Mechanical and Thermal Behaviour of Hybrid Filler Reinforced PP/ABS Blend

Mechanics, Materials Science & Engineering, July 2017 – ISSN 2412-5954

Mechanical and Thermal Behaviour of Hybrid Filler Reinforced PP/ABS Blend1 S.M.D. Mastan Saheb1, P. Tambe2, M. Malathi1 1 – School of Advanced Sciences, VIT University, Vellore, India 2 – School of Mechanical Engineering, VIT University, Vellore, India DOI 10.2412/mmse.31.28.3 provided by Seo4U.link

Keywords: polypropylene (PP), blends, composites, fillers.

ABSTRACT. In this study, the influence of Halloysite nanotubes (HNTs) and intercalated graphite (IG) on the mechanical and thermal properties of polypropylene (PP)/acrylonitrile butadiene styrene (ABS) blend were studied. Hybrid fillers reinforced PP/ABS blends were processed using twin screw extruder followed by injection moulding. The addition of hybrid fillers increases the crystallinity of PP phase of PP/ABS blends and its composites. In addition, hybrid fillers increase the thermal stability of PP/ABS blends. Transmission electron microscopy (TEM) studies and solution experiments show the selective localization of hybrid fillers in PP phase of PP/ABS blend and its composites. Further, scanning electron microscopy (SEM) studies of cryo-fractures and etched PP/ABS blends and its composites samples show the formation of matrix-droplet morphology. Due to increase on crystallinity of PP phase, selective localization of hybrid fillers and an interaction between hybrid filler and PP phase results in an enhancement in tensile modulus and impact strength of hybrid filler reinforced PP/ABS blend. The increase in tensile modulus and tensile strength are and respectively.

Introduction. Polymer blend of polypropylene (PP) and acrylonitrile butadiene styrene (ABS) are of commercial interest [1], [2]. PP is attractive commodity plastics due to its low cost, and addition of ABS overcomes the low impact properties of PP, as ABS has good impact properties [3], [4], [5], [6].

PP/ABS blends are compatible using various compatibilizers [5], [6], [7]. Recently, Kubade et.al [1] reported that the compatibilizer influences mechanical and thermal properties of PP/ABS blends significantly, because compatibilizer refines PP/ABS blend morphology. They used polypropylene grafted maleic anhydride (PP-g-MA) and styrene-ethylene, butylene-styrene triblock copolymer grafted with maleic anhydrite (SEBS-g-MA). In polymer blend, filler material are added to improve the properties and process ability of polymer blends. The various fillers added in PP/ABS blends are carbon black (CB), Halloysite nanotubes (HNTs) and multiwall carbon nanotubes (MWNT) [1, 2, 8, 9]. Hom et.al [8] shows the electrically conducting behaviour in case of 10 wt.% of CB in 55/45 PP/ABS blend, due to formation of co-continuous morphology. Khare et. al. [9] demonstrate that noncovalently modified MWNT in PP/ABS blend show enhanced electrical conductivity at low concentration of MWNT. In addition, Kubade et.al. [2] shows that surface modified HNTs helps on achieving better dispersion of HNTs in PP/ABS blends, and subsequently enhanced the mechanical properties significantly. So far, there are no reports regarding the use of dual filler in PP/ABS blends.

In this regard we are attempting to study the use of dual fillers in PP/ABS blends in presence of dual compatibilizer. The filler materials used were HNTs and intercalated graphite (IG). Compatibilizers used were PP-g-MA and SEBS-g-MA. PP/ABS blends and its composites were prepared using twin screw extruder followed by injection moulding. The prepared samples were characterized using various characterization techniques.

Materials and experimental procedure. PP of trade name REPOL 110MA was supplied by Reliance Industries, Ltd, India. PP-g-MA was supplied by Pluss Polymer Ltd, India. SEBS-g-MA was supplied by Karton, India. ABS of Terluran GP-22 was supplied by Strylotion, India. Halloysite 1

© 2017 The Authors. Published by Magnolithe GmbH. This is an open access article under the CC BY-NC-ND license http://creativecommons.org/licenses/by-nc-nd/4.0/

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nanotubes were kindly supplied by Imerys Tableware, New Zealand. Melamine and graphite powder was supplied by Sakshi Dies and Chemicals, India. PP/ABS blends in a ratio of 80/20 and its composites were processed using twin screw extruder of S. C. Dey & Co., India, which was operated at 155-210-240oC with a rotational speed of 10 rpm. In addition, pure blend sample was also prepared.

Extruded strand was injection moulded using injection moulding machine of S. C. Dey & Co., India, operated at 235 oC and applied pressure of 7 bar. The concentration of HNTs was 1 wt.%. and IG was 4 wt.%. IG was prepared by mixing melamine and graphite in 3: 1 ratio in a ball mill for 6 hours.

Characterization. HNTs and IG were characterized using transmission electron microscopy (TEM) of JEOL JEM 2100. The tensile testing of samples were tested on universal testing machine, Instron (8801) according to ASTM D638; and impact testing of samples were tested on CEAST (Instron) pendulum impact tester according to ASTM D256. Thermo gravimetric analysis (TGA) of samples were performed on Q500 from TA instruments in the heating rate of 10oC/min in temperature range of 25 to 900oC. Scanning electron microscopy (SEM) of samples were performed over Hitachi SU 3500. Differential scanning calorimetric (DSC) measurements of samples were carried out using a DSC Q200 from TA instruments in the temperature range from 25 ºC to 235 ºC at a scan rate of 10 ºC/min under nitrogen atmosphere. The degree of crystallinity (Xc) of PP phase was calculated from the ratio of normalized heat of fusion (Hm, norm) of second heating run to the heat of fusion of normalized 100% crystalline PP, (Hm)100%, which was calculates as 207 J/g [1].

Results and discussion.

Fig. 1. TEM images of (a) HNTs, (b) IG (c) & (d) PP/ABS blends and its composites, (e) SEM image of PP/ABS blends and its composites, (f) Solution experiments.

The Fig. 1 (a-b) shows TEM image of HNTs and IG respectively. It depict HNTs have hollow tubular structure, while IG having two-dimensional platelets. The measured HTTs diameter is 60-80nm, while IG size is in microns. HNTs and IG are mixed with PP/ABS blends in presence of compatabilier MMSE Journal. Open Access www.mmse.xyz

Mechanics, Materials Science & Engineering, July 2017 – ISSN 2412-5954

using twin screw extruder. The extrude strand was microtome and TEM image was taken. Fig. 1c show the TEM image of PP/ABS blends and its composites. It shows the dispersion of HNTs and IG in PP/ABS matrix. The size of IG particles in several hundred nanometers, as seen in Fig. 1d. In addition, HNTs is localized near ABS phase. The interfacial calculation of PP-HNTs pair and ABSHNTs pair suggest the affinity of ABS towards ABS phase [2]. But, due to the formation of layer of SEBS-g-MA around ABS phase, SEBS-g-MA restricts the HNTs in PP phase [1], [2]. It was noted that interfacial tension of SEBS-g-MA-HNTs pair is higher than HNTs-PP pair. The SEM image of cryo-fractured morphology of hybrid filler reinforced PP/ABS blend show the formation of matrixdroplet morphology (Fig. 1e). It was found that hybrid filler reinforced PP/ABS blends has refined morphology as compared to PP/ABS blend (not shown here). Further, solution experiments were carried out to probe the dispersion of HNTs and IG in PP/ABS matrix. PP/ABS blend and its composites was dissolved in terrahydrofurane and xylene respectively to dissolve ABS and PP phase.

Fig. 1 (f) show the dark colour solution of PP phase dissolved in xylene, depicting localization of fillers in PP phase, while other glass vial of ABS dissolved in THF shows no trace of fillers.

100

6

(b)

PA PA1H1G

80

Weight (%)

Heat Flow (W/g) exo

(a)

4

2

60 40 20

0 100

110

120

Temperature (oC)

130

0 200

PA PA1H1G

300

400

500

Temperature (oC)

600

700

Fig. 2. (a) Crystallization exotherm and (b) TG curves of PP/ABS blends and its composites.

The influence of HNTs and IG on the crystalline behaviours was characterized using DSC. Fig. 2a shows the crystalline exothermal of PP/ABS blends and its composites. The crystallization temperature (Tc) of PA/ABS blend is 121.3 oC, while Tc of PP/ABS blends and its composites is 120.3 o C depicting dereaase in crystallization rate. The decrease in crystallization is due to interaction of filler and matrix. Similar study was observed by various researcher earlier [10], [11]. Melting temperature (Tm) of blends were recorded from the melting endotherms of PP/ABS blends and its composites. The Tm of hybrid filler reinforced PP/ABS blend is higher as compare to PP/ABS blend, as noted from melting endotherms. Percent crystallinity (Xc) of PP/ABS blends and its composites was calculated. Xc value of hybrid filler reinforced PP/ABS blends and its composites is 39.1 %, while Xc value of PP/ABS blends is 46.2%. This observation depict interaction between filler and matrix helps in formation of more PP crystals.

The influence of HNTs and IG on the thermal behaviour of PP/ABS blends was characterized using TGA. Fig. 2 b) shows the TG curve of PP/ABS blends and its composites. TG curve of hybrid filler reinforced PP/ABS blends is shifted towards higher temperature as compare to PP/ABS blend. This observation confirm the enhancement in thermal stability of polymer with an incorporation of HNTs and IG. The differential of TG curve were carried out and maximum degradation temperature (Tdeg) was noted. Tdeg value of hybrid filler reinforced PP/ABS blends and its composites is 466 oC, while Tdeg value of PP/ABS blends is 485 oC. The increase in thermal stability is due to the interaction between fillers and polymer.

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Mechanics, Materials Science & Engineering, July 2017 – ISSN 2412-5954

(b)

960 PA PA1H1G

930 900 870 840

Tensile Strength (MPa)

Tensile Modulus (MPa)

(a)

32 28

PA PA1H1G

24 20 16 12

810

Impact Strength (KJ/m2)

(c)

200 PA PA1H1G

(d)

150

100

50

0

Fig. 3. (a) Tensile modulus, (b) Tensile strength, (c) Impact strength of PP/ABS blends and its composites (d).

The extruded stands were injection moulded as per ASTM standard for tensile and impact testing.

Fig. 3a-b shows the histogram of tensile modules and tensile strength of PP/ABS blends and its composites. Tensile modulus of hybrid filler reinforced PP/ABS blend is higher as compare to PP/ABS blend. The increase in tensile modulus is due to refinement in morphology of hybrid filler reinforced PP/ABS blend, increase in crystallinity of PP phase, selective localization of fillers in PP phase, and interaction between HNTs and IG with polymers. There exist an interaction between nitrile group of ABS and maleic anhydride group of SEBS-g-MAH [12], which restrict the deformation of ABS droplets result in an enhanced stress transfer from PP phase to ABS phase. The combined effect of these observation enhance the tensile modulus of hybrid filler reinforced PP/ABS blend. Tensile strength of hybrid filler reinforced PP/ABS blend is lower as compare to PP/ABS blend. The decrease is due decrease in modulus of rigidity of hybrid filler reinforced PP/ABS blend. Impact strength of hybrid filler reinforced PP/ABS blend is higher as compare to PP/ABS blend. Due to interaction between hybrid filler and polymer, it results in restricting delamination of fillers and prevent the catastrophic crack propagation. Fig. 3 (c) shows the pull out of ABS from the blend matrix. This observation depicts that droplet pull out occur due void growth at PP/ABS interface or cavitation, which resulted in enhanced energy absorption. These are the reason responsible for the remarkable enhancement in impact strength of hybrid filler reinforced PP/ABS blend.

Summary. Hybrid fillers reinforced PP/ABS blends in presence of compatibilizer were successfully prepared using twin-screw extruder followed by injection moulding. TEM observation reveals HNTs is localized near the ABS phase, while the IG is in PP phase. Solution experiments also confirm the localization of hybrid fillers in PP phase. The localization of hybrid fillers influences the crystallinity of PP phase. Percent crystallinity of PP phase is higher by an addition of hybrid fillers in PP/ABS blend. Thermal stability of PP/ABS blend increases due to addition of hybrid fillers. Due to increase on crystallinity of PP phase, selective localization of hybrid fillers and an interaction between hybrid filler and PP phase results in an enhancement in tensile modulus and impact strength of hybrid filler

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Mechanics, Materials Science & Engineering, July 2017 – ISSN 2412-5954

reinforced PP/ABS blend. The mechanism of increase in impact strength is due to void growth or cavitation.

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