler materials Aliphatic polyketone based on carbon monoxide, ethylene and a small amount of propylene, commercialised by Shell under the trademark CARILON Polymer (PK-EP), see Chapter 9.

2.33

Sample Height: 2.313 mm

2.32

heat, lng

c o o I I ng

heating

2.31

2.30 A

E E

c: 0 u) rm c2. x LU

2.29

2.28 2.27 2.26

2.25 2.24122:3 I

-50.0

I -25.0

I 0.0

! 25.0

I 50.0 Temperature

I 75.0

I tOO 0

I t25.0

! 150.0

Figure 3.1 The length change of a polyketone sample during three subsequent TMA scans

79 was m e a s u r e d to study the influence of the shape of the fillers on their l.e.c, depressing efficiency. The TMA samples of 5 x 5 x 2 mm are m a c h i n e d from c o m p r e s s i o n moulded (i00 x i00 x 2 mm) or injection moulded (60 x 60 x 2 mm) samples. Stresses, 'frozen-in' during the injection or compression moulding procedures, hamper a s t r a i g h t f o r w a r d l.e.c, determination. Figure 3.1 shows the l e n g t h / t e m p e r a t u r e relation of an injection moulded p o l y k e t o n e sample m e a s u r e d in the z-direction i.e. the plane p e r p e n d i c u l a r to the sprue xyplane. The sample shrinks about 3 % in this d i r e c t i o n due to the release of these 'frozen-in' stresses during heating and cooling between -50~ and 150~ The l e n g t h / t e m p e r a t u r e relation measured during the third heating scan is nearly equal to the cooling scan result. This indicates that the 'frozen-in' stresses are completely released. It will be clear that a p r o p e r comparison of the effect of different filler systems on the thermal expansion is only possible on basis of results measured on stress-free samples. Addition of fibre-shaped fillers introduces a n i s o t r o p y in the material. C h a r a c t e r i s a t i o n of the thermal expansion p r o p e r t i e s requires therefore m e a s u r e m e n t s in all three directions. Measurements in the x-, y- and z-direction of a pure, nonfilled material resulted in the following average l.e.c. values at 20~ Polyketone l.e.c, at 20~

9 1.lIE-4 â&#x20AC;˘ 0.02E-4 K^-I, x - d i r e c t i o n 9 1.09E-4 â&#x20AC;˘ 0.02E-4 K^-I, y - d i r e c t i o n 1.09E-4 â&#x20AC;˘ 0.02E-4 K^-I, z-direction (The sprue-plane is called the xy-plane. Results m e a s u r e d on four different TMA samples taken from an injection m o u l d e d sample, crystallinity 44 %wt.) 9

The polymer as such is c o n s i d e r e d to be isotropic i.e. the l.e.c, values in the three directions are equal, 1.10E-4 K^-I. Polyketone is, however, a semi-crystalline p o l y m e r and the l.e.c, will be influenced by the extent of the crystalline phase : Polyketone l.e.c, at 20~

: 1.02E-4 K^-I, 9 1.10E-4 K^-I, 1.16E-4 K^-I, (average l.e.c, values in the -

c r y s t a l l i n i t y 54 %wt. c r y s t a l l i n i t y 44 %wt. c r y s t a l l i n i t y 36 %wt. x-, y- and z-directions)

The l.e.c, values of a series of eight p o l y k e t o n e samples containing 30 %wt~ of six different filler m a t e r i a l s were measured. The l.e.c, values m e a s u r e d in the x- and ydirections proved to be nearly equal p o i n t i n g at a random distribution of the fibres in the xy-plane, the average values are listed in Table 3.1. A grafical r e p r e s e n t a t i o n of these data is given in Figure 3.2.

(/) L Q) C"

(.-

L "~"

tfl

.~- r

3 I

, r,,.

*--I---4

f.D

0o0~ le uo!loeJ!p ~

I---X--I

-0--

O--

1 ./

I - - ..I- --.I

~_~

U +

....

I ...

, q-

~ IS')

/ l-X---I

, __ I or)

, .. t ou

If,,

L _

i I . D

4k~

0 L-

0 , u

9 _

Nk--

0.0

,iii,

~'~E

-J I,I

F-

u! (NIL 'g-3x) "geoo uo!suedxe .meu!l

I-

I,-

E r-

.e~

,-.=

.i..

LL 0 iI

81 Table 3.1 Linear e x p a n s i o n coefficient values at 20~ of polyketone samples with different filler materials filler type

average longest dimension, micron........

x-/y-direction average l.e.c. at 20~ K^_I. . . . .

CaC03

1.5

8.7E-5

9.4E-5

kaolin

8.2E-5

I.IE-4

wollastonite

8.1E-5

I.IE-4

mica

20 80

7.5E-5 6.0E-5

125 150

4.7E-5 5.7E-5

1.6E-4 1.6E-4

7000

3.3E-5

1.9E-4

30 . .%wt. . . . . .

short glass fibres long glass fibres

z -direction l.e.c, at 20oc, K^_I .,

1.2E-4 1.5E-4

Quite different filler materials with average longest dimension values varying over four decades fairly fit the drawn straight line. This indicates that the average fibre length determines (at a constant filler concentration) the l.e.c, in the xy-plane. Scatter in the data is expected to be proportional with the filler dimension inhomogeneity (wollastonite) or with the sensitivity to the processing procedure (short glass fibres during injection moulding), see Figure 3.2. The linear expansion coefficient values shown in Table 3.1 and Figure 3.2 illustrate that filler addition results in composite systems with clearly decreased linear expansion coefficient values in the xy-plane. It also introduces, however, anisotropy in such a composite system i.e. an equal or even higher linear expansion coefficient value is measured in the z-direction. 3.1.3 Shrinkaue of polvketone and nvlon 6.6 due to moisture The dimensions of a polymeric component are temperature, time and moisture content dependent. The extent of these dimensional instability effects, especially those related to temperature and moisture content is important if the physical properties of different engineering polymers are compared. The expansion due to moisture absorption of polyketone and that of a alternative system Minlon 13TI (Nylon 6.6 with 33 %wt. mineral filler) were measured in order to obtain such a comparison.

2. i 7 4 -

2. 173 2. 172 2.i71

O. 000 min

9 7 9 5 . i 5 0 min

2. ! 7 3 mm

2.161 am

! AY

-0.012

2. 170 A

E E

2. 169 -

C 0 u~ r

2. i68

Q. x

2. t 6 7 2. 166 2. i 6 5 2.

i64

2. i 6 3 2. 162 2.16!

2. 160 0

I ' 2000

4000

6000

' "1

8000

Time (minutes)

Figure 3.3 The shrinkage of a polyketone sample due to loss by evaporation of absorbed water

! 0000

83 It proved practically impossible to keep the TMA sample immersed in water in the (small) TMA measuring cell during more than twenty days. However, measuring the shrinkage during drying instead of the expansion during water absorption is very well possible with the TMA. This assumes that the expansion (due to moisture absorption) and subsequent shrinkage (due to drying) are completely reversible effects. Witchey et al. showed that this indeed holds for poly[l(trimethylsilyl)-l-propyne] in contact with n-nonane [2]. Both TMA samples were first stored at 22~ in distilled water until an equilibrium water saturation was reached. The polyketone reached its equilibrium water saturation of 2.35 %wt. in about twenty days. The Minlon 13TI sample needed forty days to reach its equilibrium water saturation of 6.12 %wt. (based on to~al sample weight). The 'wet' samples were put in the (N2 purged) TMA and the length decrease due to moisture loss was measured as a function of time. The average temperature during these experiments was 22~ â&#x20AC;˘ 2~ (this 2~ temperature scatter was mainly caused by a day/night temperature difference). After the TMA experiments both samples were completely dried by storage at 50~ in vacuum, to determine the (residual) moisture concentration. Figure 3.3 shows the shrinkage effect of the polyketone sample due to a decrease of the moisture content from 2.35 %wt. to 0.08 %wt. in about seven days (the day/night temperature differences are clearly 'modulating' the experimental results). The smoothed results of the experiments on both samples are shown in Figure 3.4 and can (assuming a linear relation between moisture content and amount of shrinkage) be expressed as: polyketone 90.25 % shrinkage/percent of moisture loss, Minlon 13TI- 0.52 % shrinkage/percent of moisture loss.

SRMPLE T H I C K N E S S 2.78 48Ttu=t,ercont,esnt,z

DECRERSE,

G. 12 ~ut,.

Figure 3.4 Shrinkage of completely water saturated polymer samples as a function of the drying time (TMA experiment, N 2 atmosphere, 22~

2 tO l

.80

I .50

.28

.88 .G8 .38 8.88

6.6 ~~

( , ~ t t e r c o n t , ont. z 2 . 3 5 ~wt,. X,, .X X

polyketone ~ X ~ ~

~) oj

wmtercont,ent,:

8.08

~ ut,

c)o

(s) ..,.4

oJ .,"4

wat,er

+ _ I

i.,

i i

cont,ent,: _

i i

( t Cs ] ) ^ ( 1 / 2 )

85 3.2 Volume dilatometry 3.2.1 ..Introductio~ .. Polyisoprenes (IR) p o l y m e r i s e d with a Ziegler catalyst have cis contents of about 98%. The last few per cents of non-cis polymer, which makes IR different from natural rubber (NR), are very important for the physical properties of the vulcanizates. The u n c e r t a i n t y in the NMR analysis, amounting up to â&#x20AC;˘ 1 % w t . was the reason to investigate the p o s s i b i l i t i e s of dilatometric c r y s t a l l i s a t i o n rate measurements. Mitchell [3] demonstrated the use of a recording d i l a t o m e t e r for the determination of the crystallisation rate. He used as the rate characteristic the time necessary to reach 50 % of the ultimate change in volume due to crystallisation. This time is called the 'crystallisation half-time value'. The potential of the c r y s t a l l i s a t i o n half-time values to distinguish between IR batches from various sources and made under different conditions, was studied. A c o n t i n u o u s l y recording dilatometer was built for these experiments. This apparatus, the m e a s u r i n g m e t h o d and some results are d e s c r i b e d in the following sections. 3,2,2 T h e volume d i l a t o m e t e r Figure 3.5 gives a schematic d i a g r a m of the volume d i l a t o m e t e r . The cell containing the r u b b e r sample is made of stainless steel and consists of two parts which are screwed together (Figure 3.6). The lid, which contains a deep thermocouple well, is provided with a m e t a l - t o - m e t a l seal; as an extra safeguard against leakage an O - r i n g is compressed within an annular chamber outside the cell. In order to prevent b l o c k i n g by the rubber of the connection between cell and capillary, the latter is attached to the b o t t o m of the cell. Filling the system with m e r c u r y (the m e a s u r i n g liquid) and measuring is done via a system of glass capillaries and stopcocks. This permits to work at different sensitivities simply by opening one of the stopcocks, thus giving the mercury access to a capillary which acts as a shunt with respect to the m e a s u r i n g capillary. The measuring capillary tube is m e t a l l i s e d at the outside. This metallic layer acts as the fixed electrode of a v a r i a b l e capacitor, the variable electrode being the m e r c u r y inside the glass capillary tube. A wide tube which is m e t a l l i s e d except for a double slit is e l e c t r i c a l l y connected to the m e r c u r y and acts as shield. Details are shown in Figure 3.7. The variations in capacity are detected with a highly sensitive capacitance bridge assembly (Wayne-Kerr, A u t o b a l a n c e Universal Bridge B641), allowing the zero capacity of the system to be compensated, so that the variation in capacity is measured with maximum sensitivity. The bridge offers an output voltage proportional to the capacitance v a r i a t i o n which is

86 ACCESS TO VACUUM PUMP

t \ MEASURING CAPILLAR~Y

GUARD FILLING

HIGH POTENTIAL ELECTRODE ,

C A P I LLAR_Y.

BALL JOINTS

THREE-WAY STOPCOCKS

DRAIN ,.

HEAT SINK PERSPEX HOUSING DRY NITROGEN ATMOSPHERE

LOW POTE,NTI AL ELECTR,0DE

I I

STAINLESS STEEL MEASURING (~ELL

COOLING WATER I N ~

',S,~j

COOLING WATER OUT GASEOUS N 2

I ~--,

V [____

ALUMINIUM,THERMOSTAT BLOCK

COOLING (PELTIER) i ELEMENTS

ISOLATING SUPPORT

Figure 3.5 Schematic arrangement of apparatus for volumetric crystallization measurements

Figure 3.6: Sample holder

Figure 3.7: Measuring capillary

89 recorded as a function of time together with the sample temperature. The drift of the Wayne-Kerr Bridge proved not detectable by the recorder over a period of more than one week. The detection system is trimmed to ensure that the volume change during crystallisation corresponds to about full-scale on the recorder. This results in a sensitivity in (delta V)/V of the order of 10E-4. The temperature is controlled electronically with a Cu/Const thermocouple as the sensor and Peltier elements as power drains, which surround an aluminium block containing the steel cell. The measuring cell is sensitive to outside temperature variations via its metallic connection to the measuring capillary. However, this sensitivity largely eliminated by the fairly massive heat sink attached to the metal capillary inside the perspex housing, whose interior temperature varies little due to the circulation of cooling water on the 'hot' side of the Peltier elements. In general, a temperature stability of better than 0.2~ was measured. The current through the Peltier elements is reversed during the heat pretreatment of the samples (see 3.2.3). The Peltier elements act in that case as heating elements instead of cooling units. Using the Peltier elements in this way, the temperature region available ranged from -40~ up to 85~ Protecting devices are built in to prevent overheating (> 85~ and damage due to interruption of the cooling water supply. 3.2.3 The measurina procedure The rubber sample to be investigated should not contain any entrapped or dissolved air or other gas. So, prior to the admission of the confining mercury careful evacuation of the cell containing the sample is required. Other precautions to guarantee reliable measuring results are to melt any residual crystallites and to relieve any internal stress in the sample. Mitchell used a procedure of 40 minutes/100~ [3]. Martin and Mandelkern employed a thermal pretreatment of one hour at 60~ [4]. A series of scouting experiments with NR showed that one hour at 80~ was sufficient to investigate NR/IR systems. _

The system was thus heated in about I0 minutes to 80~ and kept at that temperature for one hour. Subsequently, the system was cooled in about 50 minutes to -26~ the crystallisation temperature, and kept constant at that temperature. All volume/time curves obtained in this regime initially showed a very slowly increasing slope up to a maximum at a point of inflection and a very slowly decreasing slope in the latter phase of crystallisation, so that the curve seemed to approach an end level asymptotically. The measurements were continued for at least 3 x t(0.5); further prolongation would alter the calculated half-time value only slightly. A series of seven measurements on a NR sample gives an impression of the reproducibility of these experiments-

90 tl/2,

56-

48-

40-

32-

16 & NATSYN 400 WITH 2 % STEARIC ACIO o NATSYN 2200

o o

I -e

, ,I - ~s

i - 24

,,,

! - 3z

Crystallization t e m p e r a t u r e , ~ Figure 3.8 C r y s t a l l i z a t i o n h a l f - t i m e as a f u n c t i o n of c r y s t a l l i z a t i o n t e m p e r a t u r e

91 NR, half-time value 9 141 + 3 minutes spec. volume decrease0.022 + 0.001 cm3/g (Crystallisation temperature

-25.5~

+ 0.2~

3.2.4 Isothermal crvst~llisation of IR rubber systems The c r y s t a l l i s a t i o n - h a l f - t i m e value [t(0.5)-value] was first m e a s u r e d at temperatures between -3~ and -29~ to determine the optimum crystallisation temperature. These m e a s u r e m e n t s were performed on three samples- a natural rubber and the Ziegler polyisoprene systems Natsyn 2200 and Natsyn 400 (containing 2 %wt. stearic acid as c r y s t a l l i s a t i o n promotor). The results are plotted in Figure 3.8. A smooth curve can be drawn through the m e a s u r i n g points for natural rubber and the Natsyn 2200. The Natsyn 400 results scatter more than the results of the two other samples, p r o b a b l y due to the stearic acid addition. These curves show that o p t i m u m c r y s t a l l i s a t i o n conditions are met in the temperature region from -24~ to 26~ Besides, the t(0.5)-value temperature sensitivity is low in this region. The results of a series of t(0.5)-value d e t e r m i n a t i o n s are listed in Table 3.2 along with the spectrometric data available (proton NMR at 220 MHz. and IR). There is no doubt that a variation in half-time values from I0 to 25 hours for samples of 99 %wt. cis and from 11.7 to 54 hours for those of 98 %wt. cis means that the d i s c r i m i n a t i n g power of the crystallisation data is far in excess of that of ~ R . Figure 3.9, finally, shows that m i x i n g of NR with the noncrystallising polyisoprene IR 305 (cis content < 90 %) retards the crystallisation process of the NR phase and gives a nearly proportional decrease in the final volume change. Mixing of NR with carbon b l a c k is causing the same effects. The timescale of the NR r e c r y s t a l l i s a t i o n process strongly increases due to blending the NR with IR 305 and carbon black. This sensitivity of the NR r e c r y s t a l l i s a t i o n for compounding agents offers the p o s s i b i l i t y to use this technique for mixing efficiency studies of NR based rubber compounds. References I. B. Wunderlich- Thermal Analysis, A c a d e m i c Press Inc., New York, 1990. 2. L.C. W i t c h e y - L a k s h m a n a n et.al., J. of Pol. Sc.- Part B, Polymer Physics, 31, (1993), p. 1 5 4 5 - 1553. 3. J.C. Mitchell, Techn. Rep. No. 278-60, Shell Development Company. 4. G.M. Martin and L. Mandelkern, J. Appl. Phys., 34, (1963), p. 2312.

Table 3.2 Results of t (0.5) -value determinations on commercial and experimental polyisoprene rubbers I-

,II| '

i ,I

sample

,,,

natural rubber

cis 1,4 content, NMR, %wt.

3,4 content, IR, %wt.

I00

0.00

10.0

0.5O

18.0

n.d.

20.0

0.60

21.0

0.65

25.0

12.7

n.d.

Natsyn 2 2 0 0

19.2

0.90

Natsyn 4 1 0

47.5

0.60

I PIK56, B a y e r

Z 58 Natsyn

2000

,! Amerip____~ol SN600

2.5

Z 59

[

t(o.5)value,

z sG____L____

Z 64

,,,

11 ._____/7

54.0 ,,

n.d., not determined Z numbers, e x p e r i m e n t a l

samples

........

,,,

0.45

0.80 '

A V , 10"=, cm=.g"1 _.._.f-------q

RUBBER Ar.I..4~--"4"-

1.6

1.2

RSS ~ WITH IR 305 80/20

RSS 111", IR 305 AND CARBON BLACK

0.4

1.21 AFTER 30 HOURS

RSS ]3~ WITH CARBONBLACK

Figure 3.9

Effect of compounding agents on the crystallization of natural rubber

CRYSTALLIZATION TIME, h

DYNAMIC MECHANICAL ANALYSIS CHAPTER 4

CHAPTER 4: DYNAMIC MECHANICAL ANALYSIS 4.1 The standard DMA technique 4.1.I Introduction Dynamic Mechanical Analysis (DMA) is a technique in which the elastic and viscous response of a sample under oscillating load, are monitored against temperature, time or frequency. This technique became well known by the impressive amount of information about the structure of polymers obtained with the torsion pendulum apparatus. The torsion pendulum DMA apparatus is a so-called resonant system i.e. the measuring frequency is not constant. The modern DMA systems are nearly always fixed frequency systems operating at frequencies between about 0.01 and I00 Hz. and in a temperature region ranging from about 150~ to 300~ A survey of the DMA technique and the available commercial equipment was given by Wunderlich [i]. Hooke's law describes the response of a perfect elastic material to an applied stress i.e. stress

(o)/strain

4.1

This proportionality constant is defined as: E, the elastic or Youngs modulus for tensile deformation, G, the shear modulus for shear deformation and B, the bulk modulus for compressional deformation. These three moduli are interrelated: E

2. (I

+ ~).G

3. (I

4.2

2~).B

where ~ is the Poisson ratio. Newton's law describes the response of an ideal liquid to an applied stress i.e. stress

(G)/rate of strain

(dc/dt)

--constant

4.3

This proportionality constant is called the viscosity (~). The response of a polymeric material to an applied stress shows both an elastic and a viscous component i.e. a polymer behaves visco-elastic. DMA equipment m e a s u r e s dynamically the E or G moduli; the polymer samples are assumed to behave linearly visco-elastic i.e. the stress/strain relation is only a function of time. An oscillating (sinusoidal) strain, (t) = ~0 sin ~t during such a DMA experiment results in a sinusoidal G(t)

= ~0 sin

(wt + ~)

4.4 stress4.5

with a phase difference ~ due to the visco-elastic character of the polymer sample. The absolute value of, for example, the E modulus is written as.

95 IEI

= crolco

i.e.

4.6

~o = Eo.I'~I

Substitution of 4.6 in 4.5 and application of the goniometric summing rule gives: G(t)

= E,.(iEi.sin et.cos

if, E' = IEi.cos ~ as : ~(t)

- E'.~(t)

where-

and

~ + IEi.cos ~t.sin ~) E'' = IEl.sin ~

4.7

4.7 can be written

(E''/~).d~/dt

4.8

E' = the in-phase, elastic component, see 4.1 and E' '/~ = the out-phase, viscous component, see 4.3.

The moduli can thus be written as complex values: E* = E' + iE''

G* = G' + iG'' and B* = B' + iB''

4.9

The tangent of the phase difference is given by. tan ~ = E''/E',

G''/G'

and B''/B'

4.10

Usually, the E' or G' modulus and the tan ~ are measured during a DMA experiment; E'' or G'' is then also known, according to 4.10. D M A m e a s u r e m e n t s are intensively used to investigate the amorphous phase transitions of polymers. The results of DMA studies were published by authors like Schmieder and Wolf [2], Nielsen and Buchdahl [3] and Heijboer [4]. Neat polymers, but also polymer blends and polymer systems blended with fillers, plasticisers or impact improvers were investigated by DMA. An example of such an application is given for toughened polypropylene in 4.1.2. Amorphous phase transitions (like the Tg-value for example) can be measured by DMA but also by DSC (chapter 1) and by TMA (chapter 3). The DMA technique, however, offers the highest sensitivity to detect phase transition effects. This is especially useful for the investigation of secondary relaxation effects and for the determination of very weak glass-rubber transition effects. Figure 4.1 shows the results of DMA and DSC m e a s u r e m e n t s on a (crosslinked) epoxy resin system. The (DMA) E' and the E'' curves as a function of temperature both show the system's glass-rubber transition region at about 100oc. Besides, the presence of a secondary relaxation effect with an E'' maximum at about -60~ is shown by the E'' curve. Figure 4.1 also shows the (DSC) specific heat (Cp)/temperature curve of the same sample. The glassrubber transition is easily detected by the step-wise change in the Cp/T curve at about 100oc. The higher sensitivity of the DMA technique in comparison with that of the DSC technique is illustrated by the clear absence of any relaxation effect in the low temperature part of the Cp/T curve. An example of detection of weak glass-rubber transition effects by DMA is

96 Dynamic mechanical properties of liquid DGEBA resin cured with HI-PA +

+Log E'

&Log E"

9.O0

I0.00 19.50[ +-+-4"+ + + + + + + +_+~+,,+,

OI 0 J

8.50

E,~/z~"

8.00

o~ o _J

~''~

+ +--4-

Polymer LaDS D M T A he~ltir~l rate: 2 C/rain

7.50 I-

.~~y:

10 Hz

-90

-30

7.50

7.00

- 150

150

210

Temperature. degrees C Si3er162 heat/temperature relation of liquid DGEBA resin cured with HHPA 0.75

0.75 0.63

,J~'m~le wet aht: ~K24 rr~

0.50 "~_

0.63

F~rk~ Eml~r D$C2 I~atlr~ rst~ 20 C/rain

0.38

0.50

4.+--+--+ I I + `+

0.38

d. 0

/+.-"

0.25

0.25 0.13

0.13 0.00 - 150

' -90

-30

Temperature.

Figure

4.1

DMA/DSC

90 degrees

150

0.00 210

results

comparison

d (J

97 given for rigid polyurethane foam systems in 4.1.3. Performance and results of dynamic mechanical measurements at ultrasonic frequencies, finally, are reported in chapter 4.2. 4.1.2 DMA analysis of DolvDroDvlene/ethvlene-DroDvlene rubber blends Polypropylene (PP) is often blended with ethylene/propylene (EP) rubbers to improve the impact resistance. This so-called toughened PP (TPP) can be a mechanically blended PP/C2C3 rubber system or an in-situ polymerised PP/C2C3 rubber system. A number of rubber parameters (like concentration, particle size, particle size distribution, crystallinity, molecular weight etc.) determine the ultimate effect of the rubber addition on the impact resistance. DMA is one of the analytical techniques often used to investigate blends of polymers with an impact improver. The determination of the relation between the area of the rubber relaxation m a x i m u m as measured by DMA and the rubber concentration is usually a first step in such an investigation. The method to determine this area and the results measured on a series of PP/C2C3 rubber blends are reported below. These results were measured with an automated torsion pendulum apparatus. A rectangular sample strip of 50 x i0 x I mm. acted in combination with a steel suspension wire and a rotating mass as a visco-elastic spring. The measurements were performed while the sample temperature continously increased at a rate of l~ The storage shear (G') modulus and the loss shear (G'') modulus were determined from the free, damped vibrations (frequency about 0.5 Hz.) according to (4): G'

= ((omega^2 - a l p h a ^ 2 ) . F J -

G''

= (2.alpha.omega.FJ)/FI

CST)/FI

4 .II 4.12

where omega- 6.2832/vibration time, alpha: log. decrement of the damped oscillation, FJ : moment of inertia of rotating mass, CST 9 torsial stiffness of the suspension wire, FI : geometrical stiffness factor of the rectangular sample Figure 4.2 shows the DMA results of a PP/talc (85/15) system represented in the standard way i.e. the log G' and log G'' plotted as a function of the temperature. The loss shear modulus curve shows relaxation maxima at about 60~ (the crystalline phase [u] relaxation) and at about 0"C the amorphous phase glass-rubber [K] relaxation). Blending such a PP sample with a C2C3 rubber results in an extra (rubber) relaxation maximum at about -50~ A reproducible base-line drawing procedure and a kind of peak deconvolution procedure is necessary to determine the area of this rubber loss maximum and that of the original PP relaxation maxima. A computerised deconvolution program for the separation of overlapping DMA loss maxima was described by

98 Figure 4.2 Dynamic mechanical properties of PP filled with talc (15%wt.)

storage rnodu/us

loss modu/us

I'0

I e+09

::3

"0 0

0 0._ c. c o~

coo

9 v 1

Z 3

0 O0

A-z~,,AJ

\ le+08 -90

-50

..I

-10

Temperature, deg. C

,.~--

3e+07

110

99 Charlesworth [5]. We still manually "deconvoluted" the loss maxima of the investigated PP samples by applying Heijboer's approach [6] which is based upon the symmetry of the loss maxima around 1/Tmax. when the loss values are plotted on a linear scale as a function of the reciprocal absolute temperature. The DMA results of the PP/talc sample in Figure 4.2 were replotted in this way, see Figure 4.3. The three partly overlapping PP relaxation effects hampered the drawing of a straight base-line in Figure 4.3 as suggested by Fay et al. [7]. A curve fitting model with two fixed points (1/T = 2.40 and 1/T = 5.40) was used to draw a baseline in a standardised way, see Figure 4.3. This curve fitting model was, subsequently, used to draw a baseline in all the experimental PP/C2C3 rubber loss curves. In Figure 4.4 data are replotted with separated effects for both relaxation maxima (based on symmetry around the 1/Tmax. axis) and after subtraction of the background loss. Figure 4.5, finally, shows the result of this procedure for a PP/C2C3 rubber/talc (70/15/15) blend. The loss relaxation areas of these two samples, determined by integration, were:

PP/talc (85/15) PP/C2C3/talc (70/15/15)

PP u-rel. (Nm-2 .K-I)

PP E-rel. (Nm-2 .K-I)

6.7E3

12.2E3

9.7E3

20.6E3

C2C3 rubber rel. (Nm-2 .K-I)

6.1E3

The rubber addition results, as expected, in the presence of a low temperature rubber loss maximum. The D M A m e a s u r e m e n t s also show, however, that a part of the added rubber phase influences the intensity of both PP relaxation effects. Such an effect might be important for the toughening efficiency of the used type of rubber. A series of PP/C2C3 rubber blends was measured, subsequently, to investigate the relation between the loss modulus areas of the rubber relaxation effects and the rubber concentration. The results of these measurements are listed in Table 4.1 and plotted in Figure 4.6. The Vistalon 404 and 4608 are amorphous C2C3 rubbers, while Vistalon 5600 contains a crystalline fraction of 4 %wt. The Nordel 1500 and 3391 are typical semi-crystalline C2C3 rubbers with crystalline fractions of respectively 15 %wt. and 12 %wt. Each of these rubbers was added to the PP in three different concentrations i.e. 10, 15 and 20 %wt. 0nly the amorphous fraction of these C2C3 rubbers is assumed to contribute to the measured low temperature rubber loss maximum. The difference in loss relaxation area between the amorphous C2C3 n ~ b e r s (including Vistalon 5600) and that of the amorphous phases of the semi-crystalline C2C3 rubbers is striking, it might be (one of) the reason(s) for the differences in toughening efficiency between these rubbers. Futhermore, the amorphous phase loss areas of the in-situ

i00

Figure 4.3 Loss modulus of PP filled with 15%wt. of talc as a function of the reciprocal absolute temperature

,+,+

65 60 L'q

r-50 (_9.-E

0 ~-45

I,b I/)

0 ..J

il II +

40 35

25 I

2.40

i+,++ +

+/ +

~---I- -'-+ - " + - - + ' - - + --'4 f

,.I

2.83

3.26

3.69 1000/T,

4.11

4.54

K ,, - 1

4.97

5.40

i01

Figure 4.4 Results of Figure 4.3 after subtraction of the background losses

45 40 35 0,1

(9 ~r" 2 5 (b

..._,

0 -

,,.....

E (/) u) 0 _.l

15 10 ~ I

5 0 2.40

/ I

-I-

i.%

2.83

,', I

3.26

2~ .... I

3.69

1000IT,

4.11

4.54

K(- 1)

4.97

5.40

0 0 0

4~ O

Lo",4

ยง

"' I

O7 '

~ + ~ + ~

O7 '

+~+._~+_.j:l:

~~+

~-I-..,..~.i_ ) ~โ ข

,~+~

_......4...---"+" ~ + ~

'--.

,-, -.

(Millions)

corr. loss modulus (G"), N.m2 '

0 '

_~.

~'~-

,..i.

o'mb~

~0 " -3 ~a

C)~c=

103 polymerised systems fit fairly well with the data of the mechanically blended semi-crystalline rubbers. Table 4.1 Amorphous rubber fractions versus loss relaxation areas (DMA analysis of PP/C2C3 rubber blends) r

Ill Ill

I amorphous rubber fraction

loss relaxation area Nm-2. K-I ,

i Nordel 1500 0.085 0.128

o.~vo

I Nordel 3391 0.088 0.132

0.Iv6

......

sys. sys. sys. sys. _

A B C D

0. 019 0. 022 0. 154 0. 083 If

amorphous rubber fraction

rll

, ,I'

loss

relaxation

area Nm-2. K-1

2.2 E3 3.4 E3 4.5 E3

Vistalon 404 0.I0 0.15 0.20

4.1 E3 5.5 E3 6.4 E3

2.3 E3 3.9 E3 4.8 E3

Vistalon 4608 0.10 0.15 0.20

3.6 E3 5.3 E3 6.7 E3

0.7 0.2 4.0 1.9

Vistalon 5600 0.096 0.144 0.192

4.0 E3 5.0 E3 7.3 E3

E3 E3 E3 E3

.....

,,,,

a. Nordel 1500 C2C3 rubber with 15 %wt crystallinity i.e. 10 %wt. Nordel 1500 in PP results in an amorphous rubber fraction of 0.085. b. Nordel 3391 C2C3 rubber with 12 %wt. crystallinity. c. Vistalon 5600 C2C3 rubber with 4 %wt. crystallinity. d. Vistalon 404/4608 crystallinity < 0.5 %wt. e. Systems A, B, C and D are experimental, in-situ polymerised TPPs, the amorphous rubber content of these rubber phases were determined by NMR on the extracts of the 'hot xylene solubles' (HOXS) procedure; the reported loss area is the difference between TPP loss area and the HOXS residu loss area.

104

Figure 4.6 Loss relaxation area versus amorphous rubber content

sere~c. C 2 C

amorph, C2C3

/n--situ systems

8 A

7 I O4

cO I..U

k,_

cO c 0

0 __1

0.00

0.04

0.08

O. 12

Amorphous rubber

O. 16

fraction

0.20

105 4.1.3 Tu-value determination of aqed. riuid pU foams bv DMA Insulated pipes used for district-heating Systems consist of a steel inner pipe, a rigid polyurethane (PU) foam insulation layer and a PE pipe on the outer side. This foam should be capable to withstand prolonged contact with the hot steel surface of the inner pipe, retaining thereby its original high thermal insulation value. Rigid PU foams are the reaction product of an excess of a n isocyanate, a polyol and some water resulting in a polymer network with a high crosslink density. The excess of isocyanate used is indicated by the MDI index i.e an index of 135 means an excess of isocyanate of 35 %. The water added also reacts with the isocyanate under formation of C02 which acts as an 'internal' blowing agent. An 'external' blowing agent, evaporating by the reaction heat, is usually added also to obtain the desired foam density. New PU foam formulations are anaerobically aged to test the heat resistance of the foams. The ageing process is monitored by measuring foam properties like weight, density, strength and thermal conductivity as a function of ageing time/ temperature. The Tg-value of such a foam was thought to be also an interesting property to monitor the ageing process in view of its close relation with the chemical structure of the foam. Straightforward DSC Tg-value determinations on such foam samples failed, which was ascribed to too low sample weights. Cyrogenic milling of foam samples, followed by pressing the powder obtained into sample pills increased the sample weights from about 3 mg. to about 15 mg. The sensitivity of the DSC still proved insufficient to produce reliable Tg-values of these highly crosslinked systems. Subsequently, a foam strip of 8 x 12 x 2 ~ was carefully clamped in a Polymer Laboratories DMA system and measured using a frequency of 10 Hz. and a heating rate of 1"C/minute. Figure 4.7 shows the result of such a measurement. The decrease of the Youngs modulus at temperatures > 120oC, accompanied by clear maxima of the loss modulus and the tan 8 indicate that the glass-rubber transition of such a foam is easily measured by DMA. The loss modulus (E") maximum temperature was chosen to indicate the Tg-value of these rigid foam systems. The Tg-value development during anaerobic ageing of six differently formulated foam systems was then measured. Formulation 2 (MDI index 115) and formulation 1 (MDI index 135) show the effect of a MDI index decrease from the standard value of 135 to 115. These two systems also containted some glycerol next to the standard polyol. Formulation 3 is equal to formulation 1 but contains no glycerol. The formulations 3 to 6 (MDI index 135) were added to show the effect of a partial replacement of isocyanate by respectively 10% (4), 15% (5) and 20% (6) of a liquid epoxy resin.

Figure 4 . 7

LogE"

?.4

LogE"

Results of the DMA analysis on the rigid PU foam sample i

(Pa) II

Tan d e l l ; a

.4.

~ T

8.8

8.2

II a

ยง

5.0

X x

ยง

- l._._llallaoaoo 9149

s 9

__.., 9149

IlllmldlolNlmqm'-

ยง

LI~B

5.8

Temperature (~

1~8

i 2~

IB Hz STRRZH -,x4 L degC,,'ml n -LOGk- 3.?? SZNGL.s C F I C r 2x t 2 x ? . l h m CLFII4~ H / C

~ i

5.?

ยง m9

I-= 0

5.9

5.8

IIl~ 9

49 ยง

IZIMTFI

X 9

.#.~+#"

6.1

E'/E"

IIII 9149

8.2

F'ZI.~t Ba214 BYHI~ ON O0O511O

107 The results of DMA Tg-value determinations on these foam samples during ageing at 160oC, are listed in Table 4.2. These results show three different stages in the ageing process of these foams: - first, the Tg-value increases i.e. the fresh, non-aged foam is not completely cured and the crosslinking reaction(s) proceed due to the relative high ageing temperature, - then, the cure processes are completed and the Tg-value remains constant for a certain period of time and, finally, - the thermal decomposition process starts and results in a decrease of the Tg-value as a function of the ageing time. The three Tg-value/ageing time curves in Figure 4.8 show these three stages. The Tg-value of these foams with a more or less standard formulation i.e. the systems I, 2 and 3 is about 160~ after preparation. The ageing time at 160~ after which these six foam systems (during the third stage) again reach this Tgvalue is used as criterium to compare the (long term) thermal stability of these foams. These times are plotted as a function of maximum Tg-value of the foams in Figure 4.8 (insert). The partial replacement of MDI by epoxy resin clearly increases the maximum Tg-value of the foams and thus their long term thermal stability. A MDI index increase from 115 (formulation 2) to 135 (formulation I) results in a Tg(max.) increase of about 20oC and this also improves the long term thermal stability. Additional Tg-value determinations on foams aged at different temperatures proved subsequently, to supply excellent data for foam life-time predictions.

Table 4.2 Results of DMA Tg-value determinations foams form. number

Tg before

Tc [ ~ p~ )i

189

161

195

190

176

175

158

. . . . . . . . . . .

2 ,,

160

1{ 0"C "C

T,g, 3 m,3nth 1,50"C 0C

,....

~79 th6

TllC I

186

184

142

183

180

193

196

155

183

197

195

198

199

202

201

.........

. . . .

190 i,,

III

160

. . . . . . . .

Tg, 9 month 160oc oc

184

on aged PU

,,, ,,,

,,,

LI,

,_t

141

197 i

203 .

184

::3"

::3

,,,,_1,,,

(1)

,-1.

(.Q

(.Q (1)

r,o 9

,.,,.,Ik

IX)

O (.TI

---,.

"o c

~ ...

-L~

k.) rj'l

. . . . .

"4 .

Ageing time at 160~

_.~-+

(.,0 (.71

r .

. _

month - . .

._L 0

--I.

Tg-value (E" max.), deg. C ~

IX3

::3

13 o

r t~ ID. :3 ~3

:3t~

=,,,,~

o :3 0

,,,,IN

r :3 c3 =,-i.

"13 C

--.1"1"1

109 4.2 Mechanical measurements

at ultrasonic frequencies

4.2.1 Introduction The term ultrasonics is used to describe mechanical waves propagated in gases, liquids and solids at frequencies above the upper limit for the human ear i.e. above 16,000 Hz. The characteristics of these waves are related to the mechanical properties of the medium through which they pass. Ultrasonics can be used, therefore, to investigate these properties. From a practical point of view one can consider two separate cases, one where the wavelength is much greater than and the other where the wavelength is much shorter than the sample thickness. The first case is usually called acoustic elastometry (frequencies ranging from 20 kHz. to 200 kHz.) and the second is called ultrasonic elastometry (typical frequencies 0.5 MHz. to 5 MHz.). When ultrasonic waves pass through a medium, the particles of that medium start to vibrate at ultra-audible frequencies. Part of the energy of the vibrating particle is transmitted to neighbouring particles. Because subsequent particles start their vibration one after the other with a slight time delay, the vibrational motion travels with a finite velocity c known as the wave velocity. The phenomenon is described as wave motion. Two kind of waves can be propagated in infinitely solid media- longitudinal waves and transversal waves. Longitudinal waves can be propagated in all types of media, the particles of the m e d i u m vibrate then in the direction of the propagation. Transverse or shear waves need shear elasticity and can therefore only be propagated in solids while the particles of the m e d i u m vibrate in a direction perpendicular to that of the propagation. The ultrasonic velocity and absorption (measured to examine the elastic properties of a material) can be determined using different experimental methods. A describtion of these methods is given by Philipczynski et al. [8]. The immersion technique in combination with the pulse propagation technique is commonly used to investigate polymeric systems [9, i0]. In the immersion technique, the sample, transmitter and receiver are all immersed in a liquid. Ultrasonic pulses are sent from the transmitter to the receiver both with and without the sample in the path of the sound beam. Longitudinal waves are developed in the sample when the sample is held p e r p e n d i c u l a r to the path of the sound beam. If the sample is held at an certain angle to the sound beam both !onuitudional and shear waves are generated in the sample. The longitudinal waves are totally reflected and only the shear waves are propagated if the angle at which the sample is held is greater then the socalled critical angle. .

The immersion of the system in a proper liquid ensures a good coupling between transmitter~sample~receiver and promotes" the temperature control of the system. When a wave is incident normally to the boundary between two media both transmission and reflection occur. ~"ne reflection coefficient is high for

ii0 w a v e s p a s s i n g f r o m a s o l i d or a l i q u i d to a gas i.e. u l t r a s o n i c w a v e s p r o p a g a t e d in s o l i d s / l i q u i d s do not p e n e t r a t e in the s u r r o u n d i n g air. W i t h the s a m p l e p e r p e n d i c u l a r to the u l t r a s o n i c b e a m and the b a s i c v a l u e s l i s t e d b e l o w k n o w n or m e a s u r e d : L = the s a m p l e thickness, m 1 - the t r a n s d u c e r distance, m tl - the p u l s e p r o p a g a t i o n time w i t h o u t the sample, s A1 - the p u l s e a m p l i t u d e in the liquid, V t2 - the p u l s e p r o p a g a t i o n time in the l i q u i d / s a m p l e / l i q u i d , s A2 = the p u l s e a m p l i t u d e in the l i q u i d / s a m p l e / l i q u i d , V pl = the d e n s i t y of the liquid, kg/m3 p2 = the s a m p l e density, k g / m 3 the u l t r a s o n i c p r o p e r t i e s can be c a l c u l a t e d [8, I0]. The propagation v(liq) tltl

= i/tl,

I/v(liq)

speed of the w a v e s

(i-L)/v(liq)

- L/v(1), in the

[v(liq).L]/[L

The propagation isv(s)

4.13

a n d t2 =

s p e e d of the w a v e s =

is:

m/s

- t2 - L/v(liq)

v(1)

in the l i q u i d v(liq)

+ L/v(1)

the l o n g i t u d i n a l

s a m p l e v(1)

hence, propagation

is: 4.14

- v ( l i q ) . (tl - t2)]

s p e e d of the shear w a v e s

- v(liq). [(cosu - v(liq) . (t2'-tl)/L)'

in the s a m p l e v(s) + sin'a]*"

4.15

w h e r e u is the a n g l e of i n c i d e n c e b e t w e e n sample and sound b e a m a n d t2' is the p u l s e p r o p a g a t i o n time t h r o u g h the liquid/ s a m p l e / l i q u i d in the s h e a r mode. For the w a v e s t r a v e l l i n g from the l i q u i d into the s a m p l e holds: sinu/v(liq)

T h e a n g l e u is c r i t i c a l sinu(c)

4.16

- sin~/v(1) if the sin~(1)

= 1, hence

= v(liq)/v(1)

v(1) a n d v(s) can be u s e d to c a l c u l a t e the e l a s t i c G, B a n d E in N / m 2 and the P o i s s o n r a t i o ~G =

[v(s)]'.p2

B =

[v(1)]'.p2

E = 3G/(I

= 0.5

constants 4.18

- 4G/3

+ G/3B)

- E/6B

4.17

4.19 4.20

4.21

iii Amplitude A2 is smaller than amplitude A1 due to internal friction effects in the sample i.e. a b s o r p t i o n takes place (the liquid a b s o r p t i o n << rubber a b s o r p t i o n is neglected). There is also signal loss due to reflection losses. The reflection losses of the two rubber surfaces can be c a l c u l a t e d according to [i0] : 4.22

Lr - Ln[(Zl + Z2)~/(4.ZI.Z2)] where Z is the acoustic Z2 - p2.v(1).

impedance i.e.

Zl = pl.v(liq)

and

The total signal loss is expressed asLi = Ln AI/A2

4.23

The attenuation coefficient of the sample for longitudinal waves u(1) is then calculated in N e p e r s / m byG(1)

(Li

Lr)/L

4.24

The absorption losses can also be expressed in an u l t r a - s o n i c loss factor according to [9] 9 Loss factor = [u(1).v(1)]/~.f

4.25

4.2.2 The ultrasonic m e a s u r i n g ...~quipment .. An ultrasonic m e a s u r i n g system was d e v e l o p e d to measure the attenuation c o e f f i c i e n t / l o s s factor of car-tyre rubber samples as a function of the t e m p e r a t u r e b e t w e e n about -40"C and 150"C. These m e a s u r e m e n t s were p e r f o r m e d on sample disks of v u l c a n i s e d rubber having a d i a m e t e r of 60 mm. and a thickness of 13 mm. The sample holder system used contains six sample apertures. Five samples are m a x i m a l l y p l a c e d at the same time in this holder to keep one aperture free for the reference measurement, see Figure 4.9. This whole sample h o l d e r system is lifted into a special thermostat bath p r o v i d e d with a liquid nitrogen cooling coil. This cooling p o s s i b i l i t y extends the lower temperature limit of these m e a s u r e m e n t s from 20~ to about -50"C. The bath is filled with a mixture of w a t e r / e t h y l e n e glycol (1/1) for m e a s u r e m e n t s b e t w e e n -50oC and 80~ Silicone oil (100 cS.) is used as m e d i u m for m e a s u r e m e n t s between 0oC and 200"C. The sample temperature is m e a s u r e d by a p l a t i n u m resistance thermometer, p l a c e d as close as possible to the sample in the ultrasonic beam. The sample holder can turned around in the YZ-plane (the transducers axis being the X-axis) to bring sample after sample into the u l t r a - s o n i c beam. The whole sample holder system can be rotated in the X Y - p l a n e to change the angle of incidence between 90" for longitudinal wave measurements, to 0 ~ to p e r f o r m shear wave measurements. Both t r a n s d u c e r arms are moveable in the X - d i r e c t i o n to change the

112

Figure 4.9: US total immersion sample holder system

113 transmitter/receiver distance. Besides, a micrometer controlled movement of both transducers in the Y-direction possible. This offers the possibility to correct for deviation of the ultrasonic b e a m during shear wave measurements.

One inch immersion transducers (Panametrics) are used with resonance frequencies of respectively 0.48 MHz., 0.70 MHz., 0.90 MHz. and 4.0 MHz. These transducers can be used for measurements between -50"C and 80~ The two transducers shown in Figure 4.9 are special high temperature transducers (resonance frequency 1.0 MHz.) which can be used up to 200~ Figure 4.10 shows the block diagram of the electronic setup. A pulse generator produces a 200 Hz. rectangular voltage which negative going side triggers trigger unit one (T1). The five #s. pulse produced by T1 is used to trigger the timebase of the oscilloscope and to start trigger unit two (T2). The timebase of the oscilloscope thus starts 5 #s. before the ultra sonic pulse begins, to display both the transmitting and the receiving pulses completely on the scope. The T2 pulse is adjustable between 1 and 80 ~s. A pulse length of 25 ~s. is commonly used. The T2 pulse triggers the HP3312A function generator which produces a sine wave 'filled' pulse of 25 #s. This pulsed signal is amplified to a signal of about 200 Vpp. and send to the transmitting transducer. T2 also starts the HP5327B counter. The receiving transmitter produces a signal of about 28 Vpp under standard conditions (temperature 20~ frequency 0.90 MHz., transducer distance 0.10 m. and a water/ethylene glycol medium). The amplitude of the signal received is read-out via scope channel Y1. The adjustable level detector permits a manual choice of the trigger moment on the starting-flank of the receiver pulse, even if there is some signal distorsion due to high absorption levels of rubber samples going through their glass-rubber transition regions. The detector triggers a one-shot circuit which produces the counter's stop pulse. The pulse travelling time (counter read-out) and the receiver transducer output signal (oscilloscope read-out) are measured with and without a sample in the ultrasonic beam and used subsequently to calculate the ultrasonic properties. 4.2.3 Results of ultrasonic measurements on car-tvre ~lhbers. The physical properties of a car-tyre rubber compound are a compromise between a number of often opposite demands, see 1.2.1. Two of such demands are the holding behaviour on wet roads, the wet grip (WG-value) and the rolling resistance (RRvalue). The contribution of the rubber phase to these two properties seems to be clear: increasing dynamic mechanical losses are in general causing an increase of both properties. This is good for the WG-value which has to be high for safety reasons. The RR-vaiue, however, has to be as low as possible for economical reasons.

114 200 Hz. -| -] OSC.

X 46 8

TEKTRONI

J LI

scope trigger __ _

digital storage scope

,,,

samp

f u n c t ~ on

RF amp I ~ f ~ e r

generator

I ,,

HP 5327B timer/counter

start

ii_. ,,

..........

stop

200 Hz. ,

_1 !

, ,H . I I I

I ! ! !

ps.

"~25

Figure 4.10 US electronic diagram

~s.

I I I

115 However, there seem to be possibilities for a compromise. The RR-value is related mainly to the dynamic mechanical losses at frequencies of about 10 Hz. in the temperature region 30~ 60~ The WG-value, on the other hand, is the sum of a macro hysteresis and a micro hysteresis effect. The dynamic losses in the glass-rubber transition region of the rubber at frequencies of about i0 Hz. seem to correspond with the extent of the macro hysteresis contribution, whereas the dynamic losses in the high frequency region (40 kHz. up to 10 MHz.) seem to correspond with the extent of the micro hysteresis effect. This might offer possibilities to increase the micro hysteresis i.e. the WG-value by influencing the rubber structure at an equal or only slightly increased RR level. The dynamic mechanical losses of a series of six (emulsion) styrene butadiene rubber (SBR), (solution) styrene butadiene rubber (SSBR) and butadiene rubber(BR) samples with a known (laboratory) WG-rating were measured in their glass-rubber transition region. This, to investigate if a high frequency loss/temperature region, especially related to the WG-rating of these samples, could be specified. Figure 4.11 shows four of the experimental curves, the loss factor values being calculated according to equation 4.25. Subsequently, the correlation coefficients between the ultrasonic losses of these samples at a certain temperature and their WG-ratings were calculated with a temperature interval of five degrees. The results of these calculations are plotted in Figure 4.12. The curves in this figure show that the ultrasonic losses measured at 5~ MHz and at 10~ offer the highest correlation coefficient values. The WG-rating/ultrasonic loss (10~ relation is shown in Figure 4.13. The commonly used DSC Tg(onset)/WG-rating relation is also shown in the inserted figure. These data show that the correlation WGrating/rubber property improves considerably if high frequency loss data are used instead of the commonly used (low frequency) DSC Tg-value data. The mechanical properties of an experimental SSBR sample were measured between -30oC and 5oC, see Table 4.3. A data set used to calculate these properties according to the equations given in 4.2.1 is given below as an example: Sample : Sample thickness: Frequency : Temperature : Medium : v(liq) v(1)

black vulcanised 0.0134 m., 0.48 MHz., - i0 o C, silicone oil,

SSBR

(50 phr carbon black),

: 1189.0 m/s, : 2404.5 m/s,

The critical angle necessary to measure the shear velocity is then according to equation 4.17- 29.6 ~

--I

| 0

~ยง

0 ~,

b '

~ยง

~~J"

' "~

~ L o s s factor(0.94 MHz)

0 ~0

+ +

,~'"

"X~

x;'"

Ill / ~+

ID 0

0 ''

0 '

t~o

0 o

-~0~

~ ~ z

.:rE.._,<

4-/'I" o~cr

~__J-~~,.

"1>,,~

ยง

0 :3

"TI

13"

0 .-h

_~.

m c

~~ ~

o~"

W 0

(1) D)

(I)

0 ~

.........~

Correlation coefficient

...... ,

~!>~

!> ~

~ _1_~ E I " ~

~ +'~x

. . . . .

0 0

i I

118

Figure 4.13 Correlation between ultrasonic loss at 10~ and 0.9 MHz and the W.G. rating

0.16 r,,2

0.995

0.14

0.12 N

1Correlation between the DSC onset Tg-value and the W..Q. rating

0.10 0

-31o

0.08 0.06

r , 2 = 0.924 /

-'4O

0o 6

0 m o c 0

./+

--~o

m i IU r..

-70

0.04

I--- .-eo O 03 Q -9o

0.02

-110 70

, 90

, 100

110

t20

Locked wheel Wet Grip rating

0.00 G 70

100

110

120

Locked wheel Wet Grip rating

130

140

15r

119 This experimental situation is drawn in Figure 4.14. The deviation of the u l t r a - s o n i c b e a m from the 'main' X-axis, to the shear waves is clearly visible.

due

The m i c r o m e t e r controlled m o v e m e n t option of the receiver in the Y-direction is used to move the receiver in such a way that the receiver signal again reaches its m a x i m u m value. V(s) is calculated, subsequently, a c c o r d i n g to e q u a t i o n 4.15.

v(s)

948.5 m/s,

Using v(1), v(s) and the rubber specific weight at -10~ (945.3 kg/m3) the elastic p r o p e r t i e s can be c a l c u l a t e d using the equations 4.18 - 4.21G modulus B modulus E modulus Poisson ratio

: 8.5E8 N/m2, 9 4.3E9 N/m2, : 2.4E9 N/m2, : 0.41

The results are p l o t t e d as a function of the temperature in Figure 4.15. M e a s u r e m e n t s like this are time consuming m a i n l y due to the rather long times n e c e s s a r y to reach constant temperature conditions. These results illustrate however the advantage of this technique, m e a s u r e m e n t of all three moduli and the Poisson ratio during a single experiment.

Table 4.3 Results rubber ,

, ,,

temp. , "C

,,,

of moduli m e a s u r e m e n t s ,

. _ ,

E modulus xE9 N/m2

B modulus

xE9 N/m2 3.1

i.I

3.7

1.5

-5

4.1

-10 -20 -30 * medium:

1.9

" I

G modulus 3.7 t,

....

6.8

0.42

I0.4

5.2

3.2

11.5

......

,,,,

silicone oil

0.43

2.9

5.2

4.8

0.44

8.5

Poisson ratio

xE8

2.4

4.3

at 0.48 MHz.

,,,,

0.41 ,

0.40 ,

0.40 +

,-,,

I,~,,

on SSBR

/ Rubber samp le I

v(s) I

4III

~t- I

Receiver

Transmitter II(i) i ( o . I)

i(o.s)

Figure 4 . 1 4

/ vci)

Shear velocity measurement

29.6 90 e

" 23.2 *

Sample

: solution

Temperature

: -

Medium Transducers

SIBR

9s i l i c o n e

oil

: Panarnetrics

0.5

k44z.

121

Figure 4.15 Elastic moduli of solution SBR (measuring frequency 0.48 MHz) +

le+ 10

mod

rood

r a rio

0.51

- 0.49

0.47

. . . . . .

le+09

j'-o

- O.45 0

ยง

+.--

le+08

-35

-25

- 0.43 0

-15

Temperature,

-5 deg.

0.39

5 C

Q.41

122 References 1. B. Wunderlich- Thermal Analysis, Academic Press Inc., New York, 1990. 2. K. Schmieder and K. Wolf, Kolloid Z., 134, (1953), p. 149. 3. L.E. Nielsen and R. Buckdahl, J. Appl. Phys., 21, (1950), p. 607. 4. J. Heijboer, Plastica, 19, (1966), p. 11. 5. J.M. Charlesworth, J. of Mat. Sc., 2~, (1993), p. 3 9 9 404. 6. J. Heijboer, Mechanical Properties Of Glassy Polymers Containing Saturated Rings, Thesis TU Delft, (1972) . 7. J.J. Fay, D.A. Thomas and L.H. Sperling, J. Appl. Pol. Sc., ~/, (1991), p. 1617. 8. L. Filipczynski et.al.: Ultrasonic Methods of Testing Materials, Butterworths, London, 1966. 9. H.A. Waterman, Kol. Zeitschrift & Zeitschrift fur Pol., 192, 0kt. 1963, p. I. 10. B. Hartmann and J. Jarzynski, J. Acoust. Soc., ~_~, 5, (1974), p. 1469.

THERMO-ELECTROMETRY

CHAPTER 5

123 CHAPTER

5" T H E R M O - E L E C T R O M E T R Y

5.1 The DC and AC properties

of polymers

5.1.1 Introduction Thermo-electrometry is a group of thermo-analytical techniques in which an electrical property of a sample is monitored as a function of the temperature or time. An electrical property is seen as the response of a polymer when an electric field is applied to it. In contrast to metals, where electronic conduction is the only response to an electrical field, polymers may respond in different ways. A review of the different possibilities is given recently by C.C. Ku and R. Liepins in their "Electrical properties of polymers; chemical principles [I]. Ku and Liepins separate the response of polymers to an electric field into two main partsi. The dielectric properties and 2. the bulk conductive properties. These two parts are subsequently split up into four fundamental parameters, characterising the dielectric properties of polymersIA. The dielectric constant, representing polarisation and lB. the dielectric loss angle, representing relaxation phenomena. 2A. The conductivity, representing the electrical conduction and 2B. the dielectric strength, representing breakdown phenomena. In addition to these four fundamental parameters, special electrical properties are recognised like: piezo-, pyro-, ferro- and tribo-electricity and photo voltaic/conducting properties. The contribution in this chapter will be limited to three of the four fundamental parameters: AC measurements (IA/IB) and DC measurements (2A). Besides, attention will be given to a kind of combination of AC and DC measurements- the thermally stimulated discharge (TSD) analysis technique. An analysis technique used to detect relaxation phenomena in organic and anorganic materials.

124 5.1-2 DC p r o p e r t i e s of p o l y m e r s Polymers, a l t h o u g h often c o n s i d e r e d and u s e d as electrical insulators, are never ideal i n s u l a t i n g materials. There are always some charges present w h i c h are free to move in an electrical field (E). For p o l y m e r i c systems these charges are m a i n l y ionic species. The current d e n s i t y due to the presence of an e l e c t r i c a l field m a y be d e s c r i b e d in general byj (i) - n(i).z(i).v(i) where:

5.1

n(i)

= the number of charge carriers of type i per unit of volume, z(i) = the charge on each carrier and, v(i) = the mean v e l o c i t y of this type of carrier. N(i) and v(i), and - if different ions are present - z(i) can be i n f l u e n c e d by common v a r i a b l e s such as temperature, p r e s s u r e and electrical field strength. In contrast to good conductors like metals, the specific v o l u m e r e s i t i v i t y [E/j(i)] of p o l y m e r s is- f i e l d - s t r e n g t h dependent, d e c r e a s i n g with i n c r e a s i n g - i n c r e a s i n g with i n c r e a s i n g -

temperature pressure.

and,

A r e c t a n g u l a r sheet of p o l y m e r b e t w e e n on b o t h sides a c o n d u c t i n g p l a t e forms a capacitor. Such a c a p a c i t o r can be used to m e a s u r e the p o l y m e r ' s volume resistivity. A p p l i c a t i o n of a voltage (U) over b o t h c o n d u c t i n g plates results, after a c e r t a i n p e r i o d of time, in a constant current f l o w i n g through the p o l y m e r sheet I(dc). Then holds: - (Rx.A)/d and Rx - U/I (dc)

5.2

where"

G = the specific volume resistivity, O h m . m A = the c o n d u c t i n g plate area, m2 d = d i s t a n c e b e t w e e n the c o n d u c t i n g plates, m Such an e x p e r i m e n t shows, however, that it takes time to reach this constant I(dc) value. This is caused by a p o l y m e r effect, the polarisability.

A p p l i c a t i o n of a voltage (U) over both c o n d u c t i n g p l a t e s w i t h o u t the p o l y m e r sheet inserted, results i m m e d i a t e l y in charges +Q and -Q on the plates. Charge and v o l t a g e are l i n e a r l y related a c c o r d i n g to. 5.3

Q = Co.U = ~o. (A/d) .U where:

Q = the charge in Coulombs and, co = the d i e l e c t r i c constant in vacuum, (8.85E-12 Farad/m), Co = thr c a p a c i t a n c e of the parallel plate

system.

An increase of Q to Q' at the same a p p l i e d v o l t a g e is m e a s u r e d some time after the p o l y m e r sheet is inserted b e t w e e n the c h a r g e d c o n d u c t i n g plates. For Q' holds-

125 Q' = Cx.U = ~o.cr. (A/d).U = Er. Co.U where.

~r = the (static) polymer

5.4

relative dielectric constant of the

This increase in charge is, two effects [i]-

for non-polar materials,

due to

I. Electronic polarisation, due to the displacement of the electrons relative to the atomic nuclei. The c h a r a c t e r i s t i c time for this contribution, de, is below E-16 s. 2. Atomic _ Dolarisation, associated with the displacement the atomic nuclei relative to another, da, with characteristic times of the order of E-13 s.

With polar materials like m a n y polymers, a third c o n t r i b u t i o n arises from the o r i e n t a t i o n of u n c o m p e n s a t e d dipoles in the electric field. These dipoles can be permanent dipoles which exist in the absence of an applied electrical field, and are due to differences in e l e c t r o n e g a t i v i t y of the bonded atoms (for example the carbonyl bond C=O). They can also be induced dipoles, created by the applied electrical field which causes redistribution of electrons shared between bonded atoms with similar electronegativity. This dipole orientation is counteracted by the b r o w n i a n motion of the groups carring the u n c o m p e n s a t e d dipoles. Consequently, the characteristic time for these effects is strongly dependent on the temperature. Its lower limit is of the order of E-II s. for small m o l e c u l e s and, often, of the order of E-2 to E+4 s. for polymers at room temperature. Since this Q r i e n ~ a t i o n polarisability, do, involves physical movement of parts of the m a c r o m o l e c u l e s it is not surprising that, apart from the temperature, other factors w h i c h determine the molecular mobility affect it. Thus, the total p o l a r i s a b i l i t y is given bydT = de + da + do This p o l a r i s a b i l i t y now causes that the charge increase from Q to Q' needs a clearly m e a s u r a b l e amount of time. Thus, a charging current (Ic) decreasing with time, superimposed on I(dc), flows if a voltage (U) is applied over the plate/ polymer/plate capacitor. The proper I (dc) value n e c e s s a r y to calculate the specific volume resistivity, can be m e a s u r e d only if Ic has become zero. The specific volume r e s i s t i v i t y / t e m p e r a t u r e or electrical field-strength relation is m e a s u r e d during what u s u a l l y are called DC measurements. A specific method was d e v e l o p e d to determine the volume resistivity of a polymer as a function of the temperature and/or the electrical field strength [2] without the need to wait until the Ic current component has become zero. This m e t h o d is schematically given in Figure 5.1.

126

SAMPLE

r-"R".-,

HI~!L I

i. . . . .

i Cx

DETERMINATION OF ];O SAMPLE

',-,;-~G. ~

_H,j

TIME

Io]

isยง - j CHARGING SAMPLE -

-I

TIME

i ~:::::::::~ i L I

-I

-~ ' Y

U DISCHARGING Current flows during volume resistivity measurements

Figure 5.1

127 A metal p l a t e / p o l y m e r / m e t a l plate combination often causes an extra current contribution (Io) due to electro-chemical processes and/or contact potential differences. Therefore, the sample/ electrode system is, therefore, first s h o r t - c i r c u i t e d via the electro-meter. The value of this Io current (ยง is monitored until it has become constant. Then the sample system is connected with the voltage supply and during a certain time a charging current Ic is m e a s u r e d which is the summation of the pure capacitive charging current, the dc current and the Io contribution. D u r i n g the third step, the sample system is again short-circuited via the electrometer. Now, a discharge current I(d) is m e a s u r e d which is the summation of the pure capacitive discharge current and the Io contribution. I (dc) can now be calculated because for equal charge/discharge times holdsI' (dc) = I(c,t)

+ I(d,t)

[I(d,t)

has a negative sign]

5.5

This value has still to be corrected for the Io c o n t r i b u t i o n i.e.I(dc)

= I(c,t)

+ I(d,t)

- 2.Io

5.6

I (dc) is inserted in equation 5.2 to calculate the specific volume resistivity at that temperature and electrical field strength. This m e a s u r i n g procedure is completely automated, see 5.1.4. The volume resistivity d e t e r m i n a t i o n is described in the ASTM D257 (US), BS 202A (UK), DIN 53596/51953 (BRD) and in IS0 93 [3]. The time d e p e n d e n c y of Ic is m e n t i o n e d in all these methods. Besides, all methods indicate that I(dc) is determined usually after a standard charging time of 60 seconds. It will be clear that if one assumes I(dc) = Ic(60 seconds), this current nearly always contains a time dependent charging current contribution.

128 5.1.3 A C p r o p e r t i e s of The v o l t a g e a p p l i e d to plate system described circuit, is sinusoidal

polymers the c o n d u c t i n g p l a t e / p o l y m e r / c o n d u c t i n g in 5.1.2 i.e. Cx and Rx in a p a r a l l e l during A C m e a s u r e m e n t s :

U = Uo.sinet The result

5.7

is a current

I' = dQ'/dt

current

t h r o u g h Rx of:

[Uo/Rx] .sinet

I(total)

= I' + I''

According thus:

5.8

- Cx.Uo.~.cos~t

and an a d d i t i o n a l I' ' =

t h r o u g h Cx given by:

to 5.4:

I(total)

5.9 = Uo.[Cx.~.coset

+ (I/Rx).sin~t|

Cx - or.Co

5 .II

= Uo.Co.e.[~r.coswt

Now, two f r e q u e n c y dependent, d e f i n e d as: c'r = or,

5.10

+ (i/Rx.w.Co).sin~t]

material

properties

5.12

can be

c''r = I/Rx.~.Co

c'r

= the out-phase, c a p a c i t i v e component and is c a l l e d relative d i e l e c t r i c constant; ~''r = the in-phase, r e s i s t i v e component and is c a l l e d the relative d i e l e c t r i c loss factor. ~'r and ~''r are the c o m p o n e n t s of a c o m p l e x q u a n t i t y called the relative p e r m i t t i v i t y : E*r. The p h a s e d i f f e r e n c e b e t w e e n I (total) and U is the loss angle d e s c r i b e d by the tangent ~ or d i s s i p a t i o n factortangent

~ - ~''r/c'r

= 1/Rx.w.Cx

5.13

The p o l a r i s a t i o n effects m e n t i o n e d in 5.1.2 are c h a r a c t e r i s e d by their time of r e s p o n s e to an a p p l i e d field or their "relaxation" time. In p o l y m e r s in particular, there is a d i s t r i b u t i o n of r e l a x a t i o n times rather than a single c h a r a c t e r i s t i c r e l a x a t i o n time, u s u a l l y w i t h a fairly high maximum. Height, l o c a t i o n of the m a x i m u m and w i d t h of the d i s t r i b u t i o n are o f t e n u s e d as characteristics. D u r i n g AC m e a s u r e m e n t s the f r e q u e n c y d e t e r m i n e s the d i p o l e response: if the r e l a x a t i o n time T and the f r e q u e n c y ~ are such that e.T >> 1 the dipoles are not capable of f o l l o w i n g the field and do not c o n t r i b u t e to the p o l a r i s a t i o n and thus the d i e l e c t r i c constant. If, h o w e v e r

129 ~).T

they fully contribute. In b o t h limits w ~ w and e ~ 0 no energy is spent due to the lack of e i t h e r dipole m o v e m e n t o p p o s i n g forces. In b e t w e e n these f r e q u e n c y limits e n e r g y appears to be spent, in other words, there is a form of c o n d u c t a n c e p r e s e n t w h i c h by its nature is frequencydependent. If

W.T ~ 1 there is finite m o v e m e n t and finite o p p o s i n g force, r e s u l t i n g in a m a x i m u m in d i s s i p a t e d power. This c o r r e s p o n d s to a m a x i m u m in the phase lag b e t w e e n field and p o l a r i s a t i o n . The m a g n i t u d e of e. T d e t e r m i n e s the r e s p o n s e of a dielectric. To study this response either w or 7 m a y be varied. A wide v a r i a t i o n of e means, experimentally, that d i f f e r e n t a p p a r a t u s e s have to be used. T, however, is e a s i l y and w i d e l y v a r i e d by v a r y i n g the temperature. In p o l y m e r s o f t e n m o r e than one type of r e l a x a t i o n m e c h a n i s m is encountered. Each has a specific average r e l a x a t i o n time, d i s t r i b u t i o n of r e l a x a t i o n times and t e m p e r a t u r e susceptibility. The t e m p e r a t u r e s u s c e p t i b i l i t y can often be d e s c r i b e d by an A r r h e n i u s f a c t o r [i] so that: T = ~o.exp(E*/RT) where.

5.14

To = the c h a r a c t e r i s t i c r e l a x a t i o n E* -- the e n e r g y of activation, R = the gas constant and T = the a b s o l u t e temperature.

time,

M e a s u r i n g the d i e l e c t r i c loss m a x i m a as a f u n c t i o n of the t e m p e r a t u r e at a n u m b e r of d i s c r e t e f r e q u e n c i e s p r o v i d e s the data for an A r r h e n i u s plot i.e. in(~) v e r s u s i/T(max.). A c c o r d i n g to e q u a t i o n 5.14 and ~(max.). T = I, an e x p e r i m e n t a l a c t i v a t i o n energy v a l u e can be c a l c u l a t e d from the slope of this curveE*/R = -d [In (Q) ] /d [i/T] where:

~ = 2.~.f and f = the m e a s u r i n g

5.15 frequency,

Hz.

If the d i e l e c t r i c loss factor v e r s u s T at one fixed f r e q u e n c y is available, E* can be c a l c u l a t e d from the area u n d e r the loss factor versus I/T plot. S u b s t i t u t i o n of 5.14 in D e b y e ' s e q u a t i o n for a system w i t h a single r e l a x a t i o n time i.e. E''r

where: gives-

~.T.(E'o

- E'.)/(I

E'o = ~'r for f ~ 0 c'. = ~'r for f ~ w

eat ')

5.16

130 5.17

E* = (C'o - E'.) .0.5.~r.R. [~E' 'r.d(i/T)) ^(-I)

The actual d i e l e c t r i c losses m e a s u r e d are larger than the d i p o l e losses due to the c o n t r i b u t i o n of the c o n d u c t i o n losses i.e. c''r(total)

- c''r(dipole

The c' 'r(conductance a c c o r d i n g to 5.12 9

loss)

' 'r (conductance loss)

loss)

+ c''r(conductance

contribution

loss)

can be c a l c u l a t e d

= 1/[Rx. e. Col

5.18

w h e r e Rx c a l c u l a t e d a c c o r d i n g to e q u a t i o n 5.2, is the value m e a s u r e d d u r i n g DC e x p e r i m e n t s on the same sample. E q u a t i o n 5.18 shows that the c o n d u c t i o n loss is i n v e r s e l y p r o p o r t i o n a l to the m e a s u r i n g frequency. The d i s c h a r g e current (Id) m e a s u r e d d u r i n g the DC e x p e r i m e n t s d e s c r i b e d in 5.1.2, c o r r e s p o n d s to the d i p o l a r losses while the I (dc) c o r r e s p o n d s to the c o n d u c t a n c e losses a c c o r d i n g to: e''r(total)

= I(c,tl)/[w.Co.U] = I(d, tl)/[u.Co.U]

where- u = 2.~.fl and fl, a c c o r d i n g to Hamon [4] :

5.19

+ I(dc)/[~.Co.U]

the c o r r e s p o n d i n g

frequency,

fl - 0.1/tl

5.20

The e q u a t i o n s 5.19 and 5.20 o f f e r the p o s s i b i l i t y to combine the loss data o b t a i n e d w i t h AC m e a s u r e m e n t s and those o b t a i n e d w i t h DC m e a s u r e m e n t s e x t e n d i n g the lowest m e a s u r i n g frequency from about 10 Hz. to about 10"4/10 s Hz. More e x t e n d e d d i s c u s s i o n s about the d i e l e c t r i c p h e n o m e n a be found in several t e x t b o o k s [5, 6, 7] .

can

131 5.1.4 The AC and DC measurinQ svstem The automated volume resistivity/dielectric properties measuring system is schematically drawn in Figure 5.2. The whole system is controlled by the HP9000/300 computer which runs either the specific volume resistivity measuring program or the dielectric properties measuring program. The polymer sample, clamped between a guarded electrode system is placed in the thermostat bath. This bath can be heated electrically and cooled by liquid nitrogen providing a measuring region from -150~ up to 300~ The bath inside is purged with nitrogen (about 200 ml/minute) to prevent sample oxidation at high temperatures and moisture condensation at low temperatures. A Cr/Al thermocouple measures the sample temperature. A second thermocouple, measuring the bath sidewall temperature, is connected with the temperature controller of the thermostat bath. Activation of the computer gives a menu with the possibility to choose the 'Volume resist' program or two 'LCR' dielectric programs. The 'Volume resist' program is controlling the Keithely 617 electrometer, the Keithely 237 High Voltage Source (0 - i000 V) and the high voltage switching unit. This system performs completely automated the DC measuring procedure drawn in Figure 5.1 and described in 5.1.2. This measuring procedure can be performed at twenty different temperature steps, at maximally three different voltage levels each. The current is read-out by the electrometer and stored every thirty seconds during the Ic measurement and the Id measurement (both maximally 40 minutes). The temperature of the thermostat bath is brought to the next chosen measuring temperature after performing a complete DC measuring cyclus. The 'LCR single' program measures the dielectric properties of one sample cell as a function of the temperature and frequency. The HP4284A LCR meter measures at frequencies between 20 Hz. and I MHz. The 'LCR multiple' p r o g r a m controlls an additional scanner which makes measurements on maximally five samples during one measuring scan possible. The sample temperature is then measured either with a Cr/AI thermocouple or with a Ptl00 resistance thermometer placed in the high potential electrode of the measuring cell. Both sensors are connected with the sample temperature measuring unit which is connected with the HP9000/300 computer, see Figure 5.2. During the dielectric measurements the temperature of the thermostat bath is continuously increased or decreased usually at a rate of I~ minute. This in contrast with the volume resistivity measurements where the temperature is stepwise in- or decreased. The balancing time of the HP4284A LCR meter [seconds] permits however, the use of a temperature ramp. The sample temperature follows the thermostat bath temperature with a temperature lag of about 25~ The interval time chosen determines the temperature difference between two subsequent measurements.

132

.,,..

BRTH SCR~NER I I I i I

I I I I

____t__---SRMPLE TEHPERRTURE

HP4284R prec ! 9 t on

LCR m e t e P

HIGH VOLTRGE SWITCHING UNIT

,_ .

TENPERRTURE CONTROLLER

KEITHLEY 237 HV SOURCE MERS.UNIT ....

KEITHLEY 6t? ELECTRO-METER

HP9153B DISKDRIVE HPBBBB/38B COMPUTER

i" J PRINTER

HP COLORPRO PLOTTER

Figure 5.2 Measuring system (schematically) for determination of the non-destructive electrical properties of polymers

133 Samples, often received at a thickness between 3 and 5 mm., are usually machined to a thickness of 1 mm. Subsequently they are provided with a (vacuum evaporated) silver low- and highpotential electrode system. Sample disks with two different diameters i.e. II0 mm. and 53 mm. are used, with low potential electrode diameters respectively of 80 mm. and 20 mm. The samples with their silver electrodes are clamped between a spring loaded, guarded electrode systems from the sample cells. These samples and sample cells are used both for the volume resistivity measurements and for the dielectric measurements. The dielectric measurements are performed according to the instructions given by IEC 250 [8]. Sample cells for disk-shaped rigid samples, for high viscous/zltbbery and for liquid samples are also constructed according to the directions given in IEC 250. 5.1.5 AC and DC properties of a cured resin system Figure 5.3 shows an example of a dielectric measurement. The dielectric constant and the tangens delta of a liquid epoxy/ polyamide resin system measured between -50~ and 150"C at ten different frequencies between 60 Hz. and 1 MHz. during one experiment. The results of five selected frequencies are plotted in Figure 5.3. The resin system shows a broad glassrubber transition region between about 30~ and 100~ indicated by the step-wise increase of the dielectric constant and the maximum in tangens delta. This sample was cured during 12 hours at room temperature followed by 6 hours at 100~ Heating up to 150~ during the dielectric measurements might have postcured the sample. The volume resistivity measurement was performed, therefore, on a second 'fresh' sample disk. _

The volume resistivity was measured at 14 discrete temperatures ranging from -36oc up to I06~ Figure 5.4 shows the measured charge and discharge currents and I(dc,t) current calculated according to equation 5.6 as a function of time at a temperature of -4.7oc. The sample is then in its glassy state and Ic decreases as a function of time according toIc m t.exp(-n)

5.21

Such a behaviour is also measured for PVC, PE and many other glassy and semi-crystalline polymers [9, I0, II]. The I(dc,t) values calculated make the determination of an average I(dc) value possible although the I (dc, t) values clearly scatter. This sample is just in its rubbery state at 19.6oc, under these measuring conditions. The scatter in the calculated I(dc,t) values has been practically vanished and the system approaches the ideal Ic/Id/I (dc) system described in 5.1.2, see Figure 5.5.

134 Liquid epoxyipolyamide resin s.s~

5.0 o

11.S-

|.l

kilt.

o...._ o

kH:.

O ~

8.0-

7.5-

---,

7.tl.

t'~

I;.S.

,,.o =_~=_.o "x u ~r / ="

/ /

~,a

IQID. e hH=.

1.:

+i+

////-.-+-

S.0-

X_~

..~o'--o~,,

~ =Vx

=~'

"~o

P.,.,,.,

5.5-

5.e-

4.$-

4.83,$-

T '

-30

-50

-10

1'0

:30

;PO

~mrtarRtl "'I

110

im I

130

1+0

Uquid epoxy/polyamide resin 8. I 4 -

"10 0. tZ- C:

1.=

18.8

kH=. / / v

kH=.

/ fz~ =" t ~ /

At.0

~:. o

J/i/,

-'-

O. 01; -

0.04 -

,o,_. o-~-:.~ Temperature, a . ~- -5 0

-"3, 0

- ;0

30 '

5'0'

' 70 '

90'

Figure 5.3 Results of automated dielectric constant and Tan delta measurements

.... t

110

130

~ 150

135 1 0 -10

Current, A

Figure 5.4 Results of charge/discharge current measurements on a liquid epoxy/polyamide resin sample in its glassy state

X~+,

1 0 -11

-I

(d t scharge

)

x\ \\ •

l(charge)

\§

+, •

+\ X

+ X \ X

\ X

I(dc.)

<3 <3 Temperat,

1 0 -12

ure

-4.7~ .I

IN)

Time, s

136

10 -9

Current, A

Figure 5.5 Results of charge/discharge current measurements on a liquid epoxy/polyamide resin sample in its rubbery state

I (charge) ,+

+~ "+~+.+ + -I- + + . . + .~.

l(dc.)

<3 _...<=--<=-.~-<3 <3 <3<=-<~ --~

1 0 -10 x

\ X

-I (dtscharge) x

X X

\ x

Temperature 1 0 -11 G~

lg.6eC .

J N

Time, s

9.--4

137 If the Ic-value after 60 seconds is used as 'I(dc)'-value, for both experiments shown in the Figures 5.4 and 5.5, this 'I (dc)' value contains a time dependent contribution i.e. it is too high. Thus, the calculated resistivity value will be lower than the real dc resistivity value. The results of all specific volume resistivity measurements (including the Ic[60 seconds] values) are plotted in Figure 5.6. The curves show that the difference between the I(dc)-data and the Ic(60)-data is mainly present if the sample is in its glassy phase. For temperatures higher than 29oc the time dependent part of the charging current has vanished within 60 seconds i.e. Ic(60) and Idc are equal. The volume resistivity/temperature curve clearly illustrates the strong difference in the temperature dependency of the volume resistivity of a polymer in its glassy phase and in its rubbery phase. The Tg-value, obtained by drawing two tangents near this glass-rubber transition, is determined at 1000/T = 3.58 or 6"C. This Tg-value is a real static Tg-value and its hypothetical frequency [f(h)] in the frequency/temperature plane will be lower than the f(h) = IxE-2 to ixE-4 claimed by Phillips [12] for dilatometric experiments. A good fit on the Arrhenius plot was obtained assuming an f(h) of ixE-6 for this Tg-value, see below. The dielectric loss data calculated from the I(discharge) currents according to equation 5.19 show a clear maximum due to the glass-rubber transition for the experiments at 29~ and 20~ These data are plotted in Figure 5.7 as a function of the frequency together with the AC data. The results of both measuring systems can be fitted reasonably. The measured dielectric loss and tangent delta maximum temperatures are Table 5.1

The dielectric loss/tangent delta maximum temperatures of a liquid epoxy/polyamide resin system

....

"='

. lIT'

~ measuring I frequency, | (Ln ~}

, ,~

| 1.0xe-3

1.0xE-6

-5 -

* estimated,

,I,

....

...

. . . . . . .

hypothetical

~ ........

29 20 6

: --:.

,,1"

tangent delta maximum temperatures, ~

101.5 95.5 88.5 85 76.5

7) 84)

1-Ii 98)*

AC results 1 MHz. (15.65) 400 kHz. (14.74) i00 kHz (13.35) 40 kHz (12.43)

Ii 1. ?xB-4 resui. o

...........

dielectric loss maximum temperatures, oc

Hz. ,,

~ ,,,r ......

i fl

frequency f(h).

~,,,~

L,J~,

....

,,,,,. ........

94 87.5 81 75.5 71

,,,,,,._,~,

.~,,,

"! ,,=

, .......

,,,

138

Figure 5.6 Specific volume resistivity/T(-1) relation of a liquid epoxy/polyamide resin system

/(dc) data

Ic(60) data

l e + 1 6 .-.t..+~-

le+ 15 E le+ 14 >:,

l e + 1 3 .-=-

9 .,.,--

:~ l e + 1 2 o , _ . .

"- l e + 1 1

l e + 1 0 --0 > ._o l e + 0 9 4-.

..,.,,-

0 (D EZ

09 1 e + 0 8 le+07 1000000

2.50

p*/

=.,

+ ~-"

2.90

,,I

.3.30 1000/T,

.3.70 K ,,, ( - 1 )

4.10

4.50

139

Figure 5.7 The dielectric loss/frequency relation of a liquid epoxy/polyamide resin system

temp. 29 ~

temp. 20 ~

2.20 Liquid epoxy/polyester reein ~ t e m Arrhordus plot dielectrio loss data

2.00

1.80

~- 1.00

7 5 3

--1

--3 --5

--7

J /

o 1.40

1.20

1.60

A C dmla DC dam

--9

0.80 \

0.60

--11 --13 2.60

3.20

3.40

3.60

\ "++~

0.20 0.00

3.00

lO00/T(rna)<.). K(-1)

0.40

2.80

,ii~

. i

I ,ilu,|

i lllU,

10-410-310-210

I iili,i~

i lilild

, lll,lll

lJl*li~

i illllli_

....I

I ,,lili~

t illUll

-, 1 0 ~ 1 0 ' 1 0 2 1 0 3 1 0 ~ 1 0 5

Frequency,

Hz.

I llllll

106

140 collected in Table 5.1, the dielectric loss data are plotted in an Arrhenius plot inserted in Figure 5.7. The AC and DC results can be covered by a straight line indicating an apparent activation energy of 260 kJ/mole, according to equation 5.15. The E'0 and ~'~ values might be estimated from respectively the m a x i m u m E'r value m e a s u r e d at the lowest frequency/highest temperature and the ~'r value m e a s u r e d at the highest frequency/lowest temperature. The following experimental values were available: frequency 1 MHz. 400 kHz. 100 kHz. 40 kHz. i0 kHz. 4 kHz. 1 kHz. 400 Hz. i00 Hz. 60 Hz.

~'r at -50~ 3.01 3.02 3.04 3.05 3.07 3.08 3.11 3.12 3.14 3.15

c'r at 85~ 5.07 5.44 6.08 6.52 7.18 7.57 8.11 8.48 9.33 9.78

The c'r values m e a s u r e d at -50~ slowly decrease with increasing frequencies. An estimated c'm value of 3.0 is not unreasonable. The c'r values at 85~ still increase too strongly with d e c r e a s i n g frequencies to use these values for a E' estimation The E* value of 260 kJ/mole was substituted therefore together with the area of the ~''r(l MHz.)/I/T curve in equation 5.17, resulting in a (c', - c'w)-value of 9.7. Hence, the estimated E' value is 12 7 i e the dielectric constant of this resin system is estimated to vary between 12.7 and 3.0 maximally. 0

5.1.6 T i m e / t e m p e r a t u r e suDerDosition of dielectric results Knowledge of the T g - v a l u e / f r e q u e n c y relation of SSBR car-tyre rubbers was necessary during the search for correlations b e t w e e n car-tyre properties i.e. wet grip/rolling resistance and the rubbers' chemical structures, see 4.2.3. DMA experiments are, however, limited to about 100 Hz. Dielectric m e a s u r e m e n t s were thought to offer a reasonable alternative. A series of dielectric measurements at frequencies between 10 Hz. and 100 kHz. was started on carbon black loaded rubber samples. Accurate dielectric measurements on these carbon b l a c k containing, v u l c a n i s e d rubber samples proved however v e r y difficult due to the fluctuating, high conduction level of these samples. Therefore, one of the experimental SSBR systems was v u l c a n i s e d without carbon black to avoid these conduction problems 9 The DSC Tg(onset)-value of this sample without carbon black was equal to that of the carbon black containing system i.e. -35~ The dielectric tangent delta values of this SSBR system was measured at eight different, isothermal temperatures and at nine different frequencies between i0 Hz. and i00 kHz.

141 Table 5.2 The d i e l e c t r i c tangent delta of SSBR (vulcanised /no carbon black) as a function of the t e m p e r a t u r e and the frequency. ~_

fre que ncy I0 Hz. 33 Hz. i00 Hz. 330 Hz. 1 kHz 3 kHz I0 kHz 33 kHz 100 kHz ,

,Hi

HID

1111]

"iimlll

Isothermal m e a s u r i n g 66 c

' '

0.0130 0.0017

0.0009 0.0015

0.0050

0.0240 0.0055 0.0010

0.0008 0.0024

0.0080 0.0170 0.0080

0.0090 0.0022 0.0008

0.0013

0.0040

0.0120

0.0190 0.0054

0.0036

0.0020 0.0065

0.0150

0.0185 0.0039

0. 0016 0.0009 0.0016

0.0035

0.0190 0.0150 0.0028

0.0010

0.0010 0.0028

0.0060 0.0140

0.0190

0.0011 0.0017 0.0047

0.0095 0.0180

0.0155 0.0080 0.0022

0.0019 0.0030 0.0080

0.0140 0.0190

0.0120

0.0062

0.0030 0 . 0 0 5 5

0.0190 0.0170

0.0092

0.0052

,iiii

I,I

0.0012 0.0010

III

m,l

18 c

-9 c

30 c

3 c

0.060

51 c

temperatures

0.0128 ira!"

' T

Ill

0.0100

-17 c

.....

-29c

0.0130 0.0110

0.0110 0.0023

l I I

l I

0.0023 0.0028 ...........

[I]l [.I

The results of these m e a s u r e m e n t s are listed in Table 5.2 and p l o t t e d in Figure 5.8. The tangent delta m a x i m u m value due to the g l a s s - r u b b e r t r a n s i t i o n is c l e a r l y v i s i b l e in the curves m e a s u r e d at 3~ -9~ and -17oc. These data can be used to show that time and t e m p e r a t u r e effects are often c o u p l e d for r e l a x a t i o n p h e n o m e n a (the time~temperature s u p e r p o s i t i o n p r i n c i p l e [13]). Effects due to an t e m p e r a t u r e increase can thus also be o b t a i n e d by an increase of the e x p e r i m e n t a l time scale. Hence, the curves in Figure 5.8 were shifted along the f r e q u e n c y - a x i s while the curve m e a s u r e d at 18~ was c h o s e n as r e f e r e n c e temperature. The r e s u l t i n g tangent d e l t a / f r e q u e n c y r e l a t i o n of the SSBR sample at 18~ is shown in Figure 5.9. These results indicate that such a shifting p o s s i b i l i t y offers data e x t e n d i n g over more than e l e v e n decades of f r e q u e n c y while the actual m e a s u r e m e n t s were p e r f o r m e d over only four decades. The used shift factors (Log At) are p l o t t e d as a function of the t e m p e r a t u r e in the g r a p h i n s e r t e d in Figure 5.10. Log At is d e s c r i b e d by the s o - c a l l e d W L F - e q u a t i o n [13]" Log At -- [Cl. (T - Tg)]/[C2

+ (T - Tg)]

5.22

C1 = -17.44 and C2 - 51.6 are o f t e n m e n t i o n e d as 'universal' values. The Log A t / t e m p e r a t u r e curve of this rubber s y s t e m does not fit however w i t h e q u a t i o n 5.22.

142

Figure 5.8 Tan delta/frequency/temperature relation of vulcanised SSBR (no carbon black) +

66~

510C

-I"

30~

18~

-9~

-17~

-29~

,j+~/.-

~+~.,,~-.~+-

/.j

1 0 -2 +-,

79 4-J

C r [3 c

4-'

,~~

0 .....

1 0 -3

, /

10'

+,',,~ / ~ / + /

-,OZoj _

,,/ /

,o I

Ill

10 2

II1~

, I

10 3 Frequency,

III

10" Hz.

, I

10 5

143

Figure 5.9 Tan delta/frequency relation of vulcanised SSBR (no carbon black) +

66~

51~

30~

"1-

18~

10 - 2

+t-

-9~

Zl -29oc

-17~

% e

91)

+ A+

A r

@ s

& ยง

-FJ

0 k_

q) @

A~A

0 A

. . . . .

A A

0+1~

1 0 -3

reference

-2

....

2 Log

i_.

temperature:

frequency,

8 Hz.

18 ~

144

Figure 5.10 Ln f against 1/T for tan delta maxima of vulcanised SSBR (no carbon black)

+ 16

d/electr/c data

U.S./DMA/DSC data

1412108'--'

WLF shift factor (log At)/tempemture relation for SSBR + dielectric data

{--

_..I 2 -

-I.

..j ~ 2

- 4

- - 6

-I"

\\ ยง

-1

-8 3.10

-30

-lO

Temperature, ~ _

3.34

3.58

3.82

1000/T,

K(-1)

I ,

4.06

4.30

145 These dielectric measurements provided information about the location of the g l a s s - r u b b e r transition in the frequency/ temperature plane, see Figure 5.10. An u l t r a s o n i c m e a s u r i n g system was developed later on during a research p r o g r a m on SSBR rubbers, see 4.2. That offered the p o s s i b i l i t y to measure carbon black containing samples in the frequency region around 1 MHz. The results, in combination with the low frequency DMA/DSC results, are also plotted in Figure 5.10. The differences between the dielectric results and the low and high frequent dynamic mechanical results can be a m e a s u r i n g technique effect and/or a carbon black effect (present in the dynamic mechanical samples - not in the dielectric samples). These differences illustrate that d i e l e c t r i c a l l y obtained Tgvalue information from v u l c a n i s e d rubber samples without carbon black is less suited for chemical structure/wet grip rolling resistance correlation studies of (carbon black containing) car-tyre rubber systems than dynamic mechanical data. 5.1.7 The dielectric constant of riuid PU foams Rigid polyurethane foam (PUF) p r e i n s u l a t e d pipes for district heating systems need m e a s u r i n g systems to detect leakage in a pipeline network while it is in use. One of such systems measures the absorption of a reflected pulse, transmitted via a copper wire embedded in the PUF insulation. Information about the dielectric constant and loss factor of these foams as a function of the foam density and the MDI index (see 4.1.3) was necessary to calibrate such a system. Two PUF sample series were prepared based on polyol and isocyanate. The first series of five samples c o n t a i n e d between 0 and 30 phr. blowing agent resulting in foam samples with densities increasing from 23 up to 106 kg/m3. The MDI index (see 4.1.3) of these samples was Ii0. The second series of four samples consisted of two samples with a MDI index of 90 and two with a MDI index of 125. From each of these two samples one sample was m i x e d according to the standard procedure, the other was less good or on purpose mixed. Sample disks of 6 cm. diameter and a thickness of 3.5 mm. were machined from these nine PUF samples and used for the dielectric measurements. The dielectric response of these PUF samples is weak due to the small amount of material between the m e a s u r i n g electrodes. The dielectric measurements were performed, therefore, with a General Radio 1621 Precision Capacitance M e a s u r i n g System. This system measures capacities between IxE-6 pF and ixE6 pF with a basic accuracy of â&#x20AC;˘ 0.001% (i kHz.) and resistances between IxEl6 Ohm to ixE3 Ohm with a basic a c c u r a c y of 0.1% (I kHz.) in a frequency region from 20 Hz. up to I00 kHz. Accurate sample thickness d e t e r m i n a t i o n of these thin foam disks is difficult. A guarded m e a s u r i n g cell with two lowpotential electrodes (one disk electrode for the sample and one ring electrode for the sample thickness determination) was

146

sample

(::'2

~//i11111111111111/11/

guarding temperature measurement

Figure 5.11 Sample cell with capacitive sample thickness determination

147 used, see Figure 5.11, to solve this problem. Cells like this were used earlier to m e a s u r e the dielectric p r o p e r t i e s and the linear thermal expansion of polymers s i m u l t a n e o u s l y [14, 15, 16]. The value of capacity C2 in this system p r o v i d e s the sample thickness information after a proper calibration. The C2 capacitance value versus electrode distance relation was calibrated using calibrated spacers and proved to be slightly frequency dependent: 20 Hz.

1 kHz.: I0 kHz.: i00 kHz.:

d = 19.9388/(C2 d = 20.0848/(C2 d = 20.1234/(C2

+ 0.3435) + 0.3866) + 0.3375)

where,

d = the electrode distance, C2 = the capacitance, pF.

ram.

The weight of the low-potential electrode slightly impressed the thin foam samples. Hence, capacity C2 was m e a s u r e d before and after the sample capacity (Cl) and conductance (GI) measurement. The average sample thickness during the CI/GI d e t e r m i n a t i o n was calculated using both C2 c a p a c i t y values. These measurements were p e r f o r m e d at 22~ â&#x20AC;˘ I~ and a relative humidity of 50%. The results of these m e a s u r e m e n t s are collected in the Tables 5.3 and 5.4. The dielectric constant values between 20 Hz. and i0 kHz. show a small but clearly present decrease due to the increasing frequency. All the I00 kHz. values are however slightly too high probably due to stray capacitance effects. The dielectric constant/density relation proved to be linear and can be described byE'r = 0.00172 x E'r = 0.00166 x E'r - 0.00165 x

(density) (density) (density)

+ 0.987 + 0.988 + 0.987

(f = 20 Hz.), (f = 1 kHz.), (f = i0 kHz.).

The Rval.-values of these linear relations are h i g h e r than 0.9999 and the dielectric constant values for a d e n s i t y value of zero fairly approach the theoretical value of 1.000. The linearity of this relation is also reported in literature [17, 18]. Figure 5.12 shows that the four samples with a MDI index of respectively 90 and 125 fit the index Ii0 data. This means that the composition differences (chemically - MDI index or m e c h a n i c a l l y - bad mixing) do not detectably influence the dielectric constant i.e. the density is the m a i n p a r a m e t e r influencing the dielectric constant of PUF. The tangent delta values m e a s u r e d at 1 kHz. and i0 kHz. also increase linearly with the density, see the plot inserted in Figure 5.12. The 20 Hz. tangent delta values, however, show a strong n o n - l i n e a r behaviour. A closer look at these data shows that this n o n - l i n e a r i t y is caused only by the m e a s u r e d value for the sample with the highest foam density. The strong tangent delta increase for this sample is p r o b a b l y caused by an additional DC conduction effect. The tangent delta/ density relations are described by.

(2_.

o. d)

"0 C -n

bO 4~ 0

PO 0 0

4~ 0

.... ~

b I

L~ '

x I

constant

"\ ............

Dielectric

L~ '

"I.~~

L~ I

"~ '

~-.

i,,~

II~ --I -n

heb

149 tan

6 -

[4.23

- 0.034x(density)

tan tan

~ = ~ =

[0.18x(density) [0.23x(density)

+ 0.003x(density)^2] (f = 20 Hz.), - 0.43] .E-4 (f = 1 kHz.), + 4 . 1 3 ] . E - 4 (f = I0 kHz.).

.E-4

T h e d i e l e c t r i c p r o p e r t i e s of t h e s e foams are not o n l y i n f l u e n c e d b y the f o a m d e n s i t y but a l s o b y m o i s t u r e a b s o r p t i o n a n d t e m p e r a t u r e e f f e c t s . A s i n g l e s c o u t i n g e x p e r i m e n t showed, that the i n c r e a s e of the d i e l e c t r i c c o n s t a n t d u e to h e a t i n g to 100~ is small in c o m p a r i s o n w i t h the d e n s i t y d e p e n d e n c y (a 45.7 kg/m3 f o a m s a m p l e was h e a t e d f r o m 2 2 ~ to 100~ the d i e l e c t r i c c o n s t a n t at I kHz. i n c r e a s e d f r o m 1 . 0 6 5 u p to 1.071).

150 Table I

5.3

MDI index

E'r 20 Hz.

23.0

Ii0

1.027

37.1

110

1.051

ii0 ,,

1.066

53.8

ii0

~o6. o

density kg/m3

j [ ,,

..,

c'r i kHz.

.....

1.066

1.079

1.077

1.075

1.077

Ii0

1.170

1.164

1.161

81.2

125

1.122

1.120

1.117

1.119

83.5

125

1.129

1.126

1.122

1.125

1.106

1.104

1.101

1.104

1.105

1.101

1.099

,,.~

,.,

5.4 T h e .

i. 049 .

. . . .

PUF tan

....

~/density

relation

1.162

1.100 '~'

at 2 2 ~

....

R.H.

,,,,

MDI index

tan 6 20 Hz.

tan 1 kHz.

tan 10 kHz.

tan 100 kHz.

23.0

Ii0

4.7E-4

4.1E-4

9.2E-4

12.2E-4

37.1

110

7.8E-4

6.3E-4

13.0E-4

16.8E-4

15.0E-4

22.2E-4

16.9E-4

24.8E-4

density

,kg/m3

110

9.1E-4

53.8

110

I0.6E-4

8.9E-4

106.0

ii0

34.6E-4

18.6E-4

81.2

125

14.0E-4

125 90

45.7

1.063

,.,

E'r 100 kHz.

1.065

1.026

7.1E-4

E'r i0 kHz.

1.051

Table ,

1.048

......

67.1

1.028

68.3 "

relation

1.024

45.7

constant/density

....

.~..

The PUF d i e l e c t r i c 22~ R.H.

83.5

68.3 67.1 ,,.

,,,

90 I,

28.9E-4

54.5E-4 ,

~,,,,

12 .IE-4

22.2E-4

37.3E-4

20.8E-4

13.1E-4

23 .IE-4

38.7E-4

18.3E-4

II.9E-4

21.7E-4

37.4E-4

11.8E-4

21.2E-4

34.6E-4

30.8E-4 'rl

,,,,

........

151

5.2 Effect of moisture on the electrical properties polymers

5.2.1 Introductio~ Nearly every polymeric system absorbs some moisture under normal atmospheric conditions from the air. This can be a difficult to detect, very small amount as for polyethylene or a few percent as measured for nylons. The sensitivity for moisture increases if a polymer is used in a composite system i.e. as a polymeric matriX with filler particles or fibres dispersed in it. Water absorption can occur then into the interfacial regions of filler/fibre and matrix [19]. Certain polymeric systems, like coatings and cable insulation, are for longer or shorter periods immersed in water during application. After water absorption, the dielectric constant of polymers will increase due to the relative high dielectric constant of water (80). The dielectric losses will also increase while the volume resistivity decreases due to absorbed moisture. Thus, the water sensitivity of a polymer is an important product parameter in connection with the polymer's electrical properties. The mechanical properties of polymers are like the electrical properties influenced by absorption of moisture. The water sensitivity of a polymer is therefore in Chapter 7 indicated as one of the key-parameters of a polymeric system. The water absorption of composite systems and the effect of this water on the electrical properties was the subject of many studies [2, 20, 21, 22, 23]. Cotinaud, Bonniau and Bunsell [24] observed three mechanisms of water absorption. The first mechanism is the reversible Fickian diffusion of water molecules into the matrix, causing a slight increase of the dielectric constant and the dielectric loss. The second mechanism of redistribution and regrouping of absorbed water molecules is observed at higher humidity levels and causes a strong increase of the dielectric losses and the electrical conduction. The third mechanism, which only occurs on immersion, is transport of water along microcracks in the matrix material through capillary action. The influence of moisture on the dielectric properties of three experimental resin casting systems and an epoxy based laminate is investigated in this chapter to see if the mechanisms described above, can be recognised. Besides, the resistivity of an epoxy based tank coating and that of plasticised PVC cable insulation material in contact with water is described.

152 5.2.2 Influence of moisture on the dielectric properties of resin castings and laminates. The effect of moisture uptake on the dielectric constant and the tangent delta is shown for two MDI (4,4'-diphenyl methane diisocyanate) based resin systems, cured with 2% DMP 30 (tris[dimethyl-aminomethyl]phenol), as a function of the temperature in Figure 5.13. Both resin casting samples needed about 60 days to reach their equilibrium water saturation during storage at 20~ and a relative humidity of about 70%. The MDI/lactone resin reached under these conditions a moisture concentration of 1.7 %wt. while 1.3 %wt. was measured for the MDI/styrene system. These 'wet' samples were measured from -120"C up to 240~ at a heating rate of l~ in a nitrogen atmosphere. The moisture absorbed is released during this heating procedure i.e. during the subsequent cooling scan the properties of the dried samples are measured. The increase of the dielectric constant due to absorbed moisture is clear for both systems. These measurements also showed that replacing the lactone by styrene improved i.e. decreased both the dielectric constant and the tangent delta values of this casting system. _

In contrast with the dielectric constant, the tangent delta/temperature relation between 0~ and 240"C is not (detectably) influenced by these moisture concentrations. The tangent delta/temperature curves of both 'wet' systems show, however, a clear relaxation effect with maxima between -60~ and -70~ These effects disappear after drying i.e. they stem from the water phase. Such a low-temperature, low-frequency loss process was also detected in dynamic mechanical measurements. Banhegyi et al. reported such an effect due to absorbed water for CaC03 filled polyethylene samples [21]. Wagner showed that conducting particles, dispersed in a nonconducting matrix can cause an energy dissipation maximum, the so-called Maxwell-Wagner dielectric relaxation. Absorbed water in a polymer might considered to behave like conducting 'particles' in the non-conducting polymer matrix. We tried to apply, therefore, this theory to calculate the dielectric properties of these 'wet, resin systems. The relaxation time of such a Maxwell-Wagner absorption process is according to Hill [6] given by: T

(2.E'r

where:

E'W)/(4.~.90EI0.T

5.23

E'r = MDI/lactone E'r at 20~ and ikHz., dry sample i.e. 3.39 E'w - dielectric constant of water (80), T w ~ the water conductivity, (Ohm.cm) ^ (-i), T = relaxation time, s.

The use of equation 5.23 is hampered by a lack of knowledge about the conductivity level of the absorbed moisture phase. Equation 5.23 was therefore used to calculate this absorbed water conductivity after an estimation of relaxation time T. The experimental activation energy value of the dielectrically

153 5.0

MEASURING

DIELECTRIC CONSTANT

FREQUENCY IS IOOO HERZ

- 5.0

4.0

- 4.0

3.0

- 5.0

SECOND SCAN,DRIED SAMPLES 2.0

-ZO

v M D Z l L a c t o n e 2/1 a M D Z l S t y r e n e 2/1 I

-IZO

-80

-40

,,,a~

I 9 I . I , ,,,I , 1.0 120 160 200 240 28o TEMPERATURE (CENTIGRADES)

INFLUENCE OF MOISTURE UPTAKE DURING STORAGE UNDER ATMOSPHERIC CONDITIONS ON THE DIELECTRIC CONSTANT

.TANGENT DIELTA r

MEASURINGFREOUENCY IS IOO0 HERZ

i0-I

w m

I f f "s

=, ,i m

DRIED SAMPLE,SECOND SCAN

V A

MDI/Lactone MDIIStyrene

2/1 2/1

Ily 4

-120

-80

-40

120

t60 200 240 200 TEMPERATURE (CENTIGRADES)

INFLUENCE OF MOISTURE UPTAKE DURING STORAGE UNDER ATMOSPHERIC CONDITIONS ON THE TANGENT DELTA

Figure 5.13

154 and d y n a m i c m e c h a n i c a l l y m e a s u r e d m o i s t u r e loss maxima, p l o t t e d in an A r r h e n i u s plot, was 46 kJ/mol. (Illers [25] r e p o r t e d a value of 54 kJ/mol for the w a t e r r e l a x a t i o n effect in nylons). An a c t i v a t i o n e n e r g y of 46 kJ/mol means that a 'moisture' r e l a x a t i o n maximum, m e a s u r e d at -60~ u s i n g a f r e q u e n c y of IkHz. will shift to 20"C if the m e a s u r i n g f r e q u e n c y is i n c r e a s e d to 1.22 MHz. Hence, r e l a x a t i o n time T m i g h t be I/1.22E6 = 8.2E-7 s at 20~ S u b s t i t u t i o n of this v a l u e in e q u a t i o n 5.25 r e s u l t s in a value for the w a t e r c o n d u c t i v i t y of: T (absorbed moisture)

= 9.4E- 6

(Ohm. cm) ^ (- i)

This seems to be a r e a s o n a b l e value. Hill [6] is u s i n g a c o n d u c t i v i t y v a l u e of 1.0E-6 (Ohm.cm)^(-l) for pure water. S t e e m a n et al. [19] are u s i n g a v a l u e of 5.0E-8 (Ohm.cm)^(-l) for the b u l k c o n d u c t i v i t y of p u r e w a t e r at 20~ It is questionable, however, if a b s o r b e d m o i s t u r e can be c o n s i d e r e d as pure water. Ionic i m p u r i t i e s from the r e s i n m a t r i x can e a s i l y increase the c o n d u c t i v i t y of the w a t e r phase. The d i e l e c t r i c Maxwell-Wagner ~'(U)

constant theory:

= c'r[l + 3 . U ( E ' W -

of the

'wet'

E'r)/(2.E'r

resin is a c c o r d i n g

to the 5.24

+ E'w)]

and E'

= E' (U) [i + S / ( I

+ ~'.T2)]

5.25

and S =

(9.~.E'r)/(2.E'r

where-

5.26

+ E'W)

u = the v o l u m e f r a c t i o n of m o i s t u r e i.e. ~' = the d i e l e c t r i c constant of the 'wet' 3.84.

E q u a t i o n 5.24 gives an c' (u) v a l u e of 3.57, reduces for the g i v e n w and T v a l u e to: E' = E' (~). [i ยง S]

= 3.57. [i ยง 0.007]

0.02 and r e s i n i.e.

equation

5.25

= 3.60

The d i e l e c t r i c constant at 20~ i n c r e a s e d from 3.39 to 3.84 due to the 1.7 %wt. m o i s t u r e (2.0 %v.). The c a l c u l a t e d i n c r e a s e of the d i e l e c t r i c c o n s t a n t from 3.39 to 3.60 is only about 50 % of the total effect. The M a x w e l l - W a g n e r t h e o r y thus seems to d e s c r i b e r o u g h l y the f r e q u e n c y / t e m p e r a t u r e l o c a t i o n of the d i e l e c t r i c loss m a x i m u m due to a b s o r b e d moisture. However, it does not a d e q u a t e l y d e s c r i b e the i n c r e a s e of the d i e l e c t r i c constant due to the m o i s t u r e u p t a k e from the air. A p o s s i b l e reason for this d i s c r e p a n c y might be that one of the a s s u m p t i o n s does not hold, viz. that the c o n d u c t i v i t y of the resin m a t r i x is n e g l i g i b l y small.

155 Brasher [26] adapted the H a r t s h o r n equation to describe the increase of the dielectric constant of coatings due to w a t e r absorption~'

5.27

E'r. (~'w.)^(n.u)

where-

u = the volume fraction of water and n -- an adjustable parameter, which characterises the effectiveness of a certain water c o n c e n t r a t i o n i.e.

water absorbed in pores parallel the electrical field applied,

to the d i r e c t i o n of

n = 1, w a t e r - f i l l e d spherical interstices, distributed in the sample and

randomly

n < 1, water bound to the resin: Equation 5.27 describes the increase of the d i e l e c t r i c constant of the M D I / l a c t o n e system from 3.39 to 3.84 due to 2.0 %v. of moisture using a value of 1.42 for n. The dielectric constant of the M D I / s t y r e n e system at 20~ increased from 2.94 to 3.24 due to 1.56 %v. of moisture. This increase also corresponds to a value n = 1.42 in equation 5.27. A DGEBA/HHPH (diglycidyl ether of bisphenol A/hexahydrophthalic anhydride) casting system reached an e q u i l i b r i u m moisture concentration of 0.56 %v during storage at 20"C and 70 % R.H. The dielectric constant increased from 3.31 to 3.51 due to this absorption effect. This increase is c o r r e s p o n d i n g to a value n = 2.39 in equation 5.27. The sample was subsequently immersed in d e m i n e r a l i s e d water until a new equilibrium saturation of 1.08 %v. was reached. The dielectric constant increased from 3.51 to 3.85 due to this absorbed water additionally. The results of this experiment are p l o t t e d in Figure 5.14. The drawn line corresponds to equation 5.27, using the n value of 2.39. The calculated and m e a s u r e d dielectric constant values are equal up to a water content of 0 . 7 1 % v . The m e a s u r e d dielectric constant values increase, however, stronger than those calculated at higher water contents. The same effect is m e a s u r e d for the tangent delta values. This gives the impression that we observe the m e n t i o n e d transition in the introduction from the second to the third mechanism. The transition from the first to the second mechanism is not detectable due to a lack of data points at low moisture contents. Figure 5.15 shows similar results for an epoxy b a s e d glass fibre laminate (Nelco-100, a one-side copper-clad laminate). The moisture content scale in this figure is an experimental one i.e. it is the weight increase due to m o i s t u r e a b s o r p t i o n divided by t h e ~ ~ 1 1 w e i g h t of resin, glass and copper. A l t h o u g h the moisture content scales of both figures 5.14 and 5.15 can not be compared, the change in the slopes of both

156

Figure 5.14 Influence of moisture on the dielectric properties on a D G E B A / H H P A casting

die/.

ta n g e n t

constant

de/ta

0.1

4.00

~q 3:

3.90

T"-

3.80

calculated curve Hartshorn equation

"0 c-

3.70

0 0 0

3.60 +

3.50

:3.30

0 0 (D r

3.40 0

0,1

3.20 3.10

jZ~ /

0q ~3

-(3 c

z~-

:3.00

0.00

0.20

,,I

0.40

Moisture

0.60

content,

0.80 %wt.

0.01

1.00

157

Figure 5.15 Influence of moisture on the dielectric properties of an epoxy based laminate

die/.

tangen t

cons tan t

delta

6.00

3:5.80

/+ I

"T"

-(9

E 5.60

73 C

-0.1

0 0 0 5.40

E r E 0

5.20

+7+-j

-0

5.00

E O~ E

F-

--r 4.80 @ db

0.01

..,~.

L~ ~

4.60 0.00

,i,.,

0.20 Moisture

0.40 content,

,,I

0.60 %wt.

0.005 0.80

158 resin casting curves is also clearly present in both curves of the laminate sample. Especially the inflection in the laminate tangent delta/moisture content curve is more pronounced than that in the resin casting curve. This might be caused by the relative high water/resin ratio in the laminate sample (the overall moisture concentration of 0.5 %wt. in Figure 5.15 the inflection concentration - is estimated to be about 1.3 %wt. on pure resin). Alternatively, the distribution of water absorbed water in a glass fibre laminate sample might differ from that of a resin casting system. Woo and Piggot [27] state, for instance, that absorbed water in a glass-epoxy composite is concentrated in the interfacial regions, which are interconnected by disk-shaped water clusters providing conducting paths.

5.2.3 The effect of seawater and crude oil on the electrical properties of a tankcoating system~ The vast increase in the bulk shipment of refined and chemical products has resulted in a growing interest in coatings for tanks having an improved resistance to various chemicals. The electrical properties of such systems are important in connection with: - the corrosion protection, the decay of electrostatic charge and, as an aid to monitor changes in the coating's performance. -

The principal aim of actions taken with regard to the electrostatic problems has been to promote the safe discharge of such charges during their development. The two factors which determine the ability of electrostatic charges to disappear through the paint layer are its volume resistivity and dielectric constant. The product of these, called the 'relaxation time', represents the time taken for the charge to decrease to i/e th ('e' the base of the natural logarithm) of its original value, and is used as a measure for the coating's charge dissipation ability. If the resistivity and the dielectric constant of a tank coating are of the same order of magnitude as those electrical properties of the product carried, the relaxation time of the whole system is not increased and this situation is considered acceptable. From an anti-corrosion point of view, however, coatings with a high volume resistivity are favoured. The resulting high resistance of the paint layer can act as a barrier preventing ions reaching the metal surface; this is called resistance inhibition. This factor will result in a greater disparity between the electrical properties of the coating and typical cargoes and thus tends to increase the likelihood of electrostatic charge built-up. Apart from this aspect, the volume resistivity may also considerably affect the efficiency of the (impressed) current cathodic protection systems typically used in tanker situations.

159 A further complication is that the volume resistivity of coating materials is strongly dependent on their composition and this, in turn, can be greatly affected by contact with different cargoes. Hence, knowledge of this p r o p e r t y as a function of contact time with different media is desirable. The electrical properties of a series of eight different tank coating systems in contact with respectively seawater, crude oil and kerosine were determined [2], as a part of a tank coatings' research program. The results m e a s u r e d for one of these coatings, an epoxy coal-tar system cured with an amine adduct (26 %wt. binder, 35 %wt. coal-tar and 39 %wt. talc/ barytes pigments) are reported in this chapter. Sample cells (Figure 5.16) were constructed upon the coated panels by glueing the polished end of glass tubes (internal diameter about 50 mm.) onto the coated surface w i t h epoxy cement. The sample cells were stored at 22 â&#x20AC;˘ 2~ and a relative humidity of 55 â&#x20AC;˘ 5 per cent. The steel panel served as high potential electrode (H), and a m e r c u r y electrode, connected by a p l a t i n u m wire, as low potential electrode (L). Guarding was achieved by using a b e l l - s h a p e d brass cover w h i c h also supports the connector of the low potential electrode. These sample cells were filled with the a p p r o p r i a t e liquid during the immersion experiments. Before each measurement the liquid was decanted and the surface to be m e a s u r e d was wiped dry with a soft tissue. The mercury electrode was then immediately introduced. After the measurement the mercury was removed and fresh immersion liquid was reintroduced. Figure 5.17 shows the decrease of the volume resistivity and the increase of the dielectric constant as a function of the square root of the immersion time, due to contact with seawater. The volume resistivity decreases in about six days from 4.2E14 O h m . c m to 3.3EII Ohm.cm and stabilised finally at a level of 2.2EII Ohm.cm. The dielectric constant increased from 5.49 to 9.36 in about six days and stabilised at a value of 10.25. The electrical properties of this epoxy coal-tar system hardly changed due to contact with Middle East (Kuwait) crude oil: vol. resistivity, diel. constant, 0hm.cm i kHz. epoxy coal-tar system a. before immersion 7.8E13 5.28 b. after 1300 hours of contact with crude oil 7.2E13 5.30 c. crude oil as such

2.1E 9

2.47

These results and the results in Figure 5.17 show that seawater penetrates into the coating and influences, subsequently, the electrical properties strongly. The crude oil, however, does hardly affect the coating properties.

160

PL AT INUM CONTACT

BRASS GUARDINGLIOUID MERCURY ELE

TO ELECTROMETER L ---.~

GLASS-TUBE, ELECTRODE SURFACE ABOUT 20 cm= \ PA INT COATINS

H I DC SUPPLY

Figure 5.16 Construction of the sample cell

161

Figure 5.17 Epoxy/coal-tar coating, in contact with sea-water

volume resistivity

dielectric constant 11 ~

le+14

J9 ~

.o 0 O4

le+ 13

-8 c

9 o 1e+12

4-..,

d u9

X + ~ ~

le+111, 0

, , 5

c s0 (J

Seawater

,..

, .... I

+_____.__+~ i

~+~ I

15 2 0 2 5 3 0 3 5 4 0 4 5 immersion time, h~ Q.5

(3 G) (b d3

162

Figure 5.18 Epoxy/coal-tar coating, in contact with sea-water followed by crude oil +

sea-

crude

water

le+

oil

7-1-

S /

E 0

>~ >

le+13 -

0 >

q--

r le+12

U3 / 2e+11

, -18

, -14

-10

-6

Seawater/crude

-2 oil

..t

immersion

10 time,

14 I-1~0.5

163 A nearly complete recovery of the coating's volume resistivity is measured, if an epoxy coal-tar coating after about fourteen days of contact with seawater is immersed in crude oil (Figure 5.18). This indicates that the seawater absorbed is nearly completely leached out by the crude oil i.e. crude oil absorps seawater considerably stronger than the epoxy coal-tar coating does. The relaxation time T, in connection with electrostatic /discharge processes is defined as: T = c'o.c'r.G where:

5.28

= relaxation time,

charge

8.85E-12,

F/m

'r = die1. constant coating, = volume resistivity coating,

Ohm.m.

Equation 5.28 results in a relaxation time of about 50 seconds for the epoxy coal-tar coating as such. This value decreases to about 0.2 seconds after contact of the coating with seawater. The relaxation time of the epoxy coal-tar system remains higher than the relaxation times of 0.018 s. to 0.00018 reported for different crude oils [28], even after prolonged contact with seawater. 5.2.4 The Ki-value determination of PVC cRble compounds The specific volume resistivity is the most important electrical property of an electrical grade PVC. It is measured on a heavily plasticised product, the 'cable compound', pressed to a 2 mm. thick sample sheet. Cable manufactures usually test the resistivity of these compounds on cable samples and express the results in a so-called Ki-value. The Ki-value is in fact a volume resistivity value (see below) but measured on a cable sample with tapwater as low potential measuring electrode. A series of Ki-value determinations was performed to investigate the different parameters influencing this quantity. The Ki-value determinations were performed on coils with a diameter of about 0.2 m., made of cable samples with a length of about 10 m. Such a coil is immersed in an (electrically insulated) water-bath filled with tapwater and kept at the specified temperature. The electrical resistance is then measured between the copper wire of the cable (high potential electrode) and the tapwater (low potential electrode). The Kivalue is calculated according to [29]Ki - Ri/[log(R2/Rl) ] where-

Ki - insulation constant, Mega-Ohm.km = insulation resistance, Mega-Ohm.km R2 = cable diameter, m m R1 = wire diameter, mm. Ri

5.29

"1"1 CQ C

165 We m e a s u r e d the v o l t a g e over, and the current f l o w i n g t h r o u g h a p i e c e of cable of about I0 m. instead of one k i l o m e t e r length. Hence, the Ri-value follows fromRi =

(V.I.E-6)/(I.E3)

5.30

-- (V.I.E-9)/I

w h e r e : Ri = i n s u l a t i o n resistance, M e g a - O h m . k m V = m e a s u r i n g voltage, Volt I = m e a s u r e d current, A m p e r e 1 = sample length, m. Substitution to: Ki =

of 5.30

in 5.29

is g i v i n g the K i - v a l u e

according 5.31

[V.I.E-9] / [I.Iog(R2/RI) ]

The (in this way) c a l c u l a t e d Ki-value in M e g a - O h m . k m has in fact the same d i m e n s i o n s as the specific v o l u m e r e s i s t i v i t y w h i c h is e x p r e s s e d in Ohm.m. The d e r i v a t i o n of Ki s t a r t i n g from e q u a t i o n 5.2 is straight forward: the r e s i s t a n c e of a r e c t a n g u l a r piece of m a t e r i a l b e t w e e n two flat metal e l e c t r o d e s is g i v e n a c c o r d i n g to e q u a t i o n 5.2 by: R

(G.L)/A

where:

r R L A

= = = =

5.32

specific v o l u m e resistivity, O h m . m resistance, O h m length in the d i r e c t i o n of the current, m area p e r p e n d i c u l a r to the current direction,

m2.

In the case of a cable, however, an annulus at a d i s t a n c e r from the center of the cable and h a v i n g an i n f i n i t e s m a l thickness dr, is c o n s i d e r e d (see Figure 5.19). The l e n g t h of this annulus in the d i r e c t i o n of the current is dr. Its cross section p e r p e n d i c u l a r to the d i r e c t i o n of the current is 2.~.r.1, where 1 is the l e n g t h of the cable. The r e s i s t a n c e dR of this annulus is then a c c o r d i n g to 5.32: dR =

(o.dr)/(2.~.r.l)

The total

resistance

R2 R = a/(2.~.l).;dr/r R1

5.33 of the cable becomes: = (G.Ln[R2/RI])/(2.~.I)

5.34

This resistance value is c o n v e r t e d into a R i - v a l u e in MegaOhm.kin by s u b s t i t u t i o n of 1 = 1000 m and e x p r e s s i n g of the Ohms in Mega-Ohms i.e. xE-6: Ri =

(2,30.E-9.a.Log[R2/RI])/(2.~)

Substitution

of 5.35 in e q u a t i o n

Ki = Ri/(Log[R2/RI])

5.35 5.29 gives

= 0,366.E-9.G

for Ki" 5.36

166

Figure 5.20 Ki-value/temperature relation for a cable sample ex-Dorlyl

450-

Ki VALUE, MO. i n

410 370

IOQ E

VOLTAg(

330,

(I.F.r

120

160

E~ (D

10N TIM(

200 240 200 IMMERSION TIM(, h

10; (U

IrrIT~rsion time: 2 hours Electrification t i m e : 2 rain. Voltage: 500 V

-1

0.5

55 Temperature,

deg. C

115

167 where-

Ki = insulation constant, Mega-Ohm.km = specific volume resistivity, Ohm.m.

The Ki-value and G are thus in theory linearly related. The use of a water electrode (resulting in water penetration and plasticiser dissolving effects) makes this relation, however, more complicated. The main variable during these type of measurements is the temperature. Figure 5.20 shows that the Ki-values of an exDorlyl cable, decrease from 331 Mega-Ohm.km at 20~ to 1.2 Mega-Ohm.km at 80~ It is hence not surprising that the measuring temperature of the Ki-value is specified by every cable manufacturer. A second measuring variable is the immersion time. The inserted graph in Figure 5.20 shows the effect of the immersion time on the Ki-value at a temperature of 20~ The Ki-value immediately after immersion (428 Mega-Ohm.km) decreases to 330 M e g a - O h m . k m a f t e r two hours of immersion and to 308 Mega-Ohm.km after five hours of immersion. Then the Kivalue starts to increase again to 420 Mega-Ohm.km after 220 hours and to 570 Mega-Ohm.km after 850 hours when this experiment was stopped. The Ki-value decrease might be a moistening effect. The subsequent 'recovery' of the resistance is thought to be caused by depletion of charge carriers due to the water penetration and/or perhaps some extraction of plasticiser. This immersion time effect might be one of the reasons for the relative large differences in the Ki-value results from different suppliers (the immersion time is hardly specified). In chapter 5.1.2 was shown that the electrification time affects the resistivity determination of polymeric materials. Every manufacturer is using its own (again seldom specified) electrification time for the Ki-value determination. In this case, the situation becomes more complicated: the electrification time effect proves to be immersion time dependent (figure 5.21). The Ki-values of the Dorlyl cable sample were measured at 20~ using different electrification voltages between I00 V and I000 V. These measurements showed that this variable has no significant influence on the Ki-values at 20~ Some electrification voltage effect might be expected however at higher temperatures. Table 5.5 lists the results of the Ki-value determinations on three ex-Dorlyl cable samples. These values show that a repeatability of + I0 % is possible under these conditions. Three different cable samples were, subsequently, subjected to a series of Ki-value determinations at 60~ The results of these measurements are plotted in Figure 5.22. In spite of the scatter, especially in the Silec results, the difference in electrical performance between the three cable samples is

168

650

Ki VALUE, M~.km -

570 fcAeL~Ex OORL','L' IVOLTAC3E:

eX)Ov

IT,.PeRATu~: =0% 490

I J =sh |_e

=18

" f

410

330

z~-,o~

,oo

,ooo

. . . .

,ocx)o

ELECTRIFICATION TIME, $

Figure 5.21 The Ki value of a PVC cable compound as a function of the electrification time

169

K i ~O,LUE, M,0.. km 120 B

I00

IT(MP(I~A"I;:(

eo o(E'-

i ELECT~'C,T=E=.......2 ~.

SILEC CABLE 60

40 20

DORLYL CABLE ....

I I0

................ I ......... I tO0 tOO0 IMMERSION TIME, h

Figure 5.22 Ki-values vs immersion time at 60~

170 clear. A K i - v a l u e of 65 M e g a - O h m . k m was m e a s u r e d for the Silec ~ sample after two hours of i m m e r s i o n and an e l e c t r i f i c a t i o n time of two minutes; Silec r e p o r t e d a v a l u e of 52 Mega-Ohm.km. A Ki-value of 40 M e g a - O h m . k m was m e a s u r e d for the CGFCE sample u n d e r the same conditions; CGFCE r e p o r t e d a value of 48 MegaOhm.km. No a d d i t i o n a l i n f o r m a t i o n about the m e a s u r i n g c o n d i t i o n s was a v a i l a b l e for b o t h samples. The a g r e e m e n t b e t w e e n the m e a s u r e d Ki-values and the by Silec and C G F C E r e p o r t e d v a l u e s seems to be not to bad c o n s i d e r i n g that both m a n u f a c t u r e r s o n l y s p e c i f i e d their m e a s u r i n g temperatures. The above d e s c r i b e d results indicate c l e a r l y the i m p o r t a n c e of a p r o p e r s p e c i f i c a t i o n of the most important Ki-value m e a s u r i n g c o n d i t i o n s i.e. - the temperature, - the i m m e r s i o n time, - the e l e c t r i f i c a t i o n time, - the e l e c t r i f i c a t i o n v o l t a g e and - the for the d e t e r m i n a t i o n u s e d cable length. A c o n s i d e r a b l e d i f f e r e n c e in l e n g t h (for e x a m p l e 250 m. i n s t e a d of the i0 m. samples d e s c r i b e d here) i n f l u e n c e s the w e t t a b i l i t y of the sample coil and increases the c h a n c e on w e a k spots in the i n s u l a t i o n layer due to the cable e x t r u s i o n process. Table

5.5 R e p e a t a b i l i t y

Immersion time, h

a. b. c. d. e.

Ki-value, M. Ohm. km sample .1

428

2 5 50 ,

of K i - v a l u e

Ki-value, M. Ohm. km sample 2

determinations. Ki-value, M. Ohm. km sample 3

398

466

331

399

308

319

380

359

cable sample temperature electrification electrification sample lenght

: ex-Dorlyl : 20 ~ voltage. 500 Volt time 92 m i n u t e s 9 i0 m.

171 5.3 C o n d u c t i o n improvement of epoxy resins by c a r b o n b l a c k addition 5.3.1 Electrostatic safety criteria Polymers are used in m a n y applications e s p e c i a l l y for their ease of m o u l d i n g in c o m b i n a t i o n with a high electrical insulation resistance. There are also applications where a too high electrical resistance hampers the d i s c h a r g e of electrostatic charges which can build-up. It is often necessary then to decrease the polymer's original resistivity to lower values for safety reasons. A d d i t i o n of conducting particles, for example carbon black, is one of the possibilities to decrease the resistivity of a polymer to an acceptable value. This acceptable value is set by rather simple rules: The discharge process of electrostatic charges is decribed by relaxation time T. This value stems from the c h a r g e / d i s c h a r g e processes of a capacitor C via a resistance R, given by. charging

: Uc = Uo. (I - e ^[-t/T])

discharging: where-

Uc = Uo.e ^[-t/T]

5.38

T = R.C

For the discharge of a n o n - c o n d u c t i n g object, R

(G.d)/A,

(~o.c'r.A)/d,

5.37

see

T follows from:

5.2

G.~o.~'r,

see

5.4

see 5.28

The resistance R is formed by the insulation resistance to earth of an object, while capacitance C is the capacitance of a standing person i.e. about 100 pF [30]. A T-value of 0.01 s. or less is required for p r o t e c t i o n of such a p e r s o n against discharges [30, 31]. The maximum value of R has to be in this case : R(maximum)

- 0.01/I.0E-10

= 1.0E8 Ohm

Distance (d) and area (A) are often difficult to determine. DIN 51953 gives, therefore, as a practical rule: the resistance to earth per 20 cm2 has to be lower than 1.0E8 Ohm. A too low resistance, however, can also be dangerous for persons in connection with the p o s s i b i l i t y of shortcircuiting. Hence, a resistance to earth per 20 cm2 between 1.0E5/1.0E6 Ohm and 1.0E8 Ohm is u s u a l l y considered to be acceptable.

172 5.3.2 DC properties of experimental epoxy resin/carbon black systems Polymers are often filled with carbon black to obtain antistatic compounds with specific volume resitivities of about 1 . 0 E 8 0 h m . m or less. The resistivity will in general hardly decrease during the first I0 %wt. of carbon black added. Resistivity values of about I00 Ohm.m are realised for carbon black concentrations higher than about 20 %wt., mainly due to direct contact between the conducting particles. The rather small concentration region where the resistivity decreases from a high to low resistivity is called the percolation threshold [32]. However, carbon black loadings of about 20 %wt. seriously reduce the mechanical properties (in a negative sence) . Some types of carbon black (Ketjenblack EC-2000 and Gulf AB 550-P) in certain cured epoxy resin systems showed to have a percolation threshold of less than 0.5 %wt., see Figure 5.23. The commercial relevance of this knowledge was recognised [33] and additional experiments were performed to obtain more insight in this phenomenon. Some experimental results of this investigation are collected in Table 5.6. Table 5.6 Electrical properties of carbon black filled epoxy resins cured with different curing agents at 23~ II

DGEBA resin cured with-

carbon black, %wt.

volume resistivity, Ohm. m

dielectric constant at 1 kHz.

aromatic amine

0.0 1.0

2.0El3 2.0E 4

alifatic amine

0.0 1.3

3.1E13 6.2E 7

cycloalifatic amine

0.0 0.9

5.8E12 2.5E12

4.81 45.7

72 66

4.60 25.4

107 112

Tg-value, DSC onset, oc

4.69 8.38

68 69

',,

9diglycidyl ether of bisphenol A, DGEBA : 7 days at 20~ cure post-cure- 24 hours/100~ These values illustrate the strong influence of the type of curing agent used. The phenomenon studied is clearly present in the first system where the low volume resistivity is accompanied by a high dielectric constant value. This phenomenon is clearly not present in the third, with a cycloalifatic amine cured system. The dielectric constant of this system, although increased due to the carbon black addition, is low compared with that of the former system. The resistivity decrease effect is found to some extent present

173

Figure 5.23 Volume resistivity of epoxy casting (DGEBNDDM) versus the carbon black content

101~ 1014 1 0 13 E g lO

10"

..c

0 1011

>:, 10 '0

(/) .,,.t/') &..

E 0

107

10'

10 6

105

O.O0

0.40

0,80

1,20

C a d ~ n black c ~ r e l i o r ~

"~ 104 10

-I-

10'

I+

10 9

9 1Q

,4-

10 =

1.60

2.00

%wI.

10 2

lO' f

10 ~

0.00

O. 1 0

.I,

0.20

Carbon black

0.30

0.40

concentration,

.....

0.50

%wt.

0.60

174

DOEBA/cyclo-alifatic amine cured system (x 0.9 %wt. carbon black) (A no carbon black)

zz) ._I

0 >

/ I"

/ /

DOEBA/alifatic amine cured system (1.3 % w t . carbon black)

------- m .....

I'-4

U lIJ O. tr~

cK o

X ~A

x~)i

Figure 5.24

DOEBA/aromatic amine cured system (1.0 %wL carbon black)

+,+

~+..

+ ------ ยง ~ + _ . ยง

,w-

1000/T. l

l Lr)

KT-1 ~

I' ' 'I

I'-

" I

175 for the system cured with a alifatic amine- the volume resistivity is about six decades decreased and the dielectric constant is significantly increased. The specific volume resistivity of these three systems was measured as a function of the temperature between 20~ and II0/140~ The results are shown in Figure 5.24. The DGEBA/cyclo-alifatic amine cured system shows a typical polymeric behaviour i.e. the resistivity decreases strongly with an increasing temperature due to an increase of the charge carriers mobility. The DGEBA/aromatic amine cured system behaves like a metal i.e. the resistivity slightly increases with increasing temperatures. In this case this might be caused by an increase of the distance between the conducting carbon black particles due to the difference in expansion coefficient between the carbon black and the resin matrix. This expansion coefficient difference (and thus the resistivity increase with the temperature) increases if the resin matrix changes from its glassy into its rubbery state. The volume resistivity of the DGEBA/alifatc amine cured system exhibits an intermediate behaviour. The volume resistivity increased between 20~ and 100"C as a function of the temperature (metallic behaviour). The increased charge carrier mobility seems to dominate the thermal expansion difference effect, at temperatures above the glass-rubber transition, resulting in a change in the slope of the resistivity/ temperature curve. Figure 5.25 shows the AC properties (dielectric constant/ dielectric loss factor) at 23~ as a function of the frequency. The differences found in the volume resistivity of these systems are also reflected in the AC properties. The strong decrease of the dielectric constant as a function of the frequency for the system cured with EPIKURE 160/161 indicates a certain amount of capacitive coupling between the conducting carbon black particles. The dielectric loss factor/frequency relation of this system is nearly linear with a slope of about -i, pointing at a pure resistive behaviour (see equation 5.18). Kawamoto [34] represented a single carbon black particle polymer interface - carbon black particle 'unit' by a resistor R in series with a resistor R and a capacitor C in parallel. He subsequently assumed, that the whole body of the carbon black filled system can be represented by one single RC circuit. He was able, using this model, to calculate accurately the AC properties as a function of the frequency for a carbon black filled PVC system. This model failed, however, in the calculation of the AC properties of the above decribed, conductive epoxy resin systems. A variety of microscopical techniques revealed that around some critical concentration well below 2 %wt. of carbon black there is a transition from isolated inclusions to a conducting network [35]. The presence of a conducting network in contrast with Kawamoto's randomly dispersed carbon black particles

"'""'

7a. e

es. 9X

F igur e

5.25

6g. B

DGEBA/aromatic amine cured system (!.0 %wt. carbonblack)

u u_

I ~

DGEB,~aromatic amine cured system (I.0 %wt.carbonblack)

Ill

0 u p. U

ยง

tg.

~ w D

Temperature =

55. g +

58. g

Temperature = 23~

45. S

48. II

35. g

DGEBA/alifatic amine \ cured s3~tem . . . . (1.3 %wt. carbon black)

DGEBA/alifatic amine cured s y s t e m ~ (I.3 %~. carbon black) \

fg 38.

23~

"\ ~ ~

9 ..----A ~

9" "

A~-A~

ยง

25. e

20.8

DGEBA/cycio-alifatic amine ~ 15. g

(0.9%wt.carbonblack)

+\4,

,,,,,

x - - - - - X -=---X ~

X~X'x I N

I o,4

l,,e

l.,e

/x "x" x'x Xx~X ~ x

g,i

FRE~,

X~ 9

g,I

18 I

~..~X

~xfx

DGEBA/cyclo-alifatic amine cured system (0.9 %wt. carbonblack)

lg.g

5.8

x -~

." : ; ; ":;4; I

;

." : ; .'::;; ~

;

t~HtI~-+~444H----P--F-~4~N

im I

FREQUENCY,

H=.

177 may well be the reason that his model failed to describe the AC properties of the conductive epoxy resin systems. The formation of such a conducting network was found to depend on the surface tension of the used curing agent at the cure temperature. In addition, the degree of dispersion of the carbon black particles proved to be critical [33]. A homogeneous dispersion of the carbon black particles (substantially) having a diameter predominantly below 1.0E-6 m. and a curing agent with a surface tension at the curing temperature of either at least 33 or at most 23 MN/m proved to be necessary for the formation of a conducting network. It is believed that the aforesaid surface tension criteria are related to the interracial energy between curing agent molecules and carbon black particles. This energy is exceeding a defined critical value, thus creating a driving force which causes the carbon black particles to form a network structure of coagulated particles in a resin matrix. ~.3.3 The DC properties Of anti-static epoxy_ GFR pipes The use of glass-fibre reinforced (GFR) epoxy resin pipes is, especially in tankers, hampered by the 'bad' electrostatic properties of these pipes. The possibility to decrease the volume resistivity to an acceptable level using only a small amount of carbon black (see 5.3.2) resulted in the development of the WAVIMAR anti-static GFR pipe system by Wavin BV. This pipe system is based on a liquid DGEBA/MDA (100/27) and cured for two hours at 120~ containing about 1.5 %wt. (on the resin phase) of Ketjen black EC-2000 carbon black. The specific volume resistivity of a sample of such a pipe was measured as a function of the direction, the field strength and the pipe wall thickness. The 5.1 mm. thick pipe wall consists of an about 0.5 mm. thick, with C-glass reinforced, liner layer on the inner-side followed by the 4.3 mm. thick, cross-plied glass fibre reinforced, pipe wall body. The outside of the pipe wall consists of an about 0.3 mm. thick epoxy resin layer. The investigated pipe sample had an outside diameter of 50 mm. First, the specific volume resistivity of a reference sample without carbon black was measured in the radial direction. Figure 5.26 shows the strong time-dependency of the charging current at a measuring voltage of 1200 Volt and a temperature of 23~ The Ic has not yet reached the I(dc) level after even 2.5 hours. The measuring procedure described in 5.1.2 is working satisfactorally and gives a constant I(dc)-value of 2.7E-12 Ampere between 900 and 9000 seconds measuring time. This results in a specific volume resistivity value of 3.0E14 Ohm.m for the reference system without carbon black (measured in the radial direction). Subsequently, about eighty millimeter long sample pieces (properly mounted and supplied with vacuum evaporated silver

178

Figure 5.26 Specific volume resistivity determination of an epoxy resin based, GFR pipe + Icz~ I d o I(dc)current current current

1 0 - ' ~ I::

~ [

1 0 -11

(1) !1,,_ (1) o

E ,<

~+ ~0~0

~+_

o/~

1 0 -12

Pipe wall

thickness

5 mm.

Measuring voltage 1200 V 1 0 -13

10"

0 I

10 3

Charge/discharge

10"

time, s.

179 electrodes), were used to measure the volume resistivity of the anti-static pipe in both the radial and the axial direction as a function of the electrical field strength. These measurements were p e r f o r m e d on the pipe samples as such, on the pipe samples after m a c h i n i n g away the 0.3 mm. thick outside resin layer and finally after m a c h i n i n g away a layer of 2.3 mm. Small sample disks (diameter 5 mm.) were taken out of the liner layer, the pipe body and the outside resin layer, to determine the carbon black content by TGA analysis. Some relevant results are listed in Table 5.7 and plotted in Figure 5.27. Table 5.7 Results of the specific volume d e t e r m i n a t i o n s on WAVIMAR anti-static pipe at 23~ and an electrical field strength of 4000 V/m. ,

....,

WAVIN/~ a n t i static pipe, sample set

volume resistivity axial direction, Ohm.m

7.5E5 8.4E6

2.4E3 2.0E3

9.3E6

2.2E3

1.4E7

3.5E3

~,,

volume resistivity radial direction, Ohm.m

i, total pipe 2, t o t a l p i p e 2, no resin outside layer 2, liner layer and pipe body reference system, no carbon black

. . . . .

',,

I~,,,~ ,,

3.0El4 .....

Ull

a. outside layer- 1.6 %wt. carbon black on resin, b. pipe body 9 I.i %wt. carbon black on resin, c. liner layer - 0.7 %wt. carbon black on resin. These data show a volume resistivity decrease of about seven decades in the radial d i r e c t i o n and a decrease of about eleven decades in the axial direction. The time d e p e n d e n c y of the charging currents has completely disappeared but the volume resistivity proves to be field strength dependent. The slight decrease of the volume r e s i s t i v i t y from the inner side to the outer side agrees with the increasing carbon black concentrations m e a s u r e d in this direction and this might be an effect of the glass fibre w r a p p i n g procedure during the production process. The WAVIMAR anti-static GFR pipe easily satisfies the electrostatic safety criteria given in 5.3.1, the volume r e s i s t i v i t y in axial direction is even too low to protect persons against shortcircuiting. The clear d i r e c t i o n d e p e n d e n c y of the volume resistivity might be an i n t e r e s t i n g option for other electric/electronic applications.

180 2g

E tO o 0

X 14

S P E C I F I C VOLUME R E S I S T I V I T Y OF WAVIMAR GLASS F I B R E REINFORCED CARBON BLACK F I L L E O EPOXY P I P E I N THE R A D I A L O I R E C T I O N AS A FUNCTION OF THE E L E C T R I C A L F I E L D STRENGTH AND THE P I P E WALL THICKNESS ~ WALL THICKNESS 5. I MN (I=IPE AS SUCH) x WALL THICKNESS 4 . 8 NM ( 8 . 3 HM-OUTSIOE-RENQVED) A WALL THICKNESS 2 . 5 MN ( 2 . 8 MH-OUTSIDE-REMOVED) &

._> ~

ยง

E m 0

~/(Field str.ength, E) (Vim) vz .

t B m

! m (0

t Ia O~

i m N

! ~9 I.'1

t 19 0

! m N

I IB N

" =a t~

i s 01

Figure 5.27 5.8

4.8

E E ..C

4.2

3.8

S P E C I F I C VOLUME R E S I S T I V I T Y OF WAVIMAR GLASS F I B R E REINFORCED. CARBON BLACK F I L L E D EPOXY P I P E I N THE A X I A L DIRECTION AS A FUNCTION OF THE ELECTRICAL F I E L D STRENGTH AND THE P I P E WALL THICKNESS WALL THICKNESS 5 . 2 MM ( P I P E AS SUCH) x WALL THICKNESS 4. g NM (B. 3 MH-OUTSIOE-REMOVED) 9 WALL THICKNESS 2. 5 MN ( 2 7 MH-OUTSIOE-REHOVED)

._>

3.4

3. g

2.6

,m,. 0

> 2.2

X '-'-.-,.-----.-_ ~

X..-.-,,..._..__ x

1,8

t.4

~/(Field strength, E) (V/m) tr~ 1.0.[ ED

Orl

(It

,",

"q'

I/1

181 5.4 Thermally Stimulated Discharge analysis 5.4.1 The TSD techniuue In the.preceding chapters we showed that several thermoanalytical techniques are available to study thermal transitions in polymers. The thermal transitions of new, polymeric systems are usually first investigated by DSC measurements (small amount of sample needed/high scanning speed). The DSC technique is, however, often not sensitive enough to detect weak and/or secondary relaxation effects. DMA (rigid polymers) or dielectric (rigid/rubbery/viscous systems) experiments are then necessary. The sensitivity of the dielectric measurements depends on the polymer's polarisability (see 5.1.2). Besides, DC conduction effects can seriously hamper the detection of the relaxation effects studied. The TSD analysis technique offers in such a case an attractive and sensitive alternative. TSD experiments are performed using the measuring circuit shown in Figure 5.1. The experimental method is schematically drawn in Figure 5.28. The sample is heated to polarisation temperature (Tp), at time to an electrical field (Eo) starts to polarise the sample. After a certain polarisation time (tpl) the temperature is decreased to To; the polarisation is then 'frozen in'. At temperature To (i.e. at time t,) the electrical field (E~ is removed and a small depolarisation current effect is measured. If this depolarisation effect has been vanished completely, the temperature is to increased linearly as a function of time and the thermally stimulated discharge current is recorded. 5.4.2 Bucci's TSD theory Next to electronic, atomic and orientation polarisation (see 5.1.2), two other polarisation types can occur during TSD experiments: intrinsic space charge polarisation; free electrons and/or ions present in the sample, move in the direction of the electrodes and, - extrinsic space charge polarisation; electrons and/or ions are injected from the outside into the polymer sample. The electronic and atomic polarisation can not be frozen-in and cause the small depolarisation current after removing of the electrical field at time t2. Thus, the measured discharge current is the sum of dipole and space charge relaxation effects. The exponential relation between the relaxation times of these effects and the temperature makes it possible to shorten the discharge time drastically by therm~l stimulation. -

Bucci [36] and Perlman [37] treated these thermally stimulated currents as dipolar relaxation processes with single relaxation times (the Debye model). According to this model, the thermally stimulated current is given by: I(T) - A.exp[-E/k.T

T - B.~exp(-E/k.T) .dT] To

5.39

"11

Q. c

c/;

D 0

-0 0

~ ~

,|m,.

r-+ ~

m o

-0

-o

183 where:

I (T) = the m e a s u r e d TSD current, E = an a c t i v a t i o n energy, T = a b s o l u t e temperature, k = B o l t z m a n n ' s constant.

A = (N.p 2.EO.G) / (k.Tp. T)

5.40

and B

5.41

i / ( E . T)

where-

Eo p N T~ E

= = = = =

electrical field, d i p o l e moment, n u m b e r of dipoles, p o l a r i s a t i o n temperature, characteristic relaxation T(T) = T.exp(E/k.T), and = h e a t i n g rate.

time

The shape of the TSD curve is m a i n l y d e t e r m i n e d by h e a t i n g rate K, the c h a r a c t e r i s t i c r e l a x a t i o n time T and a c t i v a t i o n e n e r g y E. The total a m o u n t of charge r e l e a s e d is l i n e a r l y related with field s t r e n g t h Eo. The d i s c h a r g e current is g o i n g t h r o u g h a m a x i m u m at t e m p e r a t u r e T m g i v e n by: Tm =

[ (E/k) .K.T.exp(ElkTm) ]0,

5.42

Hence, Tm is not i n f l u e n c e d by p o l a r i s a t i o n t e m p e r a t u r e Tp n o r by the strength of e l e c t r i c a l field Eo. The low t e m p e r a t u r e tail of the TSD curve is d e s c r i b e d by the first exponent of 5.39 i.e. : Ln[I(T)]

=_ Ln[A]

- E/(k.T)

5.43

Thus E follows from the low t e m p e r a t u r e slope of the Ln[I (T)] v e r s u s the inverse, a b s o l u t e t e m p e r a t u r e curve. The theory d e s c r i b i n g space charge d e p o l a r i s a t i o n p r o c e s s e s is c o m p l i c a t e d [38]. E q u a t i o n s like 5.39 d e s c r i b e the t h e r m a l l y stimulated d i s c h a r g e c u r r e n t s but c o n t a i n more u n k n o w n variables w h i c h are d e p e n d i n g of- the type of charge c a r r i e r s (ions or electrons), - the different p o s s i b i l i t i e s to move (drift or diffusion), - the r e c o m b i n a t i o n and d i s s o c i a t i o n p r o c e s s e s d u r i n g the p o l a r i s a t i o n process. TSD dipole r e l a x a t i o n p r o c e s s e s are in general e a s i e r d e t e c t a b l e than space charge d e p o l a r i s a t i o n effects. For nonp o l a r polymers, however, the TSD effect is d e p e n d i n g on the space charge p o l a r i s a t i o n possibilities.

184 5.4.3 Results of TSD experiments An example of a PVC orientation d e p o l a r i s a t i o n effect, m e a s u r e d with a combined TMA/TSD system is given in chapter 6. These orientation d e p o l a r i s a t i o n effects were m e a s u r e d on small (i.e. 8 mm.) diameter, samples. Such samples proved to be too small, however, to detect the space charge d e p o l a r i s a t i o n effects in non-polar SSBR rubbers. These nonv u l c a n i s e d rubber samples were pressed, therefore, at 140~ between two (i mm thick) brass disks with a diameter of respectively Ii0 m m (high potential electrode) and 80 mm (low potential electrode) to a sample thickness of about 0.2 mm. A ring (inner/outer diameter 75/85 mm) of 50 m i c r o n thick Vespel foil avoided s h o r t c i r c u i t i n g between the two brass disks. _

The investigated SSBR samples were m e d i u m vinyl SSBR systems (BR part about 50 %wt. vinyl BR; styrene content 23 %wt.). The styrene m o n o m e r was mainly added during the last stage of the p o l y m e r i s a t i o n process. This resulted in tapered SSBR systems with endblocks i.e. 'tails' with a high styrene content. D e t e c t i o n of these high styrene content tail-structures by DSC or D M A failed. V a n d e r s c h u e r e n [39] showed that the space charge d e p o l a r i s a t i o n maxima of SBR systems are structure dependent i.e. styrene content dependent. Hence, the TSD technique was used to investigate these SSBR systems with and without 'tail' structures. The TSD (space charge) d e p o l a r i s a t i o n currents of three of these non-polar polymers are shown in Figure 5.29, the m e a s u r e d m a x i m u m temperatures are listed belowWRC10805, WRCI0804, WRCI0801,

m e d i u m vinyl SSBR - very broad 'tail', Tm = I02oC m e d i u m vinyl SSBR - broad 'tail' , Tm = 82~ m e d i u m vinyl SSBR - standard 'tail' , Tm = 76~

These results confirmed Vanderschueren's conclusion that structural differences are detectable by space charge d e p o l a r i s a t i o n current analysis.

Q_ r

bO 0

0 0

C~ 0

PO 0

k~ ,o

+ \+

TSD 0 0

current, 0

x 0

1.0E-10 ~

--,.

....~

II ~

,.+ II II

+ j+..,~

"+'--.~+~

ottO oo

II 0 " ~

II I'0 II

I'0_.,.

5-~~ o ~H

Ampere --,0

,,no

c o"

,-,. t~

0,-

--I"1"1

U'I

186 References i. C.C. Ku and R. Liepins- Electrical properties of polymers, chemical principles, Hanser Publishers, Munich (1987) . 2. W.M. Groenewoud, J. Oil Col. Chem. Assoc., /22, (1979), p. l0 - 17. 3. IEC 93, Recommended methods of test for volume and surface resistivities of electrical insulating materials, the International Electrotechnical Commission, Geneve (1958) . 4. B.V. Hamon, Proc. Inst. Electr. Engr., 99, part IV, (1952) . 5. A. yon Hippel, Dielectrics and Waves, Wiley, London (1954) . 6. N. Hill et.al., Dielectric Properties and Molecular Behaviour, Van Nostrant, New York (1969). 7. N.G. McCrum, B.E. Read and G. Williams, Anelastic and Dielectric Effects in Polymeric Solids, John Wiley, London (1967) . 8. IEC 250, Recommended methods for the d e t e r m i n a t i o n of the p e r m i t t i v i t y and dielectric d i s s i p a t i o n factor of electrical insulating materials at power, audio and radio frequencies including metre wavelengths, the International Electrotechnical Commision, Geneve (1969) . 9. A. Osier, Z. Angew. Phys., 20, Heft 5, (1966), p. 375. i0. A. Oster, Z. Angew. Phys., 23, Heft 2, (1967), p. 120. ii. G. Weber, Colloid & Polymer Sci., 256, (1078), p. 923. 12. P.J. Phillips, J. Pol. Sci.: Pol. Phys. Ed., 17, (1979), p. 409. 13. J.D. Ferry, Viscoelastic Properties in Polymers, J. Wiley, New York (1980) . 14. R.D. McCammon and R.N. Work, Rev. Sci. Inst., 36, (1965), p. 1169. 15. L.C. Corrado and R.N. Work, Rev. Sci. Inst., 41, (1970), p. 598. 16. J.C. Coburn and R.H. Boyd, Macromol., i~, (1986), p. 2238. 17. E.B. Murphy and W.A. O'Neil, SPE Journal, 2, (1962), p. 191. 18. R.J. Bender, Handbook of Foamed Plastics, (1965), p. 160. 19. P.A.M. Steeman et.al., Polymer, 32, (1991), p. 523. 20. K. Kadotani, Composites, october (1980), p. 199. 21. G. Banhegyi et.al., Coll. Pol. Sci., 266, (1988), p. 701. 22. A.R. Bunsell, Reinforced Plast., 3, (1984), p. I. 23. J.D. Reid and W.H. Lawrence, J. Appl. Polym. Sci., 31, (1986), p. 1771. 24. M. Continaud et.al., J. Mat. Sci., i/, (1982), p. 867. 25. Illers (water effect in nylons) 26. D. Brasher, J. Appl. Chem., ~, (1954), p. 62. 27. M. Woo and R. Piggot, J. Compos., 10, (1988), p. 16. 28. Shell Safety Committee, Static Electricity, Shell Internationale Petroleum Mij. B.V., The Hague, 1976. 29. Silec, Catalogue Generale, (1976). 30. H. Haase, Statische Elektrizitat als Gefahr, Verlag Chemi GmbH, W e i n h e i m (1972) . 31. Richl. Nr. 4 der Berufsgenossenschaft der Chemische Industrie, Statische Elektrizitat, Verlag Chemie GmbH, Weinheim, Neufassung (1971) .

187 32. L~ Burton et.al., Rubber Chemistry and Technology, Vol. 62, (1989) , p. 838. 33. J.C.M. Brokken-Zijp, A. Noordam, W.M. Groenewoud and C.H. Klaren, European Patent Application, EP 0 370 586 A2, (1989). 34. H. Kawamoto, Carbon Black-Polymer Composites, The physics of electrically conducting composites, Dekker, New York, (1982), p.135. 35. M.A.J. Michels et.al., Physica A, !57, (1989), p. 529. 36. C.Bucci et.al., Phys. Rev., 14_~, (1966), p. 816. 37. M.M. Perlman, J. Electrochem. Soc.- Solid State Sci. and Techn., July (1972), p. 892. 38. J. Vanderschueren et.al., Thermally Stimulated Relaxation in Solids, H4, Field Induced Thermally Stimulated Currents, Topics in Applied Physics, Vol 37, Springer Verlag, New York, (1979) . 39. J. Vanderschueren, Macromolecules, 13, (1980), p. 973.

COUPLED THERMAL ANALYSIS TECHNIQUES CHAPTER 6

188

CHAPTER 6: COUPLED THERMAL ANALYSIS TECHNIQUES 6.1 Introduction Coupled or simultaneous thermal analysis techniques are gaining more and more importance for several reasons- using the same sample for two or more analytical determinations prevents sample difference effects and ensures an identical thermal sample treatment, - confimation of, or complimentary information obtainable on results, using a second independent technique may justify economically the cost of application of coupled techniques, the often small amounts of sample available during process research on new or modified polymeric systems force the use of combined techniques to obtain as much as possible information from a minimum amount of sample, new techniqual developments promote the commercial availability of coupled thermal analysis techniques. -

A number of combinations with the thermobalance (TG) as basic unit has become wellknown i.e. the TG/DSC or TG/DTA, the TG/MS and the TG/FTIR, the TG/GC/MS, but also DMA/DETA and TMA/DETA combinations have been reported 5]. Coupled thermal analysis techniques usually recall pictures of sophisticated, complicated experimental systems, but also simple combinations are possible. McCammon, Corrado and Coburn [6 - 8] reported many years ago already their dielectric measurements (DETA) in combination with linear thermal expansion (TMA) measurements. A capacitive sample thickness measurement in a dual measuring cell (as described in 5.1.7) provided the information used to calculate the thermal expansion as a function of the temperature in combination with the dielectric data. A still more simple combination of thermal expansion (TMA) and thermally stimulated discharge (TSD) is described in chapter 6.2. A significantly more sophisticated combination of a thermobalance with FTIR and MS coupled in parallel is described in chapter 6.3. [i

189 6.2 Simultaneous

TSD/TMA measurements

6.2.1 The TSD/TMA system The TSD/TMA combination is a typical example of a system developed to measure the same physical property i.e. the glass-rubber transition, on the same sample and at the same time using two independent techniques. An 'old' but still properly working Perkin Elmer TMS-I was adapted to perform TSD/TMA experiments. The TMS-I is schematically drawn in Figure 6.1 together with some of the important dimensions. The sample, between the probe and the quartz glass sample holder is placed in the furnace. The furnace temperature is programmed to increase linearly with the time. The thermal expansion of the sample is measured via the probe by the linear variable displacement transducer (LVDT). A thermocouple, placed as close as possible to the sample is giving the sample temperature information. The sample holder system had to be modified to perform TMA/TSD measurements simultaneously. This modification is reproduced enlarged in Figure 6.2. The TSD/TMA sample disk (i mm. thick, 8 mm. diameter), provided with vacuum evaporated silver electrodes on both sides, is placed between a cup-shaped silver high potential electrode and a disk-shaped silver low potential electrode. The T M A p r o b e rests in the cup-shaped high potential electrode. Both silver electrodes are connected via 0.I mm. thick, glass fibre insulated wires with two BNC connectors in a tufnol holder clamped around the upper part of the sample tube. The main problem proved to be the mechanical stability and the electrical screening of both electrode wires. Small, thin ceramic pipes proved to give the wires sufficient mechanical stability and electrical insulation. A thin (0.i mm.) brass pipe around both ceramic pipes and the quartz glass sample holder provides the necessary electrical screening. Both electrodes were connected with a voltage supply and an electrometer as shown in Figure 5.1. Polarisation voltages up to 3200 Volt were applied without any problem. The resulting discharge currents, as low as 1.0xE-13 Ampere, were measured using a Keithley 616 (autoranging) electrometer. The thermal expansion effect measured is the sum of the sample effect and that of both silver electrodes. The thermal expansion of both electrodes (in total 2 mm. silver) was measured between -130oc and 130~ A constant linear thermal expansion coefficient of I.SE-5/K was measured (the Handbook of Chemistry and Physics gives an average value of 1.9E-5/K). This value for the thermal expansion coefficient of silver is, depending on the circumstances, a factor 2 to 20 lower than that of polymer samples investigated. The overall expansion effect measured is corrected for this silver effect if the linear thermal expansion coefficient of the polymer sample as a function of the temperature is required.

190

Sample holder: made from quartz glass, inner diameter: 9.5 mm Probe: made from quartz glass, probe diameter: 4.0 mm Oven: inner diameter: 17 mm

Sample length: maximal: 10 mm Temperature region: -150~ to 325~

Figure 6.1 The Perkin Elmer TMS-1

191

I I II II I

I I I I

=-.-- oven

ceramic

insulatlon

probe

._-.-, connecting

wire

I11 sample low potential electrode

v A

....

sample holder

scale 1 "0.2

Figure 6.2 The TSD/TMA

high potential electrode

sample holder

192 The thermal expansion of the silver electrodes is neglected if only the temperature location of the glass-rubber transition of the sample is measured. 6.2.2 TSD/TMA results Figure 6.3 shows the results of a simultaneous TSD/TMA measurement on a PVC sample. The glass-rubber transition of this sample is clearly shown by an orientation depolarisation current (see 5.4.2) maximum at 75~ The slightly positive currents before and after the thermally stimulated orientation depolarisation effect are an indication that next to dipole orientation also space charge polarisation effects are involved. The dilatometric measured Tg-value (the transition from the glassy state into the rubbery state is accompanied by a strong increase of the thermal expansitivity) is 76~ The close agreement of the Tg-values measured by the TSD and by the TMA technique indicate that the hypothetical measuring frequency for both techniques is about the same i.e. f(h) is in the order of ixE-2 Hz. to ixE-4 Hz. [9]. The TSD experiments on this PVC sample were, subsequently, repeated at three different polarisation voltages. The resulting depolarisation currents are shown in figure 6.4. Base-lines were drawn as good as possible and the total charge released, determined by integration, is plotted as a function of the electrical field strength in the insert of Figure 6.4. The practically linear relation found between the released charge and the electrical field strength is in agreement with Bucci's theory given in 5.4.2. This TSD/TMA combination proved to be a convenient (small sample size) and sensitive system for the determination of glass-rubber transition effects of several experimental polymer systems, especially in cases where the DSC technique failed due to a lack of sensitivity. The advantage of this dual technique was especially felt during the investigation of experimental samples with unknown Tg-values. In such situations the confirmation of the Tg-value by a second independent technique is often very valuable. The sample diameter /thickness ratio (8.0 for this system) proved to be not high enough, however, to perform measurements on non-polar polymers where the TSD effects depend on the much weaker space charge polarisation effects. In such cases the TSD and the expansion coefficient measurements were performed using standard equipment with a TSD sample diameter/thickness ratio of about 400, as decribed in chapter 5.4.3.

193

Figure 6.3 S i m u l t a n e o u s T S D / T M A m e a s u r e m e n t on a PVC s a m p l e with 10%wt. i m p a c t i m p r o v e r

TMA results

TSD results

-3.80

1.0200

1.0150

E E

..6

Tp = 1 2 0 ~ To = - 1 3 0 ~ tp = 10 mirl Eo = 1 0 0 0 k V / m sarrl31e thickness = 1.0 mm sample diam. = 8.0 mm heating rate = 4 ~

-3.30 -2.80 -2.30

1.01 O0

=e Q.

E ql'"

- 1.80

,,=.,=.

III

,,=,.==

1.0050

- 1.30 a

-0.80 1.0000 -0.30 0.9950

-,,

60 Temperature, ~

I - -

.....

0.20 100

194

Figure 6.4 TSD/TMAsystem: I(TSD) versus Eo for a PVC sample with lO%wt, impact improver

1000 k V/m

1500 k V /m

2000 k V/m

-12 Released charge I Field strength relation

-10

- 8 -'~

LU X r

-6

:~" ,~

....

1000

1(i00

ILNIO0

Field strength, kV/m

~-4 o

1:3

or) I-

-2

.......

II N

I . . . .

65 Temperature,~

195 6.3 The T G A -

coupled - FTIR/MS technique

~.3.1 Introduction TGA experiments on polymeric systems often show complex TGA mass/temperature curves in which multiple decomposition products correspond with the weight change observed (see, for example, Figure 2.10). TGA has thus proven to be an excellent quantitative technique but less suitable for specification. This drawback can be eliminated if the components which are causing the mass losses detected, are also analysed simultaneously, the so-called evolved gas analysis (EGA). Several TGA-EGA systems are described in literature, analysing the evolved gases with different techniques i.e. thermal conductivity, cold-trapping followed by GC, mass spectrometry (MS) and infrared (FTIR). MS and FTIR have proven to be the most powerful techniques [3, i0]. User-friendly combinations of TGA/MS and that of TGA/FTIR with the essential reliable coupling of the various system components, became commercially available from different manufacturers in 1987/1988. Both systems have their own strong points. The MS technique is very sensitive and determines both polar and non-polar components, but is mainly qualitative. The FTIR technique, only detecting components with changing dipole moments, is better suited for quantitative determinations. Besides, the FTIR equipment normally used to measure gas-phase spectra, can also be used in the diffused reflectance mode. This offers the additional possibility to investigate a thermally treated sample i.e. a TGA residu. However, the results of one single detection technique are often not decisive enough to identify a certain component. A TGA coupled with both FTIR and MS (in parallel) should be a much stronger combination. Such a combination was, however, in 1990 not yet commercially available from one single manufacturer. The need for a quantitative working TGA - coupled - FTIR/MS system was clearly felt in our laboratory: mainly to study the first stage(s) of polymer degradation processes but also to determine small amounts of residual solvent and/or residual monomer(s) in polymeric systems. First, a Perkin Elmer TGA coupled FTIR system was purchased and adapted to allow quantitative determinations. A Balzers MS was subsequently purchased and coupled, using the method described by Dufour and Raemaekers [4], in parallel with the FTIR resulting in a TGA coupled - FTIR/MS system [Ii]. The TGA/FTIR and the TGA/MS coupling, the systems' modifications and calibrations and some typical results are described in this chapter. -

196 ~,3.2 The TGA/FTIR and TGA/MS coupling The original Perkin Elmer 'vertical furnace' TGA is schematically shown in Figure 6.5. The glass ball-joint coupling offers the opportunity to move the furnace tube downwards (hydraulically) in order to put a sample into the platinum sample pan. The helium purge gas flow (60 ml/minute) is simple and shown in Figure 6.5. The glass ball part of the ball-joint is replaced by Perkin Elmer to mount a stainless steel capillary lined with a PTFE (Teflon) tube, see Figure 6.6. The evolved TGA gases are sampled just above the sample pan and pass down the heated PTFE line to a 5 cm long, single pass and heated FTIR gascell. The use of a PTFE inner-liner (inner diameter 1.15 mm) allows simple and rapid replacement upon fouling. The total volume of the transfer line and the gas-cell is about 5.8 ml (gas-cell4.8 ml). This results in a TGA/FTIR transfer time of about 3.5 seconds. The temperature of the transfer line and the gas-cell are continuously variable between 20~ and 230~ The heated gas-cell is fitted with spring loaded KBr windows to maintain a gas seal at all operating temperatures. The TGA furnace tube was modified by Balzers according to the ideas of Dufour and Raemaekers [4] to connect the MS heated transfer line, see Figure 6.6. The MS interchangeable capillary tip (see Figure 6.6 insert) is shifted as close as possible to the TGA sample pan. This tip forms the end of a fused silica capillary (inner diameter 0.25 mm) which is connected with the MS and can be heated up to 400~ The FTIR capillary tip/TGA sample pan distance remains constant when the furnace tube is moving downwards to open the system for the sample loading procedure. The MS capillary, however, is connected with the moving part of the furnace tube. Hence, the MS capillary must be positioned in such a way that this tip does not hit the TGA sample pan during the downwards movement of the vertical TGA furnace. The total gas purge rate was increased from 60 ml/minute to 100 ml/minute, a balance purge of 50 ml/minute, a sample purge of 25 ml/minute and a MS capillary purge of 25 ml/minute (see Figure 6.6). The helium for the MS capillary purge is flowing between the fused silica capillary and its stainless steel support line (see Figure 6.6 insert) from the MS into the TGA. This ~eated gas stream has to keep the MS capillary tip warm enough to avoid condensation at this critical spot. About 5 ml/minute of the total purge gas flow is leaving the system via the MS capillary; the remaining 95 ml/minute is leaving the system via the FTIR capillary.

197 balance purge 40 ml/minute

sample purge 20 ml/minute

anti-static shield

ball-joint

hang-down wire sample pan (platinum) TGA oven with the sample temperature sensor

purge gas outlet = 60 ml/minute

glass furnace tube

Figure 6.5 The Perkin Elmer "Vertical Furnace" TGA 7 system ._,

198

FTIR heated transfer line

balance purge [ 50 ml/min

r. . . .

....

\~Ifi t~ll I,a 1~, !ll

I .J-~=; II J ,,

MS heated transfer line II lm~==..~. _.

..,

,. m

-~_~i :~

---7

interchangeable capillary tip L sample purge 25 ml/min -- fused silica capillary, MS inlet, 5ml min

9 ....

aluminium MS transfer line support

Figure 6.6 The TGA 7 with the flexible, heated TGA-MS and TGA-FTIR transfer lines

I' 'J I....

I J

Tandon 38GSX2B c:omputer

t r ! gge r

unlt FT IR/HS manual 8tart

Ba I ze r8

DTGS detector

720-VDU "--"-

FTIR/HS

TRS-? so'Ptware cont, ro 1 led start,

F'TIR opt t e#L1

module

t?GO-X

i -:

DTGS det. ,

'pPtntor~FX-80 |

! us-ce

]

FTIR modu 1 9 1760-X

QMG-420 HS

.... ,

, ,,

HP Co l o ~ PE 77e(~ p l o t t , e r ~ - 1 computer

TRC?

CDS-3 =oft,

TRS-? L so~t, i

W & P O

Figure 6.7: Schematic diagram of the TGA-coupled-FTIR/MS system

200 The TGA - coupled - FTIR/MS system as such is schematically drawn in Figure 6.7. The Perkin Elmer 1760-X FTIR is a single beam improved Michelson interferometer with a multicoated KBr b e a m s p l i t t e r giving a wavelength range from 370 to 7200 cm(i). The heated FTIR gas-cell and a second DTGS IR detector are m o u n t e d on an auxilary bench next to the 1760-X FTIR. The primary sample compartment has been left available for 'nonTGA' work i.e. in our case diffuse reflectance measurements. The Balzers Q M G - 4 2 0 - 1 8 0 H MS is a quadrupole analyser with a 1 512 a.m.u, mass range and a crossbeam ion source with two filaments. The whole system is controlled by three independant computers during an experiment. The TGA is controlled by the PE-7700 computer using the TAS-7 software. The FTIR spectra m e a s u r e d by the 1760-X FTIR are stored in the 1720-VDU spectroscopy terminal. The MS spectra measured are stored in the Tandon 386SX20 computer. The only 'hardware' connection between these three systems is a unit which triggers the 1720VDU terminal and the Tandon 386SX20 computer to start at the same time with measuring and storing IR respectively MS spectra. This start can be software controlled from the TAS-7 software or manual. 6.3.3 The heated capillaries tip temperatures C o n d e n s a t i o n effects in the b e g i n n i n g of the teflon FTIR capillary and in the glass MS interchangeable capillary tip during the first experiments indicated that the temperature in both capillary tips was lower than that in the heated part of the capillaries. Thin thermocouples were mounted subsequently, on these tips to measure the actual temperatures during an experiment. The measured FTIR/MS capillary tip temperatures at different TGA furnace temperatures have been collected in Table 6.1. Table 6.1 The FTIR/MS capillary tip temperatures as a function of the TGA furnace temperature (FTIR/MS heated transfer lines at 200~ .

'r,,,

~-'I~A f u r n a c e

temperature,

Ill R

FTIR capillary tip temperature, oC

MS capillary tip temperature,

100

150

20O

,,,

106

,.,

55 73 92

The results listed in Table 6.1 were disappointing. It was clear that the heating capacity of the helium sample purge via the MS heated transfer line proved insufficient to compensate for the heat losses in the non-heated end-part of the MS capillary.

201 An additional external heating source was used to solve this problem. Two Osram Xenophot HLX 64 635 (15 Volt, 150 Watt) IR heaters mounted on moveable support arms were used to heat the MS capillary tip, a third one was used to heat the FTIR capillary tip. These three heaters are controlled by one Eurotherm 808 controller with the measuring and the alarm thermocouples mounted near the small ball-joint of the MS heated transfer line/TGA furnace coupling, see Figure 6.6. The measurement of the FTIR/MS capillary tip temperatures was repeated using only these extra heating sources (no TGA furnace switched on), the results are listed in Table 6.2. Table 6.2 The FTIR/MS capillary tip temperatures as a function of the external heaters controlling temperature (FTIR/MS heated transfer lines at 200~ .

, .

,,,,,,

I IR heaters controll temperature, oc

,~,,

150

',,

. . . . .

MS c a p i l l a r y temperature,

113

105

163~ 215

159

212

tip

7a ,

FTIR c a p i l l a r y tip temperature,

i ,,

These data show that the capillary tip temperatures after this modification can be brought in line with the TGA furnace temperature (and hence the sample temperature) up to about 210oc/215oC. 6.3.4 Singl~ com_Don~nt calibration The linear relation between the IR absorption and the sample concentration makes calibration of the TGA - coupled - FTIR possible, for the determination of the total amount of components released during a TGA experiment. Quantitative MS component determinations are more complicated (due to more parameters) than quantitative FTIR component determinations but it might be possible if at least a part of the calibration curve is linear. The limitations for quantitative determinations of single components (both by the FTIR and the MS) were investigated by measuring calibration curves for the following pure component s-n-tetradecane

- benzoic acid - glycerol

(boiling point 252.5oc, (boiling point 249.0~ (boiling point 2 9 0 . 0 ~

apolar), polar), polar).

n.tetradecane, 5 mg 100.0

.9m . - " ~

,.=,, q = , = . m . , m = . ~

gO.O

I I I I t I !

QO.O 70. 0

80.0

0,0

-2. 0

_= - -4. 0

.c m

....~ o

--10. 0

441,,0

30. O

I !

--12,0

211,0 10.0

o.0

4.0

Time (minutes) 11.0

Ss 0

lO~ 0

IS. 0

2O. 0

;5. 0

Figure 6.8 The evaporation of n-tetradecane as measured by TGA (mass loss) and DTGA (mass loss rate)

30.0

DO 0

203

O. OglO

. . . . .

Gas-phase

spectrum

of n-tetradecane

A O, O884

0.0488

o.ome

I1. 0188

-I

O. 0000

lg00

c m -1

1000

dl,q0

Figure 6.9A The FTIR spectrum of n-tetradecane vapour . . . . . . w. . . . . . . . .

11,1OA I-

~0g

.... i ...... i A b s o r p t i o n a t 2 9 3 3 c m -1

i""

11.08 -

0.04

ell

o.m

I /

0.oo 0

Time (minutes)

Figure 6.9B The intensity of the CH2 vibration absorption of n-tetradecane vapour as a function of the measuring time

204 Five n-tetradecane samples with sample weights between 1 mg. and 8 mg. were heated from 30~ to 200~ (rate 5~ in the TGA using only the three external IR heaters. The TGA m a s s / t i m e curve in Figure 6.8 shows that the n-tetradecane sample completely evaporated during these experiments. No traces of condensated product were visible in both capillary tips. Figure 6.9A shows a FTIR gas-phase spectrum with a strong CH2 vibration at a w a v e l e n g t h of 2933 cm(-l) measured during these experiments. The absorption intensity of this v i b r a t i o n is plotted as a function of the experiment time (i.e. the temperature) in Figure 6.9B. The shape of this FTIR intensity/time curve agrees with the TGA first derivative curve, see Figure 6.8. Subsequenly, the FTIR intensity/time curves determined in this way were integrated. These integral values plotted as a function of the TGA sample weights resulted in a TGA - coupled - FTIR calibration curve for ntetradecane. Figure 6.10A shows a MS spectrum of n-tetradecane m e a s u r e d during these experiments. It is a typical 'linear alkane' spectrum with the highest m / z - v a l u e of 198 from the molecular ion of n-tetradecane and a fragments spectrum with m/z-values d i f f e r i n g one CH2 group and an abundance m a x i m u m around the C3 and C4 fragments [12]. The intensity of fragment m/z = 57 is plotted as a function of the (experiment) time in Figure 6.10B. The shape of this MS intensity/time curve agrees also with the TGA first derivative curve, see Figure 6.8. Subsequently, the MS intensity/time curves determined in this way were integrated. These integral values plotted as a function of the TGA sample weights resulted in a TGA - coupled - MS calibration curve for n-tetradecane. Calibration curves for (polar) benzoic acid were m e a s u r e d in the same way without any problem. Glycerol, however, was m e a s u r e d without any p r o b l e m with the TGA - coupled - FTIR system but the strong polar vapor was not able to pass the tip region of the MS inlet capillary. The thus measured three FTIR calibration curves are shown in Figure 6.11A. These curves for the 'high' boiling point components proved to be linear over the whole c o n c e n t r a t i o n range investigated with only small deviations from zero for a sample zero concentration. A series of TGA - coupled - FTIR calibration curves measured on 'low' b o i l i n g point components, see Figure 6.12, confirmed the systems' linear b e h a v i o u r . T h e s e results agree with the experimental results reported by Mittleman [13] for C02, S02 and NH3. Figure 6.11B shows the two MS calibration curves m e a s u r e d for n-tetradecane and benzoic acid. Both curves show a linear region for the lower concentrations only. These lower concentrations, however, cover the most interesting region for our area of investigation. The MS calibration curve for water, see Figure 6.13, shows that this linearity also holds for 'low' boiling point components. Hence, a careful TGA sample size choice is making quantitative determinations possible both with the FTIR and the MS for non-polar and polar components with b o i l i n g points up to about 250~

eLU!I 6u!JnseeLu eql jo uo!~ounj e se Lg = Z/IN ~ueuJ6mj SIN JnodeA eueoepm~e~,-u jo/q!sue),u! e q l EIO~'9 eJn6!_-I [u!w]

0C il

I I

,inn,

0~ i

0! |

. . . . . i. .

0 J

0000'0 000;'0

,,,,-4

Z -4

000Z '0

000r

000~'0

000g'0

fTI !

0009'0 000L '0 0008 '0 0006'0 0000' ;

jnodeA eueoepm]e~-u jo LUm~oeds SIN e q l V0 ~'9 eJn6L-I

00~ 08T 09T O~T O~T 00T 08

OT-] ,60-3

L90 - 3 ~0~

TGA

coupled-

calibration +

benzoic acid

FTIR

TGA

curves

n-tetra decane

coupled

calibration glycerol

1.00

curves

benzoic acid

n-tetra dec~e

0,45 z~ 0.40

0.80

0.35

3 r

E E

0.60

0.30

.E_ 0 . 2 5

4-'

â&#x20AC;˘

r @

.2 0 . 4 0

0.20

Q. 0

0.15

.13

0.10 -

0.20

0.05 0 . 0 0 [~ 0 Figure 6 . 1 1 A

Sample weight, rag.

0,00

0 Figure 6 . 1 1 B

Sample weight, rag.

.5 or}

(1)

::3 ~

RL Z BRRT I ON

URVE

/NH3

CRL I BRRT 1 ON

CURVE

X ~

r O

o J~ <C

S02 CRt..I BRRTI ON

ยง

โ ข

M[THRNOL CRL Z BRRT Z ON

CURVE

TOLUENE

CRL Z BRRT Z ON

Sample weight (mg) 0.0

t"u

Figure 6,12

T G A - coupled - FTIR calibration curves for "low boiling point" components

I$] e-e

S.~ k

4.1t

3-el-

e.e~

,.4

80~

Current

,.-

x time

....

(Ampere.s,

-.,

~ "

x 1 0 -4)

. . . . .

I~I

209 6.3.5 Investigation of the thermal d e c o m p o s i t i o n of Cobaltp h t h a l o c y a n i n e by TGA - coupled - FTIR/MS C o b a l t - p h t h a l o c y a n i n e (CPC), used as a anti-static additive for polymeric systems, is synthesised in two reaction steps- the reaction of C o b a l t ( I I ) p h t h a l o c y a n i n e (Figure 6.14A) with sodium cyanide in a water/methanol mixture to form the precursor, a sodium salt of C o b a l t ( I I I ) p h t h a l o c y a n i n e (Figure 6.14B), - subsequently 'polymerisation' of this precursor to form a laminar structure where the water ligands (CPC system A, Figure 6.14C) or the ammonia ligands (CPC system B, Figure 6.14D) form hydrogen bonds with the cyanide ligands of the adjacent Cobalt-phthalocyanine rings. This second step of the synthesis is carried out in w a t e r (CPC, system A) or in a aqueous solution of ammonia (CPC, system B) at I00~ Next to ammonia, some water will always 'built-in' as ligand in CPC, system B. With a number of TGA coupled - FTIR/MS experiments, the amount of ammonia and water ligand in two CPC, system B and in two CPC, system A samples was determined. Besides, the first steps of the thermal d e c o m p o s i t i o n of the CPC, systems A/B were investigated. The samples were heated, during these experiments, in a h e l i u m atmosphere from 40oc to 450~ at a heating rate of 10~ minute. The released vapours were analysed s i m u l t a n e o u s l y by FTIR and MS. The TGA mass/time (M/t) and the first d e r i v a t i v e (dM/dt) curves of such an experiment with a CPC, system B sample are shown in Figure 6.15. The sample is losing about six percent of its mass in at least two steps. The FTIR gasphase spectra measured during such a 'first step' clearly shows specific absorptions of ammonia at 933 and 966 cm-l. The intensity of the most dominant NH3 absorption at 966 cm-I and the intensity of the m/z = 17 (the molecular weight of ammonia) are also p l o t t e d as a function of the m e a s u r i n g time i.e. temperature in Figure 6.15. Obviously, This CPC, system B sample looses its ammonia mainly during the first step of the decomposition process. The FTIR gas-phase spectrum of the d e c o m p o s i t i o n products of a CPC, system B sample m e a s u r e d at 260~ (i.e. after 22 minutes) is shown in Figure 6.16 after subtraction of the dominant ammonia absorptions. The mass spectrum measured at the same time/ temperature is also shown in this figure. This FTIR spectrum shows a few low intensity absorptions at 716 cm-I and at 3272/3337 cm-i next to the CO2 (2337/2365 cm-l) and H20 (4000 - 3500 and 2000 - 1200 cm-l). The mass spectrum shows, besides the m/z values corresponding with ammonia (m/z = 15/16/17), strong m/z = 26/27 components and a smaller m/z = 52 component. The o b s e r v e d FTIR absorptions are h y d r o g e n stretch and bending vibrations of a triple bonded carbon hydrogen bond. In combination with the observed m/z = 27 value, it was identified as h y d r o g e n c y a n i d e (HCN).

210

,.,.

/ ' /_1I

I--

Nil +

X - OH 2 HCIM CH3CHL,OH

FIGURE A: STRUCTURE OF COBALT(II)PHTHALOCYANINE

//-~)-/7 I-0

IT "H''--,NC

FIGURE B: STRUCTURE OF THE PRECURSOR

/ eN..---H~N

H,O,s

FIGURE C: POSSIBLE STRUCTURE OF SYSTEM A

FIGURE D: POSSIBLE STRUCTURE OF SYSTEM B

Figure 6.14 Possible structure and synthesis of cobalt-phthalocyanine

211 100. 0

~.wt 9

96. 5

93. 0

O. 0150

~I0

966

cm- 1

O. 0000 0

1,~] 12OO

:T~:~_

O. 0075

curve

X~ ~~176 ..... .... ,"

dM/dt

INT,

R A ~ :

[

Jr .''~.

1,1='-O6

315

3 m/z

.1OOO .~OO . ~1~OO

.O2OO

Figure 6.15 Release of ammonia during thermal degradation of CPC, system B sample

<10

212 0.010

=--

A 0.008

O. 008

O. 004

==.

..=

O. 002

O. 000 4000

~1500

3000

Z500

2000

1500

I000

450

cm"

-06-07. -(Z~"

-09-

i ,._.,_..

~"~2'~~~"~~~~~~~"~"~~'~~"~~~~~"~"~~~~~~~~~~~~+~~~~ Figure 6.16 FTIR and mass spectra of the vapours released by a CPC, system B sample at 260~

213 I00.0

~wt. dM/dt

curve ~wl;. mf

r'l.

g8.5

M/t

curve

g3. 0 0

O. OOlO

3272

o. 00o5

ore- 1

O. 0000

" 5

INT,

RANGIE:

[

1E-O7

310

]

===t 45~

.3500

. 3 ~

m/z

92 5 0 0 . 2 ~

.15OO .IOOO .0500 .0000

Figure 6.17 Release of hydrogencyanide during thermal degradation of a CPC, system B sample

214 The intensity of the absorption at 3272 cm-i and the intensity of m/z = 27, p l o t t e d as a function of the m e a s u r i n g time are shown in Figure 6.17. Obviously, HCN is released during both steps of the d e c o m p o s i t i o n process! FTIR and MS spectra measured during the second decomposition step at 290~ (i.e. after 25 minutes) are shown in Figure 6.18. The FTIR s p e c t r u m contains the same absorptions as shown in Figure 6.16 (H20, C02 and HCN). In this spectrum, however, two weak absorptions at 2144/2166 cm-i are visible. The mass spectrum shows m/z values of CO2 (m/z = 44), HCN (m/z = 26/27)and a strong m/z = 52 signal. The absorptions at 2144 and 2166 cm-I are cyanide stretch vibrations. In combination with m/z = 52 it was identified as cyanogen (ethanedinitrile, NC-CN). The intensity of the absorption at 2166 cm-i and the intensity of m/z = 52, p l o t t e d as a function of the m e a s u r i n g time are shown in Figure 6.19. The results in this figure clearly show that cyanogen is released mainly during the second step of the d e c o m p o s i t i o n processZ There appears to be a large difference in intensity of the FTIR absorption and the c o r r e s p o n d i n g m o l e c u l a r ion, m/z = 52. Cyanogen is, however, a highly symmetrical molecule, resulting in IR absorptions of very low intensity. D e t e c t i o n of water and C02 with FTIR at low concentrations is unreliable, due to their presence in the atmosphere. These compounds can be d e t e c t e d with MS. The release of water (m/z = 18) and C02 (m/z = 44) during the d e c o m p o s i t i o n of a CPC, system B sample is shown in Figure 6.20. A b s o r b e d water is released during the first ten minutes of the experiment (40~ 140~ followed by an amount of chemically bound water at the very beginning of the first d e c o m p o s i t i o n step (the thermal stability of the ammonia ligand is thus higher than that of the water ligand!). -

C02 is mainly released during the second d e c o m p o s i t i o n step, and at temperatures higher than 350~ (phthalocyanine ring degradation). The m/z = 18 curve in figure 6.20 shows that the release of C02 (and cyanogen) during the second decomposition step is accompanied by a decrease of the released water intensity. This might be caused by cyanogen reacting at these elevated temperatures with traces of water to form HCN and C02. Figure 6.21 summarises the results described above. The deomposition products shown in this figure for a CPC, system B sample, were also m e a s u r e d for the CPC, system A samples, only differences in the m e a s u r e d intensities of released water (quantitatively d e t e r m i n e d with the aid of a MS calibration curve) and ammonia (quantitatively determined with the aid of a FTIR calibration curve) were found-

215 .

O. 0 0 5 5

~ ~

1500

lO00

o. 0044

O. (1033

O. 0 0 2 2

O. 0011

O. 0 0 0 0 4000

3500

3000

Z500

2000

450

c m -1

-06-OT-0809- ."T"'."T""'"I"'"'"T'"m"I""m'T'"I"'T'"I"'T'"""T'"m"r'"""T'"m"r '""1' I, i,'-r"l 20 40 60 80 100 120 140 Figure 6.18 FTIR and mass spectra of the vapours released by a CPC, system B sample at 290~

216 100. 0 ~wt.

rain.

96.5

93. 0 0

O. 0007

2166

O. D003

O. 13000

.16~

.1'q00

.12~

INT.

RAI~K:;E::

[

1E-O6

cm-1

] m/z

.1000

.~:~

.~2~ i

....

Figure 6.19 Release of cyanogen during thermal degradation of a CPC, system B sample

217 100.0

~.wt. dM/dt curve ~W%. / mtn. g6.5

M/t curve

93.0

5 INT.

.1600

RANQE:

[

15 1E-O6

~10

]

.1400

m/z

= 18

,1200 .1OO0 ,0800 _-

.0600 ,0400

INT.

.2000

RANGE:

[

1E-0?

:~_

~:.

]

lg00 1600

m/z

1400 1200 1000 .0e00 .0600 .0400

.0200 .0000

Figure 6.20 Release of water and C02 during thermal degradation of a CPC, system B sample

218 10{3 ~wt

9 9g

dH/d%

ourve ~W% o / mtn.

gS H/t,

curve

H20

NH 3 HCN

NC-CN

go 4O

I00

150

200

total

component,

release

250

I 300

.....

C02

35O

400

regton

Figure 6.21 Release of the identified products during thermal degradation of a CPC, system B sample

450

219 Cobalt phthalo cyanide systems

absorbed bound water, water, %wt. %wt.

bound ammonia, %wt.

B1 B2

0.4 0.3

0.3 0.2

1.9 2.6

A1 A2

0.7 0.6

1.9 I.i

0.3 1.1

The total amounts of bound water and ammonia are respectively 2.2, 2.8, 2.2 and 2.2 %wt. The theoretical amount, based on the possible structures given in the Figures 6.14C and D, are 2.84 %wt. for only a NH3 ligand and 3 . 0 1 % w t . for only a water ligand. Cobalt(II)phthalocyanine (Figure 6.14A) and the precursor (Figure 6.14B) were also measured to exclude the possibility that ammonia is already a decomposition product of these components. No ammonia could be detected during these experiments. A series of Diffuse Reflection measurements was performed, subsequently, on partly decomposed CPC (system B) samples to check the decomposition pattern given in Figure 6.21. Four samples were (under the same conditions) heated to different, previously selected temperatures, see Figure 6.22. The measured IR Diffuse Reflection spectra of the TGA residues of these four samples offer the possibility to monitor the changes in the molecular structure in an independent way. The measured spectra are shown in Figure 6.23. Spectrum A is the reference spectrum of the non-treated sample. The presence of ammonia in the molecular structure results in four N-H stretch vibrations between 3100 and 3400 cm-l. The cyanide ligand is visible by two vibrations at 2152 and 2214 cm-l. Spectrum B is measured after heating the sample up to 140~ only causing the release of absorbed water. The nearly identical A and B spectra confirm this conclusion. Spectrum C is measured after heating the sample up to 260~ i.e. in the middle of the first degradation step. The release of ammonia is confirmed by the clear intensity decrease of the N-H vibrations in the TGA residu sample. There also appears to be in spectrum C a decrease of the cyanide vibration at 2152 cm-i accompanied by an increase of the cyanide vibration at 2214 cm-l. This change in intensity of these two vibrations is completed after heating the sample up to 280~ (spectrum D). The N-H vibrations of the ammonia ligand have now completely disappeared. When the sample is heated, subsequently, up to 350~ (spectrum E), the cyanide vibration has prac~lcally vanlsne~.

220 tO0. O

....

'it

~W't,. dH/d%

96.6

cu r've ~Wt.

rain. g7. 2

g5.6

H/%

cuPvo

g4.4

93. 0

I~,

......

! 450

Temperat.ure

(de9.

Figure 6.22 Indication of the maximum temperatures after which the DRIFT spectra were measured

221

1.50

'i ....

A 1.35

l. ZO

1.05

0.90

O. 75

0. 80

0. 45 -

Spectrum

0. 30

O. 15

.,~'I, ,

0.00 3500

3200

Figure 6.23

3000

2800

2600

2400

2200

c m -1

DRIFT spectra of a CPC, system B sample taken

after different thermal treatments

2000

1800

[575

222 The two cyanide vibrations are the result of the presence of 'free' (terminal) cyanide ligands and cyanide ligands that form hydrogen bonds with w a t e r / a m m o n i a in these systems. H y d r o g e n bonding weakens the triple carbon - nitrogen bond, resulting in a shift to a lower frequency. This means that the observed vibration at 2151 cm-i is caused by the hydrogen b o n d e d cyanide ligand, while the vibration at 2214 cm-I is the result of the presence of 'free' cyanide ligand. The shift in intensity observed after the first decomposition step is thus caused by a loss of hydrogen bonding between the cyanide and the w a t e r / a m m o n i a ligand. This can also be the reason for the release of some h y d r o g e n c y a n i d e during the first decomposition step. 6.3.6 Investigation of the released vapours d~ring ...the . cure of an epoxy resin system by TGA - coupled - FTIR/MS. The investigated epoxy resin system consisting of the glycidyl ether of phenol novolack (GEPN) with dicyanediamide as curing agent (added as an diglycidyl ether bisphenol A (DGEBA)/dicy 60/40 masterbatch) and an accelerator in a 100/15/0.5 ratio. + This G E P N / d i c y system is used to prepare epoxy resin based castings. The mould, filled with the GEPN/dicy system, has to be heated slowly to the cure temperature of about 170~ to p r o p e r l y release the heat generated by the exothermic cure reaction. Serious thermal degradation effects inside the casting and the release of bad smell and possibly unhealthy d e g r a d a t i o n products occur if this reaction heat is not released sufficiently. A series of TGA - coupled - FTIR/MS experiments was performed to investigate the conditions resulting in the release of d e g r a d a t i o n products during the cure of GEPN/dicy systems. The reaction m e c h a n i s m of epoxy groups with dicyanediamide is complex [14]. We therefore confine ourselves to say that GEPN and d i c y a n e d i a m i d e are forming a solid resin matrix during an exothermic reaction. The reaction heat can cause thermal b r e a k d o w n of the matrix material just built-up. Earlier p e r f o r m e d experiments p o i n t e d at the release of ammonia and p o s s i b l y some p y r i d i n e - l i k e components during this thermal d e g r a d a t i o n process. But the release of water and a phenolicOH residue can also be expected, see Figure 6.24. About sixty milligramme of the GEPN/dicy system was heated in the TGA - coupled - FTIR/MS from 30~ to 400~ (rate 5~ to measure s t r a i g h t f o r w a r d the volatile thermal d e g r a d a t i o n products of the ~ resin matrix material. The G E P N / d i c y sample was cured (according to a DSC experiment under the same thermal conditions) between 160~ and 240~ Detectable mass losses due to thermal degradation processes startea at 295~ {onset temperature). The mass loss rate proved to be maximal at 385~176

- -- O__.CH2_.._cHO / __ .~CH 2 ~~R~.~O--CH2- cH/O"CH2

MRTR[X

~.~

H ยง

H2N.__C__ N _ _ C ~ N

MRTRIX

NH3

Figure 6.24 GEPWdicy resin system, cure and thermal degradation processes (schematically)

H20

Absorption

E-07

&MI

FIGURE B. The mass spectrum at 340 C of the released vapours during the degra-

E-O~

A &ll 1179 cm-lt

dation experiment of a cured, GEPN /dicy system sample in the TGA

966 c m - i l

Phenolic OIN v i b r a t i o n NH3

vibration

~ = / 1 1 cm-I 7 9

" Its 9

L eta

E'e9

E-10'

20 E-07

,--.-,.--,.,--.-,.,--.-,

.......

.... , . - , - . ,

80 100 120 140

FIGURE C. The mass spectrum of a tri-methylpyridine reference sample as measured by the TGAcoupled-FTIR/MS system

E-08

iII-- I ~ - ' - T -T -I--'---I

2SS=C t

=~O'C I

~O=C I

3SS'C I

3aO=C t

es 'Time, min.

HGURE A. The NH3 and phenolic-OH concentrations versus time/ Temperature as measured by FTIR in the vapours Feleased during the degradation experiment of a cured GEPN/dicy system sample in the TGA.

Figure 6.25 Results of FTIR/MS analysis of the vapours released during the thermal degradation of a GEPN/dicy system sample

E-09 E-10

i.elm n

I -'-

'---I----'-I--

I -I .... '--I--"- I --'-- i

80 100 120 1,t0

-o.m 73

225 The FTIR gas-phase spectra are showing clearly the absorption maxima of phenolic-OH components (characteristic vibrations at 1179 and 3652 cm-l), of NH3 (characteristic vibration at 966 cm-l) and that of water. Figure 6.25A is showing the intensity of the characteristic vibrations of the two first mentioned components as a function of the time/temperature. The highest NH3 release rate occured at about 350~ while the release of phenolic-OH components reached their highest level at about at about 390~ Pyridine-like components can not be detected by the FTIR in this case due to overlapping vibrations from the phenolic-OH components. The MS spectra, see Figure 6.25B, are showing next to the NH3 (m/z = 17) and the water (m/z = 18) contributions a clearly present component with a maximum m/z-value of 121/122. Tri-methylpyridine was measured, subsequently, as reference, see Figure 6.25C. The close agreement between both spectra makes it reasonable to assume that pyridine-like components are present in the released vapours during the thermal degradation of a cured GEPN/dicy resin sample. The degradation onset temperature measured during this experiment (295~ is a dynamic value which is strongly heating rate dependent. A static degradation onset temperature has in fact to be used to indicate the maximum temperature which can be reached in a GEPN/dicy based casting (during the cure process) before thermal degradation effects will occur. Experiments to determine the thermal stability of polypropylene (see 2.2.2) showed that the semi-static degradation onset temperatures measured during ultra-low heating rate TGA experiments were close to the isothermally measured, static degradation onset values. The semi-static degradation onset temperature of the cured GEPN/dicy system measured in this way proves to be 240~ (241~ - 0.2 %wt. mass loss). Subsequently, the release of ammonia (the only degradation product which could be measured quantitatively) was measured during a series of TGA experiments with variable heating rates. These experiments were performed to show how the heating rate influences the temperature and thus the possible occurance of thermal degradation, in a (small) curing TGA sample. Non-cured GEPN/dicy samples (about 60 mg.) were heated from 150~ to 250~ with heating rates increasing from 40~ to 140~ Each sample was then kept isothermally at 250"C until a total experiment time of ten minutes was reached. Minor sample mass losses were measured during the experiments with heating rates up to 100~ The higher nearing rate experlments, however, resulte~ in serious mass losses, see Figure 6.26. The amounts of ammonia released during these experiments are plotted as a function of the heating rate in Figure 6.27. These amounts of ammonia were all measured during the first two minutes of each experiment. The presence of other thermal degradation products (water,

100. 0

- ~

g8.0

96. 0 94.0

-I00. 0

_~_ 188 deg.

15e

258~

mr. v t r t t b ! e hea~t-O rate, | It, 2 5 B d e g .

+ ! sother'mt (etch experiment totally I8 minutes)

/', ~~

Ot ~ i I \

- 98.0

C/minute

- 98.0

~~._.~la

dog

C/minute 94. 0

- 92.0

g2. o -

e..,_ ID

9o.o

90. 0

, 13B

88. 0

- 86.0

[4B

82. 0 0.0

- 88.0

C/rot n u t s

86. 0 -

84.0

de9.

i 0.2

i 0.4

i 0.8

I 0.8

T 1.0

dep.

I 1.2

- 84.0

C/mtnut.e

I 1.4

I 1.8

Time (minutes)

Figure 6.26 -he mass losses measured during the cure of GEPN/dicy system TGA samples at different heating rates

2.0

82.0

L~ b3 O~

140

130

120

Im ,.

II0

,,, .,,

, ,|,

-%1 r i !

CA I

~3o.

Z :I: (r

Ul 0D

o lu Is o o.

t~p fJl ~0 o

40 ~

I :s D

--4

228 pyridine-like components and phenolic-OH components) was only detected during the first two minutes of the 130~ and 140~ minute heating rate experiments. The concentrations of these components released during the experiments with heating rates lower than 130~ proved to be too low for a proper detection. The shape of the curve in Figure 6.27 and the fact that ammonia (and the other degradation products) are produced only during the first two minutes of these experiments are indicating that for heating rates higher than 100~ the real temperature of the sample in the TGA pan was exceeding, during a short period of time, the temperature indicated by the TGA temperature sensor. It is assumed that sample cure and sample degradation processes occured simultaneously for a short period of time during these experiments. Thus, it proves possible to determine for a small GEPN/dicy TGA sample the rather sharp transition from a non-isothermal cure process without hardly any thermal degradation to a situation where cure and degradation processes occur simultaneously. The critical heating rate of a GEPN/dicy casting system will be strongly casting shape/dimensions dependent. The only way to prevent any thermal degradation during the cure of a GEPN/dicy casting system is to use such a heating rate that the temperature in the casting will not exceed the (static) thermal degradation onset temperature of 240oc. The examples of the use of coupled TA techniques given in 6.3.5 and 6.3.6 show the extended amount of information which is obtained by the use of such a strong combination of techniques. We are convinced that these experiments offered better results than in the case separated/single TGA, FTIR and MS systems were used. This because we experienced that a proper choice of experimental TGA conditions remained always the first (and often critical) step of a series of experimental steps necessary to reach such a result. In other words, during investigations like this, the TGA technique remains the basic technique, while the FTIR and MS are used as sophisticated and sensitive detection systems.

229 References i. D. Compton et.al., Research and Development, April, (1989), p. 68. 2. E. Charsly et.al., American Laboratory, January, (1990) . 3. J.P. Redfern, Polymer International, 26, (1991), p. 2819. 4. P.R. Dufour and K.G.H. Raemaekers, Thermochimica Acta, 175, (1991), p. 263. 5. W.H. McClennen et.al., Anal. Chem., 65, (1993), p. 2819. 6. R.D. McCammon and R.N. Work, Rev. Sci. Inst., 36, (1965), p. 1169. 7. L.C. Corrado and R.N. Work, Rev. Sci. Inst., 41, (1970), p. 598. 8. J.C. Coburn and R.H. Boyd, Macromol., 19, (1986), p. 2238. 9. P.J. Phillips, J. Pol. Sci.- Pol. Phys. Ed., 17, (1979), p. 409. i0. J.A.J. Jansen and W. de Haas, Analytica Chimica Acta, 196, (1987), p. 69. II. W.M. Groenewoud and W. de Jong, Thermochimica Acta, in press. 12. F.W. McLafferty- Interpretation of Mass Spectra, University Science Books, Mill Valley, California, (1980) . 13. M. Mittleman, Thermochimica Acta, 166, (1990), p. 301. 14. M.A. Clayton, Epoxy Resins Chemistry and Technology, M. Dekker Inc., New York, p. 501.

CHEMICAL STRUCTURE / PHYSICAL PROPERTIES CORRELATIONS

CHAPTER 7

230 CHAPTER 7: CHEMICAL STRUCTURE/PHYSICAL PROPERTIES CORRELATIONS 7.1 Introduction The continuously ongoing process of replacing or supplementing the more traditional materials such as wood, natural fibres and metals by synthetic polymers, is stimulating the development of polymeric systems covering either an even wider range or a more specific set of properties. The ability to estimate the chemical/physical properties of a polymeric system from its molecular structure before such a polymer is synthesised can reduce the research costs considerably. Besides, a thorough knowledge of chemical structure/physical properties relations is necessary to improve with success the balance of properties for current commercial polymeric systems. The list of important physical properties of a polymer is, however, long. We mention, without pretending to be complete: A. phase transitions, volumetric properties, calorimetric properties, electrical/optical/magnetical properties, mechanical and acoustic properties. B. properties determining mass transfer in polymers, rheological properties of polymer melts, chemical, thermal and UV stability. C. ultimate mechanical and electrical properties such as" creep, failure, toughness, hardness, friction, wear, yield strength, tracking and dielectric strength. ageing effects. Many chemical structure/physical property relations have been reported in literature but the most important contributions in this field have been made, we think, by Van Krevelen [1] and Bicerano [2]. Both authors present a total concept for polymer properties/molecular structure correlations based on the group contribution technique (Van Krevelen) and on connectivity indices calculations (Bicerano) covering all the properties mentioned in group A and B and some of the properties of group C. Seitz published a concept to estimate the mechanical properties (from group A and C) of polymers from their molecular structure [3]. It is difficult however to speak about 'the properties' of a polymeric system due to the many variables which determine the ond-ugo

vmluoa.

Thi~

han~orQ

mQrlouol)-

thQ

uoo

tho

estimated or calculated polymer property values. For example, nearly all properties mentioned in group A, B and C are temperature dependent while an important number of these properties is time (and pressure) dependent.

231 Other factors determining

end-use properties

can be:

- possible tacticity i.e. a-, iso- or syndio-tacticity, possible cis/trans isomerism, molecular weight and molecular weight distribution, - copolymerisation/blending, - plasticiser/filler additions, degree of crosslinking, effects of different processing techniques, presence of residual monomers and/or solvents (water). -

This extended number of variables context of this book only with a properties' instead of trying to properties mentioned in group A, are considered:

prompted us to work in the set of so-called 'keycalculate immediately all the B and C. As key-properties

- the Tg-value, - the Tm-value, the Hf-value, - the thermal stability and - the moisture sensitivity. -

Nearly all properties mentioned under group A are influenced by the temperature locations of the Tg/Tm values and the crystallinity level (Hf-value). The Tm-value and the thermal stability determine together the polymer's processing window. The moisture sensitivity, finally, is important in connection with the barrier properties of a polymeric system. Furthermore moisture absorption influences several physical properties considerably (see chapter 5.2) . In this chapter an attempt is made to improve some of the existing molecular structure/physical properties correlations. A set of consistently measured TA data is used, in order to estimate the above mentioned ,key-properties, of polymeric systems.

232 7.2 The Tg-value estimation 7.2.1 Introduction The transition region in which an amorphous glassy polymer changes from its glassy state into a rubber-like state is important because dramatic changes in the polymer's physical properties are observed during this transition. These changes are completely reversible as the transition from a glassy state into a rubbery state is a function of molecular motion, and not the polymer structure. The temperature location of this glass-rubber transition region however strongly depends on the molecular structure. This temperature location is usually indicated by one, single temperature: the Tg-value (see 1.1.3). The Tg-value is, according to Cowie

[4], depending on-

- chain flexibility ) - polarity ) molecular structure steric effects ) effects - tacticity and cis/trans isomery) branching and crosslinking ) molar mass, the presence of additives, fillers, residual monomers and/or impurities. - morphological effects, especially crystallinity, rate and type of measurement.

This extended list of factors affecting the Tg-value, is one of the major causes of the widely differing experimental values reported in literature for various common polymers. In literature, several molecular structure/Tg-value correlations are reported in spite of the often considerable amount of scatter in the reported Tg-values. It is not surprising that many of these Tg-value estimation methods are based on correlations with the chain stiffness and/or the cohesive forces, since chain flexibility is considered to be the most important Tg-value influencing factor. A well known empirical, molecular structure/Tg-value correlation based on the group contribution additivity is given by Van Krevelen [1]. Kreibich and Batzer [5] developed a correlation based on cohesive energy (Ecoh.) values calculated according to the method published by Fedors [6]. Wiff and Altieri calculated Tg-values using the relation between the density and the log Tg [7]. Hopfinger [8] used a molecular modeling technique in combination with a group additive property model to calculate Tg-values of linear polymers. Bicerano developed an impressive, and we do think the most extensive, Tg-value calculation method based on connectivity indices [2]. Without L,~laa~ ~umli~l=L~, ~ v ~ a l ULIA~L ~ U ~ I L L I D u L I u I I ~ UII LIII~ ~ U D J ~ : ~ can be found in [9 - 12] .

233 7.2.2 The 'modified cohesion e~eruy' method We expected that an improvement of the Tg-value estimation was still possible by careful selection of the reference Tg-values used. These Tg-values should preferably be self determined values measured under standard conditions (see 1.1.3) or selected literature values. They should have been determined on amorphous or low crystalline polymers with a sufficient high molecular weight i.e. Mn value a 50.000. Besides, these polymers should not contain fillers, plasticisers, residual monomer and/or solvents. We tried to improve the Kreibich and Balzers Ecoh./Tg-value correlation. This method was chosen because of a) its simplicity compared with for instance Bicerano's method and b) the possibility to calculate the Ecoh. value of every polymer repeating unit from the ~Ecoh. values of the structural groups given by Fedors in case experimental Tg-values are not available. The latter differs with for example Van Krevelen's method which needs experimental Tg-values to calculate the group contributions. Kreibich and Batzer [5] reported a linear relation between the Tg-value and the cohesion energy (Ecoh.) at 298 K: Tg-value, where:

(K) = 0.0145 x

Ecoh. Ea, i

(Ecoh./Ea, i) + 120

7.1

- cohesion energy, J/mol. = number of independent moving/rotating groups.

Kreibich and Batzer used the structural group 6Ecoh. data of Fedor [6] to calculate the necessary Ecoh. values. The average (Tgexp. - Tgcalc.) value of 63 calculated Tg-values proved to be _+ 15 K, but for 19 of these 63 values this difference is larger than 15 K (between 16 K and 62 K). we tried to modify a number of Fedors structural group ~Ecoh. values, using a basis set of 22 self measured Tg-values and some selected literature values, to improve the fit of the Ecoh./Tg correlation. This proved to be possible only if a distinction was made between polymers with only C-atoms in the mainchain and the other, mainly C6-rings and -0- containing mainchains. Thus, two sets of ~Ecoh.-values for polymer structure elements were calculated, one for linear polymers with five or more succeeding C-atoms in their mainchain and one for the other linear polymers, see Table 7.1. Using the values given in Table 7.1, the Tg-value of linear polymers can be calculated according to equation 7.1 with what we call the 'modified cohesive energy' method.

234 Table ~__ r,,,,

7.1 The

~ ,

~Ecoh.

. . . . .

structure

ii ,I

values _

element

~a, i .

.,,.

of p o l y m e r x

-(C)n-

J/mole

....~

t +

8Ecoh.,

+ - (+ C ) n - ,,.

n. ~

4936

5040 8617 17234 2928 4936

-CH-

3430

1464

9826 5040 -

-CI

-CH=

(cis)

1129 3196

-CH= (trans) i I -C= (cis) -~= (trans)

-C6H4-/-C6H5

2878 3982

z/o

27123

27951 85007

-O-CO-

3346 18405

4852 29243

-OH

23747 54839

28708

-CmN

26503 -

- C 6 H 4 - C (CH3) 2 - C 6 H 4 -

- N H -

-SO2-

-C1

in-HCC1-

42064

23885

-C1 in =CCI-, cis (-Cl} 2, symm.

13176

C1 - (C6 - ring) C1- (C6-ring) -C1

11922 -

13176 16230

-Br Br- (C6- ring) -Br

15477 -

15477 21403

18372 9169

6132

4183 -

4183 5566

-F

(-F} 2, symm.

1 1

- N - S -

-C~HI 0 - / - C ~ W 1 1 - ( C O ) - O - C H 3 in P M A a n d in P M M A -0- (CO) -CH3 (PVAc) II,,I

-CH3

I/â&#x20AC;¢

?~AK4

0 0 0

[cn-cH~3-0]m-,

14117 20188 16875 ,,,l,,l,

n ~ 3.

,,,,,,,,

J/mole

0 0 0 0 0 1

~Ecoh.,

elements.

-CH3 (CH3-)2, symm. CH3-(C6-ring) CH3-(C6-ring)-CH3 -CH3, see n o t e -CH2!

structure

235 This 'modified c o h e s i v e energy' m e t h o d does not p e r m i t the c a l c u l a t i o n of T g - v a l u e s of p o l y m e r s w i t h b u l k y side-groups. The m e t h o d s of B i c e r a n o [2] and H o p f i n g e r [8] and for a n u m b e r of s i t u a t i o n s that of V a n K r e v e l e n [i], do p e r m i t c a l c u l a t i o n of the T g - v a l u e of p o l y m e r s w i t h d i f f e r e n t k i n d of sidegroups. The effect of 'long' p a r a f f i n i c side-chains, however, can e a s i l y i n c o r p o r a t e d in the 'modified c o h e s i v e energy' method. It is w e l l k n o w n that t h e s e p a r a f f i n i c s i d e - c h a i n s d e c r e a s e the T g - v a l u e and it is p o s s i b l e to c a l c u l a t e the Tgvalues of these s y s t e m s u s i n g a p r o p e r s i d e - c h a i n l e n g t h d e p e n d i n g r e d u c t i o n f a c t o r (the same m e t h o d is f o l l o w e d b y V a n Krevelen). Vinyl p o l y m e r s w i t h l i n e a r s i d e - c h a i n s are r e p r e s e n t e d by: -[CH2-~]m) (C~H~ n

w h e r e X stands for a trivial s t r u c t u r a l unit; the p o l y m e r w i t h n = 0 is c a l l e d the b a s i c polymer.

The f o l l o w i n g series of T g - v a l u e s can be d e r i v e d w i t h effort from the g r a p h r e p o r t e d b y E i s e n b e r g [13]:

n n n n n n n n n n

= = = = = = = = = =

alphaolefins Tg,~ -21 -31 -46 -56 -61 -66 -

0: I: 2: 3: 4: 5: 7: 8: 9: Ii:

poly-alkyl styrenes Tg,~ I00 78 6 -26 -44 -52 -65 -

some

polymethyl acrylates Tg,~ 105 65 35 20 -5

-22 -65

The ~Ecoh. v a l u e of the -CH- and -CH3 g r o u p s f r o m the -CH(CH2CH3) s i d e - c h a i n of p o l y ( 1 - b u t e n e ) , is a c c o r d i n g to T a b l e 7.1: 3430 + 9826 = 13256 J/mol. This v a l u e has to be m u l t i p l i e d with 0.896 to d e c r e a s e the c a l c u l a t e d T g - v a l u e f r o m -21~ for p o l y p r o p y l e n e to -31~ for p o l y ( 1 - b u t e n e ) , (n = 1). The r e d u c t i o n factors c a l c u l a t e d in this w a y are p l o t t e d as a f u n c t i o n of the n u m b e r of CH2 u n i t s in F i g u r e 7.1. The t h i r d order p o l y n o m i n a l curve fit has a c o r r e l a t i o n c o e f f i c i e n t of 0.9844 and p e r m i t s c a l c u l a t i o n of the f o l l o w i n g a v e r a g e r e d u c t i o n factors: n n n n

= = = =

1, 2, 3, 4,

0.86 0.74 0.63 0.54

n n n n

= = = =

5, 6, 7," 8,

0.47 0.41 0.36 0.32

Values for n h i g h e r t h a n 8 are m e a n i n g l e s s ; in c h a p t e r 1.4.2 it is shown that the T g - v a l u e d e t e r m i n a t i o n for s a m p l e s w i t h n > 7 is s e r i o u s l y h a m p e r e d by s i d e - c h a i n c r y s t a l l i s a t i o n effects.

236

E f f e c t of the number of C H 2 units in a polymers' s i d e - c h a i n on the T g - v a l u e

Figure 7.1 1.00

0.90

0.80 +

0.70 L

0 0

0.60

c 0.50

o u -

O "0

0.40

0.30 +

0.20 0.10

0.00

Number

CH2

6 units

8 in the

10 side-chain

237 The T g - v a l u e of p o l y ( l - h e p t e n e ) , c a l c u l a t e d as follows : The r e p e a t i n g unit

for example,

is then

is : - [CH2-CH ( {CH2 }4-CH3) ] n-

The -CH(CH3)- unit c o n t r i b u t i o n is r e d u c e d b y 0.54 (n = 4). The m a i n c h a i n consits of s e q u e n t i a l C-atoms, h e n c e the n z 5 ~Ecoh. values from T a b l e 7.1 have to be used: ~Ecoh. ~Ecoh.

-CH-CH3

~Ecoh.

-CH2-

: :

3430 J/mol. 9826 J/tool. 13256 J/mol. x 0.54 = 7158 J/mol. : 4936 J / m o l . Ecoh. = 12094 J/mol.

En, i - 2, u s i n g e q u a t i o n Tg,

calc.

= 0.0145 x

7.1 results

(12094/2)

A T g - v a l u e of 212 K is r e p o r t e d

then in-

+ 120 = 208 K in literature,

see T a b l e

7.2.

The T g - v a l u e of p o l y ( e t h e r ether ketone), PEEK is f i n a l l y c a l c u l a t e d as a s e c o n d e x a m p l e of a T g - v a l u e c a l c u l a t i o n a c c o r d i n g to the 'modified c o h e s i o n energy' methodThe r e p e a t i n g unit

is :- [O-C6H4-O-C6H4-CO-C6H4] n-

The m a i n c h a i n does not c o n t a i n sequential C-atoms, _< 4 ~Ecoh. v a l u e s from T a b l e 7.1 have to be used: ~Ecoh. ~Ecoh. ~Ecoh.

-C6H4-: 27951 h e n c e -CO: 29243 h e n c e -0: 4852 h e n c e

En, i = 6, u s i n g e q u a t i o n Tg,

calc.

= 0.0145 x

3 x 27951 = 83853 1 x 29243 - 29243 2 x 4852 = 9704 Ecoh. = 122800

7.1 results

(122800/6)

hence

the n

J/mol. J/mol. J/mol. J/tool.

in:

+ 120 - 417 K

The m e a s u r e d v a l u e was also 417 K, see T a b l e

7.2.

The T g - v a l u e s of 48 p o l y m e r s were calculated, see T a b l e 7.2, u s i n g the 'modified c o h e s i o n energy' m e t h o d as s h o w n above. The T g - v a l u e s of t w e n t y - s e v e n of these systems w e r e u s e d to c a l c u l a t e ~Ecoh. v a l u e s of the d i f f e r e n t s t r u c t u r a l g r o u p s i.e. these v a l u e s are f i t t i n g by definition. The a v e r a g e (Tgexp. - Tgcalc.) v a l u e of the o t h e r (21) i n d e p e n d e n t l y c a l c u l a t e d T g - v a l u e s is â&#x20AC;˘ 8 K. T h i s value is g r e a t e r than â&#x20AC;˘ 8 K (between 9 and 30 K) for only six of these systems. Table 7.2 also lists t h e T g - v a l u e s c a l c u l a t e d a c c o r d i n g to V a n K r e v e l e n ' s m e t h o d and B i c e r a n o ' s method. Thus, a d i r e c t c o m p a r i s o n of the r e s u l t s of these three m e t h o d s is possible. The figures 7.2, 7.3 and 7.4 show the three T g ( e x p e r i m e n t a l ) / Tg(calculated) c o r r e l a t i o n s of the t w e n t y - o n e (for the 'modified c o h e s i o n energy' m e t h o d i n d e p e n d e n t l y calculated)

238 Table

7.2 R e s u l t s of T g - v a l u e c a l c u l a t i o n s Tgc, 1: g r o u p c o n t r i b u t i o n m e t h o d (Van Krevelen) Tgc, 2 : c o n n e c t i v i t y i n d i c e s m e t h o d (Bicerano) T g c , 3 : ' m o d i f i e d c o h e s i o n e n e r g y ' m e t h o d (*)

polymer

name/structure

Tgc, 1

Tgc, 2

Tgc,3

polybutadiene,

170 237

172 -

164 181

(a) (a)

2. p o l y o x y m e t h y l e n e , - [CH2-O] n -

223

215

191

(b)

3. p o l y e t h y l e n e , - [CH2-CH2 ] n-

195

187

192

195

(c)

4. p o l y o x l t r i m e t h y l e n e , - [ C H 2 - C H 2 - C H 2 - 0 ] n-

209

201

191

195

(b)

5. p o l y i s o b u t y l e n e , - [CH2-C (CH3) 2 ] n-

196

190

203

(a)

199

204

(a)

cis trans - [ C H 2 - C H = C H - C H 2 ] n-

6. p o l y i s o b u t y l e n e o x i d e - [CH2- C (CH3) 2-0] n-

Tg-value experim. K

7. p o l y i s o p r e n e , cis - [CH2 - (CH3) C = C H - C H 2 ] n-

196

202

206

205

(a)

8. C2C3 a l t e r n a t i n g c o p o l y m e r - [CH2 - CH2 - CH2 - CH (CH3 ) ] n-

230

215

222

211

(a)

9. p o l y (l-heptene) - [ C H 2 - C H ({C~2 }4-CH3) ] n-

213

190

208

212

(d)

10. p o l y (1-hexene) - [ c s 2 - c . ( { c~2 } 3-cH3) ] n-

218

196

216

217

(d)

218

220

(C)

11. p o l y i s o p r e n e ,

trans

12. p o l y ( c i s - c h l o r o p r e n e ) - [C H 2 - C H = C (C1) -CH2 ] n-

233

237

218

225

(e)

13. p o l y (1-pentene) - [ c M 2 - c . ( { c~2 } 2-cH3) ] n-

226

203

227

(d)

14. p o l y v i n y l i d e n e - [CH2-C (F) 2]n-

206

242

233

(b)

238

216

238

236

(a)

fluoride

15. p o l y (1-butene) - [CH2- CH (CH2-CH3 ) ] n(*) T g - v a l u e ,

K = 0.0145 9 (Ecoh./En, i)

+ 120

239 Table

7.2 c o n t i n u e d (2) Tgc, 1: g r o u p c o n t r i b u t i o n m e t h o d (Van K r e v e l e n ) Tgc, 2 : c o n n e c t i v i t y i n d i c e s m e t h o d (Bicerano) Tgc, 3- ' m o d i f i e d c o h e s i o n energy' m e t h o d

polymer name/structure

Tgc, 1

Tgc, 2

Tgc, 3

16. p o l y p r o p y l e n e , a t a c t i c - [CH2-CH (CH3) ] n-

255

235

252

(a)

17. p o l y v i n y l i d e n e c h l o r i d e - [CH2-C (CI) 2]n-

255

276

253

255

(b)

236

254

279

272

(f)

295

282

275

(a)

308

283

(b)

242

280

286

(a)

281

292

297

294

(a)

302

307

303

(a)

259

300

307

(a)

284

314

(b)

329

323

(a)

18. p o l y e t h y l e n e s u c c i n a t e - [0-CO- (CH2) 2 - C 0 - 0 - (CH2) 19. p o l y ( v i n y l p r o p i o n i c - [CH2 - CH (0 - {CO } - C H 2

2]n-

acid)

- CH3

) ] n-

20. p o l y ( m e t h y l a c r y l a t e ) - [CH2-CH (CO-O-CH3) ] n-

279

21. p o l y (4-methyl p e n t e n e - 1) - [CH2 - C H (CH2 - CH {CH3 } - CH3 ) ] n22.

PP/CO alternating copolymer - [CH2-CH (CH3) -COl n-

23. p o l y (vinyl a c e t a t e ) - [CH2 - CH (0- CO- CH3 ) ] n24. p o l y ( 3 - m e t h y l b u t e n e 1) - [CH2 - C H (CH {CH3 } - CH3 ) ] n25. p o l y v i n y l f l u o r i d e - [CH2-CH (F) In26. n y l o n

328

6.6

- [ (CO) N H - (CH2) 6 - N H (CO) - ( C H 2 ) 4 ] n -

Tg-value experim. K

27. p o l y (p-xylylene) - [CH2 -CH2- (C6H4) ] n-

361

329

303

333

(e)

28. p o l y ( e t h y l e n e t e r e p h t h a l a t e ) - [0 (CO) - (C6H4) - (CO)O- (CH2) 2]n-

369

373

340

348

(a)

29. p o l y ( c h l o r o - p - x y l y l e n e ) - [CH2 -CH2 - (C6H3CI) ] n-

407

350

366

353

(e)

30. p o l y ( v i n y l a l c o h o l ) - [CH2-CH (OH) ] n-

357

338

353

(b)

31. p o l y ( v i n y l c h l o r i d e ) - [CH2-CH (C1) n-

354

293

354

(a)

240 Table 7.2 c o n t i n u e d (3) Tgc,l: g r o u p c o n t r i b u t i o n m e t h o d (Van Krevelen) Tgc, 2 : c o n n e c t i v i t y indices m e t h o d (Bicerano) Tgc, 3 : 'modified c o h e s i o n energy' m e t h o d Tg-value experim.

Tgc, 1

Tgc,2

Tgc,3

32. p o l y (oxy [p-phenylene] ) - [ (C6H4) -0] n-

393

359

358

(b)

33. p o l y f o r m a l

407

415

361

(a)

34. p o l y [thio (p-phenylene) - [ (C6H4) -S]n-

347

357

363

(g)

35. p h e n o x y resin - [R-O-CH2-CH (OH) -CH2-O] n-

399

388

368

(a)

364

373

(b)

polymer name/structure

R = - (C6H4) - (CH3) C (CH3) - (C6H4) -[R-O-CH2-0]n-

36. p o l y (acrylonitrile) - [CH2 - CH (CmN) ] n-

37. p o l y s t y r e n e - [CH2-CH (C6H5) ]n-

373

379

377

378

(a)

38. s t y r e n e / C O altern, copolymer - [CH2-CH (C6H5) -CO] n-

362

381

380

383

(a)

39. p o l y (methyl methacrylate) 378 - [CH2- (CH3) C (CO-O-CH3) ] n- atac.

357

340

384

(h)

40. p o l y (ether e t h e r ketone) 420 - [0- (C6H4) -0- (C6H4) -CO- (C6H4) ] n -

433

417

(a)

41. p o l y c a r b o n a t e

409

419

420

423

(a)

42. Udel - [R-O- (C6H4) -S02- (C6H4) -0] n-

465

462

469

458

(e)

43. d i c h l o r o p o l y c a r b o n a t e PC with one - (C6H2C12)- unit

475

459

(i)

44. tetramethyl polycarbonate, PC 461 with two - (C6H2 [CH3] 2)- units

494

498

476

(i)

386

437

483

(j)

509

498

493

(i)

- [R-O-

(CO)

-0] n-

45. p o l y ( d i m e t h y l -

PPO)

[ (c6.2 {cs3}2 ) -o] n-

46. t e t r a c h l o r o p o l y c a r b o n a t e PC w i t h two -(C6H2C12)- units

241 Table 7.2 continued (4) Tgc, 1 : group c o n t r i b u t i o n m e t h o d (Van Krevelen) Tgc, 2 : c o n n e c t i v i t y indices m e t h o d (Bicerano) Tgc, 3 : 'modified cohesion energy' m e t h o d polymer n a m e / s t r u c t u r e

47. poly (arylene sulphone) - [ (C6H4) -0- (C6H4) - S02 ] n48. tetrabromo polycarbonate, PC with two - (C6H2 [Br] 2) - units

Tgc, 1

Tgc, 2

Tgc, 3

Tg-value experim.

469

483

493

(e)

511

523

(i)

(a) Tg-values determined according to the p r o c e d u r e described in 1.1.3. (b) Tg-values reported in the Polymer Handbook [14] (c) The Tg-value of PE is still under discussion. We accept Van Krevelen's value of 195 K [i]. (d) see ref. [13]. (e) see ref. [2]. (f) see ref. [5]. (g) see ref. [15]. (h) Bosma et.al, report a Tg-value of 383 K for atactic PMMA with a Mn value of 45000 [16]. Min and Paul [17] report a Tg-value of 386 K (both DSC onset values m e a s u r e d at a heating rate of 20~ Hence, we are u s i n g a value of 384 K. (i) see ref. [18]. (j) see ref. [19]. continued from page 237: Tg-values. The correlation coefficient is 0.9740 for the group contribution results, 0.9835 for the (Bicerano) c o n n e c t i v i t y indices results and 0.9948 for the 'modified cohesion energy' results. The results of the 'simple' m o d i f i e d cohesion energy method are for linear polymeric systems clearly improved in comparison with the other two methods. It is important to realise, however, that the group contribution m e t h o d of Van Krevelen and especially the connectivity indices m e t h o d of Bicerano are covering clearly more structural possibilities.

242

Tg(cal.)/Tg(exp.) correlation (group contribution method) Figure 7.2 510 470

Correlation

coeff.

0.9740

430 +

~" 3 9 0

++/+ > 350 I

"~310 +

270 230

190 L 190 2 3 0

270

310

350

390

Tg(exp.)-value, K

430

470

510

......

9 I'

I '' "

-I~ ~ 0 '

-I~ "-,1 0

0 -7

D_ ~--

<--I

-I CD N 0

-,,1 0

D"~"

W 9 0

-I~

CO O1 0

"-~.

CO = 0

+.....

I'0 "q 0

W 0 ,

-~ 0

~o -,,,i 0

I'0

= 0 LO +, 0

Tg(cal.)-value,

244

Tg(cal.)/Tg(exp.) correlation (modified cohesion energy method)

Figure 7.4 510 470

Correlation

ooeff.

0.9948

430 390 +

>I 3 5 0 ._,...

310

270 230 19O

190 2:30 2 7 0

310

350

390

Tg(exp.)-value, K

430

470

510

245 7.2.3 The T_u-value of c r o s s 1 ~ n k e d p o l y m e r i c systems Crosslinking reduces the m o l e c u l a r m o b i l i t y and thus causes increased Tg-values. This i n c r e a s e of the T g - v a l u e due to crosslinking is often d e s c r i b e d in l i t e r a t u r e by the semiempirical e q u a t i o n [5, 20, 21, 22]Tg = Tg, o + k/Mc where:

7.2

Tg = the T g - v a l u e of the c r o s s l i n k e d system, Tg, o = the T g - v a l u e of the n o n - c r o s s l i n k e d s y s t e m w i t h a Mn v a l u e z 50000. k = a constant and Mc = the m o l e c u l a r w e i g h t in b e t w e e n the crosslinks.

For c r o s s l i n k e d e l a s t o m e r s sulphur, Mc can be w r i t t e n

i.e. as:

rubbers v u l c a n i s e d

MC = Mn/p

where:

~ f v'

= the c r o s s l i n k density, = the n e t w o r k f u n c t i o n a l i t y = the n e t w o r k chain d e n s i t y

Hence,

7.2 can be w r i t t e n

with

(Mn.f)/(2.v')

Tg - Tg, o =

7.3

as :

(2 .v, .k) / (f.Mn)

= C.v'

7.4

Thus, the T g - v a l u e d i f f e r e n c e increases a c c o r d i n g to e q u a t i o n 7.4 l i n e a r l y with the n e t w o r k chain density. This r e l a t i o n was checked for two v u l c a n i s e d r u b b e r systems; an e x p e r i m e n t a l solution SBR (SSBR) and an commercial e m u l s i o n SBR (ESBR, Into1 1502). The e x p e r i m e n t a l v a l u e s m e a s u r e d for the SSBR system are listed in Table 7.3. Table 7.3 T g - v a l u e increase of a SSBR s y s t e m due to v u l c a n i s a t i o n with sulphur (gum v u l c a n i s a t e samples). -.,,,

,.,lq

sulphur concentration .

Tg-Tg, o

V' -value,

mol./m3

-40.0

0.0

1.0

-37.0

3.0

1.25

-36.5

3.5

........

Tg-value,

,,,

0.0

, ,,

.,,

,,,

.,.

53.3 76.7

.,.

1.50

-35.5

4 .S

2.0

-34.0

6.0

131.7

7.5

181.7

15.0

340.0

3.0 ,

. . . . . . . .

6.0

10.0

-32.5 -25.0 .

-15.0 '

.II

,,,.,,

. . . . .

25.0 ' ,,

96.7

,,,L

,,,,

__1

580.0

, j -

~ _

246

The Tg increase of SSBR due to vulcanisation versus the network chain density

Figure 7.5 25 Delta Tgcorrelation

0 . 0 4 3 v ' + 0.4 coeff.0.9993

~15 (!)

(..) E

. . . . .

-~10 >

F-

100

200

Network

I..

:300

400

500

chain density, mol./m3

600

247 The Tg-value increase plotted as a function of the network chain density in Figure 7.5, shows indeed a linear relation which nearly crosses the origin for the non-crosslinked, pure rubber. Hence, equation 7.2 decribes the Tg-value increase of an experimental SSBR system due to vulcanisation satisfactorily. The Tg-value of the emulsion polymerised SBR sample Into1 S1502 increases from -57~ for the pure, non-vulcanised polymer to -33"C after vulcanisation with 10.0 phr of sulphur. The experimental values measured for this system fit considerably less good with the linear relation predicted by equation 7.4 than the values measured for the SSBR system: ESBR ~Tg = 0.035 x v' + 2.26,

correlation

coeff.

-- 0.9827

SSBR ~Tg = 0.043 x v' + 0.30,

correlation

coeff.

-- 0.9993

The reason for this difference in behaviour of these two rubbers might be the difference in molecular structure. Mainly linear rubber molecules are polymerised in the solution process, while the emulsion process produces a product with a considerable amount of branched polymer chains. It seems that equation 7.2 already fails to describe adequatly the Tg-value increase due to crosslinking of high molecular weight linear polymers if branching disturbs the regularity of the formed network. It is then not realistic to expect that this relation will describe the far more complex, threedimensional chain building process of low molecular weight resins and their curing agents. The diglycidyl ether of bisphenol A (DGEBA) which at room temperature is highly viscous but still liquid, is used in many epoxy resin applications. A three-dimensional network is formed after reaction of DGEBA with a proper three or four functional curing agent. The structure of p/LE~DGEBA is given below:

H2C-CH-CH2-0O

CH3

-C - ~ O-CH2-HC~-~H2 CII3

The purity of this 'basic building block' is indicated by its functionality i.e 2.00 and by its epoxy molar mass (EMM) value i.e. 340/2 = 170. The commercially available DGEBA products (EPIKOTE 828, Shell Chemicals - DER 332, Dow Chemicals or MY/GY 250 - Ciba-Geigy) are not completely pure DGEBA systems and their structure is, therefore, more realistic given by-

248

,o,

H2C-~H-CH2- [O-R-O-CH2-CH-CH2 ]n-O-R-O-CH2-HC-CH2 CH3 where n is about 0.1 and R represents-

- CH3

The purity of the D G E B A u s e d influences the regularity of the network formed after the cure reaction and this is reflected in Tg-value differences. This effect is clearly shown by a series of experiments in which an epoxy resin was purified in a number of steps. These purified DGEBA resins were cured, subsequently, with a stoichiometric amount of DDM as curing agent: H2N~-CH2~-NH2,

4-4' diaminodiphenylmethane

The DSC onset Tg-values (see 1.1.3) cured systems are listed below.

of the complete,

(DDM) carefully

Table 7.4 Effect of the impurity level of DGEBA resins on the properties of the resin and on the Tg-value of the cured systems. resin t y p e

rw~m

purity, % EMM-value functionality

A 91.9 185 1.8

Tg-value, ~ Tra-value, ~ Hf-value, J/g ,

C 92.1 184.5 1.971

93.8 181.2 1.984

-17 39 0.1

-21 48 72

D 99.6 170.6 2.000 -22 46 85

DGEBA/DDM Tg-value, ~

154

168

171

186

A: EPIKOTE 828 EL commercial epoxy grade, B: experimental (improved purity) EPIKOTE 828, C: purified version of B, D- purified version of C. systems cured: 1 hour/80eC - 1 hour/150~ - 1 hour/175~ 0.5 hour/200aC, the weight losses due to the 200eC cure-step were ~ 2.0 %wt.

249 The resins A and B are l i q u i d resins at r o o m t e m p e r a t u r e w h i l e the resins Cand D are h i g h l y c r y s t a l l i n e systems u n d e r the same conditions. The strong i n f l u e n c e of p u r i t y i.e. the EMM value, and the f u n c t i o n a l i t y on the T g - v a l u e of the (DDM) cured e n d - p r o d u c t is clear. The T g - v a l u e s of cured endp r o d u c t s are also i n f l u e n c e d by d i f f e r e n c e s in the resin/ c u r i n g agent m i x i n g p r o c e d u r e and by d i f f e r e n c e s in the c u r i n g schedule. All these effects m a k e it d i f f i c u l t to speak about 'the' T g - v a l u e of a c e r t a i n r e s i n / c u r i n g agent s y s t e m and h a m p e r a p r o p e r T g - v a l u e estimation. 7.2.4 The T g - v a l u e e s t i m a t i o n of epoxy_ r e s i n based. crosslinkedresin systems The n e t w o r k o b t a i n e d after the cure of the D G E B A w i t h D D M (each D D M m o l e c u l e reacts w i t h four D G E B A molecules) can be r e p r e s e n t e d by: /X

-N

CH2 - CH - CH2 -0 -R -0 - CH2 - CH - CH2~ N ~ -

CH2 ~

N~ CH2 - CH - CH2 -Y

In such a n e t w o r k a l t e r n a t i n g D D M / D G E B A m o l e c u l e chains can be recognised. Hence, the n e t w o r k can c o n s i d e r e d to c o n t a i n long, linear m o l e c u l e chains w i t h as 'repeating unit': X - [CH2-

-CH2-O-R-O-CH2-CH-CH2-

-CH2

-N] n-

X Each of these 'repeating units' is c o n n e c t e d on two p l a c e s via the c r o s s l i n k s w i t h the o t h e r m o l e c u l e chains. The T g - v a l u e of this s y s t e m can c o n s i d e r e d to be the sum of the T g - v a l u e of a 'linear polymer' w i t h the above g i v e n r e p e a t i n g unit and a c r o s s l i n k i n g effect. The T g - v a l u e c o n t r i b u t i o n can be c a l c u l a t e d u s i n g the 'modified c o h e s i o n energy' m e t h o d w i t h the n ~ 4 ~Ecoh. v a l u e s f r o m Table 7.1: ~Ecoh. ~Ecoh. ~Ecoh. 6Ecoh. ~Ecoh. 6Ecoh. ~Ecoh.

-CH2- : 4936 hence -CH: 3430 hence -OH : 28708 h e n c e -0: 4852 h e n c e -R: 85007 h e n c e -C6H4-: 27951 h e n c e -N: 4183 h e n c e

5 2 2 2 1 2 2

x 4936 x 3430 x 28708 x 4852 x 85007 x 27951 x 4183 Ecoh.

= 24680 = 6860 = 57416 = 9704 = 85007 = 55902 = 8366 = 247935

~n,i = 16, u s i n g e q u a t i o n 7.1 results in: T g - v a l u e , 0.0145 x (247935/16) + 120 = 345 K

J/mol. J/mol. J/mol. J/mol. J/mol. J/mol. J/mol. J/mol.

250 The highest (see Table crosslinks 114 K i.e. 57 K.

T g - v a l u e m e a s u r e d for a D G E B A / D D M s y s t e m is 459 K 7.4). Hence, the T g - v a l u e c o n t r i b u t i o n of two in the above g i v e n 'repeating unit' is 459 - 345 = the m a x i m u m T g - v a l u e c o n t r i b u t i o n p e r c r o s s l i n k is

R e s i n s y s t e m D was, subsequently, cured w i t h 4-4' d i a m i n o d i p h e n y l s u l p h o n e (DDS), 4-4' d i a m i n o d i p h e n y l p r o p a n e (DDP) and 4-4' d i a m i n o p h e n y l (DP) to check the c o n s i s t e n c y of the 'c r o s s l i n k contribution' . r e s i n D/DDS system, -

'r e p e a t i n g unit' :

[CH2-CH-CH2-O-R-0-CH2-CH-CH2-

Tg(exp.) Tg(cal.)

- 499 K -- 383 K i.e.

r e s i n D / D D P system,

- ] n-

X (499 - 383)/2

= 58 K p e r c r o s s l i n k

'repeating unit':

Tg(exp.) Tg(cal.)

- 469 K - 367 K i.e.

r e s i n D/DP system, - [CH2 Tg(exp.) Tg(cal.)

(469 - 367)/2

'repeating unit':

CH2-O-R-O-CH2= 452 K - 343 K i.e.

n -

= 51 K p e r c r o s s l i n k X

(452 - 343)/2

= 55 K p e r c r o s s l i n k

Hence, the a v e r a g e T g - v a l u e c o n t r i b u t i o n p e r c r o s s l i n k is 55 â&#x20AC;˘ 3 K for resin s y s t e m D. The T g - v a l u e of r e s i n s y s t e m A / D D M is 427 K. The T g - v a l u e c o n t r i b u t i o n p e r c r o s s l i n k is for this s y s t e m (427 345)/2 ~ 41 K/crosslink. Hence, if an 'epoxy r e s i n ' / D D M s y s t e m is u s e d to d e t e r m i n e the T g - v a l u e c o n t r i b u t i o n p e r crosslink, the T g - v a l u e s of this 'epoxy resin' with o t h e r c u r i n g agents can be calculated. In other words, the c o r r e c t i o n for the resin i m p u r i t y and p r e p a r a t i o n e f f e c t s on the T g - v a l u e of the e n d - p r o d u c t occurs v i a the Tgv a l u e c o n t r i b u t i o n per crosslink. -

251 The n e t w o r k o b t a i n e d a f t e r the r e a c t i o n of r e s i n s y s t e m A / H H P A ( h e x a h y d r o p h t h a l i c anhydride) can be r e p r e s e n t e d by the s t r u c t u r e g i v e n below. X

o-~,,

0-. q:o

~ \

-0 - CH2 - CH- CH2 -0 -

~-o-

~ \

I ~:o

-~,-c~,-o-~-o-~,-~-o~--

~-o-~,

g-o

80- -CH- CH2 -O-R-O-~,~--~ - CH2 -o-'~ ~-o~H2

C> *

x_./

C-O

I X

The ' r e p e a t i n g to be:

unit',

containing

two crosslinks,

is c o n s i d e r e d

I ~-o-cH2-c~-c~2-O-R-O-CH2

- [cH-o-~

] ~-

The c a l c u l a t e d T g - v a l u e of a linear p o l y m e r w i t h this r e p e a t i n g unit is 321 K. The c o n t r i b u t i o n of two c r o s s l i n k s is 82 K. Hence, the c a l c u l a t e d T g - v a l u e for the r e s i n s y s t e m A/ H H P A s y s t e m is 321 K + 82 K = 403 K. The m e a s u r e d T g - v a l u e was 399 K. The T g - v a l u e s of five o t h e r e p o x y r e s i n s y s t e m s were c a l c u l a t e d (and measured) in the same way, all r e s u l t s are listed in T a b l e 7.5. It is important to r e a i i s e that the u s e d s t r u c t u r e s are 'idealised' structures. E v e r y d e v i a t i o n f r o m this ideal n e t w o r k s t r u c t u r e will l o w e r the e x p e r i m e n t a l Tgvalue. Thus, the c a l c u l a t e d T g - v a l u e s will in g e n e r a l be equal or h i g h e r than the m e a s u r e d Tg-values. This was c o n f i r m e d for the six systems i n v e s t i g a t e d .

252 Table 7.5 Results of Tg-value calculations on crosslinked epoxy resin systems resin system 9

Tg-vaiue ...number . of rep. unit, crosslinks/ K rep. unit

,,,

, ,,,

Tg-value calc., K

.,,

Reference resin A/DDM

345

resin A/E 112 ~

6Tg/crosslink = 41 K . ,

Tg-value meas., K

427

resin A/E 113

341 332 353

1 2 2

382 414 435

432

resin A/HHPA resin A/TMA

321 317

2 3

403 440

399 435

resin A/BABA resin A/ Alnovol

346 346

3 1

469 387

445 377

365

* two seemingly nearly equal possibilities The structural formulas of the systems in Table 7.5 are given below. EPIKURE 112

~-NH-

EPIKURE 113

CH2 -CH2- CH2-NH2

H2N-O

-CH2- O - N H 2

CH3

BABA

\CH2 ~ -

HHPA

Alnovol VPN 1981

Q ~

0 ~\0

and TMA

= o Q c==Q o= /

,crt2

HO~CH2-(~ -OH

NH2

=~176 G )o

253

7.3 The Tm-value estimation 7.3.1 Introduction The application of polymers in all kind of end-use products is often limited by their relative low melting temperatures. There has been therefore a considerable interest in determining the factors which control the Tm-value. One would hence also expect an extended amount of Tm-value/chemical structure correlations proposed in literature, just as the many correlations proposed for the Tg-value, see 7.2. It is remarkable however, that this is not the case. Van Krevelen [1] seems to be the only one with a clear Tm-value/chemical structure correlation concept. Even Bicerano [2], who is reporting such an extended polymer properties prediction system, does not mention the Tm-value at all. The Tm-value of a polymeric system is according to Young [23] and Cowie [4], depending on: i. mainchain symmetry, ) 2. mainchain flexibility, ) molecular structure 3. intermolecular bonding/polarity, ) effects 4. tacticity and cis/trans isomerism, ) 5. type and size of side-groups, ) 6. molar mass, 7. thermal history (crystal size/perfection), 8. the presence of residual monomer/solvents, 9. rate and type of measurement. A number of these Tm-value depending factors are also mentioned in the earlier mentioned list concerning the Tgvalue (see 7.2.1); in fact there is a close agreement between the two lists. Hence, some relation between Tg and Tm can be expected and is indeed reported (the Tg/Tm ratio) in literature [24]. This Tg/Tm ratio appears to vary widely however, but indicative values might be: Tg/Tm - 0.5 , for symmetrical polymers, Tg/Tm - 0.67, for unsymmetrical polymers. These values can only be used as a 'rule of thumb' not as a real correlation. Van Krevelen argued that this correspondence suggests that a treatment analogous to that proposed by him for the Tg-value could also be used for the prediction of Tmvalue. Subsequently, he calculated the group contributions (Ym) resulting in a system to estimate Tm-values of polymers with widely varying molecular structures.

254 7.3.2 The reduced Tu/Tm correlations One of the problems hampering the Tm-value/chemical structure correlations is in the experimental reference values. Most experimental values reported are non-equilibrium results while equilibrium Tm-values, the so-called Tm(o)-values, are preferred. Van Krevelen does not mention the difference between equilibrium and n o n - e q u i l i b r i u m T m - v a l u e s and used probably mainly n o n - e q u i l i b r i u m T m - v a l u e s , simply because equilibrium Tm(o)-values for many polymers are not (yet) available. A series of non-equilibrium Tm-values were measured on samples recrystallised from the melt under standard conditions (the so-called Tm2-values, see 1.1.4) and a number of nonequilibrium literature values were used to look for an improved correlation between Tm/Tg relations. We tried to improve the results of such a relation by distinguishing different groups of polymers instead of looking for one relation for all types of polymers. Three groups of polymers offering the best fitting correlations, were selected finally: Group A, polymers with cis/trans double bonds, vinyl polymers with side groups/chains and polymers with p-phenyl groups. Group B, polymers with strong intermolecular bonding effects. Group C, linear polymers with - (C) n- or - (C) n-0- mainchains. The Tm/Tg relations for these three groups of polymers (see Figure 7.6) appeared to be practically linear. The straight lines calculated have nearly identical slopes and differ only in the constant value added. Thus, it is possible to approximate the Tm/Tg relation for these 29 polymer systems satisfactorily by one relation with different constant values: Tin-value

(K) = 1.23 x

where To -

(Tg-value,

K) + To

7.5

74 for group A polymers, 152 for group B polymers and, 206 for group C polymers.

The calculated Tm-values with this 'reduced Tm/Tg correlation' method, the Tm-values calculated with Van Krevelen's group contribution method and the experimental Tm-values are listed in Table 7.6. The figures 7.7 and 7.8 show the Tm(exp.)/ Tm(calc.) correlations for both methods. The correlation coefficients of these two correlations and the average [Tm(exp.)-Tm(calc.)] values are:

Tm (exp.) -Tin(calc.), average value Correlation

coefficient

group contribution method (v. Krevelen) 38 K _+ 35 K 0. 819

reduced Tm/Tg correlation 15 K + I I 0. 981

255

Tg/Tm relation Gro~ B 6 Dolj4ners

18 polj4n~rs

620

Figure

Gro~ C 5 Dol~ners

7.6

580

540

500

+ Z~

:::3

460

I 420 E

I--

380 340

300

260

......... J ......... , 160

200

B: T m C: T m -

240

280

.......

.....

320

Tg-value,

1.23xTg + 74 1.15xTg + 169 1.1 l x T g + 232

360

400

440

256 Table

7.6 R e s u l t s of T m - v a l u e c a l c u l a t i o n s Tmc, 1 : g r o u p c o n t r i b u t i o n m e t h o d (van K r e v e l e n ) Tmc,2" r e d u c e d T m / T g r e l a t i o n s method, e q u a t i o n Tmc, 1

Tmc, 2

164 179

359

276 295

265 315

(a) (a)

2. p o l y i s o p r e n e , cis - [CH2- (CH3) C = C H - C H 2 ] n-

205

315

326

300

(b)

3. p o l y i s o b u t y l e n e , - [CH2- C (CH3) 2 ] n-

203

316

324

318

(c)

4. p o l y (1-pentene) - [CH2- CH ( {CH2 } 2- CH3 ) ] n-

227

311

353

348

(c)

5. p o l y (1-butene) - [CH2- CH (CH2-CH3 ) ] n-

236

361

364

397

(a)

6. p o l y ( c i s - c h l o r o p r e n e ) - [ C h 2 - C H = C (Cl) -CH2 ] n-

225

377

351

353

(c)

7. p o l y m e t h y l m e t h a c r y l a t e (i) - [CH2- (CH3) C (CO0-CH3) ] n-

329 (c) 473

479

442

(d)

8. p o l y ( b u t e n e terephphalate) - [O-CO- (C6H4) -CO-O- (CH2) 4] n-

307

488

452

473

(e)

9. p o l y (oxy [p-phenylene] ) - [ (C6H4) -0] n-

358

559

514

490

(e)

polymer

Group

Tgvalue K

7.5

name/structure

A _Dol~rs;

1. p o l y b u t a d i e n e , - [C H 2 - C H - C H - C H 2

Tmc,2

= 1.23xTg

cis trans ] n-

Tm-value experim. K

+ 74

i0.

poly(vinylalcohol) - [CH2-CH (OH) ] n-

353

539

508

503

(f)

11.

poly(ethylene terephthalate) - [O-C0- (C6H4) -C0-O- (CH2) 2 ] n -

348

528

502

516

(a)

12.

polyformal - [R-0-CH2-0]n- R - (C6H4) - (CH3) C (CH3) - (C6H4) -

361

656

518

524

(a)

13.

polystyrene (s) - [CH2-CH (C6H5) ] n-

378

516

539

532

(a)

14. p o l y ( s t y r e n e / C O ) copolymer - [CH2-CH (C6H5) -CO] n-

383

498

545

554

(a)

15.

363

559

520

548

(e)

poly(thio[p-phenylene] - [ (C6H4)-S] n-

)

257 Table

7.6 c o n t i n u e d (2) Tmc, I- g r o u p c o n t r i b u t i o n m e t h o d (Van Krevelen) Tmc, 2 : r e d u c e d T m / T g r e l a t i o n s method, e q u a t i o n 7.5 TgTmc, 1 Tmc, 2 Tin-v a l u e value experim.

16. p o l y c a r b o n a t e - JR-O-CO-O] n17. p o l y ( e t h e r - [0- (C6H4)

e t h e r ketone)

-0-

(C6H4)

Group B polymers:

-CO-

Tmc,2

(C6H4)

423

659

594

563

(e)

417

576

587

617

(a)

] n-

= 1.23xTg

+ 152

fluoride

233

437

439

443

(C)

2. p o l y v i n y l i d e n e c h l o r i d e - [CH2-C (CI) 2]n-

255

462

466

473

(c)

3. p o l y v i n y l f l u o r i d e - [CH2-CH (F) ] n-

314

530

538

503

(c)

4. n y l o n 6.6 323 - [ (CO) NH- (CH2) 6-NH (CO) - (CH2) 4] n-

540

549

534

(a)

5. p o l y v i n y l c h l o r i d e - [ CH2 -CH (CI) ] n -

354

576

587

583

(C)

6. p o l y (acrylonitrile) - [CH2-CH (C=N) ] n-

373

598

611

614

(c)

1. p o l y v i n y l i d e n e - [CH2-C (F) 2]n-

Grou_D C _ D o l o r s :

Tmc, 2 = 1 . 2 3 x T g

+ 206

1. p o l y o x y (isobutylene) - [CH2- (CH3) C (CH3) -0] n-

204

435

457

450

(C)

2. p o l y o x y m e t h y l e n e - [CH2-O] n-

191

426

441

451

(a)

3. p o l y f o r m a l d e h y d e - [CH (CH3) -0] n-

200

602

452

(g)

4. p o l y p i v a l o l a c t o n e - [CH2- (CH3) C (CH3) - (CO) -0] n-

260

433

526

511

(a)

5. e t h y l e n e / C 0

257

418

522

528

(a)

copolymer

258 Table 7.6 continued

(3)

(a) Tm2-values, determined according to the procedure described in I.I.4. (b) see ref. [I]. (c) Tin-values reported in the Polymer H a n d b o o k [14]. (d) see ref. [17]. (e) series of e q u i l i b r i u m Tin-values reported by Cheng and Wunderlich [25]. They report for PEEK a Tin-value of 668 K, we measured a Tm-value of 617 K. Hence a difference of 51 K. They report for PET a Tm-value of 553 K, we m e a s u r e d a Tmvalue of 516 K. Hence a difference of 39 K. The difference between the equilibrium and the n o n - e q u i l i b r i u m Tm-values seems to be in the order of 45 K for these types of polymers. The experimental Tin-values for PPO, PBT, PO, PPS and PC are the values of Cheng and W u n d e r l i c h corrected with 45 K. (f) see ref. 26. (g) see ref. 24.

259

Tm(cal.)/Tm(exp.) correlation (group c o n t r i b u t i o n method) Figure

7.7

620

580

+ + +

540

+ +

500 ~ +

-~ 4 6 0 > I

-~ 4 2 0

E F-

380

340 + +

Rval

3OO

--.--.--

0.819

260 260 300 340 380 420 460 500 540 580 620 I

I,,,

Tm(exp.)-value, K

260

Tm(cal.)/Tm(exp.) correlation (reduced Tm/Tg relations method) Figure

7.8

620 +

580 540

+ +

+ + +

500 r

.--.--,

460

420

E I-- 3 8 0 340 3.00

Rval.

0.9808

260 260 300 340 380 420 460 500 540 580 620 ,

,,,

Tm(exp.)-value, K

261 The correlation between Tm(exp.) and Tm(calc.) and thus the average difference between Tm(exp.) and Tm(calc. ) are indeed improved. The average difference is however nearly twice the average [Tg(exp.) -Tg(calc.) ] value, see 7.2.2. Hence, this 'reduced Tm/Tg correlation' system is far from ideal. Besides, each of the three groups of polymers contain a number of strongly deviating systems. The isotactic vinyl polymers (group A) which form helical structures for instance deviate strongly. The [Tm(exp.)-Tm(calc.)] values of a number of this type of polymers are:

poly(1-butene)

: 32 K, poly(1-propene) : 44 K, poly(3-methyl-l-butene) : 119 K, poly(4-methyl-l-pentene) : 62 K,

Tin(exp.) Tin(exp.) Tin(exp.) Tin(exp.)

= = = =

397 429 576 504

K. K. K. K.

Poly(oxy[di-methyl p-phenylene]), PPO is such a strongly deviating system for the high Tg, high Tm-value polymers. Tg-value of 483 K results a c c o r d i n g to equation 7.5 in a Tm(calc. ) -value of 668 K. The experimental Tin-value is, however, 535 K i.e. a difference of 133 K.

The

Polytetrafluoro ethylene is such an exception for the group B polymers. Cheng [27] reports for PTFE a Tg-value of 200 K and a Tm-value of 605 K. Equation 7.5 results in a calculated value of 398 K. PTFE behaves perhaps, by its molecular symmetry, like a group C polymer; in that case the calculated Tm-value should be 452 K. Hence, there remains a difference of at least 153 K. The Tm-value of polyethylene poses a p r o b l e m for the group C polymers. The Tg-value of 195 K results in a Tm(calc.)-value of 446 K while we measured an experimental value of 405 K for HDPE. However, the Tg-value of PE is still under discussion. Alberola et al. [28] recently suggested again a Tg-value for PE of about 158 K. The c o r r e s p o n d i n g Tm-value calculated of 400 K agrees reasonably with the experimental value. The Tm-values of p o l y e t h y l e n e oxide and polypropylene oxide are also difficult to calculate. The determination and calculation of the right Tg-values of these systems seems to be the main problem. The difference between the e q u i l i b r i u m Tm(o)-values and the non-equilibrium Tin-values was m e n t i o n e d already. The lack of sufficient reliable Tm(o)-values hampers the determination of proper Tg/Tm(o) correlations. For the polymers of group A however a number of Tm (o) -values are available [25, 27]. These data are plotted in Figure 7.9 as a function of the corresponding Tg-values and result in the following relationTm(o)-value

(K) = 1.37 x

(Tg-value,

K) + 71

7.6

The ten calculated and experimental Tm(o)-values are listed in Table 7.7. The average [Tmo(exp.)-Tmo(calc.)] value is 23 K _+

262 10 K. Hence, a p r o p e r set of 'reduced T m / T g c o r r e l a t i o n s ' seems to o f f e r b e t t e r f i t t i n g c a l c u l a t e d T m v a l u e s t h a n the m o r e g e n e r a l m e t h o d p r o p o s e d by v a n K r e v e l e n . The d i f f e r e n c e s b e t w e e n the c a l c u l a t e d and the e x p e r i m e n t a l T m v a l u e s are for b o t h m e t h o d s still to high. Thus, m o r e a n d m o r e r e l i a b l e Tga n d T m ( o ) - v a l u e s are n e c e s s a r y to d e v e l o p b e t t e r T m ( o ) / chemical structure correlations. Table

7.7 R e s u l t s

polymer

of T m ( o ) - v a l u e

name/structure

calculations. Tgvalue K

Group

A _Dol_vmers: T m (o), c = 1 . 3 7 x T g

Tin(o) value calc. K

Tin(o) value exp. K

+71

1. p o l y b u t a d i e n e , cis - [CH2-CHffiCH-CH2 ] n-

164

296

285

2. p o l y i s o b u t y l e n e - [CH2- (CH3) C (CH3) ] n-

203

349

317

3. p o l y (1-pentene) - [ C H 2 - C H ( { CH2 } 2 - C H 3 ) ] n -

227

382

403

4. p o l y (1-butene) - [CH2-CH (CH2-CH3 ) ] n-

236

394

411

5. p o l y ( b u t e n e t e r e p h t h a l a t e ) - [O-CO- (C6H4) -C0-O- (CH2) 4 ] n-

307

492

518

6. p o l y ( o x y [ p - p h e n y l e n e ] - [ (C6H4) -0] n-

358

561

535

7. p o l y ( e t h y l e n e t e r e p h t h a l a t e ) - [O-CO- (C6H4) -CO-O- (CH2) 2]n-

348

548

555

8. p o l y (thlo [p-phenylene] - [ (C6H4)-Sin-

363

568

593

9. p o l y c a r b o n a t e - [R-0-C0-0]n- R= - (C6H4) - (CH3) C (CH3) - (C6H4) -

423

651

608

10. p o l y ( e t h e r e t h e r ketone) 417 - [0- (C6H4) -0- (C6H4) -CO- (C6H4) ] n-

642

668

)

263

Tg/Tm(o) relation (group A p o l y m e r s ) Figure 7.9

620

-I-

580

540 -I-

500 460 I

F-

420 +

-I,

380 340

Tm(o)

300

1.37xTg + Rval.0.978

260 L 160

195

230

265

300

Tg-value,

335 K

370

405

440

264 7.4 The Hf-value estimation Important changes in the physical properties of polymers are observed during passage of the glass-rubber transition region and/or the fusion region. The temperature location of these two regions is indicated by respectively the Tg-value and the Tm-value. The level of m o s t physical polymer properties, especially in the temperature region between Tg and Tm, is mainly determined by the extent of the crystalline phase (the crystallinity). The crystallinity or the fraction of crystalline material x(c) can be derived from specific volume data, from specific heat data, from infrared extinction coefficient data, from X-ray scattering data, from NMR data or from h e a t of fusion data. The heat of fusion of a polymeric system as determined by DSC can give an x(c)-value" x(c)

- (Hf)/Hf(max.)

7.7

where Hf(max.) is the heat of fusion value of the completely crystallised system. Since polymers cannot be completely crystalline, Hf(max.) has to be determined by extrapolation. Reliable Hf(max.) values are scarce and this hampers the crystallinity determination by DSC. However, Hf-values as such can give an indication of the crystallinity level. Besides, this determination is frequently used to compare different samples or to compare identical samples after different thermal treatments. The maximum attainable degree of crystallisation during spontaneous, spherulitic crystallisation of flexible polymers under quasi-isotropic conditions depends to a great extent on the maximum rate of crystallisation Iv(max.)]. The v(max.) is related to the Tg/Tm ratio and this relation permits Van Krevelen [1] to report a x(c) versus Tg/Tm curve. Van Krevelen also reports a purely empirical expression for v(max.) based on the observation that the growth rate is high if the regularity of the molecular structure is strong: v(max.) where:

= 83x[(n.CH2/Z). (I/{l+I~,})]'

7.8

n - the number of CH2 or equivalent groups in the backbone of the structural unit, Z = number of atoms in the backbone of the structural unit, - number of carbon atoms in the side group.

Because of lacking Hf(max.)-values, the Hf(1)-values (see 1.1.4) of fifteen polymers as such were correlated with both their Tg/Tm-values and with their v(max.)-values calculated according to equation 7.8. The relevant data are listed in Table 7.8 and plotted in Figure 7.10. The line drawn in the Hf-value/Tg/Tm-value plot can only suggest an indicative 'maximum possible' Hf-value considering the scattering data points.

265

The H f - v a l u e versus the maximum crystallisation rate

Figure 300

Ny/c,,~ O 6.6

HI-~I~

7.10

lh~

PET

PPL

T ~ I ' ~

4l#

270 240

200

180

140 "

210

o4h

120 lO0

_ L

180

+ยง

c~ 150

0.40

4-:

0.50

0.60

0.70

0.80

Tg/Tm

120 90 "

ยง

60 3O 0"

0.001

0.01

0.1

v(max.), /Jmeter/s

100

266 Table

7.8

polymer

Tg/Tm-, v(max.)polymers

name/structure

a n d Hf (1) - v a l u e s

of a s e r i e s

Tgvalue

'I'mvalue

Tg/Tm value

v (max.) value

1. p o l y e t h y l e n e - [CH2-CH2 ] n-

195

405

0.48

195

2. p o l y o x y m e t h y l e n e - [CH2-O] n-

191

451

0.42

184

3. p o l y p r o p y l e n e - [CH2-CH (CH3) ] n-

252

436

0.58

0.32

4. p o l y (1-butene) - [CH2-CH (CH2-CH3 ) ] n-

236

397

0.59

0.064

5. p o l y ( e t h , eth. k e t o n e ) 417 - [ {O- (C6H4) } 2 -CO- (C6H4) ] n-

617

0.68

0.026

6. p o l y (3-methyl b u t e n e - 1) 307 - [ C H 2 - C H (CH{G"H3 }2} ]n-

576

0.53

0.020

7. p o l y (trans 2.3 e p o x y butane - [CH (CH3) -CH (CH3) -O] n-

242

420

0.58

0.013

8. p o l y (styrene/CO) - [CH2-CH (C6H5) -CO] n-

383

554

0.69

0.013

p o l y (4-methyl 286 pentene- 1 ) - [CH2 -CH (CH2 -CH {CH3 } 2 ) ] n-

504

0.57

0.008

378

532

0.71

0.004

11. p o l y f o r m a l 361 - [R-O-CH2-O]nR = - (C6H4) -C (CH3) 2 - (C 6 H 4 ) -

524

0.69

0.004

12. p o l y e t h y l e n e 348 terephthalate (PET) - [0-C0-(C6H4) -CO-0- (CH2)2]n-

516

0.67

2.1

13 .Nylon 6.6 323 534 - [C O -NH- (CH2 ) 6 - N H - CO- (CH2 ) 4 ] n -

0.60

21.6

14 . p o l y p i v a l o l a c t o n e (PPL) 260 - [CH2 - C (CH3) 2 - CO- O] n-

511

0.51

5.2

103

15.polybutadiene (BR, c i s ) 1 6 4 - [CH2 - C H = C H - C H 2 ] n-

265

0.62

0.61

10. p o l y s t y r e n e (s) - [CH2 -CH (C6H5) ] n-

~m/s

Hf (I) value J/g

267 Table

7.8 c o n t i n u e d

* -0= -CH2* -CO- = -CH2* -(C6H4)-, Z * -(C6H5) , E * -C(CH3) 2, E * -C(CH3) 2, E

(only for s t y r e n e / C O copolymer) -- 4 = 5 = 2 c o n j u g a t e d b e t w e e n two aromatic rings - 0 n o n - c o n j u g a t e d , a l i p h a t i c chains.

N o w m a n y v(max. ) / H f - v a l u e data p o i n t s seem to give, however, a r e a s o n a b l e c o r r e l a t i o n (Rval. is 0.9907). This c o r r e l a t i o n is d e s c r i b e d by the equationHf-value

(J/g) ~ 3 8 . S x l o g v(max.)

+ 115.5

7.9

This e q u a t i o n suggests that too low H f - v a l u e s are m e a s u r e d for N y l o n 6.6, PET, PPL and BR. This i n d i c a t e s that this c o r r e l a t i o n is g i v i n g a k i n d of 'maximum possible' H f - v a l u e and that the e x p e r i m e n t a l v a l u e s will be equal or s m a l l e r than the v a l u e s calculated.

268 7.5 The thermal stability estimation 7.5.1 IntrQduction The thermal stability of a polymer, that is the potential of its chemical bonds to withstand thermal energy, depends in general strongly on the test conditions. Usually, mainly four different situations occur: - relative short-time, high temperature isothermal or nonisothermal conditions, - relative long-time, low temperature isothermal conditions and, - both above conditions performed in an inert and/or in an oxidative (air) atmosphere. Relative long-time experiments are often performed according to the Underwriters Laboratories (UL) testing protocol [29]. The results, the retention of certain properties upon exposure to heat, are expressed in UL temperature index values. The time and material consuming UL testing procedure is usually preceded by short-time mass retention measurements, mainly performed with TGA equipment. Thermal stability/chemical structure correlations as reported by Van Krevelen [1] and Bicerano [2] are using and predicting the relative short-time, thermal stability values measured in an inert atmosphere. The mass losses measured under these (non-isothermal) conditions are caused by the damage of chemical bonds due to chain depolymerisation and/or random decomposition (see 2.2.1). Van Krevelen [1] distinguishes five experimental indices which characterise this non-isothermal decomposition process : - the initial decomposition temperature (Td, o), at which the loss of weight is just detectable, - the temperature of half decomposition (Td,1/2), at which the loss of weight reaches 50% of its final value, - the temperature of the maximum rate of decomposition (Td, max. ), - the average energy of activation (Eact. ,d), determined from the temperature dependence of the rate of weight loss, - the amount of char residue at the end of the experiment (usually at a standard temperature of 900~ Van Krevelen and Bicerano obviously consider the Td,1/2-value as the most important, for they both report a Td,1/2 chemical structure correlation. Van Krevelen mentions however, that these decomposition indices are interrelated i.e. Td,o is about 0.gxTd, 1/2, Td,max. is about Td, 1/2 and Eact.,d is about Td,1/2 - 423. We prefer to use the Td,o value as a measure for the shorttime thermal stability of a polymer. This because- the properties of a polymer sample that has lost 50% of its mass differ considerably with that of the initial product and,

269

- the Td, o - Tm temperature region offers a more realistic value for the 'processing window' of a polymer than the Td, 1/2 - Tm region. Detection of the exact temperature at which the ma~s loss process starts is experimentally far more difficult than determination of a Td, i/2-value. Besides, the determination of the Td,o-value might be hampered by mass losses due to residual solvent/ monomer and/or oligomers. We expected that a kind of compromise would be possible by using semi-statically determined Td, o-values as shown already for polypropylene in chapter 2. 7.5.2 The semi-static Td.o-value determination In chapter 2.2.2 it was shown that the isothermally determined (static) Td, o-value of polypropylene (PP) is about 190~ This value is approached reasonably in a dynamic i.e. nonisothermal experiment if a heating rate ~ 0.1~ is applied. A clear separation is obtained during such an ultralow heating rate experiment between the mass losses due to evaporation of the oligomers fraction and mass losses due to the thermal decomposition process(es). The step-wise change in the mass/temperature curve of Figure 2.6 at relative low temperature is considered to be due to evaporation of the oligomers fraction (the amount observed agreed with the values determined isothermally). The temperature or temperature region at which the zero mass loss rate or a very low, constant mass loss rate changes into clearly increasing mass loss rates with increasing temperatures, is considered to be the beginning of the overall thermal decomposition process (the Td, o-value). In connection with the ultra-low heating rate used (0.1"C/minute) this Td, o-value is called the semistatic Td.o-value. Figure 7.11 shows the result of a semi-static Td, o-value determination of poly(4 methyl-l-pentene). Mass losses & 0.05 %wt. can easily be recognised; in line with the TGA balance resolution and sensitivity. The weight loss rate is practically zero between 30~ and II0~ Between about II0~ and 267~ a small, but nearly constant weight loss rate is detected (0.003 %wt./oc). These mass losses might be caused by the evaporation of a small oligomers fraction (0.5 %wt. maximally). The mass loss rate increases strongly at temperatures > 267oc due to what is considered to be the overall thermal decomposition of the polymer sample. 7.5.3 Thermal stability estimation based on Td.o-values Van Krevelen [I] reports a correlation b e t w e e n the chemical structure and the Td, i/2-values of polymers: Td, I/2

(K) = (ENi x Yd, I/2.i)/M

which is called the molar thermal decomposition

7.10 function.

SamDle Weight' 4.5BI mg Poly- (4methyIpenteen-1) I01. O0 I00 50 100 O0 99.50 -I 99.00 J~

bO ,,,3 O

98.50 98. O0 97.50 97. O0 96.50

Figure 7.1 1 The Td,o determination

267~

96.00 50.0 nitrogen atmosphere TEMPI" 30~ TIME1: O.Omin TEMP2: 500"C

tO0.0

RATE1: 0.1~

i50.0

200.0

Temperature (~

250.0

300.0

271 Table

7.9

polymer

Td,o-values

a n d Yd, o - v a l u e s

name/structure

Td, ovalue K

group

1. p o l y e t h y l e n e - [CH2- CH2 ] n-

592

-CH2-

2. p o l y p r o p y l e n e [CH2 -CH (CH3 ) ] n-

463

3. p o l y s t y r e n e , a t a c t i c [CH2-CH(C6H5) In-, s 4. p o l y i s o b u t y l e n e - [CH2 - C (CH3) 2 ] n-

of a s e r i e s

of p o l y m e r s

Yd, ovalue K.kg/mol

Yd, 1/2 value* K.kg/mol

8.3

9.5

-CH(CH3) -

Ii. 2

18.5

504 538

-CH (C6H5) -CH (C6H5) -

44.1 47.7

56.5

496

-C (CH3) 2-

19.5

25.5

542

-C H = C H -

12.7

6. p o l y i s o p r e n e , cis 487 - [CH2 - C (CH3 ) =CH- CH2 ] n -

-C (CH3) =CH-

16.5

21.5

7. p o l o x y m e t h y l e n e [CH2-O] n-

415

-0-

8. p o l y ( p i v a l o l a c t o n e ) - [CH2-C (CH3) 2-C0-O] n-

516

-CO-

5. p o l y b u t a d i e n e 1.4, - [C H 2 - C H = C H - C H 2 ] n-

cis

4.2

19.7

77.2

103

78.2

103

105.8

143

9. p o l y e t h y l e n e t e r e 532 -CO- (C6H4) -COphthalate - [O-CO- (C6H4) - C O - O - (CH2) 2]n10. p o l y b u t y l e n e t e r e 544-CO-(C6H4)-COphthalate - [O-CO- (C6H4) -CO-O- (CH2) 4 ] n11. p o l y c a r b o n a t e 527 - [O-R-O-COIn-, R = (C6H4) -C (CH3 ) 2 - (C6H4) -

-R-

12. p o l y (l-butene) - [C H 2 - C H (CH2- CH3 ) ] n-

542

13. p o l y ( 3 - m e t h y l 1-butene)

546

-CH3

7.9

14. p o l y ( 4 - m e t h y l 1-pentene)

540

-CH3

7.5

-CH(CH2-CH3) -

22.1

- tcH2 -cH (c~ {cH3 } 2 ~ 3 n-

-Ec~2-c~ (CH2-CH(C.3 }2~ J.-

* values

reported

by Van

Krevelen

[1],

Table

21.2

646.

272 van K r e v e l e n also indicates that there is a relation b e t w e e n Td,1/2 and Td, o (see 7.5.1). We therefore d e c i d e d to look for the c o r r e l a t i o n b e t w e e n Yd, o group c o n t r i b u t i o n v a l u e s based on our s e m i - s t a t i c Td, o values and the Yd,1/2 group c o n t r i b u t i o n v a l u e s r e p o r t e d by Van Krevelen. The semi-static T d , o - v a l u e s of f o u r t e e n p o l y m e r s were determined, and used to calculate s e m i - s t a t i c Yd, o g r o u p c o n t r i b u t i o n values. These s e m i - s t a t i c Yd, o-values were then c o r r e l a t e d with the Yd,1/2v a l u e s r e p o r t e d by Van Krevelen, see F i g u r e 7.12. The c o r r e l a t i o n p r o v e d to be fairly good, w i t h its c o r r e l a t i o n c o e f f i c i e n t of 0.9953. ore r e a s o n a b l e to assume that (for a first estimation) Yd, o group c o n t r i b u t i o n values can be c a l c u l a t e d u s i n g Van Krevelens' Yd,1/2 g r o u p contribution v a l u e s with the equation: 7.11

Yd, o = 0.74 x Yd, 1/2 + 1.5 The Td, o-value of p o l y ( e t h y l e n e is then c a l c u l a t e d as follows: r e p e a t i n g unit

PET,

-CO-(C6H4)-C0-(CH2)-0-

- 77.7 K.kg/mol = 8.3 K.kg/mol - 4.2 K.kg/mol

terephthalate),

for example,

- [O-CO- (C6H4)-C0-0- (CH2) 2In- and M s 192 i.e. i.e. i.e.

1 x 77.7 = 77.7 K.kg/mol 2 x 8.3 - 16.6 K.kg/mol 2 x 4.2 = 8.4 K.kg/mol 102.7 K.kg/mol

Td, o-value, c a l c u l a t e d = (102.7 x 1000)/192 - 535 K The e x p e r i m e n t a l Td, o-value is 532 K. The T d , o - v a l u e of 535 K is 185 K lower than the c a l c u l a t e d T d , 1 / 2 - v a l u e (720 K, [i]). The Td, o - v a l u e of poly (2,6-dlmethyl calculated subsequently 9 r e p e a t i n g unit

PPO,

-[(C6H2{CH3}2)-O]n-

Yd, i/2 -(C6H2{CH3}2)a c c o r d i n g to e q u a t i o n Yd, o Yd, o

p-phenyleneoxide)

- 82.0 K.kg/mol 7.11:

and M-- 120 g/tool [i], Yd,o is then

= 0.74 x 82 + 1.5 = 62.2 K.kg/mol -0= 4.2 K.kg/mol 66.4 K.kg/mol

Td,o-value, c a l c u l a t e d = (66.4 x 1000)/120 = 553 K. This Td, ovalue is 197 K lower than the c a l c u l a t e d T d , 1 / 2 - v a l u e (750 K,

[:z)).

The Td, o-values of the most common p o l y m e r i c systems can thus be c a l c u l a t e d u s i n g e q u a t i o n 7.11 and Van Krevelens Yd,1/2values.

120 u

E v_

D > c 0 0

Yd,o

Semi-static

100

80 60 4-

I o

correlation

Yd, 1/2

Yd,o - 0 . 7 4 x Y d , 1 / 2 + Rval.0.9953

1.5

0 Figure 7.12

......... L +

....

I ....

Yd, 1 / 2 - g r o u p

,L,,,

100

120

contr. values, K.kg/mol

140

160

274 7.6 The moisture sensitivity estimation Low molecular weight components such as residual solvents and/or monomers have a strong influence on the physical properties of a polymeric system. The presence of water forms a special case in this respect. Firstly because nearly every polymer absorbs a certain amount of moisture from the air. Secondly because of the special character of the water molecule, i.e. relative small but with a strong tendency towards hydrogen bond formation in its own liquid as well as with other polar groups. The equilibrium water saturation of a polymeric system increases with the number of polar groups present in the polymeric matrix. Circumstances like the accessibility of the polar groups, the relative strength of the water-water versus water-polymer bonds and for semi-crystalline polymers the degree of crystallinity, hamper a straightforward correlation between the number of polar groups and the solubility. Van Krevelen [1] presents the amount of water per structural group at equilibrium (expressed as molar ratio), as what he calls the best possible approach to the sorptive capacity of (amorphous) polymers versus water. For many polymers it takes a long time to reach a real equilibrium water saturation. Resin samples, for instance, need immersion times of at least eighty days to reach a real equilibrium water saturation conditions, see chapter 5.2. The immersion times necessary to reach equilibrium water saturations increase to more than threehundred days for glass fibre filled, resin laminate systems. Based on these relative long immersion times it was expected that also for nonpolar polymers like polyethylene very long immersion times are necessary to reach real equilibrium conditions. Hence, we determined a number of structural group molar water content values by a series of long-term water absorption experiments. Nine sample strips (about 100x10x0.1 mm) of the polymers listed in Table 7.10 were first dried at 50~ in vacuum until constant sample weights were reached. The dry samples were stored subsequently for more than two years in ion-free water (in the dark) at 20 â&#x20AC;˘ 1~ Then the weight increase due to water absorption was measured on surface-dry samples. The samples and the equilibrium water saturation values measured are listed in Table 7.10. The molar water content of these polymers per structural group was calculated using these equilibrium water content values. The contribution of the -R- and -(C6H4)- groups was assumed to be zero to calculate the contributions of respectively the -OCO-O- group and the -S02- group. Hence, these contributions will be slightly too high. The molar water content values per structural group calculated are listed in Table 7.11 together with the values published by Van Krevelen [1].

275 Table

7.10 T h e e q u i l i b r i u m w a t e r s a t u r a t i o n v a l u e s m e a s u r e d a f t e r m o r e t h a n t w o y e a r s of w a t e r i m m e r s i o n .

polymer

name/structure

crystalline phase estimated % wt.

1. A l k a t h e n e - 2 L D P E - [CH2 -CH2 ] n-

equilibrium water saturation, % wt.

molar water content calculated for group

0. 0 0 4 7

-CH2 -

0.0543

- C H (Cl)

0. 0772

- C H (CH3) -

4. D o w 666 p o l y s t y r e n e - [CH2 -CH (C6H5) ] n-

0. 0 7 2 1

-CH(C6H5) -

0.1633

-O-

0. 3 4 6 0

-CO-

0. 3 9 2 2

-O-C0-0-

8. p o l y s u l p h o n e 0 - [O- (C6H4) -S02- (C6H4) -O-R] n-

0.7431

-S02-

9. A k u l o n n y l o n 6 - [ (CH2) 5-NH-CO] n-

5. 8515

-NH-CO-

531 PVC - [ C H 2 - C H (C1) In-

Carina

3. K M 6 1 0 0 p o l y p r o p y l e n e - [ C H 2 - C H (CH3) ] n-

Penton

- [CH2 -C (CH2CI) 2 -CH2 -0] n-

6. p o l y ( p i v a l o l a c t o n e ) - [ C H 2 - C (CH3) 2 - C 0 - 0 ] n7. L e x a n G E p o l y c a r b o n a t e - JR-O-CO-O] nR = - (C6H4) -C (CH3) 2 - (C6H4) -

a. H f - v a l u e L D P E : 103 J/g, Hf (max.) PE : 276 J / g i.e. x(c) -- 0 . 3 7 b. H f - v a l u e PP : 90 J/g, H f ( m a x . ) PP: 188 J / g i.e. x(c) - 0.48 c. T h e c r y s t a l l i n i t y v a l u e s of P P L a n d N y l o n 6 a r e e s t i m a t e d values.

276 Table 7.11 M a x i m u m molar water content values per structural group at 20~ I

measured molar water content value

molar water i content value Van ..,Krevelen ....... , .

-CH2-

5.8E-5

-CI

1.8E-3

-CH(C6H5)-

S t ructual

group

4.1E-3 ..

1.0E-2 ,,,

-0-

I -c0-

3.8E-2 ,

3.4E-3

-CH (CH3) -

1.0E-I ,

..,

3.0E-I . ,

5.5E-2

-. o - c o - o -

I ~.'S02-.,

(5.0B-s) I (~.0E-I) I (I.0E-4) 1 5.0E-3 _I

1.5E-1 7.3E-I Ill

i i

2.0E0 II

The values m e a s u r e d for the -CH2- group and the -CH(C6H5)group agree reasonably with the values of Van Krevelen. All the other new values are however clearly lower. The m a x i m u m e q u i l i b r i u m water saturation of a cured epoxy system (resin system A/HHPA, see 7.2.3) was calculated succesfully using these new molar water content values. As 'repeating unit' was recognised for this three dimensional network structure (see 7.2.4) : - [CH-O-CO- (C6HI0) -CO-O-CH2-CH-CH2 -O-R-O-CH2 ] nwhere R = -(C6H4)-C(CH3)-(C6H4)Using the measured molar water content values results in: 2 4 5 3

x x x x

-CO: 2x3.SE-2 -O: 4x1.0E-2 -CH2/CH9 5x5.8E-5 -C6H4/C6H10-: 3x4.1E-3

tool. mol. mol. tool.

water/per water/per water/per water/per

from Table 7.11

repeating repeating repeating repeating

unit unit unit unit

0.1286 mol. water/per repeating unit i.e. 0.1286x18 = 2.32 gram of water per 464 gram of resin. Thus 0.50 gram of water per 100 gram of resin or 0.50 %wt. The equilibrium water saturation measured of this epoxy resin casting sample was 0.90 %wt. Using the molar water content values reported by Van Krevelen ([1], Table 18.11 page 572), an equilibrium water concentration of 2.4 %wt. is calculated.

277 This r e s u l t seems to c o n f i r m t h e s e new, l o w e r e x p e r i m e n t a l m o l a r w a t e r c o n t e n t values. But it will be c l e a r that a l s o the r e s u l t s c a l c u l a t e d w i t h this small n u m b e r of n e w m o l a r w a t e r c o n t e n t v a l u e s c a n be o n l y i n d i c a t i v e ones. M o r e e x p e r i m e n t a l r e s u l t s like s h o w n in T a b l e 7.10 are n e c e s s a r y to o b t a i n r e a l l y f i r m m o l a r w a t e r c o n t e n t g r o u p data.

7.7 E s t i m a t i o n

of the k e y - p r o p e r t i e s

of a n e w p o l y m e r

C h a p t e r n i n e shows h o w the d i f f e r e n t T A t e c h n i q u e s f o c u s s e d on one p r o d u c t , c o n t r i b u t e to the c h a r a c t e r i s a t i o n of a n e w p o l y m e r i c system- a l i p h a t i c p o l y k e t o n e . T h i s p o l y k e t o n e is a perfectly alternating copolymer from carbon monoxide and e t h y l e n e (PK c o p o l y m e r ) . T h e k e y - p r o p e r t i e s of this n e w p o l y m e r i c s y s t e m w e r e c a l c u l a t e d as an e x a m p l e . Repeating

unit : - [CH2-CH2-CO] n-

1. The T g - v ~ l u e The m a i n c h a i n 6Ecoh. v a l u e s ~Ecoh. 6Ecoh.

-CH2-CO-

c o n s i s t s of s e q u e n t i a l C-atoms, f r o m T a b l e 7.1 h a v e to be used. 2x 4936 lx18405 Ecoh.

En, i = 3, u s i n g Tg(calc.),

= 9872 = 18405 = 28277

equation

K = 0.0145

7.1

hence

the n _> 5

J/tool. J/mol. J/mol. results

(28277/3)

in.

+ 120

= 257

2, The T m - v ~ A u e The linear mainchain makes Tin-value is then a c c o r d i n g Tm(calc.),

K -

(1.23 x 257)

PK c o p o l y m e r a g r o u p to e q u a t i o n 7.5: + 206

C polymer.

= 522 K

3 J The H f - v a l u e The v(max.) v(max.)

value

-- 83 x

is,

J/g

to e q u a t i o n

7.8:

to e q u a t i o n

7.9,

(2/3) 4 = 16.4

The H f - v a l u e is then, s m a l l e r than: Hf-value,

according

38.5 x log(16.4)

+ 115.5

equal

= 162 J / g

The

278 4. The Td. o-value The Yd, o value of PK copolymer is (2 x 8.3) + 19.7 = 36.3 K.kg/mol. According to equation 7.10 the Td, o temperature is then calculated asTd, o-value - (36.3 x 1000)/56 = 648 K 5. The m a x i m u m water saturatiop Using the new molar water content values results in: 2 x -CH21 x -CO-

from Table 7.11

: 2xS.8E-5 mol. water/repeating unit : 1x3.8E-2 mol. water/repeating unit 0.03812 mol. water per repeating unit i.e. 0.03812 x 18 - 0.686 gram of water per 56 gram of polymer.

Thus 1.23 gram of water per 100 gram of completely amorphous PK copolymer can be expected. Hence, the estimated maximum water saturation of the semi-crystalline PK copolymer as such (assuming that only the amorphous phase absorbs water) is about 0.5 %wt. 6. Comparison of the calculated and measur%d values A computer p r o g r a m was developed to perform the calculations necessary to obtain these key-propertles. A print-out of the results obtained with this program is shown in Figure 7.13. The values calculated above are shown again, but the program also performs a data base search and gives the experimental values, if available for comparison (values between brackets). The calculated Tg-value is the Tg-value of the completely amorphous polymer. Thus, the experimental Tg-value has to be equal or higher than the estimated value due to the presence of a considerable crystalline phase (PK copolymer, x(c) = 0.63, see 9.2.2). The agreement between the estimated and measured Tg values seems therefore not too bad. The agreement between both estimated crystalline phase values (the Tm- and Hf-value), and the experimentally obtained values is also not too bad. The estimated Td, o-temperature giving an indication of the polymers' thermal stability, holds only for polymers with the more or less 'simple' thermal degradation processes of chain depolymerisation and/or random decomposition. S. Shkolnik and E.D. Well [30] reported, however, that for non-stabilised PK copolymer a process of furan ring formation can start at temperatures of about 250 ~ Water, one of the reaction products, is coming free during this intramolecular

279 c y c l i s a t i o n process. This r e a c t i o n w a t e r will e v a p o r a t e d u r i n g a T G A scan and will be d e t e c t e d as a mass loss effect. Hence, the results of the TGA s e m i - s t a t i c Td, o - v a l u e d e t e r m i n a t i o n and that of the Td, o - v a l u e c a l c u l a t i o n can not be c o m p a r e d in this case. The c a l c u l a t e d e q u i l i b r i u m w a t e r s a t u r a t i o n of 1.23 %wt. h o l d s for c o m p l e t e l y amorphous PK c o p o l y m e r i.e. if x(c) = 0.63, the e q u i l i b r i u m water s a t u r a t i o n value of the s e m i - c r y s t a l l i n e p o l y m e r as such, b e c o m e s 0.50 %wt. The e q u i l i b r i u m w a t e r saturation, m e a s u r e d on sheet m a t e r i a l in d e m i n e r a l i s e d w a t e r at 20~ was 2.55 %wt. The c a l c u l a t e d w a t e r s a t u r a t i o n d e p e n d s in this case m a i n l y on the m o l a r w a t e r content v a l u e of the CO group used. The c a l c u l a t e d value is about five times too low and this illustrates a g a i n the n e c e s s i t y of l o o k i n g for b e t t e r d e f i n e d m o l a r water c o n t e n t values. These results show that the e x i s t i n g chemical s t r u c t u r e / p h y s i c a l p r o p e r t i e s r e l a t i o n s still n e e d to be c o n s i d e r a b l y i m p r o v e d to become real d e v e l o p m e n t 'tools '. I m p r o v e d m e a s u r i n g / c a l c u l a t i n g t e c h n i q u e s (like the m o d u l a t e d DSC and c o m p u t e r modelling) and m e a s u r e m e n t s on well d e f i n e d series of p o l y m e r s m i g h t result in a clear i m p r o v e m e n t of these c h e m i c a l s t r u c t u r e / p h y s i c a l p r o p e r t i e s relations.

FIGURE 7.13 Print-out of the results of the polymer keyproperties calculation program

*************************************************************************

***

EXSYS4, P o l y m e r K e y - p r o p e r t i e s

Repeating unit Polymer name

estimation

***

: -[ (CH2)2-CO-]n :

PK copolymer

Calculated Tg-value

-16

(4)

Estimated Tm-value Estimated Hf-value i.e. a semi-crystalline polymer

: <

249 162

(258)

Estimated Td, o-value i.e. processing window

: :

375 127

C C

( - )

%wt

( - )

Estimated Eq. water saturation : 1,225 (estimated EWS of the amorphous phase only) ( ) reference data

J/g

(152)

280 References I. D.W. van Krevelen" Properties of Polymers, third edition, Elsevier, Amsterdam, 1990. 2. J. Bicerano: Prediction of Polymer Properties, Marcel Dekker Inc., New York, 1993. 3. J.T. Seitz, J. of Appl. Pol. ~c., Vol. 49, (1993), p. 1331 1351. 4. J.M.G. Cowie: Polymers: Chemistry & Physics of Modern Materials, Int. Textbook Company Ltd., Aylesbury, Bucks., 1973. 5. U.T. Kreibich and H. Batzer, Die Angew. Makromol. Chemie, 83, (1979), p. 57 - 112. 6. R.F. Fedors, Pol. Eng. & Sc., 14, (1974), p. 147 - 154. 7. D.R. Wiff and M.S. Altieri, J. of Pol. Sc.: Polymer Physics Edition, Vol. 23, (1985), p. 1 1 6 5 - 1176. 8. A.J. Hopfinger et al., J. of Pol. Sc. : Polymer Physics Edition, Vol. 26, (1988), p. 2007 - 2028. 9. V. Bellenger et al., J. of Pol. Sc.: Polymer Physics Edition, Vol. 25, (1987), p. 1219 - 1234. 10. Yong-GU Won et al., J. of Pol. Sc. : Polymer Physics Edition, Vol. 29, (1991), p. 9 8 1 - 987. 11. Xinya Lu and Bingzheng Jiang, Polymer, Vol. 32, 3, (1991), p. 471 - 478. 12. R.F. Boyer, Macromolecules, 25, (1992), p. 5326 - 5330. 13. A. Eisenberg, J.E. Mark and W.W. Graessley: Physical properties of Polymers, American Chemical Society, Washington (DC), 1984. 14. J. Brandrup and E.H. Immergut: Polymer Handbook, Wiley, New York, third edition 1989. 15. S.Z.D. Cheng, Zong Quan Wu and B. Wunderlich, Macromolecules, 20, (1987), p. 2 8 0 2 - 2810. 16. M. Bosma et al., Macromolecules, 21, (1988), p. 1465. 17. K.E. Min and D.R. Paul, J. of Pol. Sc., Part B: Polymer Physics, 26, (1988), p. 1 0 2 1 - 1033. 18. A.F. Yee and S.A Smith, Macromolecules, 14, (1981), p. 54 64. 19. S.Z.D. Cheng and B. Wunderlich, Macromolecules, 20, (1987), p. 1 6 3 0 - 1637. 20. T.G. Fox and S. Loshaek, J. Polym. Sci., 15, (1955), p.371. 21. F. Rietsch, Polymer, 17, (1976), p. 859. 22. L. Banks and B. Ellis, Polymer, 23, (1982), p. 1466. 23. R.J. Young: Introduction to Polymers, Chapman and Hall, London (1983) . 24. R.F. Boyer, Rubber Chem. Techn., 36, (1963), p. 1303. 25. S.Z.D. Cheng and B. Wunderlich, Thermochimica Acta, i/~, (1988), p . 1 6 1 166. 26. Y. Nishio and R. St. J. Manley, Macromolecules, 21, (1988), p. 1270 - 1277. 27. S.Z.D. Cheng: Polymer Analysis and Characterisation, Editor H.G. Barth, J. Wiley, New York (1989). 28. N. Alberola el al., Eur. Polym. J., 28, (1992), p. 935 948. -

281 29. Modern Plastics Encyclopedia, McGraw-Hill, New York (1989) p. 659. 30. S. Shkolnik and E.D. Weil, Journal of Applied Polymer Science, Vol. 69, (1998), p. 1 6 9 1 - 1704.

TG-VALUES OF POLYMERS WITH DOUBLE BONDS IN THE MAIN CHAIN

CHAPTER 8

282 C H A P T E R 8: T g - V A L U E S OF P O L Y M E R S CHAIN AND Tg-VALUES OF NON-POLAR

W I T H D O U B L E B O N D S IN THE M A I N POLYMERS WITH SIDE-CHAINS

8.1 Introduction The presence of double bonds in the mainchain of a polymer increases the number of appearance forms of such a polymer. Well known examples of such systems are polybutadiene rubber (BR) and polyisoprene rubber (IR). BR for instance, can be polymerised into the following configurations:

CH2

CH--CH

CH2

\]n

1,4 cis-BR

CH2

/ CH-CH

CH2

1,4 trans-BR

\] n

CH2

/] n

I CH=CH2 1,2-BR

But, 1,2- or vinyl BR can be polymerised in the atactic, the syndiotactic or the isotactic form. Hence, five different configurations can be obtained by polymerisation reactions with butadiene (CH2=CH-CH=CH2) as monomer. The product obtained depends on the catalyst system used but is usually a mixture of 1,4 cis-, 1,4 trans- and atactic 1,2-BR. The commercial processes using Co-, Ni- or Ti-based catalyst systems, for instance, produce BR with a 1,4 cis-BR content higher than 90 %wt. But butyllithium initiated homopolymerisation of butadiene results in a product with 1,4 trans-BR contents up to 60 %wt. All these commercially produced BR systems are amorphous rubbers under atmospheric conditions. The Tg-value of these systems, depending on their structure, is described by the Gordon-Taylor relation, see Chapter 1. BR becomes a semicrystalline polymer under atmospheric conditions if the 1,4 trans-BR content is higher than about 70 %wt. or if a syndioor isotactic 1,2-BR phase is present. This is shown by the results of thermo-analytical measurements on experimental BR systems with a high trans content and with a high syndiotactic 1,2-BR content which are reported in this chapter. Moreover, the Tg-values of two series of IR samples containing 1,2- and 3,4-IR are used to determine the Tg/structure relation for non-polar polymers with side-chains. 8.2 Experimental

BR systems

8.2.1 BR with a hiuh 1.4 trans content Five BR samples with 1,4 trans-BR contents between 60 %wt. and 90 %wt. (as determined by FTIR) were prepared with an anionic, Ba containing catalyst system. These systems wer~ heated in the DSC from 20~ to 80~ to detect the presence of a possible

283 crystalline phase due to spontaneous crystallisation during storage under atmospheric conditions. Subsequently, the samples were cooled to -120~ and reheated to 80~ at a rate of 20~ The results of these measurements are collected in Table 8.1. Table 8.1 Results of DSC measurements content of 1,4 trans-BR . ,,,

sample number /ProPerty

1,4 trans, %wt. 1,4 cis, %wt. .......vinyl, %wt. scan I, amorph. or semi-cryst. Hf-va!u e, J/g scan 2, Tc-value,

. Hc-value,

scan 3, Tg-value, Te-value, ,

, ,, ,,,

rill

85.0 11.6 3.4

81.0 14.5 4.5

78.0 17.7 4.3

S . C .

J/g

37 72

25 22

7 23

-7 15

~ oC

-91 78

-92 65

-93 57

-93 43

90.0 6.5 3.5 -

on BR with a high

65.5 28.2 6.3

I' r

-96 I

These data show that spontaneous crystallisation during storage under atmospheric conditions occurs for 1,4 trans-BR contents higher than about 75%wt. The amorphous character of system E does not mean that a BR system with an 1,4 trans content of 65.5 %wt. stays amorphous under all circumstances. Comparison of the (scan 1) Hf-value with the (scan 2) Hc-value of the systems C and D shows that cooling to lower temperatures promotes the crystallisation process. A decrease of the cooling rate from 20"C/minute to 10"C/minute was already sufficient to obtain also a crystalline phase in system E, see below. Due to the shift of the baseline of the fusion endotherm the heat of fusion value of the samples 'as received' can only be indicated approximately. Figure 8.1 shows the recystallisation curves of the systems A/D. The three minima in the exothermic effect of sample A and the two minima in that of the systems B/D indicate the presence of a complex crystallisation/fusion process. The fusion process is for this reason characterised by its Te-value instead of a Tm-value. Figure 8.2 shows the fusion curves measured (at a rate of 20"C) for system E after cooling this sample at a rate of respectively 10~ 1~ and 0.1aC/minute. These three fusion curves clearly show how a lower cooling rate promotes the formation of crystallites melting at higher temperatures, i.e. larger and/or more perfect crystallites. Figure 8.3 finally, shows the strong 1,4 trans-BR content dependence of the fusion and recrystallisation temperatures.

284 ---3.0

3"0l

-f-f

.; ~_l-~LTf_.-.----~_

2.5

-2.5

2.0

.2.0 A

I.S

~,,

1.5 (81 X)

r I.O-

(85::D

(9BZ)

1.0

0 "11"

0.5-

0. 5 (

0.0 I -80. 0

)

trOno

I -50. 0

oon~ent

I -40. 0

I -30. 0

"1 -20. 0

Figure 8.1

I -10. 0

I ' 0. 0

I IIX 0

Temperature (~

I 20. 0

I 30. 0

I , 40. 0

~ -0.0 50, 0

W. de Jong

Crystallization curves of high trans content BR samples iO.O ooolin

g.O

eo~e,

do~

III A

C/min.|

-0. 0 A

7.0

e.0

.~0

7 v

~ ID "1"

4.0

3.0 2.0 1.0

o.o

-~oo.o

-?s.o

-so. o

Temperature (~

-2s. o

o. o

Figure 8.2 Fusion curves of BR rubber (trans content 65%) after crystallization at different cooling rates

285

Figure 8.3 The Te- and Tc- values of BR rubbers as a function of the trans-BR content +

Te-values

To-values

85 75 65 55 0

-(]

4-" 2 5 (P o

E15 5 -5 -15

-25

, ,

~ ............

Trans-BR

84 content,

92 %wt.

100

286 The small, but clearly detected, increase of the Tg(onset)value with an increasing 1,4 trans-BR content, confirms that the Tg-value of I00 %wt. 1,4 trans-BR is higher than that of I00 %wt. 1,4 cis BR. Tg-values of 1,4 cis- and 1,4 trans-BR of respectively -I09~ and -94~ obtained by extrapolation, were reported in Chapter 1.2.2. An 1,4 trans-BR content of 54 %wt. was however the highest trans content value of the results used for that calculation. The extrapolated Tg-value of 1,4 trans-BR shifts from -94"C to -92~ when taking into account these high trans content data. The extrapolated Tg-values of 1,4 cis- and 1,2-BR of respectively -I09~ and -16~ did not change significantly. 8.2.2 BR with a hiuh svndiotactic 1.2-BR content The thermal analytical properties of an experimental syndiotactic 1,2-BR were measured and compared with that of a commercial product RB 830 (ex-JSR). The results are collected in Table 8.2. Table 8.2 Results of DSC measurements on BR with a high content of syndiotactic 1,2-BR II

ffPl

sample

experim. sample

.Itype/pr~

scan i, fusion region, ~ Tm(1)-value , ~ xf.(%)-value

scan 2, Tc-value Hc-value

scan 3, Tg-value Tm(2) -value Hf (2) -value I

' 'l I,I

J/g

1 6 8 - 213 207 93

, ~ , J/g

173 61

, ~

27* 202 59

, J/g

* only detectable

830 (ex- JSR )

III

after quenching

50-

96 23

130

63 18 -13 101 18 I

in liquid nitrogen

The difference of more than 100~ in the Tm-values and the nearly four times higher heat of fusion indicate that the syndio-tactic 1,4-BR content of the experimental sample is considerably higher than that of the commercial sample. The extrapolated Tg-value of 100 % atactic 1,2-BR is -16~ The m e a s u r e d values of -13~ and 27oc need not to be in conflict with the extrapolated value. The presence of a small and a relative strong crystalline phase for respectively sample RB 830 and the experimental sample might cause a Tgvalue increase. The m a s s / t e m p e r a t u r e

curves of the commercial

sample measured

both in air and nitrogen are shown in Figure 8.4. Remarkable

287

I00. 5

f~'"--'" "~.

I00. 0

AIR

u . . . _ .

9g. 5

\,\

99,0

0 ~:

98. 5

,11

:12:840~3:C C

"~i\'~

g8. 0

97. 5 .

150. 0

t00.0

50. 0

.................... I

200. 0

250:0

300. 0

350. 0

400. 0

450. 0

Temperature (~

Figure 8.4 Mass/temperature curves of syndiotactic 1,2-polybutadiene RB830 (ex-JSR) I00. 20

1.860 min 29.900 min 99.934 Wt. % 100.121 Wt. %

T1 T2 Y1 Y2

I00. 15

Delta Y

I00. I0

0.187 Wt. %

;-~

~ o 100.05

~1~I00-00 ~ 99.95 99. 90 gg. s5 gg. 80

0.0

5. 0

'. . . . .

I 0. 0

15. 0

Time (minutes)

20. 0

25. 0

30. 0

Figure 8.5 Mass increase of a syndiotactic 1,2-polybutadiene (ex-JSR) sample during an isothermal TGA experiment at 240~ in air

288 is the small, sudden mass increase effect starting at 223~ during the measurement in air. We thought that this effect was caused by some cyclisation reaction of the BR and attempted to confirm that by additional Tg-, Tm- and Hf-value measurements. The mass increase of an RB 830 syndiotactic 1,2-BR sample was measured as a function of time at 240~ in an air atmosphere. About thirty minutes were necessary to obtain a mass increase of 0.19 %wt. (0.22 %wt. during the non-isothermal experiment), see Figure 8.5. This sample was cooled and then placed in the DSC. A crystalline phase with a Tm- and Hf-value of respectively 91~ and 23 J/g was detected; the Tg-value of the amorphous phase proved to be -13~ Hence, the Tg-, Tm- and Hf-values were not influenced at all by the samples' heat treatment. Even the strength of the glass-rubber transition effect (0.26 J/g."C) was not changed. Thus, the detected mass increase effect can not be explained by some cyclisation reaction of the BR. The experimental (high syndiotactic i, 2-BR content) sample was, subsequently also heated in air and in a nitrogen atmosphere in the TGA. Figure 8.6 shows the measured mass/temperature curves. This sample is first losing about 2 %wt. residual solvent but then again shows the mass increase effect during heating in air. This effect proved to be stronger than that measured for the RB 830 sample: onset mass increase effect, ~ total mass increase , %wt. Hf-value , J/g

exp.

sample 211 1.05 93

RB 830 223 0.22 23

The mass increase effect correlates roughly with the heat of fusion. This seems to confirm that this effect occurs only in the syndiotactic phase of these systems. However, what really is happening with syndiotactic 1,2-BR during heating in the presence of oxygen remains still an unanswered question. 8.3 Experimental

IR systems

Isoprene CH2-C(CH3)-CH=CH2 can, just like BR, be polymerised as cis 1,4-IR (natural rubber) or trans 1,4-IR. But 1,2 and 3,4 polymerisation is also possible. CH3 - [CH2 -~=CH- CH2 ]n-

1,4-IR,

cis/trans

3 -[CH2- ~H]n=CH2 i, 2-IR

-[CH2-QH]n~=CH2 CH3 3,4-IR

The 1,2- and 3,4-IR can in theory be polymerised in the atactic, the syndiotactic and in the isotactic form. Hence eight different IR modifications might be possible. The Tg-value of a mixture of cis 1,4-IR and (atactic) 1,2- and

Perkin-Eimer 7 Series Thermal Analysis System 100. 0

IOC. 0

gg. 5

AIR

gg. 0

o~ g8.5

.~ gs. 0 g?. 5

gg. 0

NITROGEN

g8. 5

g8. 0

gT. 5 g7.0

g?. 0

g5. 5

gs.o -,,

51i 0

i .... I . . . . . . . . . I........................ ~.............................. i ........ 300. 0 100.0 150. 0 200.0 250. 0

350. 0

Figure 8.6 Temperature(~ Mass/temperature curves of syndiotactic 1,2-BR-polybutadiene

k I

4O0. 0

tlg~ - g6. o 45O. 0

RATE 1" 1.0~

290 3,4-IR is described by the G o r d o n - T a y l o r to: Tg-value, where:

K = wl.Tg(l;4)

relation according

+ w2.kl.Tg(l.2) ยง w3.k2.Tq(3.4) wl + kl.w2 + k2.w3

8.1

wl - cis 1,4-IR fraction, w2 = 1,2-IR fraction, w3 = 3,4-IR fraction and wl + w2 + w3 = 1.0

The DSC T g ( o n s e t ) - v a l u e of cis 1,4-IR is 205 K. The Tg-values of 1,2- and 3,4-IR and the constants kl and k2 were, subsequently, d e t e r m i n e d by extrapolation. The Tg-values of a series of samples containing atactic 3,4IR, cis 1,4-IR and only a small amount (< 3 %wt.) of 1,2-IR were e x t r a p o l a t e d to I00 %wt. 3,4-IR to estimate the Tg-value of this material. The m e a s u r e d DSC T g ( o n s e t ) - v a l u e s are listed bel ow: sample code A B C D E(1) E(2)

3,4-IR weight fraction 0.775 0.76 0.63 0.54 0.47 0.47

Tg-value 273 271 254 244 235 234

K ( 0~ K (-2~ K (-19~ K (-29~ K (-38~ K (-39~

The Tg-values of these samples are plotted as a function of their 3,4-IR content in Figure 8.7 and fit a straight line d e s c r i b e d by: Tg-value,

K = 125.4.w(3,4)

+ 175.6

8.2

The estimated DSC T g ( o n s e t ) - v a l u e calculated by extrapolation to w(3,4) = 1.0 is 301 K. Hence, the T g ( o n s e t ) - v a l u e of 1,2-IR and the constants kl and k2 were still to estimate. A series of six s t y r e n e / i s o p r e n e / s t y r e n e sequential blockcopolymers were analysed. The styrene content of these systems was constant (about 14 %wt.) but the cis 1,4-IR, the 3,4-IR and the 1,2-IR contents varied. The Tg-value of the IR (rubber) phases of these samples is not or hardly influenced by the polystyrene phases. Thus, these samples could be used to estimate the lacking values for kl, k2 and the Tg of 1,2IR. The measured Tg-values of these systems are listed in Table 8.3. The Tg-values of 1,2-IR and 3,4-IR are expected to differ not more than a few degrees. The samples 512 and D515 can therefore considered as samples with a cis 1,4-IR phase and a 3,4-IR phase. Equation 8.1 reduces then to.

Figure 8.7 DSC Tg(onset)-value of IR as a function of the 3,4-1R content

320

Wood plot for IR samples of similar 3,4/1,2 ratio 300

::s

302

~280 260

> 284 i

I-- 240 (9 GO t:3 220

r 03 {.....

200

o 266 F-

,,,

[Tg-Tg(1,4)][(1-w(c))/w(c)]

9 oo G 248

230 0.00

0.10

0.20

0.2,0

0.40

i/f

. i

0.50

3,4-1R

0.60

fraction

l...

0.70

0.80

0.90

1.00

292 Tg-value,

K = 205.wl wl

+ 301.k2.w3 + k2 .w3

8.3

where:

w3 = 0.106 (D512) r e s u l t s in a k2 v a l u e w3 = 0.208 (D515) r e s u l t s in a k2 v a l u e an a v e r a g e v a l u e of 0.41 w i l l be u s e d for k2.

Table

8.3 C o m p o s i t i o n

and Tg-values

0.894

D515

0.792

D513

0.596

D517

0.348

0.119

D514

0.216

0.137

0.161

0.176

3,4 fraction

Tg-value K

,,,

D512

, ,,

,,"

1,2 fraction

i.e.

systems

II I

1,4 fraction ,

of SIS

of 0.367 of 0.443

0.021

,,,

209

0.036

0.172

0.047

0.357

228

0.533

246

,, ,

* determined

0.085

,,,

0.647

fill

0.663 I

215

...

,,,,,,

263 265

by FTIR

T h e s a m p l e s D512, D514, D515, D516 a n d D 5 1 7 can c o n s i d e r e d to be a c o p o l y m e r of cis 1 , 4 - I R and a 1 , 2 / 3 , 4 - I R c o p o l y m e r for w h i c h holds- w(3,4) - 4 . w ( 1 , 2 ) . E q u a t i o n 8.1 can than be w r i t t e n as : Tg-value, where:

K = Tg(1.4)

w(c) Tg(c)

= w2

+ [k".Tg(c) - Tu(1.4)]_ .w(c) i - [I - k"] .w(c)

+ w3

= kl.Tg(l.2) + 4.k2.Tg(3.4) kl + 4 .k2

8.3 can be w r i t t e n

Tg-value,

K - Tg(c)

8.5 8.6

k" -- (kl + 4 . k 2 ) / 5 Equation

8.4

as:

[Tg - T g { 1 . 4 ) ] . [1 - w(c)1 k" .w(c)

8.7

T h e p l o t of T g as a f u n c t i o n of [Tg - T g ( l , 4 ) ] . [i - w ( c ) ] / w ( c ) , see the f i g u r e i n s e r t e d in F i g u r e 8.7, is g i v i n g a Tg(c) v a l u e of 299.3 K and k" v a l u e of 0.415. S u b s t i t u t i o n of the k n o w n v a l u e s for Tg(c), T g ( 3 , 4 ) , k" and k2 in the e q u a t i o n s 8.5 and 8.6 r e s u l t s in Tg(1,2) = 293 K and kl = 0.44. Thus, for IR holds : Tg(I.4)-IR Tg(I,2)-IR Tg(3,4)-IR

= 205 K - 293 K = 301 K

(-68~ ( 20~ ( 28"C}

kl = 0.44 k2 = 0.41

293 Equation

8.1 can now be written as-

Tg-value

IR, K = 205.w(I,4) + 129.w(1.2) + 123.w(3.4) w(l,4) + 0.44w(I,2) + 0.41w(3,4)

8.8

The subsequently calculated values are compared with the measured values in Table 8.4: Table 8.4 Measured and calculated Tg-values copolymers Ir

llr

T~(c) -Tg (e)

code

T~ (calc.)

T~ (exp.)

D512

209.4

209

D515

214.2

215

-0.8

D513

225.6

228

-2.4

D517

246.0

D514

261.3

D516

269.0

, ,,,,,

,,,

I n'

I~I

of SIS block

,,,,

265

+0.4 ,

+1.0

245 263

-1.7

, ,,

+4.0 I

........... M .

The fit between the calculated a n d the measured Tg-values acceptable. 8.4

A Tg/structure correlation w i t h side-chains

for non-polar polymer systems

The difference between the calculated Tg-values of 1,2-IR and 3,4-IR proved to be only eight degrees C. This relative small difference prompted us to look for a separate Tg/structure correlation to confirm this calculated difference. The mobility of polymer mainchains is mainly determined by the barrier to rotation around the backbone carbon-carbon bonds. In polymer systems without polar groups and/or hydrogen bond effects, this barrier to rotation is primarily determined by the size of side-groups. Hence some correlation was e x p e c t e d to exist between the Tg-value increase due to a side-group addition and the increase in the molecular weight of the repeating unit. The difference in Tg-value between 1,2-IR and 1,2-BR, example, is 36 K"

1,2-IR:

Tg = 293 K

1,2-BR:

for

Tg = 257 K

This is caused by the presence of the -CH3 side-group 1,2-IR. Thus, a molecular weight increase of 15 gram

in the

294 Table

8.5

polymer

Tg-value increase group addit ion

name/structure

linear

polymers

due

side-

Tgvalue, K

mol. weight rep. u n i t

Tg-value increase, K

fract. m o l . wt. increase

- [C H 2 - C H - C H - CH2 ] n- [CH2 -C (CH3) = C H - C H 2 ] ncis 1,4-BR/cis 1,4-IR

163 205

54 68

0.28

trans trans

181 220

54 68

0.28

1,4-BR 1,4-IR

i, 2 - B s

- [ c H 2 - q s ] n-

257

1,2-IR

-[CH2-C(CH3)]n-

293

0.28

195 252

28 42

0.56

195 301

28 68

106

1.52

195 307

28 70

112

1.59

195 378

28 104

183

2.85

378 409

104 118

0.15

PE - [ C H 2 - C H 2 ] ni, 2 - B R - [CH2 - ~H] nCH-CH2

195 257

28 54

1.00

PE PB-I

- [ C H 2 - C H 2 ] n- [CH2-CH] n t.2-cH3

195 236

28 56

1.07

- [C H 2 - C H 2 ] n -

195 227

28 70

1.59

PE PP

CH=CH2

--c~2

- [ C H 2 - C H 2 ] n- [ C H 2 - C H (CH3) ] n-

PE 3,4-IR

- [C H 2 - CH2 ] n-[CH2-~H]n-

~-cH2 CH3

3-methylbut ene -1 PE PS

- [CH2 -CH2 ] n[CH2-~H]3 nCH3

- [CH2- CH2 ] n- [ C H 2 - C H (C6H5) ] n -

PS - [CH2-CH2] npoly-alpha-methylstyrene ************************

295 influences a repeating unit molecular weight of 53 grams i.e. a repeating unit fractional molecular weight increase of 15/53 = 0.28 is resulting in a Tg-value increase of 36 K. The Tg-value differences and the repeating unit fractional molecular weight increases were determined in this way for eight different systems. The results are listed in Table 8.5 and plotted in Figure 8.8. A linear relation was found for these non-polar polymeric systems: Tg increase = 55.7 x

(fractional mol.wt,

increase)

+ 23.4

8.9

The fit between with the calculated Tg-values using equation 8.9 and the experimental values is three degrees or better. The Tg-value differences of 1,2-BR, polybutene-1 and polypentene-1 with polyethylene are also plotted in Figure 8.8. in chapter 7.2 it was discussed already that linear, alifatic side-chains are acting as plasticisers, causing a Tgvalue decrease in stead of a Tg-value increase. The three separate data points in Figure 8.8 clearly illustrate that the plasticising action of a linear, alifatic side-chain starts already for a -CH=CH2 side-chain (17 K too low) and a -CH2-CH3 sidechain (42 K too low respectively) and increases with increasing side-group length (-CH2-CH2-CH3, 80 K too low).

296

Figure 8.8 Tg-value increase of linear polymers due to side-group addition /X

1,2-BR

PB- 1

PP-

200 180

dTg = 55.4 x (fractional mol.wt. Increase) + 2 3 . 4 Rval. = 0 . 9 9 9 3

160 140

120 (1) 0

c 100 (b

:3 80 65 > I

I--

ยง

20 OI

0.oo

0.60

......

1.20

Fractional

_.1,

1.80

2.40

mol.wt,

increase

3.00

CHARACTERISATION OF POLYKETONE POLYMER SYSTEMS BY THERMAL ANALYSIS TECHNIQUES CHAPTER 9

297 CHAPTER 9: C H A R A ~ R I S A T I O N OF POLYKETONE BY TRERMAL ANALYSIS TECHNIQUES

POLYMER SYSTEMS

9.1 Introduction A unique catalyst invention at the Shell Research Laboratories in Amsterdam in 1982 [I, 2, 3] made it possible to polymerise carbon monoxide and alpha-olefins such as ethylene into linear, perfectly alternating structures. This led directly to the development of a new class of thermoplastic polymers known as aliphatic polyketones (PK), which Shell is commercialising under the trademark CARILON. Aliphatic polyketones based on carbon monoxide and ethylene are called PK copolymer, while the first commercialised grades based on carbon monoxide, ethylene and a small amount of propylene are called PK terpolymer. It was exciting to follow the development of this polymer from the very first beginning on the laboratory bench up to a product ready to enter the engineering polymers market. This commercial significance also makes it a nice example to illustrate how different TA techniques (DSC, DMA, TMA and thermo electrometric analysis) focussed on one product contribute to the characterisation of such a new polymeric system. All data given are measured on non-stabilised, development phase PK co- and terpolymer samples made more than five years ago. Hence, these data can be different compared with those of the present, further developed, commercial grades. 9.2 Investigation of the crystalline phase of PK co- and terpolymers by DSC 9.2.1 PK CoDolvmer and PK terDolvmer The product-obtained after washing and drying of the reactor product is a white, semi-crystalline powder soluble in only very few exotic solvents i.e. hexafluoro-isopropanol (HFIPA) and meta-cresol. The presence of a crystalline phase in PK copolymer, as indicated by X-ray diffraction (XRD) analysis, is confirmed by a clear fusion effect measured during heating the sample in the DSC showing a Tm-value of about 258 C and a heat of fusion effect (Hfl-value) of about 152 J/g. It is well-known that the occurrence of chain defects, in the form of for example small methylene sidegroups, could reduce this Tm-value [4]. This offered the possibility to reduce the relative high processing temperature of PK copolymers. The effect of addition of small amounts of propylene to the carbon monoxide/ ethylene mixture on the Tm-value is shown in Figure 9.1. A nearly linear decrease of the Tm-value as a function of the weight percentage of C3 was found for propylene concentrations between 0 and about 15 %wt. i.e. for the Tmvalue holds:

298

Figure 9.1 Tm-value depression of PK copolymer due to C3 addition

550 54O

. . . . . . . . . . . . .

-\Tm, K

-5.9

(%wt.

C3)

529

530520

50O

Tm(calc.) + 5K

E I-- 4 9 0

T m ( c a l c . ) - 5 K .-

470

460

450

, ,~ 0

C3-content,

10 %wt.

299 PK t e r p o l y m e r Tm(calc.),

(K) - 529

The scatter in the w i t h e q u a t i o n p r o v e d to be + 5 K.

- (5.9 x C3,

%wt.)

9.1

9.1 c a l c u l a t e d T m v a l u e s

9.2.2 The Tm(o)- and Hf (max) -values of PK CoDol_vmer T h r e e e x t r a p o l a t i o n m e t h o d s are, a c c o r d i n g to C h e n g [5], a v a i l a b l e to d e t e r m i n e the e q u i l i b r i u m m e l t i n g t e m p e r a t u r e [Tm (o) -value] of a polymer: data for small m o l e c u l e s (low m o l e c u l a r m a s s homologs) are e x t r a p o l a t e d to m a c r o m o l e c u l e s , - m e l t i n g t e m p e r a t u r e s are e x t r a p o l a t e d as a f u n c t i o n of the c r y s t a l l i s a t i o n t e m p e r a t u r e s and, - small crystal m e l t i n g p o i n t s are e x t r a p o l a t e d to large crystal m e l t i n g points. -

The first m e t h o d m e n t i o n e d was u s e d to d e t e r m i n e the Tm(o)v a l u e of PK copolymer. E x t r a p o l a t i o n of the fusion t e m p e r a t u r e s of low + m o l e c u l a r mass h o m o l o g s is p o s s i b l e u s i n g the r e l a t i o n s h i p d e r i v e d by H a y [6] b e t w e e n the T m - v a l u e of o l i g o m e r s and t h e i r d e g r e e of p o l y m e r i s a t i o n (n): Tin-value,

K =

(-2.R. [Tm(o)]z/Hf) . (Ln[n])/n + Tin(o)

9.2

The T m - v a l u e s of a series of o l i g o m e r s are p l o t t e d as a f u n c t i o n of (Ln[n])/n, e x t r a p o l a t i o n of (Ln[n])/n to zero results in a v a l u e for Tm(o). Five o l i g o m e r samples, w i t h the chemical s t r u c t u r e : CH3 -CH2 -C0- (CH2 -CH2 - CO) x- CH2 - CH3 were s y n t h e s i s e d w i t h the x v a l u e s 2, 3, 5, 6 and 8. The d e g r e e of p o l y m e r i s a t i o n gives the n u m b e r of basic m o n o m e r i c units in a m a c r o m o l e c u l e i.e. for x = 2, for e x a m p l e , n = 7. The results of the f u s i o n m e a s u r e m e n t s on these o l i g o m e r samples are l i s t e d belowTable

...........

9.1 R e s u l t s of D S C fusion m e a s u r e m e n t s on PK copolymer, e x p e r i m e n t a l o l i g o m e r samples J,,rl

n -

value

185

116

192

156

200

170

217

19 i,

190

Hfvalue, j / g

15 i

Tmvalue, oC.

222 I,L

â&#x20AC;˘

300 The Tm-values of these samples increase, as expected with increasing values for x. These Tm-values are plotted as a function of (Ln[n])/n in Figure 9.2. Linear extrapolation to (Ln[n])/n is zero results in a Tm(o)-value of 599 K. Subsequently, using the slope value of - 868.8 K and the Tm(o)-value of 599 K, a Hf(max.)-value of 246 J/g was calculated. The crystallinity, the x(c)-value, of a p o l y m e r is usually d e t e r m i n e d by X-Ray Diffraction (XRD) analysis. The ratio of the integrated crystalline intensities and the sum of the integrated amorphous and crystalline intensities is giving the x(c)-value. The XRD x(c)-values and the DSC Hf-values were m e a s u r e d for a series of PK copolymer samples. This permitted calculation of the Hf-value of completely crystalline PK copolymer, see Table 9.2 : Table 9.2 Results of XRD/DSC crystallinity measurements on PK copolymer samples I

III

0.65

157

0.66

144

0.58 ,

242

IUl

146 I

218

,,,

144

0.59

Hf-value, x(c) - 1.0 J/g

Hf-value, DSC J/g

x(c) -value (XRD)

_ _

IIIIII

252 .

244

The by XRD determined average Hf-value for 100% crystalline PK copolymer is thus 239 J/g. This value r e a s o n a b l y agrees with the value of 246 J/g as determined by e x t r a p o l a t i o n of the oligomer results. Hence, the following basic properties for PK copolymer were obtained: PK coDolvmer Tm (o) -value Tin-value (DSC, 20~ --

Hf (max.) AHf ASf ASf (bond) Hf-value (DSC, 20~ i.e. crystallinity x(c)

= 599 -- 531

(326~ (258~

_+ 1

(n = II)

, J/g - 242 , kJ/mol - 13.6

, ,

J/mol J/mol

J/g

22.6

7.5

152

0.63 _+ 0.03

II)

Lommerts et al. [7] report a heat of fusion value between 215 and 330 J/g (12.0 kJ/mol and 18.5 kJ/mol) also based on extrapolation of Tm-values of PK oligomers. They are using,

301

Figure 9.2 Ln(n)/n - Tm relation for PK copolymer oligomer systems

620

590 560 0

d~ "(3

530

500

:::3 >

470

F--

0 03 a

440 410

38O 350 0.00

0.05

O. 10

O. 1 5 Ln(n)/n

0.20

0.25

0.3

302 however, the Tin-value of a highly drawn fibre sample (i.e. 551 K) as Tm(o)-value. Allen et al. [8] report a heat of fusion value of 224 J/g (12.5 kJ/mol) for completely crystalline PK copolymer based on PK copolymer/ethylene glycol melting point depression measurements. The crystallinity of a series of PK terpolymers was also determined by XRD and DSC to determine the Hf (max.)-value. following basic values for a PK terpolymer system were obtained: PK terDolvmer system Tm-value-(DSC, 20~ Hf (max.) Hf-value (DSC, 20~ i.e. crystallinity x(c)

- 493

, J/g

= 207

J/g

111

(220~

_+ 3

0.54 _+ 0.05

The

(n = I0)

10)

9.2.3 AiDha- and beta-crvstallinitv in PK CoDolvmer The PK copolymer chains can crystailise under certain circumstances into two different modifications i.e. the u-form and the E-form. Lommerts et al. [7] deduced from the observed X-ray reflections an orthorhombic unit cell for the u-form with a = 6.91 (2) ~, b = 5.12 (2) ~ and c = 7.60 (3) ~; the calculated crystalline density is 1.383 g/cm3. Chatani [9] reported for the E-form a, b a n d c values of respectively 7.97, 4.76 and 7.57 ~; the calculated crystalline density is 1.297 g/cm3. All carbonyl dipoles in the u-form crystallites are pointing in about the same direction at equal height z. The dipoles of the carbonyl groups of the corner and the center chains are pointing in different directions for E-form crystallites. This difference makes the packing of the u - f o r m v e r y effective. Lommerts et al. [7] report a cross-sectional area of the unit cell perpendicular to the fibre axis of 35.2 ~ while this value increases to 37.9 ~2 for the E-form material. The u-phase crystallites are stable up to maximally 120~ The u-form crystallinity changes into E-form crystallinity at higher temperatures. This u/E crystal transition is indicated as the Tm'-value of PK copolymer. The fusion effect at about 258~ which is important for the processing of the polymer, is thus fusion of E-form material only. Polyketone containing mainly u-form crystallinity at room temperature was reported by Lommerts et al. [7] for drawn fibre samples. Both Lommerts and Klop [7, 10] concluded that low molecular weight as-polymerised oligomers crystallise at least partly in the u modification whereas virgin high molecular weight PK copolymer (polymerised under the 'standard' conditions described in the patents [1, 3]) crystallises almost completely in the E modification with a

303 smaller crystalline perfection. Experiments with different polymerisation liquids showed, however, that under certain circumstances PK copolymers are obtained containing both uand K-crystallinity. K-Crystal phase material also changes (partly) into u-crystal phase material due to high pressure and/or shear forces at 20~ Moreover, a proper annealing procedure proved to promote the presence of u-phase crystallinity in virgin high molecular weight PK copolymer Table 9.3 Effect of annealing at T(isothermal) of a PK copolymer sample on the temperature location (Tm' -value) and the strength (Hct-value) of the u/E crystal transition ,,,,

,,,,,

III

Tin' -value,

T- isothermal* oc 230

J/g

240

108

245

115

....

250

120

, i

255

120

260

,, .....

. . . . .

,,,, J,

265

,,......

I,,I!

Hct-value,

,,,

4 I

, I

* DSC procedure- heating from 20~ to T-isothermal, sample six minutes at T-isothermal, followed by cooling to 20~ heating from 20~ up to 275~ heating/cooling rates 20~ samples, see Table 9.3. The nummerical values in Table 9.3 and the transition effects in Figure 9.3 clearly show that both the temperature location and the strength of the u/E crystal transition go through a distinct maximum. One minute heating at 250~176 proved to be sufficient already to obtain a maximum amount of u-crystallinity in an originally only Ec~istallinity containing powder sample. Figure 9.4A shows the XRD spectrum of the non-thermally treated powder sample (only E-crystallinity). The XRD spectrum in Figure 9.4B is measured on the same sample after a thermal treatment of five minutes at 250~ Now, clear u-crystallinity reflections are present; the u/K ratio of this sample proved to be about 70/30. Thus, next to polymerisation liquid induced and pressure/shear forces induced u-crystallinity, thermally induced ucrystallinity is possible. This third method proved to offer PK copolymer samples with the highest u/K crystallinity ratio's.

304

o.,o ,SC'h..,.,,,g.:,.

0.55

illi\~'r. 255c

Ctmtnute

0.50 O. 45

~__

o.lo

= o.,, t

,,,..,.-"

t -

" ....

50.0

""""~"'*"~"-~"~"~1

_~,~.,,'-

o.~-L . . . . . . . . . . . . . . . .

245C

__..-

0 t0 ~

0.00

.//

",,.

-\,

~;-':-;: ....... --.~., - z3.C .....................

70 0

go.o

"~'~l"""'~"~"i'~"='~'l

"""'"-"-"~"'~''*'"~"'~'~

iiO 0

i30.0

i50 0

Temperature (~ 0.50 DSC

0.45

heating

-~/'"

==can

Clmtnute

14.

0.30 o~ ~

0 20

i, \

._...t"

0 15

255C

035

Ta "

0 40

"X.

....................

26OC

"'~""

.....

0.t0 0.05

1I , . ~ . . . . ,..,,,. - - -

00050 0

.~.

-~*

,~,Ta

~-"

I 70 0

265C ~*'~ ~ . ~ * ~ . . ~ . .

i g0.0

Temperature

it0 0

,,..~ ...... #.,.....~. ~ . p .,~,. ~

I t30 0

.~,..~_

..e~ - .,~

i50 0

Figure 9.3 The alpha/beta crystal transition of a virgin PK copolymer sample after annealing (6 minutes) at the indicated temperatures Ta

305

1.20 1.08 0.96 0.84

Figure 9.4B Thermallytreated sample alpha and beta (70/30) crystallinity

0.72 O. 60 O. 48 0.36 0.24 0.12

10.0

20.0

I .00

30 0

50.0

40 0

i,,

60.0

0.90 0.80 0.70

0.60

Figure 9.4A only beta crystallinity

0.50 0.40

ii II

0.30 0.20

I I

non-thermally treatedsample

O.iO

10.0

20.0

30.0

40.0

50.0

Figure 9.4: XRD spectra of PK copolymer samples

60.0

306 Polymerisation liquid induced and pressure/shear forces induced u-crystallinity effects proved to be irreversible (DSC) or partly irreversible (XRD) after heating through their u/g-crystal transition. Additional DSC experiments were performed to investigate this aspect for the thermally induced u-crystallinity. A sample with a thermally induced u-crystallinity phase was heated in the DSC to respectively 140~ 250"C, 270~ and 280~ The relative strong u/g-crystal transition proved to be completely reversible (see Figure 9.5) after heating to temperatures between 140~ and 250"C. First after heating to 270"C, the u/E-crystal transition is strongly reduced and is shifted to lower temperatures. The results in Figure 9.5 also show the g/u crystal transition at about 50~ during the cooling scans from 140~ and from 250~ down to 20~ The recrystallisation effects become small i.e. non-detectable by DSC, after heating up to temperatures 9 250~ The optimum u-crystallinlty promoting annealing temperatures proved to be 250"C/255~ (Table 9.3) i.e. in the melting region of the g-phase. Thus, the E-phase crystals might also be influenced by this annealing procedure. The results of fusion experiments showed that both the Tm-value and the Hfvalue of the g-crystal phase increase due to the annealing procedure. The following average values were measured for the same PK copolymer powder sample: Tm-value, oc non-treated powder samples: 258 â&#x20AC;˘ 1 (DSC first heating scan) therm, pretreated samples: (u/g transition at 120~

264 _+ 3

Hf-value, J/g 152 + 6 166 + 4

(n = 11) (n =

These results indicate that the perfection or the size of a part of the g-crystallites is improved/increased during the annealing procedure at 250~176 Only the g-crystallites with a certain degree of perfection or a certain minimum size are able, subsequently, to transform from a g-structure into the u-structure during cooling to temperatures below 50~

307 Io el I1

~,,

I.i.

9 9

lip,

~---

ee.

it.

t40

tl.

loin

I.I

.J.

I tno

,,~,

,~,

,.~o

Temperature (~

)lit

I.t. IO,

)

II. t.4,

II,

,.,.

'*~

el.

I 258

(--.,

3: "i

"'~'""

o.,

IO t .

.,,~.

,,,;o

.."

0.4

::J,~ '=.

" "~

,do

.,,

Temperature (~

=.,

I .....

~' -

s.~ / tl~ I n I

.--"

200

"'1

----"

I.I

* 9 scln Ol"j

}

" ' L

=oo w,,.,o

1.1"

I.l t / hi

I ~'

Nee

--"

"~ "l

I.I]

% J; ........ k Itoe

"F,,,...._ "1"

;

Temperature (~

I !

COO 1 I n 9 " , ~ ,

s~lln , 2. 9 ,4.

I I I

coo I I n o I

! -

ItO

~ " Mill

" ' 1i IIII

Pill

--i

~ ~l~O

Figure 9.5 Temperature (~ Results of subsequent DSC heating/cooling scans on a virgin PK copolymer sample

308 9.2.4 Alpha- and beta-cry_s~llinity in PK GQpol_vmer ~fter a common processinu procedure During the most frequently used processing procedures i.e. injection/compression moulding, the polymer is first completely fused. That implies for PK copolymer that the Kcrystalline phase first completely is destroyed, before development of any u-crystallinity due to certain annealing conditions can be expected. This fusion/recrystallisation process determines the degree of perfection of the E-crystalline phase formed and this (as we saw above) partly determines the efficiency of an annealing procedure ment to promote u-crystallinity in such an article. The extent of such an effect was first investigated by a series of DSC experiments, see Table 9.4. The experimental results in Table 9.4 indeed show that the optimum annealing temperature shifts from 250~ for a non-fused powder sample to about 225~ for a first sample. Annealing during less than one minute at 250"C/255oc was already sufficient for the formation of an u-crystalline phase with a maximum Tm'- and Hct- value in a non-fused powder sample. This time increased for the fused samples from less than one minute into about six minutes. Moreover, the maximum Tm'-value reached now proved to be 106~ instead of the 120~ measured for the powder sample. This illustrated that after recrystallisation from the melt either less perfect Ecrystallites or smaller E-crystallites are obtained than after crystallisation from a liquid. The annealing process is clearly not able to eliminate this difference completely. _

Table 9.4 Effect of annealing at T(isothermal) of PK copolymer on the temperature location (Tm'-value) and strength (Hct-value) of the u/E-crystal transition (totally fused sample series) ,

Tin' -value, oc

Hct-value,

180

200

210

215

I00

220

103

225

106

T(isoth. ) * oc ,,

....

;

230 240 250 I

J'/g ,

309 Table 9.4 continued. * DSC procedure- heating from 20~ to 275~ cooling to T(isothermal), sample six minutes at T(isothermal) followed by cooling to 20oc, heating from 20~ to 275~ heating/cooling rates 20~ Subsequently, the effect of fusion before annealing was investigated using a series of compression moulded samples. First a one millimeter thick sample sheet was prepared by compression moulding during 2.5 minutes at 280~ followed by cooling as fast as possible (water-cooled mould) to 20~ Two other sample sheets were prepared in the same way, but first placed in a second mould heated at 240~ during respectively 6 minutes and i0 minutes before cooling to 20~ too. These samples were analysed subsequently, see Table 9.5. Table 9.5 Introduction of u-crystallinity in compression moulded PK copolymer sheet material by an annealing procedure -

measured property . ,

u-phase Tm' -value, Hct-value, u/E ratio, estimated

J/g

E-phase iTin-value, oC Hf-value, J/g

x(c)

density,

g/cm3

die1. constant tan delta 9 JL

, I

llrll

PK copolymer virgin sample n ~

n.p.

o/~oo

III

~,.,

compr. moulded 2.5 rain. , 280" C

2.5 min.

280~

6 min. 240oc

106 5.1

n o p .

n.p.

2.5 min. 280~ + 10 min. 240oc 112 8.3

o/loo

25175

40160

258 152 0.63

255 111 0.46

n.d.

253 119 n.d.

251 116 n.d.

1.267

1.284

1.299

n.d. n.d.

5.30 0.0171

5.08 0.0150

4.99 0.0127

[II

n.p. -- not present, n.d. = not determined, properties measured at 22~ dielectric properties measured at 1 kHz. Lo~nerts [7] reports for u-phase PK copolymer a density of 1.383 g/cm3 and for E-phase PK copolymer a density of 1.297 g/cm3. Besides, he assumed a density value of 1.21 g/cm3 for

310 the PK copolymer amorphous phase material. The compression moulded reference sample (i.e. 2.5 min./280~ consisted next to an amorphous phase of an fully E-modification crystalline phase. The crystallinity of such a polymeric system can be calculated according tox(c)

= [p - p ( a ) ] / [ p ( c )

where:

- p(a)]

9.3

x(c) p

= crystalline fraction i.e. 0.46, = sample density i.e. 1. 267, p(c) - density of E-crystalline phase i.e. 1.297, p(a) = density of amorphous PK copolymer,

Using the mentioned values, an amorphous phase density of 1.241 g/cm3 was calculated, which seems to be an acceptable value. (The x(c) values of the virgin powder sample and the sample after compression moulding at 280~ (2.5 minutes) can be calculated using the Hf(max.)-value of 242 J/g (see 9.2.2) because both the DSC and the X R D m e a s u r e m e n t were performed on PK copolymer with only an amorphous and a E-crystalline phase. This XRD value does not hold, however, for PK copolymer with both an u-crystalline and a E-crystalline phase). The measured density values increase due to the annealing procedure and this increase agrees with the increase of the estimated u/E-ratio. Both the dielectric constant and the dielectric tan delta values are (partly) depending on the possibilities to move on molecular scale, see 5.1.2. Hence, the level of both dielectric values has to decrease with an increase of the density and this effect is confirmed by the experimental values in Table 9.5. Six minutes isothermal at 240~ is a condition which will be rarely met during common processing operations of PK copolymer systems. Hence, the u/E-ratio of PK copolymer articles after 'standard' processing operations will be low. The u/E-ratio strongly increases, however, if high shear rates are present during the processing procedure. Klop et al. [10] reported that high molecular weight PK copolymer with an almost completely E crystalline phase changed due to a process of melt-spinning into nearly completely u crystalline material.

9.2.5 Alpha- and beta-crystallinitv in PK terpol_vmers Klop et al. [10] showed that for PK terpolymer fibre samples, the b and c dimensions of the E-phase unit-cell insensitive are to changes in the C3 concentration. The a dimension, however, clearly increases with increasing C3 concentrations. This suggests, according to Klop, that the methyl groups are incorporated into the PK terpolymer E-phase lattice as defects. They also calculate for an uniformly random distribution of methyl groups along the polymer backbone chain, an average distance between in-chain neighbouring

311 methyl groups of about 54 ~ for a PK terpolmer with about 7 %wt. C3. The crystallite size in the fibre axis direction ranged from 120 to 200 ~. Hence, the methyl groups can indeed be incorporated into the E-phase crystal lattice. It will be not surprising therefore, that the presence of methyl groups hampers the formation of u-phase crystallinity. The results shown in Table 9.6 confirm.this idea. These data show that for PK terpolymer systems with a C3 content ~ about 5 %wt. hardly no u-phase crystallinity can be induced by a thermal treatment. Table 9.6 Thermally induced u-phase crystallinity in PK terpolymers. ,

PK terpolymer C3 cont., %wt. 0.0 ,

annealing, rain. at T isoth., ~ .

I "

,,,,,,

T ~

value "C

Hotvalue,

l -

J/g

123

248

106

245

1.5

,= I

255

...................

1.24 3.7

243

........

'I I It' r. . . . . . . .

.....,.,,

Summarising, PK copolymer chains can crystallise in an umodification and in a E-modification. The crystalline phase of virgin low molecular weight oligomer systems is at 20~ mainly in the u-modification. The crystalline phase of high molecular weight virgin PK coploymer, on the other hand, is (again at 20~ completely in the E-modification. PK copolymer systems containing both crystal modifications are obtained by- the use of different liquids/solvents during the polymerisation process, - cold compression of virgin reactor samples, - a proper annealing procedure, - compression/shear forces in combination with the thermal treatment during processing operations like compression moulding and gel-spinning. Besides, u-phase crystallinity was found to be present only in PK terpolymer systems with C3 contents less than about 5 %Wt. For PK copolymer u-phase crystallites, all carbonyl dipoles are pointing in about the same direction at equal height z, whereas in the E-phase crystallites the dipole of the cabonyl group of the corner and the center chain point in different directions [7]. This might mean that the presence of a strong electric field during the recrystallisation from the melt of PK copolymer also might promote the formation of u-phase crystallinity. A high u/E-crystal ratio might improve the strength/stiffness properties of PK copolymer but perhaps the most important effect might be an improvement of the barrier properties.

312 9.3 Investigation of the amorphous phase of PK terpolymer by

D~/DSC

9.3,1 Amorphous Dhase transition effects Dynamic mechanical analysis (DMA) on both a cold (20"C) compressed powder sample and a compression moulded (240~ sheet sample was used to investigate the relaxation processes i.e. especially the glass-rubber transition, of the amorphous phase of PK terpolymer. Figure 9.6 shows the (shifted along the E" axis) dynamic loss modulus (E")/temperature curves of the cold compressed powder sample and that of the compression moulded sheet sample. The crystallinity of the cold compressed sample is about 57%, while the crystallinity of the sample after compression moulding at 240oC i.e. after recrystallisation from the melt, is decreased to about 42%. Both samples are measured at a frequency of 1 Hertz and a heating rate of 2"C/minute. The relaxation behaviour proved to be clearly changed due to this difference in crystallinity of about 15 %. The higher crystalline, cold compressed sample shows a socalled crystalline phase (u) transition at about 130~ a (weak) glass-rubber (E) transition at about 50~ and a secondary, amorphous phase (Y) transition at -75~ This weak glass-rubber transition effect is typical for a semicrystalline polymer. It indicated already that it would be difficult to detect this effect by DSC. The (crystalline) u-transition has been disappeared completely for the lower crystalline (at 240~ compression moulded) sample. The intensity of the glass-rubber (g) transition, however, has been clearly increased. Moreover, the gtransition E" (max.) temperature is shifted from about 50~ to 15~ The Tan ~ (max.) temperature is used to indicate the (DMA) Tg-value of compression/injection moulded PK co- and terpolymers. This Tg-value proved to be 19"C _+ 2~ with no significant difference between these values measured for PK copolymer and PK terpolymer. The y-transition in Figure 9.6 is the only transition effect which seems to be not influenced by the difference of about 15 % in crystallinity between both DMA samples. 9.3.2 Ageing and moisture absorption effects Two effects were noticed during the determination of the mechanical properties of PK terpolymers: - the flexural modulus increased as a function of time during storage at 23~ and 50 % R.H. and, - a weight increase of the test samples due to moisture uptake. Soon became clear, however, that a short thermal treatement (15 minutes/140~ was sufficient to restore the original modulus value.

8.5

Figure 9.6 The dynamic loss (E") / temperature curves of a PK terpolymer sample after room temperature compression and after compression moulding at 240~ 7.0

8.25

POWDER SAMPLE COLD PRESSED AT 28 deg. C . o ~ , ' * " ~ 9 ,,.4 %

m a.

'' s:

j 9..S

9 9

w a.

9 e0 :cOe

....-"

7.3

9 "t

:-.

tee

9 ~.~,..

SAMPLE COMPRESSI ON MOULDED AT 24~ ~

~,,,,r

OD 0 _1

?.75

% "t

7.5

""2..%..'" .. -o.~,,~,,',, t . " eee'li~

9o o - "~

9 9 9 6

8.8 !

I, . I

~ !

I,,

~ t

~I . I

. l

Temperature (~

| ~

7',25

314 A modulus value increase upon storage under ambient conditions is also reported for other semi-crystalline polymers like, for instance, polypropylene. Struik [11] measured for PP a continuously increasing dynamic stiffness at 20~ in combination with a decrease of the intensity of the glassrubber (8) transition of PP (the temperature location of the g-transition did not change). Struik called this phenomenon an amorphous phase ageing effect; a densification process of the amorphous PP phase due to a free volume relaxation effect. This explanation was thought to hold also for the modulus increases measured for the polyketone systems. Two 'aged' samples were, therefore, investigated by DMA: - one sample stored during 720 hours at 21~ in an exsiccator i.e. a moisture free sample and, one sample stored during >1500 hours at 21"C and 50 % R.H. -

Both samples were measured in a Polymers Laboratory DMA with a frequency of 1 Herz and a heating rate of 2"C/minute from 100"C up to 150"C in a nitrogen atmosphere. Possible ageing and absorbed moisture effects are removed during heating to 150~ The first DMA scan was, therefore, immediately followed by a second DMA scan to measure the same properties but now on the non-aged, dried sample. The DMA results in Figure 9.7 of the dry, aged sample show an increased dynamic stiffness at ambient temperatures (Figure 9.7B) and a decrease of the intensity of the glass-rubber transition (Figure 9.7A). These results confirmed the idea about amorphous phase ageing of polyketone polymer systems especially because no secondary crystallisation effects could be detected. The sample stored at a relative humidity of about 50 % contained an equilibrium moisture saturation of 0.74 %wt. The Tan 6 maximum of the ~ relaxation in Figure 9.8A is now not only decreased due to the ageing effect but also shifted from 19~ to 5"C due to the plasticising action of the absorbed moisture. The dynamic stiffness at 20~ of the aged sample (Figure 9.8B) is now I E W ~ than that of the non-aged, dried sample due to the plasticising action of the absorbed moisture. The same sample was, subsequently, stored during seven days in ion-free water to reach an equilibrium water saturation of 2.33 %wt. The Tg-value shifted, due to this absorbed water phase, from 19~ to -8~ It will be clear that the mechanical properties of polyketones at ambient temperatures are sensitive for these ageing and these moisture absorption effects especially due to the presence of the glass-rubber transition in that temperature region. The influence of both effects is in general opposite to each other; the stiffness increases due to ageing and decreases due to moisture absorption. Moisture absorption effects are time and object dimensions dependent whereas ageing effects are only time dependent.

315

non-aged 8 amp I e (after' heattng to

150~

"o s o)

aged =amp le

"ill. 40

-tO

Temperature (~

FIGURE 9.7A

0.41-

0.!1. m I1. UJ r

O.Ib |.11"

=tamp l e

.c "o.o. c

an.o, |.0.

0.7.

r -Ill

'-tO

Temperature (~

FIGU~d~ 9.7B

The results of the DMA m e a s u r e m e n t s on a PK terpolymer sample after 720 hours of ageing in an exsiccator under vacuum and a temperature of about 21 ~

316

Sample a f t e r drytnS~ (by h e a t i n g to LSBuC) ( u e t g h t loss B.?4 ~.)

.g,

.(r/ 9

aged eemp le

"0 C: O) r :6 rQ irTt

.0l. __

-m

-IO

,;,

Temperature (~

,;,

FIGURE 9.8A

11.4.

II.J

0.1 UJ r

0') C ..~ "0

=amp I e.t

O.O,

O.O-

O.Y.

-W

;

-I0

Temperature (~

FIGURE 9.8B

The results of the DMA measurements on a PK terpolymer sample After > 1500 hours ageing under room temperature conditions

317 Figure 9.9, finally, shows the Tan 6/T curve of the aged DMA sample with an equilibrium moisture saturation of 0,74 %wt. and the same curve after drying due to heating to 150~ The 7-relaxation, clearly present in the 'wet' sample, is strongly reduced in intensity in the dried sample. Hence, absorped moisture is for an important part responsible for the intensity of the y-relaxation of polyketone (such an effect of moisture absorption was described before, see 5.2.2). This might also be the reason for the nearly identical 7-transition effects as shown in Figure 9.6.

Secondlry t r a n 8 ! t ton8

.on.

(gamma-re

-o c

| tlxat

Glass-rubber (beta-re

! ons )

transitions

I axa% t ons)

.OT.

moisture

s a t u r-lLtecl

.04.

.O~l,

.Or, t - I |@

I ...... -70

v -SO

~ -30

v - I0

1 !0

u 30

t SO

I~ 70

Temperature (~

FIGURE 9.9

The effect of a sample drying procedure (by heating to 150 C) on the low-temperature gamma relaxation of a PK terpolymer

318 9.3.3 Determination of the Tu-value of PK terpol_vme~ by DSC The first attempts to determine the PK co- and terpolymer Tgvalues by DSC seemed to fail until we realised that the above mentioned ageing and moisture absorption processes might hamper this measurement. The Tg-value determination of PK coand terpolymer by DSC was tried, therefore, using non-aged and dried samples. These DSC experiments were performed as specific heat (Cp) determinations on samples of about fifteen milligramme, using a heating/cooling rate of 20~ and the following temperature programme: - heating from 20~ to 150~ 15 minutes at 150~ to dry the sample and to remove ageing effects, - heating from -100~ to 250~ to measure the Tg-value and the first fusion effect i.e. after crystallisation from solution (scan i), - heating from -100~ to 250~ to measure the Tg-value and the fusion effect after recrystallisation from the melt (scan 2). The Cp/temperature curve of the non-aged, dried powder sample is shown in Figure 9.10A. Now, a weak glass-rubber transition effect (onset 6~ is indeed visible in the Cp/T curve. The crystallinity of the, from solution crystallised, powder sample is 57 %wt. (based on a Hf-value of 207 J/g for I00 % crystallinity, see 9.2.2). The crystallinity decreases, due to recrystallisation from the melt during the second scan, to 43 %wt. (Hf-value 88 J/g). Figure 9.10B shows that the resulting increase of the amorphous phase is reflected in a stronger glass-rubber transition effect (onset value 3~ Both Cp/T curves are plotted on an enlarged scale in Figure 9.11. The glass-rubber transition effect of the second Cp/T curve, measured after recrystallisation from the melt, approximates the for a glass-rubber transition characteristic step-wise Cp/T change. The glass-rubber transition effect of the first scan, measured after crystallisation from solution, is that of an amorphous phase strongly influenced by the presence of the crystalline phase. Such an effect was already detected with the DMA experiments, see 9.3.1. PK co- and terpolymer Tg effects can be detected by DSC both on dry, non-aged virgin powder and on fused samples. The results of the DSC Tg(onset)-value determinations on (virgin) powder samples proved to scatter, however, considerably due to the too strong influence of the crystalline phase on the shape of the Cp/T curve. Thus, a real DSC Tg (onset) -value determination of PK co- and terpolymer samples is only possible on non-aged, dry and one time fused samples. The reproducibility of this DSC Tg(onset)-value determination proved to be _+ 3~ The average DSC Tg(onset)-value of a series of PK co- and terpolymer samples proved to be 4"C. The ~ crystallinity of the sample in Figure 9.11 after recrystallisation from the melt is also reflected in the hiuher Cp values in the temperature region between Tg and Tm,

319

g.O

8.0

0 o

7.0

6.0

0 -r.

T m - v a l u e = 2'23'~ .Hf-value = 119 J/g

5.0

E ~

4.0

T g - v a l u e = 6 deg. (DSC onset)

3.O

.....

[

~2 /

2.0

....

I.O-[ I

-50 0

-I00.0

0 0

50 0

tO0 0

t50 0

-I"

;~00 0

250.0

Temperature (~

RATE1: 20~

FIGURE 9.10A The (DSC) Tg effect for a PK t e r p o l y m e r dried, n o n - a g e d p o w d e r sample

g.o

Tm-value Hf-value i.e.

B.O O) ~,, -3 v

-1._o

x[c]

= 217 ~ = 88 J/g =

6.0

~.o

0 ~-

4.0

T g - v a l u e = 3 deg. (DSC onset)

3.0

/.- ..

9 -tO0.O

I -50 0

RATE1"

1 0 0 20~

...... I 50 0

I . . . . 100 0

Temperature(~

I" 150.0

---

-+1 200 0

FIGURE 9.10B The (DSC) T g effect for a PK t e r p o l y m e r after r e c r y s t a l l i s a t i o n from the melt

ZSO.O

sample

2.5

.//

•

. X:

2.3

"-~ q) o. 09

2.1

Figure 9.11 ...., ,

t.9 1.7

t.5

......

T h e s p e c i f i c heat (Cp) of PK t e r p o l y m e r as a f u n c t i o n of the temperature (dried, n o n - a g e d sample) + non-fused, powder sample, Hf = 119 J / g x sample after recrystallisation f r o m the melt, Hf = 88 J / g

/•

t.3

•

/• +/ • / +

Both

/§ -

dotted 'base, lines

coincide, a f t e r e x t r a p o l a t i o n into the p o l y m e r s ' me1 tphase. The C p - v a l u e s at 240 C measured during both scans are 2.340 J / g . C ............

+--X -'+ --X -

+.-•

•

/x.,. ;..

...........................

t.1

ED oJ

E~ u3

C~ r

Temperature, ~

CD --. 9 - - 4

321 see Table 9.7Table 9.7 Specific heat of PK terpolymer at temperatures between Tg and Tm. I

temper ature, oC

Cp-value, J/g.C x(c) =0.57 scan 1 i

Cp-value, J/g.C x(c)-0.43 scan 2

1.334

1.386

1.501

1.440

1.557

1.495

1.612

0.117

I00

1.555

1.669

0.114

110

,,,

,.,

1.615 If

1.447

ACp, J/g.C

0.113

o .,~5

0.117

1.730

Ill

i,w

0.115

The average ACp value of 0.115 J/g.C is assumed to be the increase of the glass-rubber transition ACp-step due to a crystailinity decrease from 57 %wt. to 4 3 %wt. The ACp-step at Tg measured on the sample after recrystallisation from the melt (scan 2) ~ is 0.323 J/g.C. The ACp-step at Tg during scan 1 can, due to the shape of the Cp/T curve, not be determined directly. It can be estimated, however, by subtracting the ACp increase between Tg and Tm from the ACp-step at Tg measured during scan 2 i.e. 0.323 0.115 - 0.208 J/g.C. A third phase, next to the amorphous phase x(a) and the crystalline phase x(c), is thought to be present in the temperature region between Tg and Tm of semi-crystalline polymers which is called the rigid amorphous phase x(r,a). This is amorphous material hindered to such a degree by the crystalline fraction that it behaves rigid [12, 13]. Assuming that a ACp-step at Tg of 0.115 J/g.C corresponds with a polymer weight fraction of 0.14, the extent of the possible rigid amorphous phase in PK terpolymer can be estimated. The sum of x(c), x(a) and x(r,a) is 1.00, thus might hold for PK terpolymer (after recrystallisation from the melt): 0.43 + ([0.323/0.115]

x 0.14)

+ x(r,a)

= 1.00

x(r,a)

= 0.18

9.4

Thus, PK terpolymer after recrystallisation from the melt might have a rigid amorphous phase (in the temperature region between Tg and Tin) of about 18 %wt.

322 9.4 TMA measurements

on PK terpolymer systems

9.4.1 The linear thermal expansion coefficient of lona ~lassfibre reinforced PK terDolvmer systems Glassfibre reinforcement is often used to modify the physical properties of thermoharding and thermoplastic polymer systems. The linear thermal expansion coefficient (1.e.c.) of a polymer is one of these properties which can be influenced (i.e. decreased) by glassfibre addition. In chapter 3.1.2 is shown that the 1.e.c. of a polymeric system at equal filler/ glassfibre concentrations decreases with an increasing average fibre length. The processing techniques for thermoharding polymers allow application of long glassfibres resulting in systems with low 1.e.c. values. - -

Long glassfibre reinforced (LGFR) thermoplastic sheets can also be prepared using the so-called wet deposition technique. First, the polymer particles and the about 10 millimeter long glassfibres are thoroughly mixed by preparation of a water based slurry. Subsequently, the water phase is removed by cold compression, followed by a compression moulding step at a temperature 9 Tm. The 1.e.c. reducing possibilities of this method for PK terpolymer was investigated with a series of samples with respectively 0, 5, 13.6 and 20 %v. of glassfibres. Sample sheets of 100 x 50 x 4 millimeter were prepared with the wet deposition technique. Two rectangular TMA samples and one circular TMA sample were machined from these sheets. The rectangular samples, i0 x 7 x 4 mm, were taken in the length (X) direction and in the width (Y) direction of the sample sheet. The circular sample, diameter 5 mm, was used to measure the l.e.c, in the Z direction. The samples, placed in a TMA 7, were measured from -20oC to 120~ with a heating rate of 2"C/minute. Subsequently, the sample was cooled with the same rate and heated again for the real measuring scan. The first heating scan was ment to remove the frozen-in stresses which influence the thermal expansiDn behaviour (see 3.1.2). Figure 9.12A shows that this stress release effect for the Xdirection of the reference sample (no glassfibres) results in a permanent length decrease, just like the effect shown in Figure 3.1. The same effect was also measured in the Ydirection. In the Z-direction (Figure 9.12B), however, an expansion effect is measured. The extent of the measured shrinkage/expansion effects are listed in Table 9.8. These values show that these shrinkage/expansion effects are clearly caused by the compression moulding process; the measured effects decrease with increasing glassfibre contents. The l.e.c, values measured during the second heating scan proved to be nearly equal for the X- and Y-direction. Figure 9.13A shows the l.e.c, as a function of the temperature for the

323 lO0. O

100.8

100.6

100,6

100.4

fleet

100.2 o~ I 0 0 . 0

chr I nkege

-1-

effect

100.4 100.2 I00.0 ~l.O

9g. 6

Ic Q

~.~ g9. o C 0

gg, o

second

gg. 4

0,,

99, 2

coo l l n s l

asCam

~1.4

.J ~.2 gg.o

gg. 0 go. 9

-~o

I ,

o.o

~.o

Temperature

so.o

?s.o

Ioo.o

gB.o

Figure 9.12A The length change of a PK terpolymer compression moulded sample during heating/cooling scans (X-direction) .

. -lO'J. 0

103.0 ..~~

-102, 5

102.5

aeocnd cool Ing s c l n / ~ 1 7 6 -r-

102.0 i

-I02. 0

101.5

-tOt.

c 0

..=. .s,...

expmns t on effect,

I01.0

"101.0

100.5

100. 5

I00. 0

100.0 i

zs.o

.....

o.o

l~i

zs.0

Temperature

so.o (~

?5.o

.....

1o~o

Figure 9.128 The length change of a PK terpolymer compression moulded sample during heating/cooling scans (Z-direction)

LIN.

15.8

EXPRNSION COEFF.

(x(-5,

LIN.

I/K) + / +

COs

(xE-5,

(no

2;'

;]1 rose)

12.9

10.5

4 X

[3.6~.v ; ] l u = x

%v ;]lass

//x

/x/ ql

Figure 9.13A Linear expansion coefficient of LGFR PK terpolymer composites as a function of temperature and glass-fibre content (Y-direction)

9.9

/ 4

/ + ยง

I/K)

~J /

reference sample

13.5

/x/ <1

7.5

/ . +

reference samp

) --.--- X ~

~'-x

6.0

" ~

X ~--X-...--X-----

X .-..-- X - - . - - X

5 Y,v. ;]lass

12' ยง

4.5

\ a

\ ~o..~.o__...o..__.o....__o~O__..

o 20 ~,v. g l a s s

1.5

3 TEHPdRRTURE,

0.(] Q

Figure 9.13B Linear expansion coefficient of LGFR PK terpolymer composites as a function of temperature and glass-fibre content (Z-direction)

1 3 . 6 ~ v ;] I ass

+-/

+/ /

3..'

(.,J

le g I ass)

(no

(,D

9 i

_ .

m ,.4

de;]. t

m --. ~

C .

N =.4

TIEHPERflTUREt Q

-ml

_~..

de;], I

C L

325 Table 9.8 Thermal s h r i n k a g e / e x p a n s i o n effects of LGFR PK terpolymer systems due to h e a t i n g to 120"C ,,

fibre content %

I I

X-direc -tion, shrinkage %

1.08

0.42,

13.5 20

_J"

rill

Y-direc -tion, shrinkage % i

0.99

1.19

0.44 ,

0.48 J ,,,

0.19

0.18

O.O7

0.20

0.10

III

Z-direc -tion, expansion %

, , ,'

0.20

Y-direction. The l.e.c, values decrease not only due to the glassfibre addition; the temperature d e p e n d e n c y of the l.e.c. also decreases. The e f f i c i e n c y of the glass a d d i t i o n strongly decreases for volume percentages ~ 13.5 %. Figure 9.13B shows the same results but m e a s u r e d in the Z-direction. Both the level and the temperature sensitivity of the l.e.c, values increase in this d i r e c t i o n due to the g l a s s f i b r e addition. These data illustrate that addition of long g l a s s f i b r e s indeed strongly reduce the l.e.c, values of PK t e r p o l y m e r in the Xand Y-directions but at the cost of a c o n s i d e r a b l e amount of anisotropy in the Z-direction. 9.4.2 The repeatability of the l.e.c, d e t e r m i n a t i o n A large injection m o u l d e d PK terpolymer sheet sample (350 x 110 x 2.5 ram) was used to determine the r e p e a t a b i l i t y of the 1.e.c. determination. Four 40 x 15 x 2.5 m m samples were taken out of such a large sheet, see Figure 9.14: 110 ram. *

sprue

350 mm~. "15 ~

* * X-direction * ~ Y-direction

15 mm.

U-7

measuring direction

* 9 ,

~ ~- 1 5

40 mm.

~m.

Figure 9.14 The location of the TMA samples in the c.m.

sheet

326 Table

9.9 Results of l.e.c, injection m o u l d e d

linear expansion 0~ 20~

sample number

X-direction sample A sample C sample D

average values _

average values Z-direction sample A sample B sample C sample D

8.85E-5 8.85E-5 9.31E-5 9.00E-5

Y-direction sample A sample B sample C sample D

average values

r e p e a t a b i l i t y measurements PK terpolymer samples.

• 0.27

9.41E-5 9.00E-5 9.17E-5 9.02E-5

coefficient l/K, at 80oC 40~ 60"C

. . . . . . .

1.13E-4 1.09E-4 1.11E-4

1.21E-4 1.16E-4 1.17E-4

1.11E-4

• 0.02

.....

1.06E-4 1.09E-4 1.11E-4 1.09E-4

1.18E-4

1.28E-4 1.23E-4 1.24E-4 1.25E-4

1.32E-4

• 0.03

+ 0.03

1.12E-4 1.17E-4 1.18E-4 1.16E-4

1.18E-4 1.24E-4 1.25E-4 1.23E-4

1.26E-4 1.32E-4 1.31E-4 1.31E-4

1.36E-4 1.30E-4 1.31E-4

• 0.03

9.15E-5 1.09E-4 1.16E-4 1.23E-4 1.30E-4 • 0.i0 • 0.02 • 0.03 + 0.03 ~ 0.03 9.15E-5 8.43E-5 9.02E-5 9.03E-5 - - - - - - - - - - - - _

1.05E-4 9.95E-5 1.04E-4 1.04E-4

1.14E-4 1.07E-4 1.12E-4 1.12E-4

1.22E-4 1.13E-4 1.18E-4 1.20E-4

1.28E-4 1.21e-4 1.25E-4 1.27E-4

8.91E-5 1.03E-4 1.11E-4 1.18E-4 1.25E-4 • 0.32 • 0.02 + 0.03 • 0.04 • 0.03 III

III

TMA sample pieces for the d e t e r m i n a t i o n of the 1.e.c. in the X-, Y- and Z-direction were machined out of these A, B, C and D samples. The l.e.c, was measured between -20~ and 120~ subsequently, after a 20~176176 thermal pretreatment to remove frozen-in stresses. The results of these measurements are listed in Table 9.9. A r e p e a t a b i l i t y of • 0.03 was m e a s u r e d for the 1.e.c. value d e t e r m i n a t i o n of PK terpolymer b e t w e e n 20~ and 80~ This r e p e a t a b i l i t y value is the reason that the 1.e.c. values in the X- and Y - d i r e c t i o n are considered to be equal. The 1.e.c. values m e a s u r e d in the Z-direction proved to be about 6 % ~ower than the values measured in the X-, Y-directions.

327 9.5 Determination of electrical properties of PK terpolymers 9.5.1 The influence of moisture on the dielectric properties The relative high dielectric constant of water makes the dielectric constant of a polymer very sensitive for small amounts of absorbted moisture, see 5.2.1. PK terpolymer absorbs under room temperature conditions 0.5 - 0.7 %wt. of moisture. The influence of such a moisture concentration on the dielectric constant and the dielectric losses were determined. _

A two millimeter thick injection moulded disk sample was, placed in a three terminal guarded sample holder and provided with golden electrodes applied by a vacuum evaporation process, connected with the automated dielectric measuring system described in chapter 5.1.4. The dielectric properties of the moisture saturated sample were measured from -100"C to 150~ using a heating rate of 0.5~ The investigated sample is nearly completely dried during this heating procedure. Besides, amorphous phase ageing effects (see 9.3.2) are also removed by this thermal treatment. A second measuring scan from -100~ to 150~ gives then the dielectric properties of the dry, non-aged sample. The weight loss of the dielectric sample, determined immediately after this second scan, was considered to be caused by evaporated moisture. A third heating scan was performed, subsequently, to measure the specific volume resistivity between -40~ and 140~ A small mass loss effect (0.07 %wt.) was still measured after this third heating scan; the moisture content of the sample was considered to be zero after this third scan. Both dielectric measuring scans were performed at nine different frequencies between I00 Hz. and 1 MHz. The dielectric constant/temperature curves measured at a frequency of I000 Hz. are shown in Figure 9.15, nummerical values are listed in Table 9.10. A dielectric constant increasing effect due to the absorbed moisture phase is clearly present. The extent of this effect is smaller in the glass-rubber transition region (0~ - 40~ than at temperatures < 0~ and > 40~ The reason for this difference is the ageing effect of the amorphous phase during the first scan which decreases the extent of the step-wise dielectric constant increase. This ageing effect was already detected during the DMA experiments (see 9.3.2). The dielectric loss curves (Figure 9.16) show, just like the dynamic mechanical loss curves two relaxation effects- the glass-rubber (E) relaxation effect at about 20~ and a low temperature (7) relaxation effect. Both loss curves in Figure 9.16 illustrate again that ageing decreases the strength of the E relaxation without influencing the temperature location of the relaxation effect. This ageing effect is strong enough to make the dielectric loss values of the dry, non-aged sample for temperatures above Tg h i g h e r than that of the 'wet', aged sample. At temperatures below Tg, however, the dielectric losses of the dried sample are ~ than that of the 'wet'

first/second heating scan

/ pO"

O /

Figure 9.15 Influence of moisture on the dielectric constant of

7.5 u~ cO 0

PK terpolymer

0 r

O tD

/ o' ~@

//o

~ O ~"

6.5

0 mo

5.5

I s l ; u r e

content

~t 0/0 /mo!stur'e /0 / e~c~

4.5

0/0 "/O -50

measur'tng ~Pequency: 9

-30

- 10

- 0.07 Y. wt.

L000 Hz 1

Temperature (~

Figure 9.16 Influence of moisture on the dielectric losses of PK terpolymer

o 0

0 ~-

._e o

0 ~ 0

mot=ture

.Of { ~,"~O~ / 9

content

0.47

ut.

O~ 9 \

/.,,

,, o

/.o,=,~ ooo,oo, \ \ I

10-t-

4o--o\\

\, Xo 0

\o-~/ I ~ I "

kHz.

1.8 '

-?8

-58

-38

-10

Temperature(~

330 sample. The dielectric losses at temperatures below Tg are shifted to a higher level due to the moisture absorption. Remarkable, however, is that the intensity of the dielectrically measured 7-relaxation as such is practically not influenced by the samples' moisture content. Dynamic mechanically, a strong influence of the moisture content on the intensity of the 7relaxation was measured, see Figure 9.9. Table 9.10 Dielectric properties of PK terpolymer between 20~ and 120~ at a constant frequency of I000 Hz. I

,i I

die1. loss factor, Ell

Tan ~, EIt/E

I . . . . .

0.0222 (0.0191)

5.14(4.92)

0.114(0.094)

5.55(5.32)

0.086 (0.083)

6.37 (6.26)

0.106 (0.120)

6.83 (6.72)

0. 099 (0. 115)

0.0145(0.0171)

7.33(6.97)

0.236 (0.308)

0.0322 (0.0442)

7.86 (7.41}

0.462 (0. 880)

0.0588(0.1186)

i00

8.35(8.20)

0.850(1.712}

0.1018(0.2088)

120

9.15

1.768

0.1932

. . . . . . .

,,,

[]

die1. constant,

temperature oC -

. . . . . . . . . . . . . .

,,,

0.0155(0.0156)

5.14, moisture content = 0.47 %wt. (4.92}, moisture content = 0.07 %wt.

0.0166(0.0192) ,

. . . . . . . .

331 9.5.2 The freuuencv dependency of the dielectric properties The presence of relaxation effects makes the dielectric properties not only temperature but also frequency dependent. The data listed in Table 9.11 show the extent of this effect at room temperature. The curves in Figure 9.17 give an impression of the temperature and frequency dependency of the dielectric losses of PK terpolymer due to the E- and Yrelaxation effects. Table 9.11 Dielectric properties of PK terpolymer between 0.1 - 1000 kHz. and at a temperature of 20~ (moisture content = 0.07 %wt. ) i

freq. kHz. .

0.1

, ,,,

1.0

[]

100 300

!.o0.0

Tan

Eft

s t/61

6.26

0.209

0.0333

6.31

0.143

0.0227

0.120

0.0191

0.120

0.0194

0.135

0.0221

6.02

0.163

0.0271

5.88

0.213

,,, ,,

6.26 ..

6.20

3.0 10

die1. loss factor

E I

0.3

I'I

die1. constant,

6.11

,. . . . . . . .

,,..

5.72 5.54

,,,

0.355

n'l

..,..

0 048 i

0.277 Inl

0 0641 I

~lll

I ~'

These curves show a rather complicated relaxation behaviour: the E-relaxation seems nearly disappeared at low frequencies due to a high level of background losses, see the 0.1 kHz. curve, - the ~- and y-relaxation effects overlap in the 30 kHz. - 100 kHz. frequency region, see the 100 kHz. curve, the Y- and E-relaxation seem to behave like one single effect for frequencies > 300 kHz., see I000 kHz. curve. The dielectrically measured relaxation maxima are plotted in an Arrhenius plot together with the DMA data (9.3.2) and the result of the Tg(midpoint) determination by DSC (9.3.3), Figure 8.36. The g-relaxation hardly shifts as a function of the measuring frequency due to the presence of a large crystalline phase. The y-relaxation is c l e a r y m u c h stronger frequency dependent. An activation energy value of 63 kJ/mole was calculated for the y-relaxation from the slope of this curve. Some typical y-relaxation activation energy values for linear polymers are 63, 54 and 54 kJ/mole for respectively PVC [14], PC and PET [15]. The mechanisms of these y-relaxations are often described as local mode relaxation effects [15]. The same mechanism might also be responsible for the y-relaxation effect in polyketone polymers.

18e-

-i

second heatingscan

0 I k Hz 9

0 ~

.,&~&

I .o~o-O-~ IS -z'-

, ._Iv

" ~/ "" /

,o 0

o // . /

~,/

-"/

/'-

-'-

~\ v ~ '

v--

"~I~

~\"a

~ /~

v /o

/ /

18.0 kHz.

<>. o / ~"\,,

~ o ~%", 0

0 ,..,/

\ ~ . . < > / <> 180.0 kHz.

O O

~e,808.8

kHz

Figure g. 17 Dielectric loss / temperature - frequency relations of PK terpolymer

motst, ure

-188

/ 0/

BA/

10-Z-

8~I

.o~_

t 0 k Hz

-88

cont.enr

-68

-8.8P

-48

~ wt,.

-28

Temperature(~

100

128

140

333

Figure 9.18 Frequency/temperature relation of the beta and gamma relaxations of PK terpolymer +

diel, loss

mech. loss

DSC midpoint

16 14

E c

relaxation +

+ 6

gamma

i,,,,,,,,,,=,l

'--'

10 "T

beta

N+

+ relaxation

2 0-2 3.20

& I 0 I ,

3.60

\ \

4.00

4.40

1000/'r(max.), K -1

4.80

5.20

5.6O

334 9.5.3 The volume r e s i s t i v i t y d e t e r m i n a t i o n of PK terp_ol_vmer The specific volume resistivity was m e a s u r e d between -40~ and 140~ during a third, step-wise heating scan. The sample/ sample cell c o m b i n a t i o n used for the dielectric measurements was connected for this purpose with the automated resistivity m e a s u r i n g system d e s c r i b e d in 5.1.4. The measurements, at nine discrete temperatures, were performed with an e l e c t r i f i c a t i o n voltage of 500 Volt and an e l e c t r i f i c a t i o n time of thirty minutes. The m e a s u r e d currents were used to calculate the so-called p-60 value and the p-dc value, see 5.1.5. The results of the specific volume resistivity measurements on PK terpolymer are listed in Table 9.12 and p l o t t e d as a function of the reciprocal, absolute temperature in Figure 9.19. The p-dc value of PK terpolymer decreases about five decades (from about I E I 4 0 h m . m to IE9 Ohm.m) due to the change in the amorphous phase from a glassy into a rubbery state. The m e a s u r e d resistivity level is too high to be responsible for the low frequency 'background' losses as m e a s u r e d in the 0.i kHz. curve of Figure 9.17. Table 9.12 The specific volume resistivity of PK terpolymer. (average m o i s t u r e content 0.07 %wt. ) I

temp., oC

p-60, Ohm.m

p-dc, Ohm.m

-38

3.4E14

6.2E15

-21

1.4E14

8.5E14

- 1

9.3E12

6.3E13

4.9EII

5.6EII

i. 9El0

2.0El0

1.5E 9

2.1E 9

4.1E 8 .J

1.1E 9

112

3.1E 8

1.0E 9

136

9 .

2.4E 8 II

,,,

I 7.1E 8 j I

The dielectric loss factor measured is the sum of a dielectric contribution and a dc conductance contribution, see 5.1.3. The dc conductance contribution to the loss factor given in equation 5.19 can be written as: Er"(dc)

- I/(w x p-dc x 8.85E-12)

9.5

335

Figure 9.19 PK terpolymer specific volume resistivity absolute temperature relation (dried, compression moulded sample) + A Rho(60)

Rho(dc)

.E 1 4 E

O ._~ m ccj i1)

ft. -

d CI.

0 ._J

10 9

2.40

2.80

3.20

3.60

lO00/T(max.), K -1

J ............

4.00

4.40

336 The p-dc value of 5.6Ell (Table 9.12) is u s e d to c a l c u l a t e the dc loss c o n t r i b u t i o n at 20oC. Thus e q u a t i o n 9.5 reduces to: ~r" (dc) = i/(31.12 x f) where

9.10

f - the frequency,

Hz.

The m e a s u r e d ac/dc d i e l e c t r i c loss v a l u e s at 20~ and r e s p e c t i v e l y 100, 300 and 1000 Hz. (Table 9.11) and the c a l c u l a t e d dc loss e f f e c t s are: frequency,

Hz.

i00 300 1000

or" (ac/dc) 0.209 0.143 0.120

cr" (dc) 0.00032 0.00011 0.00003

Hence, the dc c o n t r i b u t i o n to the d i e l e c t r i c loss f a c t o r at 20~ can be neglected. First at lower f r e q u e n c i e s and higher t e m p e r a t u r e s a still r e l a t i v e small dc c o n d u c t i o n e f f e c t is calculated, for e x a m p l e at 100 Hz: 40~ 65~ 88"C

Er"(ac/dc) ,, ,,

-- 0.454 = 1.70 . 3.87

~r"(dc) ,, ,,

= 0.009 = 0.086 = 0.164

It will be c l e a r that the d i e l e c t r i c losses of PK t e r p o l y m e r systems are m a i n l y s t e m m i n g from the strong d i p o l a r r e l a x a t i o n effect of the carbonyl g r o u p s p r e s e n t in the p o l y m e r mainchain.

337 9.6 Survey of PK t e r p o l y m e r thermal analytical c h a r a c t e r i s a t i o n results A. The crystalline phase XRD and TA analysis-have both shown the s e m i - c r y s t a l l i n e character of the in this chapter d e s c r i b e d PK terpolymer system. The main properties of the crystalline phase m e a s u r e d on non-stabilised, p o w d e r y reactor samples, are: Tin-value

(DSC, 20~

first heating)

= 220 â&#x20AC;˘ 3~

Hf-value

(DSC, 20~

first heating)

= 111 _+ 10 J/g

Hf (max.) -value

(calculated value)

crystallinity x (c)

20~

J/g

0.54 _+ 0.05

B L T h e amorohous phase PK terpolymer shows three r e l a x a t i o n effects in the temperature region from -100~ to 180~ (DMA, sheet samples compression m o u l d e d at 240oC): - the u-transition, a crystalline phase relaxation effect w i t h tan delta maxima at temperatures b e t w e e n 130 to 145~ - the fi-transition, the g l a s s - r u b b e r t r a n s i t i o n of the amorphous phase w i t h tan delta m a x i m a at about 19~ and, - the 7-transition, a secondary amorphous phase relaxation with tan delta m a x i m a at about -75oC. _

Tg (onset) -value

(DSC, 20oC/minute

- second heating)

4 _+ 3~

The E - t r a n s i t i o n is influenced b o t h by an ageing and a moisture absorption effect: Ageing; a d e n s i f i c a t i o n process of the amorphous phase, the strength of the g - t r a n s i t i o n decreases (tan delta (max.) from 0.08 to 0.05). Moisture absorption: p l a s t i c i s i n g the amorphous phase i.e. the temperature location of the E - t r a n s i t i o n decreases. e.w.s.* = 0.74 %wt. (due to storage at 20~ and 50 % RH) tan delta(max.) decreases from 19oC to 5~ e.w.s.* = 2.33 %wt. (immersion in ion-free water) tan delta(max.) decreases from 19~ to -8~ Both the strength and the temperature location of the 7transition p r o v e d to be sensitive for absorbed moisture. C. PK terp_ol_vmer sgecific m~terial properties at 20~ Lin. expansion coeff. X/Y'direction--- 1 10E-4 â&#x20AC;˘ 0'02 Z-direction = 1.03E-4 _+ 0.02 spec. volume resitivity

= 5.6Ell O h m . m

dielectric constant , frequency dielectric loss factor, is dielectric tan delta , 1000 Hz.

= 6.26 = 0.120 - 0.0192

(*e.w.s. : e q u i l i b r i u m water saturation)

338 References 1. E. Drent, European Patent 121,96 (Shell), 1984. 2. E. Drent et al., J. Organomet. Chem., 417, (1991. p. 235. 3. J.A.M. Broekhoven and R.L. Wife, European Patent 257,663 (Shell), 1987. 4. P.J. Flory: Principles of Polymer Chemistry, New York, (1953) 5. S.Z.D. Cheng- Polymer Analysis and Characterisation, Applied Polymer Symposium 43, editor H.G. Barth, New York (1989) p. 336. 6. J.N. Hay, J. Pol. Sc.: Pol. Chem. ed., 14, (1976), p. 2845 2852. 7. B.J. Lonlnerts et al., J. of Pol. Sc. : Part B: Polymer Physics, Vol. 31, p . 1 3 1 9 - 1 3 3 0 (1993). 8. R.C. Allen, Internal Shell Report, Westhollow Research Centre, (1986). 9. Y. Chatani et al., J. Pol. Sc., 55, (1961), p. 811. I0. E.A. Klop et al., J. Pol. Sc.: Part B: Polymer Physics, Vol. 33, (1995), p. 3 1 5 - 326. 11. L.C.E. Struik, Plastics and Rubber Processing and Applications, 2, (1982), p.41 - 50. 12. B. Wunderlich: Thermal Analysis, Academic Press Inc., New York (1990). 13. J. Grebowicz, Pol. for Advanced Techn., 3, (1992), p. 5 1 59. 14. C.C. Ku and R. Liepins: Electrical Properties of Polymers, Hanser Publishers New York (1987), p. 95. 15. N.G. McCrum, B.E. Read and G. Williams" Anelastic and Dielectric Effects in Polymeric Solids, J. Wiley London (1967). -

THERMO-ANALYTICAL CASE STUDIES

CHAPTER 10

339

CHAPTER I0: THERMO A N A L Y T I C A L CASE STUDIES I0.1 Introduction The thermal analysis techniques treated in this book are used to study the physical properties of polymeric systems in relation to their chemical structure. These thermal analysis techniques are however also well suited for short case studies. Many of such case studies are p e r f o r m e d in several technical service laboratories all over the world. The results of such (short) case studies are rarely reported although they often contain interesting information. A number of such case studies, initiated by technical support questions, are reported in this chapter to illustrate the often interesting product information obtained with a limited number of TA experiments performed just to answer a 'simple' question.

10.2 The effect of the presence of a solvent d u r i n g the c u r e of a t h e r m o h a r d i n g

system.

The physical properties of cured resin systems are u s u a l l y tested using rectangular casting samples and/or film samples on a metal background. The casting test samples are obtained after the cure of a proper resin/curing agent m i x t u r e without any solvent present. To make a film test sample h o w e v e r nearly always a solvent has to be added. The physical properties, like the Tg-value, of such film samples after cure seem often to be lower than those of the solvent-free p r e p a r e d casting samples. This effect might be caused by a difference in the network structures formed but it might also be a simple residual solvent effect. A number of DSC Tg-value d e t e r m i n a t i o n s were performed to obtain more information about this subject. The diglycidyl ether of bisphenol A (DGEBA, EPIKOTE 880 exSHELL) resin was cured with a stoichiometric amount of d i a m i n o d i p h e n y l m e t h a n e (DDM). A thick casting sample was of about i millimeter p r e p a r e d from a part of this m i x t u r e (sample A). Subsequently, about 50 %wt. of methylisobutylketon (MIBK; boiling temperature = I16oc) was added to the remaining part of the DGEBA/DDM mixture. A sample of one millimeter (sample B) thick and a sample of 13 m i c r o n thick (sample C, on a metal background) were made from the DGEBA/ DDM/MIBK mixture. The three samples were cured then using the more or less 'standard' temperature treatments i.e. 1 hour/80~ hour/150~ hour/175~ for both castings and 2 h o u r s / 1 2 0 o c for the film sample.

340 DSC m e a s u r e m e n t s were used subsequently to measure the Tg (onset)-values of these systems (measured d u r i n g the heating mode, scanning rate 20~ 9 Sample A, 1 m m thick/prepared without MIBK 9 172~ Sample B, 1 m m thick/prepared with MIBK - 70~ Sample C, 13 micron thick/prepared with MIBK: 155~ Non-isothermal TGA experiments showed that sample B still contained 13.5 %wt. MIBK while sample C still contained 4 %wt. MIBK. The TGA experiments also showed that a temperature of about 250~ is necessary to remove the residual solvent from the samples B and C within a reasonable amount of time (I to 2 hour). Subsequently, the three samples were stored in an oven at 250oC (in a nitrogen atmosphere). The weight loss of the samples and the increasing Tg(onset)-values were followed as a function of time. The T g ( o n s e t ) - v a l u e s of the samples B and C did not further increase from the moment that the sample weights became constant. The following end-values were measured: Sample A, wt. loss after 150 min./250~ Sample B, wt. loss after 150 min./250~ Sample C, wt. loss after 90 min./250~

0.4 %wt...Tg = 172~ 13.7 %wt...Tg = 166~ 4.0 %wt...Tg = 165~

These experiments clearly show that the presence of residual solvent (after the standard cure procedure) is the main reason for the sometimes considerable differences in properties. The time/temperature necessary to remove the residual solvent is d e t e r m i n e d by the sample dimensions and the viscosity of the resin system. The boiling temperature of the residual solvent seems to be less important. Figure i0.i shows the relation between the Tg(onset)-values and the amount of residual MIBK for the samples B and C. Both systems arrive, after evaporation of the solvent phase, at equal Tg(onset)-values. Figure I0.I shows, however, that these equal end-values are reached along different ways. The T g ( o n s e t ) - v a l u e of both in the presence of solvent cured systems is indeed lower than that of the solvent-free cured system. This difference of 6~ â&#x20AC;˘ I~ was also measured for a second identical series of D G E B A / D D M samples prepared with bis(2-ethoxyethyl) ether (BEE, boiling temperature about 150~ as solvent phase. We expect that the impact of this difference on the physical properties will be small because it is m a i n l y caused by a difference in the shape of the glass-rubber transition effect. The temperatures at which the Cp-curve really starts to deviate from the base curve i.e. the real starting temperature of the g l a s s - r u b b e r transition effect, appears to be p r a c t i c a l l y identical for all three systems!

341

Figure 10.1 The Tg-value of DGEBA/DDM resins as a function of the residual solvent (MIBK) content

1 mm casting

13 u film

ref. casting

180

170 ......

160

\ +

150

140 r O

I---

130

120 + 110

.............

-~'

2 3 Residual MIBK, %wt.

~ j

......

342 10.3 The thermal transitions of a l i q u i d crystalline polymer. T h e r m o t r o p i c liquid crystalline polymers (LCP) show during heating one or more mesophase t r a n s i t i o n effects before they change after an endothermic fusion m a x i m u m into an isotropic melt. These transition effects are u s u a l l y indicated by Tm, Tm' etc. for the mesophase transitions and by Ti for the transition to an isotropic melt. The p r e s e n c e of such a mesophase (for m a i n c h a i n LCP systems u s u a l l y a nematic one) offers the p o s s i b i l i t y to use these polymers as a reinforcing fibre phase in so-called 'self-reinforcing' composite systems. The LCP system Vectra B950 (an ~romatic copolyesteramide) from H o e c h s t - C e l a n e s e was intended to be used as such a reinforcing fibre phase in a polypropylene (PP) matrix. We were requested to determine the thermal transition effects of Vectra B950 in order to use these effects to determine small amounts of Vectra B950 in a PP matrix by DSC. A DSC h e a t i n g / c o o l i n g scan (scan rate 20~ from 20~ to 450~ and back to 20~ with a Vectra B950 nib sample showed a mesophase transition effect and an isotropic melt effect. Two m e s o p h a s e transition effects were detected in the extruded Vectra B950 systems. All three endothermic effects mentioned, see Figure 10.2, proved to be thermally reversibleTm' -value : 161~ Hf (m') -value: 4 J/g Tc(m')-value: 112~ Tm-value Hf (m) -value Tc(m)-value

9 280~ : 2 J/g : 227~

Ti-value Hf (i) -value Tc(i)-value

9 396~ : 84 J/g : 374~

The DSC technique was not sensitive enough to determine a reproducible Tg(onset)-value of this system. The Tg d e t e r m i n a t i o n was performed therefore with a Polymer Laboratories DMA, see Figure 10.3. The g l a s s - r u b b e r transition region of Vectra B950 starts (measured at a frequency of 10 Hz. and a heating rate of 2~ at about 110~ and ends at about 170~ The Tg-value i.e. tan delta(max.) is 140~ Thus, the Tm' transition effect and the g l a s s - r u b b e r transition occur in the same temperature region. The dynamic stiffness (E')/temperature curve in Figure 10.3 shows a strong decrease for temperatures higher than the mesophase transition Tm. This stiffness decrease is sufficient to allow extrusion of this polymer at 285~ Extrusion of a small amount of such a LCP with PP results in LCP particles with a fibre shape in the PP matrix.

343 500-

4.50

~ i

CURVE

4.00

(I,

H(RT ING )

3.50 3.00

............

---

2.50

CURVE

.....~.j.~

-r- Z.~o:

(2,

COOLINGI

I'00 t 0.50

0.t~ 200.0

:300 0

250 0

350.0

I00 0

Temperature

1.50 .0

500 0

Vectra B950 nib sample

o.e5 0 40

Tin" -

I l l iC

Tm - 2BIBtC

03'3 A v

(F'iRgT) H[RTING .~CriN

~:oas o

~.~

LL '*" 0 2. 0

..~

/ "~'-.~.,~

0 15

/'~"... ...........

0 5O0

i! Te" I

100 0

ft,.,/ T~

, _ . ~ / - ~ .~..

9 !

0 10

...,...,,.~..--. ...--. 9 e....~........

(SECOND) COOL l NG SCRN 112~C I

"l 150 0

! ' 200 0

Temperature

I 250 0

300 0

Results of DSC heating/cooling scans on a Vectra B950 extruded string sample Figure 10.2

"9"

sac i

(0o) mrqmeawel "

oc ! I

as t .

o~ I

eldWes (0o06~ / u!w cj) pePlnOW

uo!sseJdLuoo 0cj68 eJ],oeA e uo slueweJnseew V~E] jo s~lnseEI

80L eJnSL-I

8"8 i

!2"/.

tpll"

§ § § § § § §

BiD"

"4 ~U :3

8"/.

t,'8

m 8"8

4" ,4.

4. § § §

~'S

41-

8"S

t,Z"

345 The Ti and Tm' transitions are not suited to detect such a relative small LCP phase in a PP matrix by DSC. The PP m a t r i x is thermally not stable enough at the Ti temperature of 396~ while the LCP Tm' temperature of 161~ coincides with the fusion region of the PP matrix. The relative weak Tm transition (280"C) is thus the only possibility to detect this LCP phase in a PP matrix by D S C . The results of the first measurements on a PP/Vectra B950 (90/10) blend were disappointing, the fusion effect of Tm was not detectable. Subsequently we tried to increase the strength of the Tm transition by a proper annealing procedure. A heat t r e a t e m e n t of the DSC sample of two hours at 260~ increased the Hf(m)-value from 2 J/g to about 6 J/g. This Hf(m)-value increase proved to be sufficient to make a Vectra B950 phase of I0 %wt. detectable in a PP matrix using a single DSC scan. The Tm-value itself also proved to increase due to this annealing procedure. A series of additional experiments was performed to investigate the extent of the changes in the strength and the temperature location of this mesophase transition, see Figure 10.4. A kind of an equilibrium situation seemed to be reached first after 1440 hours annealing at 260~ The Tm-value then increased from 280~ to 3580C and the Hf(m)-value increased from 2 J/g to 17 J/g, see Figure 10.5. These results clearly illustrated the metastable character of the Tm transition but did not contribute to a further improvement of an DSC detection method of this LCP system in a PP matrix due to the possible long sample preparation time required.

10.4 The optimal crystallisation temperature of diphenylol methane The 'raw' diphenylolmethane (DPM) is a mixture of p,p-DPM, o,o-DPM, o,p-DPM and tri/tetramers. An HPLC analysis of such a DPM sample determined 3 1 % w t . p,p-DPM, 40 %wt. o,p-DPM, 16 %wt. o,o-DPM and about i0 %wt. trimers to be present. Such a mixture crystallises very slowly (several days) during storage at 20~ We investigated if this crystallisation process could be accelerated to improve the process efficiency, by optimising the crystallisation conditions. A purified DPM reference sample (p,p-DPM > 80 %wt.) showed two endothermic fusion effects (Tml = 158~ = 124 J/g, Tm2 = 108~ = 14 J/g) and a clear recrystallisation effect (Tc = 120~ = 88 J/g) during heating and cooling scans at 20~ in the DSC. The difference between the Hfl-value (124 J/g) and the Hc-value (88 J/g) shows already that recrystallisation from the melt for this relative pure sample clearly occurs slower than recrystallisation from solution. The relative weak Tm2 effect has completely disappeared during the cooling scan in the DSC.

346 . . . . . . . . . . . . . . .

.....

. . . .

. . . . . . . . . . . . . . . . . . . . .

1.30

S~'g H / 2 S g I

I. 20

]

1.10

t zo

1.130

H-~+e

llnnl Ileal

..,,+o. t.. =:~e c

g ~ O. O0

I % i \ /

.nneeled

~L tm ,, 3 4 g C ! Hr * lib J / l l

I t

0o110

j ~ 0,70

.~,.

,,~ 0 , 8 0 i OP :::p.., O. 50 -

a,__

Z H / ~ G I I C I I n . I I II I lld 1 IIi1~ I II tm

211G C -

I1 3,'11

O. l O 0.30

I-heeled

n o t .

0.20

Tm -

200

jmmpll

C - HI' " 2 J / g

O. I0 0.00 2; +0. 0 +

. . . . . . . .

| -

275. 0

. . . . . . . . . . . . . . .

300. 0

. . . . . . . . . . . . . . .

325. 0

" . I.- . . . . . .

350, 0

........ : . . . . . . . . . .

375. 0

Temperature (~

Figure 10.4

Effect of annealing a Vectra B950 fibre sample at 260~ Xl

3 4 6 . 2 6 6 "C

t. tO

lt2

3 7 0 . 0 0 0 *C

t.O0

Peak 1t4

350.03! "C

Tm ,,, 3511 C

16.9416 d/g

HI' ,- I ?

J/G 1' ! -

o9o A

IC~

3911 c I;2

Jt11

0.80 0

0.60

9~ | :I:

o~ o.Jo

0.30 0 20 0.I0 0.00

............

200.0

"- ~'=--+ - . . . . . . . . . . . . . . .

. . . . . . I

250

_ ....... 0

.. . . . . . . . . . . . . . . . . . . . . I

300.0

-..... _ . . . . . . . . . . . . . . . . . . . . .

350 0

dO0.O

Temperature (~

Figure 10.5 First DSC heating scan on a Vectra B950 fibre sample after 1440 hours annealing at 260~

454)

347 These results indicate that it would be very difficult to measure dynamically recrystallisation effects of 'raw' DPM samples in the DSC. A 'raw' DPM sample recrystallised during storage at 20~ showed an endothermic fusion effect between about 40~ and 140~ with maxima at 125~ and 94~ and a Hf-value of 105 J/g. Recrystallisation effects during cooling scans were, as expected, not detected during these experiments. The extent of the fusion effect after a certain storage time and temperature did give however a clear indication of the progress of the recrystallisation effect. Figure 10.6 shows the fusion curves of 'raw' DPM mixture samples which were, after heating to 160~ stored during respectively i, 16.5, 24 and 65.5 hours at 20~ The slow increase of the crystalline phase is accompanied by a decrease of the extent of the amorphous phase i.e. the strength of the glass-rubber transition has to decrease at the same time. This is confirmed by the results shown in Figure 10.7. After heating to 160~ 'raw' DPM samples were subsequently cooled at maximum speed and stored at different temperatures while the increase of the Hf-value as a function of the storage time was followed. The results of these experiments are plotted in Figure 10.8, the curve measured at 50~ is omitted for clarity reasons. These results clearly show that the recrystallisation speed of this DPM mixture reaches a maximum value at about 60"C. The Hfl-value of 124 J/g m e a s u r e d for the reference sample indicates that a Hfl-value of 48 J/g for this 'raw' DPM sample containing 3 1 % w t . p,p-DPM might be possible. The results presented in Figure 10.8 show that after two hours storage at 60"C a Hf-value of 49 J/g was measured. This indicates that the recrystallisation process of the p,p-DPM phase is nearly completed is after these two hours of storage at 60~ Thus, a solid 'raw' DPM product can be obtained within a reasonable amount of time (about two hours) if the recrystallisation process occurs at 60~ instead of 20~

348

o~ ot

.............

~.o' 1

.___~~ y ~ ,,,,,/~:;~~,:~~,~--~,~~

o 9 o, 1

o 1 ~~/~y 04

i oo to., t~' t~.

0.4

0.~

0.3

0.2

0 I V / O0

(

70.0

) stornge

00.0

90.0

time

roomtemper.tur

100,0

I 120.0

110,0

t 0"1

I 130.0

I 140.0

I ........ 1 "0"0 150.0 160.0

Temperature (~ Figure 10.6 Fusion curves of at ambient temperature recrystallised crude DPM .

PERKIN-ELMER 7 Sedes Thermal Analysis System .

0"50 i O. 45

o.50 o. 45

0.40-.,

(I)

0.35

__~r ]s_s.~----

~0.30 0 0.25 LL ..,..

020

r0. 40

(24)

-0.30

(ss. S T - - ~ - ~

r0,~ -0.20

0.15

I.O. 15

O. I 0 1

0,10

0"05 1 o oo ~ -40. 0

(

) storage v -:30. 0

Figure 10.7

time i -20. 0

roomtemperltuPe I - tO. O

I O. 0

t IO. O

I 20.0

I :310.0

ii ~

40. 0

Temperature (~

Glass-rubber transition curves of at ambient temperature recrystallised crude DPM

349

Figure 10.8 Hf-value development of "raw" DPM as a function of the recrystallisation time/temperature +

80~

70~

60~

40~

30~

.... ()

40 ~

m 930 ,.T "~

_=__

+ / . ~ ~ " 10

I ......

Isothermal crystallisation time, min.

100

120

350 10.5 The dynamic stiffness of u l t r a - h i g h m o l e c u l a r weight polypropylene in its melt U l t r a - h i g h molecular weight polypropylene (UHMW-PP, Mn about 5,000,000) is used in applications where a high melt strength is necessary. The dynamic stiffness i.e. the storage shear modulus (G'), is related with the melt strength and can thus be used to compare the properties in the melt of different UHMW-PP systems. A number of experimental UHMW-PP systems was investigated in this way. The measurements were p e r f o r m e d with an automated torsion p e n d u l u m (DMA) apparatus working at a frequency of about 0.5 Hz. (varying frequency system, see Chapter 4). The use of a low-stiffness suspension wire permitted stiffness measurements as low as 5E4 N/m2. These DMA measurements were performed from 50~ up to 250~ using a heating rate of l~ the samples were, during these experiments, purged with nitrogen. The dimensional changes of the sample strips during the heating of the samples through their melting regions made calculation of the dynamic stiffness in two steps necessary. The sample dimensions at room temperature were used to calculate the storage shear modulus values between 50"C and 170~ The sample dimensions after heating to 250~ were used to calculate the storage shear modulus values between 170~ and 250oc. Figure 10.9 shows the results of the measurements on an experimental UHMW-PP sample as such and filled with 20 %v. of mica. A standard J-grade PP, filled and non-filled, was m e a s u r e d as reference system. The dynamic stiffness of both reference systems is for temperatures below 160~ higher than that of both UHMW-PP systems due to a difference in crystallinity, x(c) as determined by DSCUHMW-PP J-grade PP

, x(c) , x(c)

UHMW-PP/20 %v. mica , x(c) J-grade PP/20 %v. mica, x(c)

= 0.33) = 0.45) ) based on a Hf-value of = 0.43) 188 J/g for x(c) = 1.0 = 0.52)

The crystallinity is promoted by the mica addition (mica is, just like talc and carbon black acting as a nucleating agent for PP, see Chapter 1.3.2). This effect is also detected by an increase of the DSC recrystallisation temperature (Tc-value) from 108~ to 120~ for the UHMW-PP and from 106~ to 121~ for the standard J-grade system. Both reference samples fused completely out of the sample clamps at tempertures between 160~ and 170~ The dimensions of the URMW-PP samples did change considerably (length not changed, width -23 % and thickness +40 %) but the shape of the samples was still rectangular, which permitted us to continue the measurements up to 250~ The consideable difference in dynamic stiffness (and hence in strength) between the standard

351

Figure 10.9 Dynamical stiffness of PP grades as a function of the temperature +

II 9

le+09

UHMW PP

PP/20% mica

"1'

U--t/20% mica

~ยง

0 ~+~

+ ~ +.~ + ~

le+08

I,,,,,

le+07

"+ ----_. + +

10000QO

s\ s I

0 100000

, ~=

.._=

130 Temperature, ~

, 1

170

,_'

210

25O

352

Figure 10.10 Dynamical stiffness of UHMW PP/J-grade PP blends as a function of the temperature -4'-

PP J-grade

U/J.--g. 20/80

U/J-g. 40160

'4"

U/J-g. 60/40

I e+081 ~ +

le+07

1000000

100000 I I

10000 150

...

I I

170

t I

I j,

t I

....

190 Temperature, ~

210

23O

250

353 J-grade PP and the UHMW-PP, both in their melt, difference even increases due to mica addition.

is clear.

This

The nearly constant (about 5E5 N/m2) storage shear modulus level of the UHMW-PP between 170"C and 250~ is assumed to be a part of the so-called rubbery plateau of the amorphous polymer. The length (in ~ of this plateau depends on the molecular weight. The modulus level in this plateau depends on the number of chain entanglements which are acting as temporary physical crosslinks. However, also the number of these entanglements increases with the molecular weight of the polymer. Hence the shape of this rubbery plateau is completely molecular weight dependent [1,2]. D M A m e a s u r e m e n t s on a series of UHMW-PP/J-grade PP showed that such a physical network is able to "carry" a considerable amount the standard J-grade PP before the rubbery plateau of the UHMW-PP collapses. The results in Figure i0.i0 show that for a blend of UHMW-PP/J-grade PP (60/40) the rubbery plateau is still present up to 250~ This rubbery plateau starts to disappear quickly for J-grade concentrations higher than 40 %wt.

354 10.6 The effect of an anti-static additive on the electrical resistivity of a p o l y s t y r e n e foam Polystyrene (PS) foam is only accepted as packaging material for electronic components if the electrical resistivity is low enough to prevent components damage due to electro-static charges. Anti-static additives are added to PS foam batches to reduce static charge and discharge effects to an acceptable level but reliable electrical resistivity values of such foams were not available. Hence, a series of measurements was p e r f o r m e d to determine such values. A series of four PS foam samples with a density of 20 g/l was made using the so-called vacuum process. Neostatic HBI55 (an alkyl substituted, kationic a m m o n i u m salt) was, as the antistatic additive, added in concentrations of respectively I, 2 and 4 %wt. This anti-static additive was added, dissolved in a constant amount of water, to the expanded PS particles and thoroughly mixed. This mixture was used to press PS foam block samples of 30 x 30 x 5 cm. Subsequently, samples of 9 x 9 x 0.42 cm were cut from these PS foam blocks to measure the electrical surface and volume resistivity. These samples were first stored, however, during six weeks at a temperature of 20 1 ~ and a relative humidity of 50 %, to reach equilibrium m o i s t u r e uptake conditions. The foam samples were mounted for both surface and volume resistivity d e t e r m i n a t i o n in a Keithely 6105 m e a s u r i n g cell. The electrode configuration of this cell consists of a fixed h i g h - p o t e n t i a l electrode and a spring-loaded low-potential electrode, both completely guarded. The samples were clamped between the high potential electrode and the guard ring of the low-potential electrode using 4.0 m m spacers. The 4.2 mm thick foam samples were thus slighly compressed in a reproducible way (between the high potential and the spring-loaded low potential electrodes) in order to obtain a good sample/ electrode contact. All measurements were performed with an electrification voltage of i000 Volt and an e l e c t r i f i c a t i o n time of twenty minutes. This electrification time proved to be sufficient to avoid contributions of time dependent charging currents (see Chapter 5.1). The in this way performed measurements agree with the recommendations given in ASTM D257 and IEC 93 methods. The nummerical results of these measurements are listed in Table I0.I. Figure i0.II shows resistivity values plotted as a function of the anti-static additive concentration. The addition of this additive certainly works; the surface r e s i s t i v i t y decreases about four decades and the volume r e s i s t i v i t y decreases about eight decades due to the addition of 4 %wt. of Neostatic HBI55 anti-static additive. The shape of these curves indicates that addition of higher concentrations of this additive will be hardly effective.

355

Figure 10.11 Resistivity of PS foam as a function of the anti-static additive content -'t-

surface resistivity

volume resistivity

l e + 14

le+15 I 4"

Volume/surface resistivity correlation le+ 15

le+13

. . . . . . . . .

le'+ 14

le+14 + " I.

E r 0

l e + 13

le+12

:=~ l e + 1 2 le+11

i=,,=,

i iii

t~ .~_ l e + 1 1

\ \ \\

le+09

~..~_

E t--

._> t~ ,===

le+lO 'e+lO

le,'0-11

'le,"*'-12

le.+13

Specific surface re.iStivity. ~

le"t";

e= q)

le+09

,0 m o,===

o Q. or) G)

le+08

le+ 10

le+07 I e+09

.........

0.50

1.50

.....

2.60

3.50

Anti-static additive conc., %wt.

4.50

356 Table i0.i Results of electrical resistivity measurements on PS foam samples Neostatic HB155

I content,0 %wt. 9

spec. volume resistivity, Ohm. m ,

spec. surface resistivity, Ohm .,

6.6E14 9.5E 7 6.0E 7 9.4E 6 =

.....

3.4E14 2.7El0 7.2E 9 1.9E 9

Physical measurements performed on foam samples instead of solid, isotropic polymeric systems nearly always show an increasing scatter of the results with a decreasing foam density. Besides, the scatter of the surface resistivity measurements is always higher than that of the volume resistivity results due to the higher sensitivity of the surface resistivity determination for the sample/electrode contact quality. The relative good correlation found between the measured volume and surface resistivity values, see the inserted figure in Figure i0.ii, indicates that the electrode configuration used resulted in reproducible contact conditions during this series of measurements. 10.7 The dielectric constant of polyethylene foil One

of the first polymeric products in which a relative high amount of recycled product was used, was low density polyethylene (LDPE) foil. In connection with the calibration of foil thickness transducers) it was necessary to determine the influence of a certain amount of recycled product (replast) on the dielectric constant of the foil. Accurate dielectric constant measurements on polyethylene foil samples are not easy. The apolar character of this polymer with a very high electrical resistivity and very low dielectric constant/losses requires high resolution measurements to detect the potentially small differences. These capacitance measurements were performed therefore with a General Radio GRI621 Precision Capacitance Measurement System with a resolution better than 0.0001 pF. The accuracy is at least 0.001 pF and the temperature sensitivity is less than 0.003 pF/~ The measuring frequency of this system can be varied between i0 Hz. and I00 kHz. The liquid displacement method, described in ASTM D1531-62, is in fact the only proper method for accurate dielectric constant measurements on the thin (about 0.2 ram) foil samples. A gold plated ERA liquid cell with an electrode spacing of 1.435 mm was used for these measurements. The measuring

357 temperature was 21 + 0.4~ The density of the foil samples was also m e a s u r e d in order to correlate the dielectric constant results with the density values. These density m e a s u r e m e n t s were performed according to ASTM D1505-68 with the aid of a water/ethanol density gradient column at a temperature of 21.00~ _+ 0.01~ The frequency d e p e n d e n c y of the m e a s u r i n g m e t h o d was first investigated. The dielectric constant (E'r) of a CARLONA LDPE 25002FA (with 1.5 %wt. Ti02) was m e a s u r e d twice between i0 Hz. and I00 kHz.CARLONA LDPE 25002FA + 1.5 %wt. Ti02

~'r-value, I0 Hz.: 2.339 and i00 Hz.: 2.332 and 1 kHz.: 2.330 and 10 kHz.: 2.329 and 100 kHz.: 2.320 and

21~ 2.345 2.334 2.332 2.331 2.322

The ~'r value of the a p o l a r polyethylene should be frequency independent. Von Hippel [3] reports c'r values of 2.25 and 2.26 for a frequency r e g i o n from I00 Hz. up to I000 MHz. An electrode polarisation effect [4] might be the reason for the relative high ~'r values measured for frequencies ~ I00 Hz. The decrease of the ~'r values for frequencies ~ I00 kHz. is probably caused by the effect of parasitic m e a s u r i n g cell capacities which increase at higher frequencies. The m e a s u r i n g results in the frequency region b e t w e e n I00 and I0 kHz. are therefore considered to be the most reliable values. All measurements were p e r f o r m e d subsequently with a m e a s u r i n g frequency of 1 kHz.; the results are listed in Table 10.2. Lanza and Hermann [5] found for polyethylene a linear relation between the density and the dielectric constant a c c o r d i n g to. E'r = (2.01 x p) + 0.427

I0.I

Wurstlin investigated the validity of this relation and reported [6] that his experimental results agreed with the values calculated with equation I0.I. The dielectric constant values of the three pure i.e. nonfilled LDPE grades in Table 10.2, are calculated with e q u a t i o n i0.I. The agreement of these values with the experimental values is good. A d d i t i o n of Ti02 results in a density increase and in a slightly stronger increase of the dielectric constant. Both experimental dielectric constant values of the Ti02 filled samples can be calculated, however, with equation I0.i if the value of the added constant is increased from 0.427 to o.446. Subsequently, the dielectric constant values of the LDPE foil samples with different amounts of replast were c a l c u l a t e d u s i n g this m o d i f i e d relationship.

358

Figure 10.12 Correlation between measured and calculated dielectric constant values of LDPE 4-

2.35

LDPE foil

LDPE/TiO2

LDPE/TiO2/ 'replast' i

2.34

"0 m

:3 t~ 0

2.33 2.32

._~ D

r r 0 0 0

2.31 2.30 2.29 2.28 2.27 2.27

2.29

2.31

Dielectric constant (measured)

2.33

2.35

359 Table 10.2 Dielectric constant values of LDPE foils at 21~ and a frequency of 1 kHz. LDPE foil sample LDPE nonfilled CARLONA 18003GA DOW 150 ~j bOW ,L,~'X. 2 ~

p-value, g/cm3 ........

C 'r-value, measured

'r-value, calculated

0.9210 0.9208 0.9404

2.279 2.318

2.280

2.278* 2.278 2.317

,,,

......

C A R L O N A 25002FA/TiO2 + 0.7 %wt. Ti02 + 1.5 %wt. Ti02

0.9327 0.9384

2.322 2.330

2.321"* 2.332

C A R L O N A 25002FA w i t h 1.5 %wt. Ti02 and+ 0.0 %wt. replast + 4.7 %wt. replast + 12.8 %wt. replast + 22.7 %wt. replast i+ 32 -9 %W t- r e p l a s t

0.9386 0.9386 0.9305 0.9349 0.9326

2.332 2.324 2.322 2.321 2.319

2.333** 2.333 2.316 2.325

,,,

f ~

* calculated with constant** calculated with constant:

ii i,,

~':

"~!

,',"!

2.3,21 ......... j

0.427

0.446

The effect of the addition of recycled LDPE on the dielectric constant of the resulting foil m a t e r i a l s proved to be small. The dielectric constant value d e c r e a s e d for the i n v e s t i g a t e d system from 2.332 to 2.321 (average value); a decrease of 0.47 % due to the addition of up to 33 %wt. of recycled LDPE. The correlation (see Figure 10.12) b e t w e e n the m e a s u r e d and calculated dielectric constant values c e r t a i n l y decreases indicating an increase in the scatter of both the d i e l e c t r i c constant as well as the density values due to the a d d i t i o n of a certain amount of recycled LDPE.

10.8 The volume r e s i s t i v i t y e p o x y b a s e d m o u l d i n g p o w d e r systems during immersion in hot w a t e r Retaining a high electrical volume r e s i s t i v i t y in the p r e s e n c e of moisture is one of the most important p r o p e r t i e s of moulding powder resin systems w h i c h are used for the encapsulation of electronic components. The resistivity m e a s u r i n g p r o c e d u r e to compare such m o u l d i n g powder systems within an a c c e p t a b l e p e r i o d of time is accelerated by immersion of the samples in hot water. The volume resistivity of three epoxy based m o u l d i n g p o w d e r systems was m e a s u r e d as a function of the storage time in water at a temperature of 90"C.

===D~

(I) CO :3

"13 --(I) (I) _..Jk 0m ~. . 0 9

(/'3 "rl

3 3

,I~===,,-==,=~

0'~

0"~

361 Resistor shaped test samples with two embedded wire electrodes, see Figure 10.13, are used to p e r f o r m these experiments" These test samples were p r e p a r e d at a mould temperature of 180~ and a compression time of two minutes. Subsequently, the samples were p o s t - c u r e d during four hours at 180oC. The volume resistivity was determined by m e a s u r i n g the current flowing 60 seconds after application of a i000 Volt m e a s u r i n g voltage i.e. the so-called p(60) -value. This value is calculated according top - (v x A)/(I x d) where:

V I A d p

= = = = =

I0.2

applied voltage, Volt measured current, Ampere electrode area, m2 electrode distance, m a specific volume resistivity value, 0 h m . m

The electrode area and distance are a p p r o x i m a t e d by considering only the two opposing surfaces of the embedded wires as electrodes. S u b s t i t u t i o n of the known values for V, A and d results then inp

1.31/I

I0.3

The samples were immersed in d e m i n e r a l i s e d water for the ageing experiments and placed in an oven at 90~ â&#x20AC;˘ 2~ After a certain immersion time, a sample was taken out of the oven and cooled in water at a temperature of 20~ Subsequently, the sample was surface dried, connected with the m e a s u r i n g equipment and measured. This procedure was p e r f o r m e d in about five minutes. A separate sample was used for each measurement. It is important to realise that although the samples were stored in water at 90~ the resistivity m e a s u r e m e n t itself was p e r f o r m e d at room temperature. The m e a s u r i n g procedure was kept as short as possible, p(60) i.e. some time dependency of the m e a s u r i n g currents could stil be measured, to keep the moisture evaporation losses as low as possible. The results of the m e a s u r e m e n t s on the three epoxy based moulding powder systems are listed in Table 10.3. The same results are plotted as a function of the immersion time in Figure 10.14. The shape of these curves is clearly different. The best system (A) retains a high r e s i s t i v i t y value after more than 900 hours of immersion. The worst sample (C) clearly shows a kind of b r e a k - t h r o u g h effect after about 500 hours of immersion. System B is showing an intermediate behaviour.

362

Figure 10.14 Resistivity decrease of moulding systems versus the hot water contact time

system A

system B

system C

le+12 +

le+11 E ,,C

0 .>_

l e + 10

0~0

ct}

~ + ~

"~0

-~ 0 1e+09

le+08

le+07

,,j

200

, j,

400

.,,

600

Immersion time, hours

8OO

1000

363 Table

10.3 Results of the r e s i s t i v i t y m e a s u r e m e n t s on m o u l d i n g p o w d e r systems a f t e r i m m e r s i o n in w a t e r at 90~ .

Immersion time, hours

......

160 232 498 692 905

volume resistivity system A, Ohm.m ,

1.3E12 2.2Eli 3.9E10 2.0El0 7.7E 9 5.5E 9 5.5E 9 r

., r., r

~ I

volume resistivity s y s t e m B, Ohm.m

2.6E12 1.2El0 2.8E 9 2.2E 9 1.3E 9 9.4E 8 4.9E 8 I.,

,,,

,, J

, ....

volume resistivity s y s t e m C, Ohm. m

1.9E12 8.2E 9 4.1E 9 3.7E 9 3.1E 9 3.3E 8 2.3E 7 .

.....

364 10.9 The determination of the composition of a car-tyre rubber Carbon black filled, vulcanised rubber is still difficult to analyse with standard analysis techniques like FTIR and NMR. Application of the thermal analysis techniques TGA and DSC offers the possibility to obtain a reasonable impression of the composition of such a rubber sample. This is illustrated below by the results of TGA and DSC measurements on a rubber sample from a Michelin MXT 185/65-R14 cartyre. A sample of about i0 milligramme was subjected to the following temperature/time programme- heating from 20~ to 300~ at a rate of l~ and in a nitrogen atmosphere, - thirty minutes isothermal at 300~ heating from 300~ to 480~ at a rate of l~ five minutes isothermal at 480~ and switchting from nitrogen as sample purge gas to air, heating from 480~ to 980~ at a rate of I~ The so-called extractables or oil fraction are removed from the sample due to evaporation during the first two programme steps. The polymer fraction is, subsequently, removed during the third programme step due to thermal degradation. The carbon black fraction burns completely during heating from 480~ to 980~ in an air atmosphere. The anorganic components present in the rubber form, finally, the measured residues. -

The TGA experiment was performed during the night and took 15 hours and 35 minutes 'instrument' time. The results of this experiment are listed in Table 10.4. Figure 10.15 shows the DTGA curve measured during the thermal degradation of the polymer fraction (300~ - 480~ This DTGA curve shows two minima; the second m i n i m u m is slightly a-symmetrical on its low-temperature side. The temperature locations of both DTGA minima indicate that this cartyre sample is a blend of BR and NR rubber. Subsequently, about 15 milligramme of sample was used for a DSC Tg(onset)-value determination (heating rate 20~ This Tg-value determination was used to confirm the possible presence of a BR and a NR phase. All the values measured of this sample and the necessary reference values are collected in Table 10.4 The two separate Tg-values at -99~ and at -64~ confirm that the vulcanised rubber sample consists for 52 %wt. of a BR/NR blend (the Tgvalue of the BR phase might be shifted to higher temperatures due to the oil addition; the Tg-value of the NR phase is hardly influenced by the oil addition). The sample also contains 15 %wt. of oil and 32 %wt. of carbon black. About 25 milligramme of sample and about 16 'instrument' hours were necessary for this analysis.

PERKIN-ELMER 7 Series Thermal Analysis System

-0. !

-0, 2 A

-0, :8

.>_ !.._

-0, 4

o -0. 5

-0. 6

ItTX t O 5 / S 5 - R 14

-o. 7-

Figure10.15 DTGA/temperaturecurve

[ ........... 300.0

I. . . . . . . . . . 325. 0

~ . . . . . . . I.......... 350.0 375. 0

1 ...... 400. 0

Temperature

i 42S. 0

I 450. 0

! 475. 0

366 Table

10.4 R e s u l t s

,,, ,,

,,,,

',.,

of T G A / D S C analysis

14.5 52.0

o r g a n i c material,

, %wt.

66.5

, %wt. , %wt.

31.5 2.0

, %wt..

33.5

total

2. T G A r e s u l t s D T G A m i n i m a (primary) (secundary) DTGA reference minima BR r u b b e r (97 % cis) SSBR r u b b e r (23 %wt. styrene) NR r u b b e r (primary minimum) (secondary minimum) .

3. D S C r e s u l t s Tgl (onset) -value Tg2 (onset) -value DSC r e f e r e n c e v a l u e s BR r u b b e r ( v u l c a n i s e d / n o oil) NR r u b b e r ( v u l c a n i s e d / n o oil) ,.

10.10 The t h e r m a l

, oc , oc

448 360

, , , ,

440 430 345 397

~ ~ ~ ~

, ~ , "C

, ~ , ~

rubber r

, %wt. , %wt.

.. a n o r @ a n i c material,

I. . . .

1. T G A r e s u l t s e x t r a c t a b l e s (oil phase) polymer phase

carbon black residue

on a cartyre

-99 -64 -108 -66

s t a b i l i t y of A S B

It is n e c e s s a r y sometimes, t o increase the p o l a r i t y of an o r i g i n a l l y non- or l o w - p o l a r polymer, for e x a m p l e to print text on p o l y m e r films. One of the p o s s i b i l i t i e s to realise a p o l a r i t y i n c r e a s e is c a r b o x y l a t i o n of such a p o l y m e r with 3a z i d o s u l f o n y l b e n z o i c acid (ASB), see Figure 10.16. A f t e r l o o s i n g its n i t r o g e n atoms, the ASB r e s i d u e reacts w i t h the p o l y m e r molecules; the n u m b e r of acid g r o u p s b o u n d per polymer m o l e c u l e d e t e r m i n e s the p o l a r i t y of the c a r b o x y l a t e d system. A series of such c a r b o x y l a t i o n e x p e r i m e n t s w i t h PP p r o m p t e d us to i n v e s t i g a t e the thermal s t a b i l i t y of A S B itself and that of A S B in contact w i t h PP. A b o u t four m i l l i g r a m m e of A S B was, d u r i n g a n o n - i s o t h e r m a l TGA experiment, h e a t e d from 30oc to 500~ w i t h a h e a t i n g rate of 5~ U s i n g a h i g h e r h e a t i n g rate r e s u l t e d in an 'explosive' d e g r a d a t i o n reaction. The m a s s / t e m p e r a t u r e curve s h o w e d a t w o - s t e p d e g r a d a t i o n p r o c e s s w i t h D T G A m i n i m a at 191~ and 320~ A mass loss of 24.4 %wt. was m e a s u r e d b e t w e e n 1400C and 220~ The loss of the three n i t r o g e n atoms per atom ASB should results, however, in a mass loss of only 18.5 %wt. Hence, there h a p p e n e d m o r e than only loss of n i t r o g e n atoms d u r i n g this process.

367

Figure 10.16 3-azidosulfonylbenzoic acid

COOH I

O-S-O I N II N II N

368

0. 0 O I 3

O. 0013 C02,

o. o o 1 0

O. O00g

2364

502,

1376 ,:m-i J 2132

O, 0 0 0 5

O. o o l o

cm-I

1177

" 0.0000 cm-t

O. O001

O. O00S

O. 0003

O, 0 0 0 0 ' 4OOO

3500

3000

leJO0

,11

Iooo

I'rJO

ISOO

1250

tO00

I "rJO

450

O. 0000

Figure 10.17 cm" The average FTIR gas-phase spectrum measured between 175~ and 180oc during an A S B - 180~ experiment lO0.O

J ~

9. . . .

C 0 2 8bS. 8t 2364 c r n "

1 3 7 0 c r n "1

95.0

co2-=,,,.v.

O. 8 e 3 2

~.0O . OOOG

0.0024

e.eee4

8,0gl6

05.0

', \

so2-=,...-,,. ; / ,, \

,,'/-\

00.0

8.0906

,'5.0

1z4r O.O00g 5

3'3

Time, minutes Figure 10.18 The "I'GA mass/time and the FTIR S02-CO2 absorptio~time curves measured on ASB during a 180~ experiment

369 ASB samples were heated, subsequently, in a TGA - coupled FTIR system, to r e s p e c t i v e l y 160~ 170~ 180~ 190~ and 200~ The heating rate was 5~ T(isothermal) was m a i n t a i n e d for about twenty minutes until no further mass losses were detected. Figure 10.17 shows the FTIR gas-phase spectrum measured d u r i n g the 180~ experiment. C l e a r l y present in this this s p e c t r u m are absorptions due to C02 (2364 cm-l), S02 (1376 cm-l) and an azido effect (2132 cm-l). The presence of C02 is p o i n t i n g at d e c a r b o x y l a t i o n of the acid group. The presence of S02 is indicating that at 180oc already a further thermal d e g r a d a t i o n of the ASB molecules occurs. The azido absorption (2132 cm-l) and the absorptions at 1765, 1348 en 1177 cm-I indicate that a part of the ASB spontaneously evaporates. Figure 10.18 shows the T G A m a s s / t i m e curve during the 180oc experiment together with the intensity/time curves of the S02 and C02 absorptions. It is clear that the mass loss due to nitrogen loss is starting before the C02 and S02 p r o d u c t i o n starts. The S02 was less than ten minutes detectable in the TGA purge gas while the d e c a r b o x y l a t i o n process took about twenty minutes. These two effects proved to be nearly equal for all experiments p e r f o r m e d between 160~ and 200~ Integration of the absorption intensity/time curves and using calibration curves p e r m i t t e d to determine q u a n t i t i v e l y the amounts of C02 and S02 released during these experimentsexperiment with T(isothermal)

) ) ) ) )

160~ 170~ i80~ 190~ 200~

1.0 1.2 1.0 I.i I.i

%wt. %wt. %wt. %wt. %wt.

SO2 S02 S02 S02 S02

and and and and and

1.4 1.8 2.3 3.5 3.5

%wt. %wt. %wt. %wt. %wt.

C02 C02 C02 C02 C02

The S02 p r o d u c t i o n proved to be more or less constant over the temperature region investigated; it is the result of the d e c o m p o s i t i o n of about 3.5 %wt. of ASB. The acid group (-COOH) d e c a r b o x y l a t i o n process is clearly temperature dependent. The amount of C02 released during the 160~ experiment is the result of the d e c a r b o x y l a t i o n of 7.2 %wt. of the ASB sample. This amount increases to about 18 %wt. of the ASB sample during the 190~ experiments. Subsequently, these m e a s u r e m e n t s were p e r f o r m e d on PP/ASB mixtures. A PP powder samples was m i x e d with i0 %wt. of ASB on a rollerbank. About 40 m i l l i g r a m m e of this mixture was used for the TGA experiment i.e. the total amount of ASB present (4 milligramme) was the same as used d u r i n g the first series of experiments. Figure 10.19 shows again one of the FTIR gas-phase spectra m e a s u r e d during the 180oc experiment. Both the C02 and the azido absorptions are clearly present in this spectrum. The S02 absorption, however, is now clearly not present. D u r i n g all experiments was shown that no S02 was released if ASB

370

0.00|6

'|= r

2364

' u

0.0056

om-I

0.00t3

0.0013

! 176 c m - t

O.OOlO

m-|

0.0~1

O.m3

0.0003

0.0000 4000

3000

]000

WOO

17110

51900

1160

t040

?IS0

Figure 10.19 cm" The average FTIR gas-phase spectrum measured between 175~ and 180~ during a PP/ASB 9 0 / 1 0 - 180~ ex~dment

0.0000 480

371 decomposes in close contact with PP. The excess of reaction possibilities with polymer molecules seems to prevent the ASB decomposition process. The decarboxylation process of the acid group however p r o v e d to be not influenced be the presence of a p o l y m e r phase. These experiments thus clearly showed that e s p e c i a l l y the thermal instability of the acid group (decarboxylation) influences the efficiency of the PP carboxylation process.

i0.ii The thermo-analytical 'green' p o l y m e r

c h a r a c t e r i s a t i o n of a m a i z e based,

There is a growing interest for b i o l o g i c a l l y degradable polymer systems due to a combination of increasing environmental conservation demands and the continuously increasing technological progress of such so-called green polymers. Several research groups in the United States, Japan ans Europe are studying the p r o d u c t i o n processes and properties of these green polymers. A m a i z e - b a s e d polymer film sample, made in Japan, was investigated t h e r m o - a n a l y t i c a l l y in order to follow these developments. The film sample investigated proved to be a semi-crystalline polymer system with a DSC T g ( o n s e t ) - v a l u e of 16~ The DSC Tm(1)-value was 146~ with a Hf(1)-value of 18 J/g. The socalled 'processing-window' of this polymer p r o v e d to be about 50~ from 150~ to about 200~ This b i o - p o l y m e r proved to be (as usual) strongly moisture dependent. The e q u i l i b r i u m w a t e r saturation of the film in contact with water was 64 %wt., however visual detectable swellings effects were not noticed. TGA - coupled - FTIR/MS experiment was subsequently performed to get an impression of the thermal stability and the chemical structure of this material. A starch sample (p.a., ex-Merck) was used as reference material.

The TGA results in Figure 10.20 show a mass loss of 5.8 %wt. due to the loss of moisture absorbed. Besides, the DTGA curve shows two weak effects at r e s p e c t i v e l y 200oc and 236~ which were not detected for the reference sample (the d e g r a d a t i o n onset temperature of the reference sample was about 250oC). The TGA purge gas mass~time i.e. temperature curves in the Figures 10.21 A and C confirm the loss of absorbed moisture between 30~ and 100~ (mass intensity m a x i m a of m/z = 17 and 18 during the first fifteen minutes). The Figures 10.21A and 10.21B show at 200~ (35 minutes) a clear maximum for m/z = 17 i.e. a NH3 concentration maximum and at 230oC (40 minutes) a clear m a x i m u m for m/z = 44 i.e. a C02 c o n c e n t r a t i o n maximum. The MS results in the Figures 10.21B, 10.21C and 10.21D also show the release of C02 , H20 and some CO d u r i n g the main thermal degradation process (60 minutes/330oC) of this on maize based polymer sample.

100.0

-0.4

g5.0 "

1"1

38, t 65 ,C ~

T2 90.0 -

75.0

70.0

g4. 175 Wt.. Z

"0,0

\/ \

"0,2

.>_.

gg. g79 Wt;. Z

~ (9

85. 0 -

80. 0 -

131. 686

--0, 2

--0. 4

"-0. 6

-0. B

65.0 -

60.0 -

50.0

100.0

150. 0

200. 0

Temperature (~

250. 0

300, 0

--1.0

350. 0 RATE +: s.o'cJm~

Figure 10.20 The mass loss (TGA) and mass loss rate (DTGA) of the maize-based polymer sample during heating in a helium atmosphere

L~ ,,,.3 b3

373 e, T i

O. II~IB o.m

t (A)

= 17,

U.E. NH3

O . 4 N ~

----

TOTA+~

, J,

III " 1 ~ . _ , , ml.~.

PlMM+CX: I

Ill

e+_mm+T r

, ,

,_-,-

Sll

. . . .

.UC .: O,

llt~Inl

CPe CYCU[ ". e,W . . . .

(B) M ~ = 4 4 ,

I . I i

I.E. C02

I l'Ijlll

I'IJM

,:;.--.

TO+TIIL

.......

ID.3(IBm

.9, , u

.Ill..

INT.

re,slim

9,,,,,,

III :

? k * "

RA~,

_ _

III

[

â&#x20AC;¢

,.+

1[-~

M~=

.....

411 IT~tRT r162

:HI .

lie

SID

41,11

:__ IL_I

INrT.

[ ,q, e+I

"PU

CYC:LI: :. IP~!O

18,

I.E.

H20

+ TOTML t t ~ :

Q.&EllU

,,, _. . . . .

(C)

.,-/ 9 +

:.II

I~,

t , I

....

tl~..

Re~:~E-

"+. ? + ~ O , _ S l . . t

Lira

...... ST_mm+T C + C L [

ll:-I~

~0 :_ I . . . .

?ID

C~ln~l

.:_ e 4 l . . . . .

(D) M/Z=28,

I.E. CO

B. 4 B I O I.,qIQO

TOtlk

In T ! ! . "

IQ+ ?8,M,,On. 12_I

2~ . . . . .

I T M

~ t

r162

: +41

61 ....

~O CY.CU~"

[~ |

In J

. !

Figure 10.21 MS

intensityltime

curves for four different M/Z values as measured

during the TGA experment with the maize-based polymer sample

374 Figure 10.22 shows an average FTIR gas-phase spectrum measured at TGA temperatures between 200~ and 202.5~ after subtraction of the dominant C02 and H20 absorption effects. The strong absorption maxima at 932 and 966 cm-I confirm the release of NH3 as detected already with the MS. Also the strong absorption maxima at 2253 and 2285 cm-i are pointing at the presence of R-N=C=0 isocyanate groups in the TGA purge gas. These components were not detected by the MS (only a weak m/z = 43 m a x i m u m i.e. possibly H-N=C=O), possibly due to fragmentation of these components in the MS. The release of components like NH3, CO2 and R-N=C-O due to thermal degradation processes between about 150"C and 250~ from the maize-based polymer sample were not measured for the starch reference sample. This indicates that this maize-based polymer is in fact a chemically-modified-maize based polymer.

The case study reports 10.2 and 10.4 have been published before in the Thermische Analyse Bulletin (TAB). TAB is issued four to five times a year by the Thermische Analyse Werkgroep Nederland (TAWN), the Dutch Thermal Analysis Association. The case study reports 10.3, 10.5 and 10.7 will also be published in TAB.

375

O. o o s I

Ills

Ira- I ) ) M"NmC'O V|blPIt|OInll ~ISll eel-. I)

loll lilt

| . oo41

I~ql 9111

on-ll let)

) H

om"-I) e=-- I )

v i i i = i t , lone

I||OS

111 slim-I

Illl

II ll~JI

oam-I

en-l

" O.OOil

ZZllil ore- I II'll

O.ml

O,m

O, 0010

o. OOlO

4ooo

O. 00)!

O. OOlO

iSOO

=0oo

zsoo

~TSo

~50o

,zso

~ooo

75o

-O. 0000 4110

C m -1

Figure 10.22 The average FTIR gas phase spectrum (CO2/H20 subtracted) measured between 200~ and 202.5~ during the TGA experiment with the maize-based polymer film sample

376 References I. Nielsen, Mechanical Properties of Polymers and Composites, New York, 1974. 2. G.V. Vinogradov e.a., J. Pol. Sc., A-2, 1971, 1153-1171. 3. A. von Hippel, Dielectric Materials and Applications, J. Wiley, New York, 1954. 4. N. Hill, Dielectric Properties and Molecular Behaviour, Van Nostrand, London, 1969. 5. V. Lanza and D. Hermann, J. Polym. Sci., 28, (1958) p. 622. 6. F. Wurstlin, Ko11. Zeit., ii/, (1967) p. 79.

Index

377

abrasion resistance, 17 absorption, 81, 111, 151 " level, 113 abundance, 204 accuracy, 145, 356 ac properties, 123, 133, 175 acoustic elastometry, 109 " impedance, iii activation energy, 129, 140, 154, 183, additive, 26, 209, 232 ageing, 105, 312 alifatic acid, 47 " polyketone, 77 " amine, 172 alpha- crystallinity, 302 " -olefins, 235 alumel, 61 amine curing agent, 40 ammonia, 209 amorphous, 232, 233, 278, 283 " phase, Ii, 337 " " ageing effect, 314 " " transitions, 95, 312 amplitude, iii anaerobically aged, 105 angle of incidence, Ii0 iii anhydrite curing agent, 40 anisotropy, 79, 325 annealing, 28, 303, 342 annulus, 165 anti-static compound, 172 " " additive, 209, 354 " " epoxy GFR pipe, 177 aromatic oil, 22 " acid, 51 " amine, 172 Arrhenius, 129 " plot, 137, 154, 331 ASB (3-azidosulfonylbenzoic acid), 366 atactic-PP, 26 " vinyl BR, 282 atomic polarisation, 126, 181 attenuation coefficient, 111 axial direction, 179 Bo

backbone, 264 base-line, 16, 97 bending vibration, 209 benzoic acid, 201, 204 beta- crystallinity, 302 bis (2-ethoxyethyl) ether blend, 17, 95, 99

(BEE),

340

268

378 blowing agent, 105 boiling point, 204 Bolzmann' s constant, 183 bound ammonia, 219 " water, 214 branching, 232 brass disk electrodes, 184 breakdown phenomena, 123 brittle, 14 brownian motion, 126 Buccsi's theory, 181, 192 butyllithium, 17, 282 bulk modulus, 94, 119 CO

cable compound, 163 calibration DSC, 10 " TGA, 61 " TMA, 77 " dielectric cell, 147 " FTIR, 201 " MS, 201 capacitor, 171 capacity, 85, 124 capacitance bridge, 85, 356 capacitive coupling, 175 capillary, 85, 151 " tip temperature, 200 car-tyre, 17, 140, 364 carbon black, 26, 91, 140, 171, 177, 364 " monoxide, 77, 297 Carilon polymer, 77, 297 carbonyl dipoles, 302, 311, 336 carboxylated system, 366 case studies, 3, 339, 374 casting, 152, 155, 173, 222, 276, 339 chain flexibility, 232 " stiffness, 232 char, 268 charge carrier, 124, 173, 175, 183 " current, 133, 177 " process, 171 chemical structure, 230 cis-, 17 cobalt, 18, 282 " phthalocyanine, 209 cohesive force/energy, 232 compatibility, 19 compressional modulus, 94 compression moulding, 309, 312 complex quantity, 128 composite system, 151 condensation effects, 200 conduction, 171 conductive properties, 123

379 conductance loss, 130 connectivity indices, 232 coupled techniques, 188 correlation coefficient, 235, 241, 254, 355 corrosion protection, 158 Coulomb, 124 counter, 113 creep, 230 critical angle, 109 crossbeam ion source, 200 crosslink density, 105, 245 crosslinking, 14, 95, 232, 245 cruse oil, 158 crystallinity, 264, 283 crystallisation temperature (determination), " half-time value, 85 " process 345 crystalline phase (transition), 312, 337 crystallite perfection, 303, 306 " imperfection, 14 " size, 306 crystallinity, 318 cup-shaped electrode, 189 cure exotherm, 40 " reaction conversion, 43 " schedule, 248, 339 curing agent, 40, 177 current density, 124 cyanogen, 214 cycloalifatic amine, 172 cyclohexane, 10, 19 m

14, 345

dc properties, 123, 133, 172, 177 " conduction, 147, 334 Debey' s equation, 129 decay, 158 decomposition process, 62, 209 " products, 195 " temperature, 268 deconvolution procedure, 97 degradation product, 222 " onset temperature, 225, 228 density, 105, 147, 232, 302, 309, 310, 354, 356 derivative curve, 204 densification process, 314 DETA (dielectric thermal analysis), 3 4-4'diamino diphenyl methane (DDM), 248, 339 4-4'diamino diphenyl sulphone (DDS), 250 4-4'diamino diphenyl propane (DPP), 250 4-4'diaminophenyl (DP), 250 dicyanediamide, 222 dielectric analysis, 3 dielectric constant, 124, 133, 145, 147, 152, 158, 172, 309, 331

380 dielectric constant, 356 " properties, 123, 131, 327 " strength, 230 diffuse reflectance, 200, 219 diglycidylether bisphenol A (DGEBA), 222, dilatometry, volume-, length-, 77 diphenylolmethane (DPM), 345 dipole, 126, 183 " loss, 130 dipolar relaxation, 336 dipolarisation, 181 discharge current, 133, 163, 189 " process, 171 dissipation factor, 128 dissociation process, 183 distorsion, 113 distribution, 128 DMA (dynamic mechanical analysis), 3, 94, " /DETA, 188 double bonds, 282 drybox, 69 DSC (differential scanning calorimeter), " high pressure-, photo-, modulated-, DTGA curve, 364 dynamic stiffness, 342, 350

247,

339

314,

350

I0, 318, 3

E Q

emulsion SBR, 17 elastic response, 94 " (Youngs) modulus, 94, 105, 119 " constants, ii0, 119 electrical grade PVC, 163 " properties of, 327 electric field, 123, 179, 183, 192 electrification time, 166, 170, 354 " voltage, 167, 170, 354 electrode, 85, 133 electronegativity, 126 electronic conduction, 123 " polarisation, 126, 181 electrometer, 127, 131, 189 electrostatic charge, 158, 171 " properties, 177 " safety criteria, 171 embedded wire electrodes, 359 endblock, 184 endothermic effect, I0, 13 " fusion, 29, 345 end-use properties, 230 engineering polymers, 77 enthalphy relaxation, 11 epoxy coal-tar system, 163 " moulding powder system, 359 " powder coating, 40 epoxy resin, 43, 95, 105, 133, 171, 222,

247, 276

342,

364

381 epoxy coating, 151 " molar mass value (EMM), 247 equilibrium water saturation, 83, 152, 274, 276, 278, ethylene, 77 " glycol, iii evaporation, 72 evolved gas analysis, 195 exothermic process, i0, 222 expansion coefficient, 175, 322 extinction coefficient, 264 extractables, 364 extrinsic space charge polarisation, 181 F O

failure, 230 ferro-electricity, 123 ferromagnetic (Curie) transition, 61 field strength, 124, 177, 179 filler, 231, 233 fixed frequency system, 94 flexural modulus, 312 fragments spectrum, 204 free volume relaxation, 314 frequency, 94, 97, 105, 109, 113, 140, 192, friction, 230 frozen-in stresses, 79, 322 FTIR (fourier transform infra red),3 function generator, 113 functionality, 247 furan ring, 278 fused silica capillary, 196 fusion, 26, 297

331, 356

gamma relaxation, 312, 317, 331 guarded electrode, 131, 133, 145, 159 gas cell (FTIR), 196 gas constant, 129 gas-phase spectrum, 204, 209 glass-rubber transition, 189, 192, 327 " " " temperature determination, " " " region, 113, 137, 232 glass fibres, 26, 81, 322 glassy state, 175, 232 glycerol, 105, 201, 204 glycidylether of phenol novolack (GEPN), 222 gold electrodes, 327 green polymer, 371 group contribution additivity, 232 HI

Hamon equat ion, 130 Hartshorn equation, 155

314

382 Hct-value, 303, 309, 311 heat flow shift, 13 heat-flux DSC, 10 heating rate, 14, 62, 69, 97, 131, 183, 185 heat of fusion, ii, 14, " " reaction, 40, 47 " " vaporisation, 52 helium, 196 heterogeneous catalyst, 26 hexafluoro-isopropanol (HFIPA), 297 hexagonal crystal lattice, 26 hexahydro-phthalic anhydide (HHPA), 251 Hf-value, 14, 16, 29, 36, 231, 264, 277, 297, 302, 309, 345 Hf (i) -value, 342 Hf (max.)-value, 264, 299 high-potential electrode, 88, 159, 163, 184, 189, 354 high voltage source, 131 " " switching unit, 131 hydrogencyanide, 209, 222 hydrogen bonding, 222 " stretch, 209 hysteresis, 115 I I

immersion (water), 83, 109, 159 " time, 159, 167, 170 " transducer, 113 impact improver, 95 " resistance, 97 inclusion, 175 Indium, ii, 77 induced crystallinity (pressure-, polymerisation liquid-), 303 inert atmosphere, 62, 268 injection moulded, 327 inflection point, 89 in-phase component, 95 insulation resistance, 171 insulator, 124 interface, 175 interracial region, 158 internal mixer blended, 19 interferometer, 200 intramolecular, 278 intrinsic space charge polarisation, 181 ion-free water, 274, 314 ionic impurities, 154 ionol, 69 IR heaters, 201 IR spectrum, 204 IR absorptions, 214 IR vibrations, 219 irganox, 69 iron, 61 isocyanate, 105, 145

shear-,

thermally-,

383 isotactic-PP, 26 " vinyl BR, 282 isothermal crystallisation, isotropic, 79, 342

kaolin, 81 KBr windows, 196 kerosine, 159 key-parameter, 151 " -properties, 231, 277 Ki-value, 163 L O

laminate, 152, 155 LCP, 342 9 LCR meter, 131 1.e.c. (linear expansion coefficient), 79, 322 length dilatometry, 77 level detector, 113 life-time predictions, 107 ligand, 209, 214 lithium, 18 liquid displacement method, 356 liquid nitrogen, 111, 131 local mode relaxation, 331 long glassfibre reinforced, 322 longitudinal waves, 109 low-potential electrode, 88, 159, 163, 184, 189 " " " (spring-loaded), 354 loss factor, 331, 334 loss modulus, 94, 105, 312 loss maximum, 154 LVDT (linear variable displacement transducer), 2, 189 MO

mainchain, 233, 282 " " symmetry, 253 " " flexibility, 253 Maxwell-Wagner absorption, 152 mass increase (TGA), 288 " spectrum, 209 " transfer, 230 masterbatch, 47 matrix, 151, 175, 222, 342 MDI-index, 105, 145 measuring capillary, 88 mechanical waves, 109 " properties, 115 melting temperature determination, melt strenght, 350 mercury, 85, 159 mesophase, 342

384 metallocene catalyst, 26 methyl group, 311 methylisobutylketone (MIBK), 339 MgCI2 catalyst carrier, 69 mica, 81, 350 micrometer, 113, 119 mixture of, 111 moisture, 69, 81, 151, 155, 231, 274, molar mass, 232, 253, 299 " thermal decomposition function, " water content, 274, 276 molecular modeling technique, 232 " structure, 232, 247, 253 " weight, 231, 233 " " distribution, 231 " " increase, 293 monoclinic crystal lattice, 26 MS (mass spectrometry), 3 MS spectrum, 204 m/z-value, 204 N

312, 327 269

naphtenic oil, 22 natural rubber (NR), 19 network, 105, 175, 177, 247 " functionality, 245 " chain density, 245 n-dodecane, 54 nickel, 18, 61, 282 NMR, 264 non-linear behaviour, 147 non-polar, 183, 184, 282 n-tetradecane, 201 nucleating agents, 26 " efficiency, 35 nylon 6, 275 nylon 6.6, 81, 239, 256, 266 O I

oil-extention, 19 oligomers fraction, 269 " in PP, 62 oligomer sample series, 299 orientation polarisation, 125, orthorhombic unit cell, 302 oscilloscope, 113 out-phase component, 95 oxidative atmosphere, 268 P I

Peltier elements, 89 perkalloy, 61 permittivity, 128

181,

184,

192

385 phase transition, 230 phenolic-OH curing agent, 40 " " residue, 222 phenoxy resin, 240 photo voltaic properties, 123 piezo-electricity, 123 pKa-value, 47 plasticiser, 95, 151,. 167, 231, 233, 314 platinum, IIi, 159 Poisson ratio, 94, 119 polarisation, 123, 181, 183, 189 polarisability, 124 polarity, 232, 253 polar vapour, 204 poly-acrylonitrile (PAN), 240, 256 poly-alkylstyrene, 235 poly-arylene sulphone, 241 poly-butadiene (BR), 17, 115, 256, 262, 266, 271, 282, 294 poly-l-butene (PIB), 38, 235, 238, 256, 262, 266, 271, 292 poly-butene-terephthalate (PBT), 256, 262, 271 poly-carbonate (PC), 240, 256, 262, 271, 275 . " dichloro- , 240 " " , tetramethyl- , 240 " " tetrachloro240 " " , tetrabromo- , 241 poly- (cis-chloroprene), 238, 256 poly- chloro-paraxylylene, 239 poly-ether ether ketone (PEEK), 237, 240, 256, 262, 266 poly-ethylene (PE), 238, 261, 266, 271, 275, 294, 356 poly-ethyleneoxide (PEO), 261 poly-ethylene-propylene rubber (C2C3 rubber), 97, 238 poly-ethylene-terephthalate (PET), 239, 256, 262, 266, 271 polyethylene- succinate, 239 poly-formal, 240, 256, 266 poly- formaldehyde, 256 poly-l-heptene (PIH), 237, 238 poly-l-hexene (PIHex), 238 poly-isobutylene (PIB), 238, 256, 262, 271 poly-isobutylene oxide, 238 poly-isoprene (IR), 85, 238, 256, 271, 282, 288, 294 polymerisation process, 184 poly-methylacrylate (PMA), 235, 239 poly-methylmethacrylate (PMMA), 240, 256 poly-3-methyl butene-1, 239, 261, 266, 271, 294 poly-4-methyl pentene-l, 239, 261, 266, 271 polyketone (PK), 77, 297 polyol, 105, 145 poly(l-olefin) s, 36 poly- oxyisobutylene, 256 poly-oxymethylene (POM), 238, 256, 266, 271 poly- oxyt rimethylene, 238 poly-oxy-paraphenylene (PPO), 240, 256, 262 " " " , dimethyl- , 240, 261 poly-paraxylylene, 239 poly-l-pentene (PIP), 38, 238, 256, 262, 292 poly-pivalolactone (PPL), 256, 266, 271, 275

386 poly-propylene

(PP),

14, 26, 38, 64, 235, 239, 261, 266, 271, 275, 292, 342, 350 poly-propyleneoxide (PPO), 261 poly-styrene, 240, 256, 266, 271, 275, 294 " " foam, 354 poly-styrenebutadiene (SBR), 17, 115, 140, 184, 245 poly-sulfone, 241, 275 poly-tetrafluorethylene (PTFE), 196, 261 poly-trans 2.3 epoxybutane, 266 poly-thio-paraphenylene, 240, 256, 262 poly-vinylacetate (PVAc), 239 poly-vinylalcohol (PVA), 239, 256 poly-vinylchloride (PVC), 151, 163, 175, 184, 192, 239, 256, 275 poly-vinylfluoride (PVF), 239, 256 poly-vinylidene fluoride (PVDF), 238, 256 poly-vinylidene chloride (PVDC), 239, 256 poly-vinylpropionic acid, 239 poly-urethane (PU), 105 postcured, 133 power-compensating DSC, 10 precision, 13 precursor, 209, 214 processing procedure, 308 " window, 231 propagation direction, 109 " speed, Ii0 propylene, 77 pulse, 109, 113 " generator, 113 " length, 113 " travelling time, 113 purge gas DSC, 10, 54 " " TGA, 61 " " TMA, 77 " " TGA, 196 pyridine, 225 pyro-electricity, 123 O

quadrupole analyser,

200

radial direction, 177, 179 reaction exotherm, 47 recrystallisation temperature, 14, 26 receiver, 109, 119 recombination process, 183 reflection, 109 relative humidity, 147 relaxation effect, 95, 123, 141, 331 " time, 129, 158, 171, 183 repeatability, 13, 16, 167, 325 reproducibility, 13, 16, 89, 318 residual monomer, 231, 233, 253

387 residual reaction exotherm, 47 " solvent, 233, 253, 340 resistance thermometer, 131 resistive behaviour, 175 resistivity (volume), 3 resonant system, 94 resonance frequency, 113 rigid, 181 " PU foam, 105, 145 " amorphous phase [x(r,a)], 321 rolling resistance, 17, 113, 140 round robin test, 13 rubber, 17, IIi, 113, 181, 245, 282 " compound, 91 rubbery state, 175, 232, 282 " plateau, 350 So

sample " " " " " " " "

apertures, 111 dimensions, 77 disks, 111, 133, 145, 189, 327 high pressure pans, 47, 52 holder, 87, 111, 189 loading procedure, 69 " table, 72 nib, 64 pans, 14 " pill, 105 " sheet, 322, 325 " strips, 274 " weight, 14, 204 screen, 88, 189 seawater, 158 secondary relaxation effects, 181, 312 self-reinforcing composite system, 342 self-seeding effect, 16 semi-crystalline, 14 " -static Td(o)-value, 69, 269 shear modulus, 94, 119 " waves, 109, ii0 shift factor, 141 short-circuited, 127 shortcircuiting, 171, 179, 184 shrinkage, 77, 81, 322 side-chain crystallisation, 36, 235 side-group, 235, 253, 282 signal distorsion, 113 silicone oil, 111 silver effect, 189 " electrodes, 134, 189 simultaneous techniques, 3, 189 sinusoidal, 128 solution blended, 19 solvent in a thermoharding system, 339 SIS sequential block copolymers, 290 space charge polarisation, 183, 192

388 specific " " " " "

absorption, 209 heat, 95, 264, 318, 321 material properties, 337 thermal expansivity, 17 volume, 91, 264 volume resistivity, 124, 131, 133, 327, 334, 355 " surface resistivity, 355 spherical interstices, 155 spherulite size, 26 spherulitic growth rate, 264 sprue-plane, 79 stability, 189 " DSC, i0 stainless steel capillary, 196 steric effects, 232 step-wise heat flow shift, 13 stoichiometric, 43, 248 strain, 94 stray capacitance, 147 stretch vibrations, 214, 219 stress, 94 surface resistivity, 354 surface tension, 177 susceptibility, 129 symmetrical polymers, 253 syndiotactic- PP, 26 " vinyl BR, 282, 286 synthesis, 209

158, 163,

172, 177,

tacticity, 232, 253 tail structures, 184 talc, 26 tan delta, 95, 105, 128, 133, 140, 147, 152, 309, 331, 342 tankcoating system, 158 tapered SSBR, 184 tapwater, 163 TA (thermal analysis), 2 Tc-value, 14, 16, 28, 36 Tc (i) -value, 342 Td(0.5)-value, 62, 268 Td (o) -value, 62, 268, 278 Te-value, 14 TGA (thermogravimetric analysis), 3, 268, 288, 364 " /DSC, /DTA, /FTIR, /GC, /MS, 188 TGA - coupled - FTIR/MS, 195, 369, 371 Tg-onset value, 13, 172, 231, 277, 283, 286, 290, 314, 318, 340, "342 Tg-value contribution per crosslink, 250 " " determination, ii, 318 " " increase, 293 " " of, 17, 36 " " " crosslinked epoxy resin systems, 249 " " " crosslinked polymeric systems, 245

389 Tg-value of vinyl polymers with linear sidechains, 235 Tgl-, Tg2-value, 51 Tg (midpoint) -value, 77 Tg/Tm correlation, 254 thermal expansion coefficient, 77, 189 " history, 16, 28, 253 " insulation, 105 " stability, 61 ,231, 268 " transitions, 181 thermally stimulated current, 181 thermo-luminosence, -magnetometry, -optometry, - sonimetry, 3 " -electrometry, 123 " -dilatometry, 77 thermogram, 13, 30, 31, 34, 37, 40, 41, 42, 48, 55, 57. thermosetting resin, 40 thermostat bath, 111, 131 Ti-value, 342 TIC14 catalyst, 69 ,' .DIBP complex, 69 time, 94, 141 " /temperature superposition, 140 " dependency, 177 tin, 11, 18 Tin-, Tml-, Tin2- (value), 14, 16, 28, 36, 231, 253, 277, 286, 297, 302, 309, 345 Tin-value depression, 297 Tm(o)-value, 254, 299 Tm'-value, 303, 309, 311, 342 TMA (length -, volume - thermomechanical analyser), 2, 3, 322 " /DETA, 188 T-onset, II torsion pendulum apparatus, 94 toughened PP, 95, 97 toughness, 230 tracking, 230 trans-, 17 transducer, ii0, 113 transfer line, 196 transmitter, 109 transmission, 109 transition, 175 transverse waves, 109 tribo-electricity, 123 triclinic crystal lattice, 26 trigger signal, 113 " unit, 113 trimethylpyridine, 225 TSDA (thermostimulated discharge analysis), 3, 123, 181 TSD/TMA, 189 UO

Udel, 240 UL-index, 268 ultimate properties, 230 ultra-high molecular weight PP, 350

390 ultra-low heating rate TGA, 225, 269 ultra-sonic beam, 113 " " loss factor, iii " " measurement s, 109 " " properties, Ii0 Underwriters Laboratories Testing Procedure, unsymmetrical polymers, 253 VQ

vertical furnace TGA, 196 vibrate, 109 vibration, 204 vinyl-, 17, 235 viscous response, 94 voltage, 166 " supply, 189 volume dilatometry, 85 volume resistivity, 354 vulcanizate, 85, 245 vulcanised rubber, 364 WO

water absorption, 151, 274 " clusters, 158 wavelength, 109, 204 wear, 230 weight loss, 268 wet deposition technique, 322 wet grip, 17, 113, 140 WLF-equation, 141 wollastonite, 81 X.

x (c) -value, 300, 302, 309, 310, X-direction, 322, 325 x-ray diffraction (XRD), 297 x-ray scattering (XRS), 264 XRD spectrum, 303 Y"

Y-direction, 322, 325 yield strength, 230 Z Q

Z-direction, 322, zero, 126, 147

325

321,

350

268