Efficient Networking Towards Novel Products and Processes Programme Report 2010–2013 by Fibic

Ohjelmatunnukset

Efficient Networking Towards Novel Products and Processes Programme Report 2010â&#x20AC;&#x201C;2013

13 Ohjelmatunnukset

Efficient Networking Towards Novel Products and Processes Programme Report 2010â&#x20AC;&#x201C;2013

Content

Foreword .........................................................................................................................................................5 High consistency forming of microfibrillated composite webs ................................................. 14 Foam Forming ............................................................................................................................................30 Fiber-based products for new applications ....................................................................................48 Microcelluloses and their characteristics .........................................................................................66 Resource-efficient papermaking concepts .....................................................................................90 Management of web uniformity based on imaging measurements .................................... 108 Expanded operating window for printing process enabling efficient use of newly engineered fiber-web substrate ........................................................................................... 130 Optimizing structures and operation of entire production systems .................................... 146

Copyright Finnish Bioeconomy Cluster FIBIC 2013. All rights reserved. This publication includes materials protected under copyright law, the copyright for which is held by FIBIC or a third party. The materials appearing in publications may not be used for commercial purposes. The contents of publications are the opinion of the writers and do not represent the official position of FIBIC. FIBIC bears no responsibility for any possible damages arising from their use. The original source must be mentioned when quoting from the materials. ISBN 978-952-67969-0-1 (paperback) ISBN 978-952-67969-1-8 (PDF) Layout: Brand United Ltd Printing: Kirjapaino Lรถnnberg

FOREWORD

The Finnish forest industry is undergoing radical changes. The decline of the graphic paper sector means urgent efficiency improvements in existing products and processes are needed together with the establishment of a new earnings base from novel products and processes. In 2008 these needs initiated the Forestcluster research programme Intelligent and Resource Efficient Production Technologies (EffTech), of which the three-year research programme Efficient Networking towards Novel Products and Processes (EffNet) was a direct extension. The high business volumes of the forest industryâ&#x20AC;&#x2122;s existing products presents a big challenge for any new product to reach similar volumes. Transformation of the industry will, for this reason alone, take time. All possible means to improve the competitiveness of current production must therefore be taken in the meantime, as it is this competitiveness that will enable the risky, but necessary, renewal of the industry. The overall goal of EffNet was to improve the competitiveness of the whole forest cluster by developing radically new energy- and resource-efficient production technologies and by finding means to reduce capital intensiveness. The focus was twofold: firstly to develop new energy- and resource-efficient web production technologies and, secondly, to re-engineer the product concept of fibre-based products with nanocellulose. The target was to develop and demonstrate new types of products manufactured from wood-based fibre material and to expand the current product portfolio offered by forest cluster companies. New technologies always carry risk. Cooperating across the whole value chain in a common programme towards a common goal, however, gives us the combined force needed to create and evaluate new ideas and to bear the development and implementation risks. EffNet has created bright opportunities to improve raw material efficiency and develop new products. Our goal now is to carry these forward as successful innovations.

Jyrki Huovila Metso Paper Chairperson of Programme Management Group

NEW SOLUTIONS AND ADDED VALUE FROM THE EFFNET PROGRAMME

Raw material, energy and water efficiency are

and use of new raw materials and novel fibre-

increasingly dominant drivers of forest indus-

based product concepts were created. Several

try investment. Incremental changes and lin-

technologies demonstrated at laboratory and

ear extrapolation of current practices will no

pilot scale show remarkable techno-economi-

longer guarantee a healthy and robust indus-

cal potential.

try. Future paper machine concepts will far outperform current technologies in resource and capital efficiency. The most competitive prod-

Raino Kauppinen, Stora Enso:

ucts of today must be used to bridge the gap to

â&#x20AC;&#x153;The high applicability of the results reflects

the renewed forest industry of tomorrow.

the quality of the research and a clear

The EffNet programme addressed these

understanding of real-life challenges.â&#x20AC;?

challenges by exploring novel applications for new materials, particularly nanocellulose. The aim was to improve resource efficiency and create a wider product space also within existing product categories.

Sharper competitiveness through foam forming The technology with the highest value crea-

New ideas, successful product concepts

tion potential was foam forming. The method was shown to significantly reduce capital inten-

The EffNet programme targeted research ar-

siveness and resource consumption and thus

eas of key strategic importance to the paper

improve the competitiveness and sustainabil-

industry, the renewal of which requires high-

ity of current paper and board products. The

risk research towards achieving radical devel-

technology also paves the way for forest in-

opment steps. EffNet succeeded in delivering

dustry renewal by enabling raw materials to be

this calibre of research.

combined in revolutionary new ways, creating

In the EffNet research programme new knowledge, practicable ideas for new products

unique opportunities for companies to enter new value chains.

The development of foam forming in EffNet has opened up a totally new research track for

Novel tools to improve production efficiency

the development of novel products. This important achievement may not have been possible

Image-based measuring systems were devel-

without the combined force of a sizeable con-

oped to improve the process efficiency of both

sortium and public support. Foam forming pre-

existing and potential production systems,

sents exciting opportunities for the use of ex-

such as foam forming. The image-based quali-

isting raw materials and current production

ty monitoring technologies enable process op-

infrastructures, but also offers fertile ground for

timization and lead to direct improvements in

new, competitive applications beyond conven-

production efficiency. A developed new image

tional paper and board. Foam forming brings

analysis method for tissue paper provides fast

a fundamental change to the way fibre webs

and accurate information for optimizing crep-

can be formed and enables milestone improve-

ing in tissue production. The new method en-

ments in raw material efficiency. The technology

ables evaluation of the effect of chemicals in

opens up new product property windows and is

the creping process, thus leading to radical

set to make significant inroads in board making.

process efficiency improvements. Fast imaging technologies can improve competitiveness in both current and future paper processes.

Knowledge and cost optimization In todayâ&#x20AC;&#x2122;s cost-pressure environment, the need for new solutions is acute. In EffNet, the

Marjatta Piironen, Kemira:

biggest

â&#x20AC;&#x153;Innovative image-based technologies were

innovations in papermaking have

been achieved with high-filler concepts. Re-

developed in the EffNet programme. Without

search into microfibrillated cellulose filler ag-

EffNet this would have been very difficult or

gregates and starch-based biominerals also

even impossible.â&#x20AC;?

showed high potential for achieving good paper properties and cost savings. The development of binding fillers and novel utilization of cellulose fibrils opens opportunities to develop new paper grades and bring cost benefits.

Big potential from microfibrillated celluloses

Printability research achieved important new findings, expanding current knowledge

New technologies and utilization of microfibril-

and supporting the further development of

lated cellulose (MFC) in paper and board man-

printing papers. The printing efficiency results

ufacturing will impact the paper chemicals

have proven useful and practical. The partici-

industry in the future. The new knowledge cre-

pating companies have been able to utilize the

ated by EffNet will help companies design their

results in their existing business, for example

future chemical portfolios. MFC has consider-

by providing new pillars of customer support.

able application potential through combining

From the viewpoint of printing companies, one

various materials and techniques. One prom-

of the most promising results came from the

ising future application for MFC is in the fast-

development and test runs of a novel printing

growing industry of super-absorbent polymers.

paper. The test runs demonstrated good runnability of the new paper and the concept provides a firm basis for future development.

Power through networking

Creating value and new business

Close collaboration between companies and

The EffNet programme has contributed to new

EffNet researchers created new opportunities,

value and business creation in key areas of the

broader insight and networks for the future.

forest sector. These valuable results must now

According to the participants, networking has

be carried forward with further testing and eval-

been valuable and productive both within and

uation, for example at the pilot scale. Sever-

outside the research consortium. Close and

al participating companies have already based

open cooperation between key players and

their future business and development projects

experts generated a broad pool of expertise

on the research areas of the EffNet programme

and was considered an essential aspect of the

and will implement these projects in collabora-

programme.

tion with one or more EffNet partners.

The networks established in product safety

The results and technology concepts devel-

and characterization of nanocellulose were a

oped in the EffNet programme provide a sol-

valuable addition to the programme, and com-

id basis for further development towards new

pany seminars were also highly appreciated.

industrial solutions, generating value and new

Participants also gained insights into interna-

business opportunities for the forest industry.

tional research in several leading areas, such as process design, image-based measurement, nanocellulose applications and foam chemistry. The networking opportunities and contacts built during the programme will be of significant value in future development projects. Knowledge of the competence areas of researchers in different universities and institutes will also greatly facilitate future cooperation.

Jyrki Huovila, Metso: â&#x20AC;&#x153; Networking means having more power to create new ideas and evaluate them throughout the value chain, and to share the risks of new technologies.â&#x20AC;?

The EffNet programme has had two impor-

Human technology, one of the strategic re-

tant strengths: effective networking between

search areas of the University of Jyväskylä,

partner companies, research institutes and

plays a central role in the interactive method-

academia in Finland, and a sufficiently long

ology for multi-objective optimization devel-

funding period. These have enabled serious

oped by the university’s industrial optimiza-

research efforts to generate radical solutions

tion research group. The research conducted

to improve the competitiveness of Finnish for-

in EffNet supports this major research area.

est industry companies.

The industrial optimization research group

The role of VTT Technical Research Centre of

participated in the Effnet programme in devel-

Finland in the EffNet programme has been cen-

oping and applying theory and methods and

tral and in line with VTT's objectives of creat-

software development for decision support.

ing high-level scientific and techno-economic knowledge and know-how and generating technology and innovations for industry and society.

Kaisa Miettinen, University of Jyväskylä, Department of Mathematical Information Technology:

Erkki Hellén, VTT:

“The programme provided interesting and

“Without the five-year funding period, the next-

novel research problems and gave valuable

generation resource-efficient technology with

experience in dealing with the challenges of

the highest potential, foam forming, would have

complex real-world problems.”

not been developed to the level it is at now.”

The EffNet programme has demonstrated how The research strategy of the Measurement In-

companies can collaboratively use Finnish

formation Group at Tampere University of Tech-

world-class research environments in effec-

nology is to develop generic design and oper-

tive and iterative ways to develop new prod-

ational methods for dynamic systems whose

ucts, leading to fruitful and continuous dia-

behaviour includes stochastic aspects. There

logue between researchers and industry. The

has been a strong synergy between programme

programme has activated international collab-

objectives and research objectives: the prob-

oration, built new contacts, educated young

lems specified by the programme have provided

researchers, created novel information and

practical test benches for generic research.

generated strategic opportunities for future research and solutions development.

Risto Ritala, Tampere University of Technology: “The combined scientific and application oriented research has provided us good opportunities for publishing results and advancing the doctoral studies of our researchers.”

introduction

1. Background The National Research Strategy of the Finnish

The focus of the EffNet programme is on de-

forest-based sector was published in 2006.

veloping radically new energy- and resource-

To help implement the strategy, the public-

efficient web production technologies and

private partnership Forestcluster Ltd was es-

designing

tablished in 2007 with the main goal of taking

concepts and novel, innovative products.

nanocellulose-based

production

forward the research priorities outlined in the

The overall goal of the EffNet programme

strategy. Today, the Finnish Bioeconomy Clus-

was to develop sustainable solutions to en-

ter (FIBIC) has activities in three strategic fo-

sure the leading position of the Finnish for-

cus areas: Intelligent, Resource-Efficient Pro-

est cluster in the large-scale production of fi-

duction Technologies, Future Biorefinery and

bre-based printed and packaging products.

Sustainable Bioenergy Solutions.

The three-year research programme had total

Research programmes are the core of FIBICâ&#x20AC;&#x2122;s

budget of 15 million euros. The Finnish Funding

operations. Their aim is to foster collaboration

Agency for Technology and Innovation (Tekes)

between end-users, companies and research-

provided 60% of the financing, with the re-

ers in creating opportunities for research and

mainder sourced from the participating com-

new business through open innovation and new

panies and research institutes.

ways of networking, and to speed the transition from research results to commercial products. Intelligent and Resource Efficient Produc-

2. Programme portfolio and goals

tion Technologies (EffTech) was the first re-

search programme launched by Forestcluster

The Efficient Networking Towards Novel Prod-

in 2008. In the second phase (2010-2013), the

ucts and Processes (EffNet) programme aimed

EffTech programme was divided into two in-

to enhance the competitiveness of the whole

terlinked programmes in order to sharpen the

forest cluster by developing radically new en-

research focus and to diversify the number

ergy- and resource-efficient production tech-

of research participants. The three-year re-

nologies and by finding ways to reduce the

search programmes, Value Through Intensive

capital-intensiveness of the cluster. The pro-

and Efficient Fibre Supply (EffFibre) and Effi-

gramme portfolio for the three years included

cient Networking Towards Novel Products and

ten work packages (see Figure 1).

Processes (EffNet) together cover the whole

One half of the programme was targeted at

value chain from forest to printing press. The

demonstrating new products and technolo-

EffFibre programme focuses on improving the

gies based on the utilization of microfibrillat-

availability and supply of high-quality raw ma-

ed cellulose (MFC). The main emphasis was on

terial from Finnish forests and developing new

next-generation

production technologies for chemical pulping.

technologies to expand paper and board prop-

resource-efficient

forming

erties and to allow the development of new fi-

solutions, most notably the printing process.

bre-based products outside traditional value

Concept generation by the participating com-

chains. The research focused on the two high-

panies orchestrated the detailed research or-

est potential technologies: foam forming and

ganized into studies on unit processes, quality

ultra-high consistency forming. In addition,

control and management, image-based meas-

the processability of microfibrillated cellulos-

urements, and the printing process.

es, development of binding fillers for paper applications, and demonstration of new, value-added products were addressed. Special attention was given to the sustainability and

3. Management of the programme

product safety of microfibrillated cellulose. The second half of the EffNet programme

The EffNet programme was administered by

developed production system concepts for

a Management Group (MG) comprising repre-

the existing printed products and packaging

sentatives from industry and academia. The

markets. The concepts seek efficiency excel-

execution of was headed by Programme Man-

lence in total cost of ownership and sustain-

ager together with Industrial and Scientific Co-

ability performance, such as water and carbon

ordinators. The daily management tasks were

footprint. Three core concepts were identified

performed in each Work Package (WP) under

and analysed: novel fines-coated printing pa-

the leadership of the WP manager.

per, high filler content SC paper based on a

The main tasks of the Management Group

bindable filler concept, and reduced material

have been to supervise the progress of the

consumption in folding boxboard production

programme with respect to the objectives of

based on a foam-formed middle ply. The re-

the national forest cluster research strategy

search went beyond the boundaries of current

and the EffNet programme plan, and to assess

business models by analysing opportunities

the scientific progress and techno-economic

for optimal efficiency throughout the whole

feasibility of the results. In 2011, the MGâ&#x20AC;&#x2122;s main

supply chain, including intensive analysis of

tasks included mid-term evaluation of the pro-

the processes involved in producing customer

gramme, organization of the discussions with

Efficient Networking towards Novel Products and Processes

High consistency forming

Foam forming

Fibre-based products for new applications

Microcelluloses and their charasteristics

New processes and product based on nanocellulose

Production system concepts management

Resourceefficient papermaking

Verification of concepts

Image based measurements

Printing

Optimizing structures and operation of entire production systems

Efficient mill concepts with new unit processes

Figure 1. EffNet programme portfolio.

the shareholder companies of Forestcluster Ltd in order to harmonize the EffNet pro-

4. Participants and international cooperation

gramme with the companies’ research strategies and to define the most important focus

The EffNet research programme brought to-

areas for the second period of the program.

gether the leading forest cluster companies

MG had the following members:

and research organisations related to papermaking technology, material science, modelling

• Jyrki Huovila, Metso Paper, Chairman

and simulation and machine vision research in

• Erkki Hellen, VTT, Scientific Coordinator

Finland. Eight companies and eight Finnish uni-

• Mika Hyrylä, UPM-Kymmene

versities and research institutes participated in

• Raino Kauppinen, Stora Enso

the programme. In addition, research was also

• Markku Leskelä, FIBIC

subcontracted from external partners.

(Lars Gädda until April 2012) • Marjatta Piironen, Kemira

Industrial partners:

• Ari Pelkiö, Andritz • Erkki Peltonen, Myllykoski

• Andritz

• Risto Ritala, Tampere University of

• Kemira

Tehnology, Scientific Coordinator

• Metso

• Hannu Saarnilehto, Sanoma News

• Metsä Board

• Pauliina Tukiainen, VTT,

• Myllykoski

Programme Manager

• Sanoma News

• Lauri Verkasalo, Metsä Board

• Stora Enso

(Ari Kiviranta until September 2011)

• UPM

• Seppo Virtanen, UPM, Industrial Coordinator

Research organizations:

• Mikko Ylhäisi, Tekes • Aalto University Dissemination of EffNet programme resultsis

• Lappeenranta University of Technology

achieved with a number of different tools, the

• Tampere University of Technology

most important being the FIBIC research por-

• University of Eastern Finland

tal, accessible to EffNet programme partici-

• University of Helsinki

pants, and the FIBIC Ltd website (http://fibic.fi/

• University of Jyväskylä

programmes/effnet). Detailed project reports

• University of Oulu

and publications are available via the FIBIC por-

• VTT Technical Research Centre of Finland

tal. Programme seminars have also been held annually, bringing together experts from ac-

International cooperation was built into the EffNet

ademic and industrial fields and providing a

programme and plays an important role in the de-

comprehensive overview of the programme’s

velopment of novel resource-efficient production

research activities and results.

technologies. Research organizations were encouraged to pursue international collaboration for this purpose with the aim of strengthening the position of Finnish research groups in international communities and opening up new cooperation opportunities. The programme participated in cooperation with six countries:

Canada, Germany, Ireland, Sweden, the UK and the USA. Close links with the international scientific community are maintained, particularly in the areas of foam forming, multiparameter optimization, image analysis and nanocellulose research. The cooperation initiated during EffTech was continued and broadened in EffNet. Programme participants have been active in presenting the programme results at international conferences and researchers have arranged international workshops and conferences, such as the 21st International Conference of Multiple Criteria Decision Making, at which EffNet research groups held a special session on multi-objective process design for systems with multi-objective operation. The session generated valuable input from numerous international methodology experts. EffNet participants have also been active participants in international workshops aimed at promoting the standardization of nanocellulose safety and characterization test methods. The EffNet programme was designed to minimize research overlap with related projects and to maximize synergy between other research activities. Many of the programmeâ&#x20AC;&#x2122;s researchers were also involved in other related projects, which ensured active information exchange and rapid application of results. EffNet research groups participated, for example, in the European Community's 7th Framework Programme projects and several COST actions. The EffNet programmeâ&#x20AC;&#x2122;s core research also supports several industry-driven projects aimed at developing industrial applications. While many of these projects are confidential, active participation of industrial partners within the programme has ensured active information flow, in turn speeding the development process.

High consistency forming of

microfibrillated composite webs

c o n ta c t p e r s o n Thad Maloney, thaddeus.maloney@aalto.fi

pa r t n e r s Aalto University Metso Paper Mets채 Board

Abstract The purpose of this project was to develop a high consistency forming process suitable for microfibrillated cellulose (MFC) composite webs and to outline a paradigm for manufacturing such webs. A MFC composite furnish was evaluated, and a modular high consistency headbox and suitable approach flow system were constructed. It was found that 8-10% solids was a suitable forming consistency. Webs as low as 150 g/m2 were formed. It was also found that under certain conditions the web could be vacuum dewatered to as high as 33% solids with retention close to 100%. Lab pressing studies showed a solids content of around 45% to be achievable with a single shoe press. Excellent physical properties were attained, including good formation, smoothness and light scattering. The results show it should be possible to manufacture composites of this nature in large scale, both the furnish cost and the investment costs look very attractive, and desirable product properties can be achieved. This project demonstrates the manufacture MFC composite papers to be both rational and feasible. The excellent intrinsic properties of MFC composite webs means that it should be possible to find many viable new products in this category. The manufacturing solution is very different, and in many ways superior, to traditional papermaking. There is ample value creation potential across the raw material supplierâ&#x20AC;&#x201C;machinery manufacturerâ&#x20AC;&#x201C;producerâ&#x20AC;&#x201C;converter value chain.

Keywords: microfibrillated cellulose composites, high consistency forming, MFC dewatering

1. Background

must be removed, improve energy efficiency, and simplify the manufacturing process. The

This project has its roots in the â&#x20AC;&#x153;Reengineer-

starting point of our investigation into the po-

ing Paperâ&#x20AC;? philosophy. Simply put, this says

tential forming technology was a process pre-

that by rethinking the architecture of paper on

viously developed for traditional furnishes

a fundamental level we can design a new gen-

called ultra-high consistency forming (UHC), in

eration of paper products. More specifically,

which applied shear is used to deflocculate the

we are interested in the use of microfibrillat-

suspension before forming the web. The form-

ed cellulose, not as a functional additive, but

ing strategy investigated here has its origin in

as a major structural component in paper. The

the earlier UHC work of Professor Gullichsen

vast majority of current paper and board prod-

and co-workers. The possibility to use the UHC

ucts are essentially produced from mixtures

technology for a traditional furnish was also

of various pigments and pulp fibres. The func-

investigated.

tional performance of paper is largely limited by the relatively large size of fibres. Moreover, the product and property space of the fibre/

2. Objectives

pigment furnish approach has been largely exploited and existing products are mature. By

The objective was to develop a semi-pilot scale

including microfibrillated cellulose as a major

high consistency forming technology suitable

structural component in paper, the structure is

for forming MFC composite webs and establish

fundamentally altered and the potential prop-

a paradigm for manufacturing such webs. This

erty space is greatly expanded.

involved the following specific goals: 1) Construct a modular high consistency headbox and

By the time this project started it was already

approach flow system for the Aalto pilot ma-

clear that various MFC/pigment/fibre compos-

chine, 2) Develop the forming technology for

ites could achieve interesting properties. How-

MFC/pigment/fibre webs, 3) Outline a means

ever, it was not clear whether large-scale man-

for large-scale manufacturing, i.e., determine

ufacture of the composites would be possible.

the forming solids content and develop a water removal strategy after forming, and 4) Test the

In order for MFC composites to become an

UHC concept on a folding box board (FBB) fur-

industrial reality, several problems must be

nish to identify any structural or potential pro-

solved. 1. The MFC must be manufactured in a

cess advantages to this forming method.

robust process with a rational cost structure; 2. Suitable forming technology must be found; 3. An energy efficient process must be devel-

3. Research approach

oped to dewater the web. This project did not deal with point (1), but focused instead on the

1. Laboratory rheometer and former con-

forming technology. Sufficient evidence was

struction and tests. A lab device was built

gathered to show that dewatering was possi-

which allowed a suspension to be fluidized and

ble, and to outline a water removal strategy.

a web formed from the fluidized furnish. Several different slice arrangements for the lab

For composite webs containing a large amount

former were constructed and tested. Torque

of MFC, dewatering is a potential problem. It is

and energy values could be collected from the

therefore important to form at high consisten-

rheometer. This gave valuable information for

cy in order to reduce the amount of water that

the construction of the headbox. The objec-

tives of this study were to determine the upper

and increase bulk. Two MFC composite trials

solids content at which webs could be formed,

were carried out at the end of the project. A

identify possible speed limitations, quantify

bent blade bevelling system was added to the

web characteristics, and investigate 3-phase

headbox for the last trial.

systems to determine whether dispersed air could help web forming.

The combination of lab and pilot studies was used to determine whether the manufacture

2. Design and construction of the headbox. A

of pigment/MFC/fibre composites was rational

modular UHC headbox was designed and built.

and feasible and, if so, how it could be done.

The headbox has segments that can be taken off, modified and reattached. Two slice arrangements were constructed, and a third was

4. Results

later added.

4.1 Defining the property space 3. Design and construction of the approach flow. An approach flow was added that al-

In traditional papers, the main structural com-

lowed handling of the high consistency fur-

ponents are fibres, with length dimensions of

nish, introduction of gas or other chemicals

1-5 mm and pigments usually in the range of

and in-line high shear mixing.

1-3 Âľm. The forming concept, dewatering strategy and unit operation design are all based on

4. Lab studies on composite sheet structure.

this broad raw material concept. In this pro-

The property spaces for combinations of pig-

ject, we introduce the use of microfibrillated

ment/MFC/fibre blends were examined. Need-

cellulose as a major structural component. In

ed sheet preparation methods were devel-

doing so, we are fundamentally changing the

oped. From this work a 70/20/10 mixture was

furnish characteristics, the product proper-

defined as the test furnish for process devel-

ties and the needed manufacturing concept.

opment.

A key problem faced is the fact that the range of furnish mixtures is almost infinite, leading

5. Lab studies on the dewatering/rheology

to very different rheological and dewatering

of MFC composite furnish was carried out

characteristics and thus different forming and

using an immobilization cell rheometer. The

manufacturing strategies. In order to narrow

idea was to better understand factors govern-

the 3-component furnish to a more workable

ing the rheology at high consistencies and de-

concept, a laboratory study on various pig-

termine how MFC swelling and other factors

ment/MFC/fibre mixtures was carried out. For

control dewatering. Lab pressing studies were

this work the usual laboratory sheet forming

done with a press simulator.

method was modified by: increasing the forming solids, using a very fine wire, adding over-

6. Pilot studies with the UHC former. The first

pressure to the sheet mould, and using a press

pilot studies were done with traditional fibre

drying method to prevent sheet shrinkage.

furnishes â&#x20AC;&#x201C; bleached hardwood (BHW) and BHW/BSW blends. Here we learned to use

The raw materials used were scalenohedral

the equipment and ironed out many practi-

PCC with 2.4 Âľm average particle size, VTT

cal problems. 3-phase systems were also in-

coarse MFC, bleached birch Kraft, lightly re-

vestigated in which 10% dispersed air was

fined. The experimental design is shown in

used to reduce viscosity, improve formation

Figure 1. A sample of the results for certain

strength properties is shown in Figure 2. The

It should be noted that in this study we are tak-

important conclusions from this study are:

ing a snapshot of only one particular solution. There are a huge range of pigments, fibrillated

• There are non-obvious synergistic effects

celluloses and fibres that can be brought to-

of the components, such as maximum

gether to meet various end-use requirements.

stiffness at 20/60/20 pigment/MFC/fibre.

We would also like to emphasize that the role

• There are synergistic optical effects

and requirements of each of the main compo-

between the MFC and pigment.

nents can be very different to classical paper-

Scalenohedral precipitated calcium

making systems. In this project, the idea was

carbonate (SPCC) prevents the MFC from

to find a furnish concept that would allow web

collapsing in consolidation, thus leading to

formation and dewatering and lead to a prod-

high light scattering for certain mixtures.

uct with desirable intrinsic properties. This

• MFC contributes to bonding, light scattering

puts certain restrictions on the needed com-

and surface smoothness; pigment to light

ponents and the workable mixtures. For ex-

scatter and surface properties; fibre mostly

ample, a high degree of pigment structure is

to tear strength.

desired to give bulk and to maintain poros-

• The combination of high pigment/modest

ity throughout water removal (a requirement

MFC quantity/low fibre was of specific

for efficient dewatering, pressing and drying).

interest to our study. This combination

Thus, highly structured PCC was chosen. Even

delivers excellent optics, high smoothness,

with suitable components, not all mixtures will

reasonable tensile and tear strength and

be workable. For example, in cases where the

very good bulk/smoothness. We therefore

fibre content becomes too high the formation

specified a composite mixture of 70/20/10

may deteriorate, and if the MFC content is too

SPCC/MFC/fibre. The furnish cost structure

high, water removal can be a limiting factor.

is also attractive due to the high amount of pigment. In later work, the BHW was

4.2 Headbox design

changed to a previously dried, unrefined bleached softwood Kraft to further improve

Our initial hypothesis was that when high

tear strength and dewatering properties.

amounts MFC are used, dewatering limitations

Figure 1. The experimental design used to define the property space of pigment/MFC/fibre composites.

were likely to be the most serious obstacle to

certain simplifications to the headbox design

developing an industrially feasible process.

and made the headbox modular in nature. The

This implies that the forming process should

headbox design is shown in Figure 3.

be carried out at high consistency. The higher the consistency at which we could form, the

The basic idea in UHC forming with classical

less water that needed to be removed in sub-

furnishes is to deflocculate the pulp suspen-

sequent operations.

sion with a spinning rotor. If enough energy is applied, the viscosity of the suspension

As a starting point, we focused on the earlier

approaches that of water and the fibre flocs

work of Gullichsen et al., who developed ultra-

completely break up. This, in principle, pro-

high consistency forming (UHC). This concept

vides a route for forming webs at high consist-

has its roots in the development of medium

ency with good formation. The difficulty is that

consistency pulp technology, which is based

it is rather challenging to form a coherent web

on the deflocculation of a fibre suspension by

with an even velocity profile from a highly tur-

the application of sufficient shear. In several

bulent suspension. Thus, the design and relat-

projects, UHC headboxes were constructed

ed flow phenomena around the slice are cru-

and tested with traditional furnishes of up to

cial considerations.

10% solids content. The technology met with some degree of success. Based on this earlier

Two different slice arrangements were con-

work a UHC headbox was designed which was

structed for evaluation (Figure 4). The â&#x20AC;&#x153;wedgeâ&#x20AC;?

suitable for the Aalto pilot machine. We made

arrangement was conceived by Gullichsen et al.

Figure 2. Results for strength properties from the experimental design.

In this arrangement, the distance from the fluid-

a coherent free jet which would then impinge on

ized suspension to the slice is very short, which

the forming wire. The distance from the turbu-

has a potential benefit in minimizing the refloc-

lent zone to the slice exit should be sufficient to

culation time. With the wedge assembly, the web

attenuate disturbances and create the required

is formed in the gap between the bottom of the

pressure drop to ensure an even flow profile. The

headbox and the moving wire. The shear from

design was based on the best results of lab tri-

the wire can potentially rearrange the fibres and

als where, somewhat surprisingly, a converging

improve formation. The wedge space also effec-

slice gave the best free jet formation for both fi-

tively attenuates disturbances arising from the

bre and MFC composite furnishes.

turbulent mixing conditions inside the headbox. The rotor in the headbox is capable of a maxThe second slice geometry constructed was a

imum speed of 4500 rpm and is driven by a

converging geometry with an adjustable slice

22 kW motor. The pattern on the rotor is 3mm

opening. The idea in this arrangement is to form

high diamonds.

Figure 3. The high consistency headbox. The headbox is modular and can be taken apart and refitted.

Figure 4. The two slice arrangements. Right: A converging geometry with controllable slice profile; Left: The â&#x20AC;&#x153;wedgeâ&#x20AC;? concept.

4.3 Approach flow and wet end

tion only and pressing and drying of samples would be done in lab devices. The UHC experi-

The approach flow that was designed and

ments with BHW furnish also utilized the press

built is shown in Figure 5. A 1-cubic metre,

and dryer section of the pilot paper machine.

well-mixed delivery tank is used as both the

It was originally planned that the forming ex-

make-down and machine chest. A number

periments would be done at low speed, 5-10

of pumps were tested. The most suitable for

m/min. It was our initial hypothesis that the

our system was a flexible impeller pump with

forming dynamics would be fairly decoupled

variable speed control. This system can han-

from the machine speed, since the turbulence

dle fibre furnishes in the range 1-5% and MFC

is generated by external means. However, this

composite furnishes up to 10% solids. A high

turned out not to be correct â&#x20AC;&#x201C; the forming me-

shear mixer was installed before the headbox.

chanics were strongly coupled to speed and

Prior to the mixer, gas or chemical additives

generally improved as the speed increased.

could be added. A recirculation line after the

The operating speed was thus often 30-40 m/

mixer could be used for basis weight control or

min. A method for capturing samples off the

for mixing the furnish before the trials. Three-

wire at this higher speed was developed.

phase forming experiments can be done by adding air and a suitable surfactant and then

4.4 Lab-scale forming studies

forming microbubbles either in the high shear mixer or directly in the headbox.

The above concept presented a number of design challenges. Various mechanical designs

The headbox contact and position relative to

needed to be tested with different furnishes,

the wire can be adjusted. Furthermore, the

each with different rheological characteris-

vacuum box positions can be adjusted to allow

tics. This required focusing in from a range of

forming either directly on the vacuum zone, or

furnish characteristics and possible headbox

prior to vacuum. Since the main experimental

design solutions to a more narrowed forming

work will be done at elevated consistencies, no

and furnish concept. To facilitate the design of

provision for capturing or recirculating white

the pilot headbox and investigate web forming

water was made. It was planned that MFC

mechanics for a range of furnishes, a small-

composite trials would utilize the former sec-

scale lab former was constructed. The principle of the former was that several li-

Figure 5. Approach flow for the UHC former.

tres of stock could be fluidized in a chamber.

number of different furnishes (Figure 7). The

The torque, rotor speed and temperature were

experiments with BHW explored whether small

recorded. The suspension could then be ex-

amounts of dispersed air could be used to im-

truded through a slice (different slice geom-

prove the flow and web forming characteristics.

etries were constructed) forming a free jet.

The MFC composite furnish experiments con-

The condition of the free jet could be exam-

centrated on finding the upper solids content

ined with a high speed camera. A system for

at which jet forming was still achievable. At this

evaluating the quality of the free jet was put

stage we were certain that dewatering the fur-

in place. With this set-up it was possible to ex-

nish would be extremely difficult, so emphasis

amine what types of furnishes, conditions and

was placed on maximizing the solids content.

slice geometries would lead to the best qual-

The main findings from the experiments are:

ity jets (Figure 6). The limitations of the device were that it did not allow web capture, the web

• From the BHC furnishes coherent jets

speed could not be controlled, and the flow

could be achieved at 6% and lower solids.

duration was short, so that steady-state con-

The presence of 10% dispersed air (0.02%

ditions were not really achieved.

sodium dodecyl sulphate SDS dispersant) improved jet formation.

The lab rheometer/former was used to test a

• The jet speed was 200-300 m/min,

Figure 6. Schematic and actual lab rheometer/forming device. The various possible slice openings are shown on the right (slice opening 2mm). On average, the “modified long narrowing lip” gave the best web forming characteristics.

Figure 7. Examples of free jets formed under high shear conditions from the lab rheometer. On the left is a poor jet formed from a BHW suspension at 6% solids with one of the less successful slice geometries. On the right is an excellent coherent jet of MFC composite furnish at 9.3% solids.

indicating that sufficient machine speed is

ological properties and dewatering can be

needed to form good webs. Pilot trials later

gathered. In these studies, a couple of differ-

confirmed this.

ent MFC grades were used, with either high or

• The application of high sheer generally improved jet formation. • The jet quality of the 70/20/10 MFC

low swelling. The influence of the fibre fraction was studied, as was the solids content. A sample of the results is shown in Figure 8.

composite furnishes was excellent. • The highest solids content at which web

The main findings from these experiments are

forming was possible for MFC composite

summarized below (note that further descrip-

furnish was 15% in the case of PCC as a

tion of this work and related publication can be

filler and 18% in the case of dispersed filler-

found in the Processability and preservability

grade ground calcium carbonate (GCC).

of microcelluloses section of this report).

Because the GCC had poorer dewatering properties than PCC, the pilot trials were conducted with 2.4 µm SPCC. • While these experiments show that

• The furnish behaves as a gel and is highly shear thinning. • The gel rheology is governed by its water

maximum forming solids could be as high

binding, which in turn is controlled by the

as 15-18%, practical pumping difficulties

swelling of the MFC. Thus, although MFC

limited the pilot trials to around 10% solids

is only 20% of the furnish, it governs the

in the case of MFC composite furnishes.

rheological characteristics. • MFC swelling also strongly influences

4.5 Lab rheology/dewatering studies Common experience is that the addition of just a few per cent of MFC to a handsheet or pilot paper machine can often have a severe negative impact on all stages of water removal. In deploying 20% MFC, we therefore expected water removal to be highly problematic. Indeed, handsheets formed for the 70/20/10 furnish required overpressure and several minutes to drain the water. However, forming and removing water from a high consistency furnish is very different to a handsheet and the furnish is so completely different to traditional fibre stock that poor water removal could not be assumed. Practical experience proved this to be the case. The first clues that the 70/20/10 furnish could be dewatered came from studies performed with a Physica MRC-300 rheometer. This instrument allows simultaneous application of shear and vacuum dewatering, so that information about the relationship between rhe-

Figure 8. Immobilization cell dewatering experiment with different composite furnishes. Lower gap position corresponds to easier dewatering. The upper curves use a highly swollen grade of MFC (24 ml water/g solids swelling), the lower curves a less swollen grade, VTT course MFC (9 ml/g swelling), used in machine trials. The closed simples show the effect of 10% fibre in the furnish, which increases dewatering for the furnish with VTT course MFC.

dewatering of the furnish. The VTT coarse

tion, the PCC does not bind any water. The net

MFC with a network swelling of 9 ml/g

bound water in the web is less than traditional

(measured in a modified WRV test) had

paper, even when considering that MFC has a

much better dewatering characteristics

higher bound water content than Kraft fibres.

than a fine oxidized MFC with a swelling

Although our wet pressing research is still in

power of 24 ml/g.

its early stages, it is worth commenting that

â&#x20AC;˘ The application of shear helps dewatering

the pressing characteristics of the composite

â&#x20AC;˘ The presence of pulp fibres appears to have

web material are very different to traditional

a small positive influence on dewatering by

paper. The composite web is compressible to

helping to open flow channels.

the point where the filler network does not allow further compression and does not re-ex-

Further studies were begun at the end of the

pand. In ordinary paper, the web is highly com-

project to examine the press dewatering of

pressible, but expands and draws water back

the composite furnish. These studies are being

into the structure in the nip-rewetting phase.

carried out with a MTS press simulator which

It is clear from both the vacuum and press

can simulate fairly realistic pressing condi-

dewatering experiments that water remov-

tions. The results are shown in Figure 9. The

al from this kind of furnish can be surprisingly

results show that for this furnish at 100 g/m2

easy if the furnish characteristics and appro-

and 20% initial solids content, 45% solids con-

priate water removal strategy are understood.

tent can be achieved with a single shoe press.

Clearly, this is an area for further research.

Thus, if the web can either be formed at about 20% solids or at lower solids and vacuum de-

4.6 FBB trials

watered to 20% solids then pressing is completely feasible. Although we have not yet be-

The aim of this part of the project was to test

gun the drying experiments at the time of this

the UHC forming method with a fibre fur-

report, it is unlikely that the drying will be a

nish to determine whether suitable formation

problem. If the web permeability is sufficient

could be achieved and bulk could be improved.

to allow water transport in wet pressing, then

About 10 trials were run with a BHW or BHW/

it will allow steam transport in drying. In addi-

BSW furnish. Overall, the technology proved

Figure 9. Moisture ratio after pressing for a 100 g/m2 70/20/10 MFC composite web with 20% initial solids content. The MFC used was MF-Daicel.

challenging with fibre furnishes. However, the

• Based on these trials it was decided that the headbox needed to be rebuilt with a

following findings were also made:

free jet geometry and that the furnish flow • Several trials were conducted with the

and flocculation characteristics should be

wedge arrangement shown in Figure 4. In

improved. This was achieved by dispersing

these trials, it was found that a web could

10% gas into the furnish stabilized with

be formed in the solids range 1-5%, but the formation of the web was not acceptable.

0.01% SDS dispersant. • The use of the free jet improved the

Figure 10 shows that when the headbox is

forming, but low machine speed was still

lifted from the wire and the rotor is on, the

a problem. When 10% air was dispersed

condition of the jet is chaotic. The wedge

in the headbox with the high shear mixer,

attenuates pulsation, but formation is

the formation and bulk improved markedly

limited if the velocity flow through the slice

and were at a good level for this machine

is not even. In these trials the application of

type (Table 1). In our opinion, the 3-phase

shear helped the forming somewhat.

forming solution has potential and further

• The low speed of our pilot machine gave a

improvements can be made by adjusting

somewhat misleading picture, especially at

the headbox turbulence conditions and

higher solids contents. Forming conditions

attenuating flow disturbances.

clearly improved as the machine speed increased.

Figure 10. Left: Jet condition with the headbox lifted from the wire; Right: The web formed with the headbox against the wire.

Test point

SDS (% stock)

Added Air (%)

Deflocculation

Bulk (cm3/g)

Formation (g/m2)

before HB

1,99

In HB

1,96

before HB

1,92

In HB

1,94

0,01

before HB

2,15

Table 1. Sheet bulk and formation for 3-phase forming at 1.8% solids content with free jet arrangement. Samples were pressed and dried on machine.

4.7 MFC composite trials

als require about 0.5 m3 of material, so a considerable quantity of MFC is needed. Note that

The aim of this project was to demonstrate the

we have made some modifications that allow

feasibility of producing MFC composite webs in

trials to be made with about 200 litres of stock.

a reel-to-reel operation. The lab work, equip-

Sample capture is a further challenge.

ment construction and the fibre furnish trials were conducted in preparation for the com-

Three trials were conducted, as summarized

posite forming trials. The industrial realization

below:

of MFC composite products requires broader research beyond the lab scale. Furthermore,

Trial 1: The furnish was 70/20/10 PCC/VTT

pilot-scale experiments are needed to identify

course MFC/BSW unrefined. Machine speed

the fundamental issues for in-depth research.

5-10 m/min. Grammage was about 500 g/m2.

Our first MFC trials validate this point.

Free jet arrangement. Solids 7-8%.

The MFC trials entailed numerous practical

• A web could be formed that was not

challenges, especially as the target was a highconsistency process. The MFC is produced locally at about 3% solids content, the PCC from a decanter is at 30-35% solids, and ordinary

visually very even. Low speed was also a limiting factor here. • Samples were collected by applying blotting paper to the web to remove samples

chemical pulp is available at 4%, unless thick

(Figure 11). This proved cumbersome.

stock is used. This limits the solids of the furnish

• Retention was close to 100% and some

to 9-10%, unless the MFC solids content can be raised. Furthermore, the components must be

dewatering was achieved on the vacuum section with couch solids at 10.5%.

brought together and thoroughly mixed. Mixing

• When the sample was pressed-dried, bulk

is of paramount concern when using any nano-

was 1.30 cm3/g and smoothness 3.5 PPS.

material, especially MFC-type products. The tri-

Formation was also good, showing that the

Figure 11. Taking samples in the first MFC composite trial.

gelatinous characteristic of the web means

• The web is still quite plastic even after wet

that the structure can be greatly altered

pressing. Final surface smoothness will

after forming the web, contrary to a normal

likely be controlled by the drying section

papermaking furnish. Fibres in the gel,

conditions.

when well dispersed, do not reflocculate like a normal papermaking suspension.

Trial 3. The purpose of this trial was to reduce the Grammage further to the 100-200 g/m2

Trial 2: The purpose of this trial was to push

range, to test the bent blade concept, and to

the solids content to 10%. At this point we

examine wire section dewatering. The furnish

were still convinced that a high forming solids

was the same as in Trial 2, but the solids con-

content was needed due to dewatering limita-

tent was lowered to 7%.

tions. The furnish composition was the same,

• A bent blade with adjustable contact angle

except that Daicel MFC was used. 400 g/m2 grammage. Conclusions:

and blade flexibility was added to the headbox, as shown in Figure 13. • The first suction box was moved under the

• At 10% solids, trial conditions were considerably more difficult, e.g. pumping, flow through headbox. • Recirculating 1 hour through the high shear mixer proved a good way to mix components. • A methodology for capturing samples was developed (see Figure 12). • Bevelling experiments indicted that both the grammage and profile could be controlled and any formation issues corrected by appropriate use of a bent blade system after web formation. • The role of both the wire and felt were of apparent importance. It seems that different forming fabrics than are normally used for traditional furnishes will be

blade. • The slice opening was reduced to achieve a target grammage of 200 g/m2. The grammage in the trial ranged from 150 g/m2 to 250 g/m2. • The lateral spread of the furnish was remarkable at high blade pressure: a 15 cm wide web of 300 g/m2 spread to 30 cm and 150 g/m2. • Couch solids content varied in the trial considerably from 12% to as high as 33%. Ash retention also varied from 92-100%. • The basic forming concept is moving in a promising direction, though considerable development is still needed to test and adjust various aspects. • Based on observations during the trial, we

required. This aspect should be included in

do not believe there are any restrictions on

continuation projects.

producing low-grammage webs.

Figure 12. Left: The sampling method of placing wire on wire. Right: Bent blade experiments demonstrate the plasticity of the furnish and that extreme lateral movement of the furnish is possible.

A major aim of this project was to outline a para-

tained through the consolidation process, other-

digm for manufacturing MFC composites of the

wise efficient water removal will not be possible.

type investigated here. Shortly stated, the forming consistency should be 8-10% solids content. The forming should include high shear mixing either before or in the headbox, as component

5. Exploitation plan and impact of results

mixing and the shear thinning behaviour of the suspension are essential. A bevelling blade or

Nanocellulose is one of the most promising devel-

other means can be used to adjust the profile

opments in the forest cluster in recent years. The

and grammage. The web can be vacuum dewa-

development of industrial processes to produce

tered to a suitable solids content for press entry.

high-volume composites or next-generation pa-

Pressing can be done with existing press technol-

per and board products from fibrillated cellulos-

ogy, though attention must be paid to the press

es represents one of the most important manu-

fabric. The web can be smoothed prior to drying

facturing challenges of our time. This project did

to achieve good surface properties. Since web

not, and could not, develop such a manufacturing

shrinkage and planar deviation are an issue, re-

process. This requires a project of much greater

straint during drying via Condabelt technology or

scope. However, we did obtain strong evidence

some other approach is warranted. The furnish

that it is very possible to manufacture MFC com-

must be designed such that porosity is main-

posite webs on a large scale and that it is rational

Figure 13. Bent blade used to bevel the furnish after forming.

Figure 14. The bentblade UHC former in use. Under some conditions the web had a high solids content, was surprising strong and could be peeled off the table. The web had the feel of a fabric. The trials gave many surprising and fascinating insights into the nature of the new composite.

and feasible to do so â&#x20AC;&#x201C; both from the product and

Dimic-Misic, K., Puisto, A., Gane, P., Niemin-

process point of view. While further research is

en, K., Alava, M., Paltakari. J. and Maloney, T.

required, we obtained considerable evidence that

The role of MFC/NFC swelling in the rheologi-

we are on the right track and gained useful expe-

cal behavior and dewatering of high consist-

rience in dealing with MFC furnishes and forming

ency furnishes, Submitted to Chemical Engi-

on a somewhat larger scale.

neering Journal, 2013.

The successful development of MFC compos-

Rantanen, J., Lahtinen, P. and Maloney, T.

ite manufacturing technology should not be

(2013): Property Space for Fibre, Microfibrillar

viewed as an instrument to improve cost struc-

Cellulose and Precipitated CaCO3 Composite

ture, but rather as a gateway to an entirely new

Sheets, Int. Paperworld IPW,(5).

industry. The bulk of the results have not been widely published yet. Despite this, several inter-

Rantanen, J., Lahtinen, P. and Maloney, T.

national companies are interested in exploiting

(2012): Property space for fibre, microfibril-

the results and continuing development work in

lar cellulose and precipitated CaCO3 Compos-

this area. Discussions are underway.

ite sheets, Zellcheming annual conference and expo, June 26.-28. 2012, Wiesbaden.

6. Networking

Rantanen, J., Lahtinen, P. and Maloney, T. (2012): Strength property space for fibre, mi-

The project was carried out in cooperation with

crofibrillar cellulose and precipitated CaCO3

Aalto University and Finnish forest cluster com-

Composite sheets, PaPSaT annual seminar

panies. The pilot former was built at the Depart-

2012, October 2.-3. 2012, Espoo, 48-52.

ment of Forest Products Technology, Aalto University. The project was headed by Thad Maloney

Rantanen, J. and Maloney, T. (2011): Novel

at the Department of Forest Products Technol-

manufacturing method for nanocellulose con-

ogy. Professor Kuosmanen at the Mechanical

taining web based products, PaPSaT annual

Engineering department lead the former con-

seminar 2011, August 22.-24. 2011, Lappeen-

struction. Professor Mika Alava at the Phys-

ranta, 42-49.

ics Department lead the furnish rheology work. Each of the above is located at Aalto University.

Rantanen, J. and Maloney, T. (2011): Ultra high consistency forming research using novel raw

7. Publications and reports

materials, COST Training school - New technologies for treatments in the end-of-use of packaging materials, September 12.-15. 2011,

Dimic-Misic, K., Puisto, A., Paltakari, J., Alava,

Zagreb, 107-116.

M., Maloney, T. The influence of shear on the dewatering of high consistency nanofibrillated cellulose furnishes, Cellulose, 8/6/2013. Dimic-Misic, K., Sanavane, Y., Paltakari. J., and Maloney, T. Small scale rheological observation of high consistency nanofibrillar material based furnishes. Journal of Applied Engineering Science, ISSN, 1451-4117, 2013

Foam Forming c o n ta c t p e r s o n Petri Jetsu, petri.jetsu@vtt.fi

pa r t n e r s VTT Metso Paper Mets채 Board Stora Enso UPM-Kymmene

Abstract

Foam forming shows high resource efficiency potential and great promise as a next-generation technology in the manufacture of fibre products. It enables production of lightweight structures (high bulk) from various raw materials, gives excellent formation independent of fibre length and shows excellent dewatering properties for furnishes containing MFC. All of these offer ways for forest industry companies to improve their competiveness, reduce capital costs, significantly save resources, and promote sustainability. A semi-pilot foam forming environment, built at the Technical Research Centre of Finland (VTT), enables the production of structures with grammages from 15 to 150g/ m2 and forming at speeds up to 300m/min with consistencies as high as 4-5%. The results indicate that in the case of folding box board, foam technology together with advanced raw materials (here MFC as the strengthener) could reduce manufacturing costs by 25% and carbon and water footprints by 45% and 38%, respectively. The estimated reduction in total cost of ownership is about 35%. Currently, the technology is being scaled up to pilot scale in another project to ease the adoption of the technology by industry. The potential is huge, but several technological issues, such as an optimal foaming aid concept, automation and control systems, and suitable processes to achieve excellent printing surfaces while maximizing bulk, have to be tackled before foam technology can be transferred to production scale.

Keywords: Foam forming, folding box board, microfibrillated cellulose

1. Background

refining. Forming structures from a wide variety of raw materials ranging from nanomaterials

The foam forming research continues the work

to centimetre-long fibres and materials of lower

started within the Re-Engineering Paper (REP)

density than water make this an attractive tech-

project during the first two years of the Ef-

nology for new fibre-based products. For exam-

fTech programme. The REP project originally

ple, foam forming naturally provides excellent

aimed at developing resource-efficient means

formation even with long fibres as well as the

of paper production utilizing microcellulose

possibility to form high-bulk structures. It also

and at developing advanced multi-scale mod-

enables forming of multilayered structures with

els to support this aim. The main findings of

excellent layer purity even for lightweight prod-

REP related to foam forming were:

ucts. The technology is already used for nonwoven applications on an industrial scale.

• Foam forming has been identified as the most potential resource-efficient and sustainable technological alternative

2. Objectives

to produce microcellulose-containing products. It enables efficient dewatering

Objectives of the study were to expand paper

and production of fibre-based products

and board properties with new resource-effi-

not achievable with current papermaking

cient furnish and technology concepts and to

technology.

offer ways to radically improve energy, water

• Lightweight packaging board is the product

and raw-material efficiency by utilizing foam

concept with highest potential in terms of

forming technology with microfibrillated cellu-

market size and growth and product value.

lose containing furnishes.

• Microcelluloses have been demonstrated to give various novel product properties (e.g. high stretch). These properties

3. Research approach

have been shown to depend strongly on both microcellulose quality and process

The work is based on the competencies de-

conditions.

veloped in the EffTech programme. In the ReEngineering Paper (REP) project, two main

The main technical challenges in utilizing mi-

advantages of foam forming were identified:

crocelluloses in product manufacturing re-

1) Possibility to generate extremely uniform

lated to forming and dewatering. Since mi-

webs (very good formation) and 2) Potential

crocelluloses bind water efficiently, they are

to make bulky structures. In the REP project

not compatible with current paper machines,

some demo structures were generated, but

where high wire section drainage is important.

very little attention was put to control of pro-

Therefore, forming at high solids content is a

cess and product properties such as forma-

crucial step in solving the dewatering prob-

tion, orientation and strength.

lems inherent in nanomaterial applications. In the EffNet programme, a semi-pilot scale

Foam forming is a potential technology for next-

foam forming research environment with sin-

generation paper and board making. It enables

gle and multi-layer features was constructed

forming of web structures at high consistency

at VTT’s KISU facility. Controllability of sheet

with closed water systems and offers high en-

structure, product properties and process lim-

ergy saving potential in pumping, drying and

its, such as jet-to-wire ratio, consistency and

vacuum levels, were studied in dynamic condi-

The following improvements were carried out

tions. Laboratory-scale experiments were also

during the first modernization of the single-

carried out. The main focus was utilization of

layer foam forming environment:

foam forming technology combined with microcellulose (MFC) containing furnishes in mul-

• New headbox

ti-layered board making. The target was to in-

• New headbox feeding pump

crease the bulk of the folding box board (FBB)

• Improved foam recovery capacity through

middle ply by 50-100%, which offers radical en-

additional exhaust pump

ergy, water and raw material savings and considerably reduces carbon and water footprints.

As the new headbox and forming section is a

Other studied cases were SC and fine paper.

closed unit, there is no free slice jet in the head-

Development work also included foam chem-

box area. The headbox was designed on the ba-

istry research together with the SP Technical

sis that the same headbox could also be used

Research Institute of Sweden. Research related

for forming multi-layered web structures. The

to manufacturing of MFCs was excluded, so all

new headbox feeding pump enables pumping

utilized MFC grades were developed elsewhere.

of foamed suspensions at high consistency levels (up to 5%). Start-up of the single-layered

The foam forming results were highly promis-

web forming environment took place in No-

ing. Significant potential was identified for raw

vember 2011. The single-layer foam forming en-

material and energy savings in the manufacture

vironment modernization was finalized in May

of folding box board. Changing from water-laid

2012 and provides the following features:

technology to foam forming reduces manufacturing costs and carbon footprint by 25% and

• Improved foam recovery capacity

45%, respectively. Investment costs are also

• Improved pumping capacity

reduced by 25% in greenfield installations. In

• Improved mixing conditions in the feeding

addition, foam forming broadens the range of product properties and products, creating new business opportunities for the forest industry.

pulper • Improved approach system for foamed furnish • Measurements for process control

4. Results

A schematic picture of the single-layer foam forming process is presented in Figure 1. The

4.1 Dynamic foam forming environment

main principle of the foam-laid forming process consisted in the process foam being recirculat-

The objective was to construct a dynam-

ed within the flow loop and the raw materials

ic foam forming research environment to en-

being mixed with the process foam in a pulper.

able the forming of single and multi-layered

The quality of new and recovered process foam

web structures at speeds of up to 200 m/min

is controlled on-line by adjusting mixing condi-

to be studied. During the project a new foam

tions within the foam generator. Mixing condi-

forming research environment was designed

tions are then adjusted on the basis of these

and constructed around an existing semi-pi-

foam conductivity measurements. In single-

lot scale forming environment at VTT. Devel-

layer mode, both open and closed headbox-

opment work was divided into two phases: 1)

wire geometries are possible to run (Figure 2).

construction of single-layer facilities and 2) construction of multi-layering facilities.

Figure 1. Schematic diagram of the single-layer foam forming process.

Figure 2. Left: Single-layer open headbox based forming unit; Right: Closed headbox based forming unit.

Figure 3. Schematic diagram of the multi-layer foam forming process.

The modernization of the multi-layer foam forming environment was finalized in June 2013 and includes a manifold, a feeding chest and a feeding pump for each layer. The layered web structure is generated within the headbox. A schematic diagram of the multi-layer foam forming process is presented in Figure 3. Achievements of the developed dynamic foam forming environment:

Single-layer structures in a continuous process • Grammages up to 150 g/m2 • Headbox consistency up to 4-5%

Figure 4. Formation in foam forming is independent of fibre type and of superior quality to water laying.

• Speed up to 300 m/min • Open and closed headbox-wire geometry Multilayer structures in batch mode • Forming of two- and three-layer web structures

formed samples typically starts to decrease when the grammage decreases below a cer-

4.2 Enhanced product properties

tain value (typically 50 – 60 g/m2) as the flocks start to dominate the lateral strength behav-

One of the inherent properties of foam-formed

iour. As foam prevents flocculation to a great

products is their excellent formation. Figure 4

extent, the tensile index remains constant

illustrates this for three types of fibres. Most

even at very low grammages. This can have an

notable is that with foam forming the forma-

important impact on low-grammage products.

tion is independent of fibre type. Especially,

The experiment was conducted with both dy-

the specific beta formation was enhanced by

namic foam and water formers.

69% when spruce chemithermomechanical pulp (CTMP) was used. The experiments were

Sheets made in the laboratory (static forming)

done with a dynamic, single-layer former.

were compared with dynamic foam and waterformed samples and sample data from the Finn-

One consequence of the excellent formation

ish Pulp and Paper Research Institute (KCL) pilot

is enhanced strength at low grammage, as

paper machine. The data for the static and dy-

shown in Figure 5. The tensile index of water-

namic samples is shown in Table 1.

Table 1. The data for the static and dynamic foam and water formed samples. Static (laboratory sheet mould)

Dynamic

Pulp: CTMP spruce MFC: Daicel MFC Grammages: water 230 g/m2; foam 75, 105 and 150 g/m2 Pressing: no pressing, 1 pin roll and 10 pin roll Disintegration: hot and cold

Pulp: CTMP spruce Grammage: 105 g/m2 Pressing: no pressing, 0.5, 1.5 and 3.5 bar Disintegration: hot

When MFC is added to the foam-forming furnish we enter brand new territory in terms of the bulk â&#x20AC;&#x201C; Scott Bond relationship. We can make lightweight structures that are strong enough with high bulk. Such structures are unattainable with water forming because high bulk levels cannot be reached. Figure 7 further illustrates this by showing that with a 10% addition of MFC, all of the critical strength properties of Figure 5. At low grammages the tensile strength of foam-formed sheets is clearly higher due to improved formation.

the 54% lighter laboratory-scale sheets are at the same level as the water-laid reference. As a consequence of the positive effect of MFC, a test series using six different grades of MFCs

The most important outcome of our research

were run at the laboratory scale in order to de-

is shown in Figure 6: structures with the same

termine their effect on both z-directional and in-

strength can be produced with half the raw

plane strength properties. The pulps used in the

material. Without MFC a clear trend can be

study were pine kraft and spruce CTMP pulp and

seen. Scott Bond values decrease rapidly as

the amount of MFC added was 0% (a reference),

bulk increases from 2 cm3/g to 4 cm3/g. Howev-

5% and 15%. The sheets prepared were dried

er, if the bulk is greater than 4 cm3/g, increased

after forming without wet pressing. The results

bulk lowers the Scott Bond values only slowly.

from the test series are shown in Figure 8.

Very high bulk (> 6 cm3/g) can be achieved only with foam forming. Thus, without any strength

According to the results, different MFC grades

additives, the only way to obtain a strong

seem to behave rather similarly in bulk vs.

enough structure (Scott Bond > 100 J/m2) is to

strength comparisons. However, in the case of

compress the structure sufficiently.

modified Scott Bond, the coarser and cheaper

Figure 6. Scott Bond values of CTMP sheets as a function of bulk. Board properties can be expanded through a combination of foam forming (for high bulk) and strength additives. The green triangles are typical values for CTMP sheets made on the KCL pilot paper machine. The blue squares and brown diamonds are values from static and dynamic water-formed and foam-formed studies, respectively. The circles show the values of the foam-formed samples with different Daicel MFC contents.

Figure 7. With a combination of foam forming and MFC it is possible to make sheets at the laboratory scale that are 54% lighter but have the same strength values as water-formed, heavier sheets. Water-formed sheets of grammage 230g/m2 (red squares), foam-formed sheets of grammage 105g/m2 with MFC (purple circles) and without MFC (blue diamonds). The green triangles indicate the estimated strength values achievable with wet pressing for foam-formed sheets.

Figure 8. Effects of addition of six different MFC grades to pine and spruce CTMP pulps. Above: Modified Scott Bond as a function of bulk. Below: Tensile index as a function of bulk. The right end points of the lines equate to 5% addition and the left end points to 15% addition.

VTT MFC gave slightly higher values compared

ter laboratory wet pressing (3.5 bar, 5+2 min).

to the more refined and expensive VTT MFC.

The shrinkage potential study was based on

On the other hand, the more refined VTT MFC

a free shrinkage drying method allowing in-

gave a higher tensile index value. This exam-

plane shrinkage, but partly constraining curl-

ple illustrates that the choice of MFC should

ing (drying between wires). The results of the

depend on the required paper properties.

shrinkage potential measurements are shown in Figure 9 (Left). According to the results,

In order to study the dimensional stability

the shrinkage potential of foam-laid papers is

of water-laid and foam-laid papers and sol-

smaller compared to water-laid papers. Foam-

ids content, the next test series were run us-

laid papers are also not as sensitive to MFC

ing pre-refined pine kraft pulp and VTT coarse

content as water-laid papers. The dryness lev-

MFC. The characteristics were measured af-

el of foam-laid papers is also higher after wet

Figure 9. Left: Foam-formed samples shrink less in free drying than water-formed samples at MFC contents of 0, 2.5, 5, 10, 15 and 20% and wet pressing conditions 0, 1.5 or 3.5 bar. Right: The solid content of foam-formed sheets is higher after wet pressing (3.5 bar 3+2 min) than that of water-formed sheets at MFC contents of 0%, 2.5%, 5% and 10%. The MFC used in the test series was VTT coarse MFC.

Figure 10. Left: In-plane strength properties of foam and water-laid samples (geometric average of tensile index values of foam samples) as a function of bulk (variables: MFC content and wet pressing pressure). Right: Z-directional strength of unpressed foam and water-laid samples as a function of bulk (variable: VTT coarse MFC content).

pressing (Figure 9, right). The MFC amounts

namic water-laid and foam-laid forming meth-

used can be reasonably high due to the open

ods are presented in Figure 11. Water is removed

structure of the foam-formed samples. This is

more easily than viscous foam, leading to lower

not an option in water forming, because the

vacuums in water-laid forming. Corresponding-

water drainage properties would be deterio-

ly, vacuums were higher in the removal phase

rated excessively. In our foam forming stud-

of process foam. After the removal phase, vac-

ies the solids content after wet pressing varied

uums were approximately at the same level in

from 45 to 55% also at high levels of MFC ad-

both forming methods. In the closed headbox

dition (10%, 15% and 20%).

based forming process vacuum levels were still higher. This was mainly because most of the

In summary, foam-laid technology enables the

process foam was dewatered under the deck of

production of high-bulk structures. When this

the closed headbox and the quality of the paper

is combined with its good water drainage prop-

web was better with the closed headbox, thus

erties, allowing the addition of high levels of

leading to higher vacuum levels.

strengthening agents such as MFC, products with both very high bulk and adequate strength

The tensile strength ratio and specific beta-

can be made. Figure 10 shows the possibili-

formation behaviour in the case of the closed

ties for strength compensation in foam-formed

headbox former is presented in Figure 12. The

samples for different wet pressing levels.

results show that a wide tensile strength ratio can be achieved. The minimum tensile strength

4.3 Process research

ratio was around 3 and, correspondingly, the maximum tensile strength was around 8. The

In the process research, refined chemical pine

achieved maximum tensile strength ratio was

pulp was used as the fibre raw material and the

exceptionally high compared to normal wet-

average grammage of the samples was 80 g/m2.

forming values. The specific-beta formation values were also at a very good level, varying

The vacuums in the forming section for dy-

between 0.35 â&#x2C6;&#x161;g/m â&#x20AC;&#x201C; 0.60 â&#x2C6;&#x161;g/m.

Figure 11. Vacuums in the forming section.

Figure 12. Tensile strength ratio can be controlled extensively in foam forming by altering the jet-to-wire ratio without affecting the excellent formation.

Figure 13. Geometric tensile index and specific beta-formation as a function of forming consistency.

Figure 14. Geometric tensile index and specific beta-formation as a function of density of the process foam.

The geometric mean of tensile index and spe-

ing agents and papermaking raw materials in

cific beta-formation as a function of forming

aqueous foam-fibre systems was of great inter-

consistency is shown in Figure 13. As can be

est. The research was carried out in close coop-

seen, paper quality deteriorates with higher

eration between SP (Technical Research Insti-

consistency. The maximum forming consist-

tute of Sweden, formerly YKI) and VTT.

ency achieved was ~ 4.5%. The limited mixing capacity in the foam chest (foam pulper) and

Foaming aid screening and foaming tests

the limited dewatering capacity in the form-

The foaming behaviour of pulp formulations, in

ing section prevented the attainment of higher

the presence of three ionic and four non-ion-

forming consistencies.

ic foaming aids, was tested with a tailor-made foaming testing device and procedure devel-

The geometric mean of tensile index and specif-

oped by VTT. Foaming aids for testing were

ic beta-formation as a function of density of the

chosen based on their reported good foam-

process foam is shown in Figure 14. Paper qual-

ing properties, availability as bulk chemicals,

ity was weakened significantly when the aver-

as well as insensitivity to changes in tempera-

age density of the process foam was increased.

ture and pH within limits relevant to the foamforming process. The results from foaming

4.4 Foam chemistry

tests indicated that, of the foaming aids tested, three enabled relatively rapid generation

Much is known about the properties of pure

of the required foam-fibre volume. The list and

aqueous foams. However, extremely little is

molecular structure of the most rapidly foam-

known about the chemical interactions be-

ing chemicals are shown in Table 2.

tween foaming agents and papermaking raw materials in aqueous foam-fibre systems. The

Foam-formed handsheets with different fur-

objective of the study was to increase under-

nish recipes (44 different recipes) were made

standing of the basic mechanisms related to

and tested to evaluate the effect of the select-

fibre-foam chemistry, foamability and foam

ed foaming agents on the formation and re-

stability. In particular, gaining an understand-

tention processes, the technical properties of

ing of the chemical interactions between foam-

the handsheets and the performance of other

Table 2. The most rapidly foaming chemicals and their molecular structures.

chemicals used in paper/board manufacturing

(see Figure 15, left). Furthermore, at AKD

in the presence of the foaming aids. The results

dosages â&#x2030;Ľ 3 kg/t, the water absorbency of

obtained from the handsheet tests showed

water-formed handsheets was higher than

that the type of foaming aids used has signifi-

that of foam sheets made using the non-

cant effects on the mechanical properties and quality of paper. The main findings of the handsheet tests can be summarized as follows:

ionic surfactant. 5. Foam-formed sheets gave higher dryness after forming and wet pressing than waterformed sheets. Foaming type and dosage

1. Foam-formed handsheets are bulkier than

had a significant impact on dewatering (see

water-formed handsheets after constant

Figure 15, right). Foaming aid dosage had no

wet pressing conditions. The type of

effect on the mechanical properties of the

foaming aid has a significant effect on bulk. 2. The formation of foam-formed sheets was better than that of water-formed sheets. In the presence of ionic polymers, the charge of the used foaming aid has a significant effect on formation. 3. The in-plane mechanical properties (tensile strength) of foam-formed samples were

samples. 6. Filler retention was significantly higher with foam-formed sheets utilizing a non-ionic foaming aid than an anionic foaming aid. 7. The effect of cationic strength additives on the strength increase of foam-formed handsheets was lower in the presence of anionic foaming aids than with non-ionic foaming aids.

somewhat similar to water-formed sheets at a given bulk level. However, the out-of plane

The potential of utilizing the selected foaming

properties (Scott Bond delamination energy

aids in the practical foam forming of paper was

and Z-directional strength) of foam-formed

verified in a semi-pilot trial based on a fine pa-

samples, which are crucial for the functionality

per recipe. The results obtained during the tri-

of board, were clearly lower than for water-

als indicated that the findings made in the lab-

formed sheets at a given bulk level.

oratory tests were also valid in more dynamic

4. Sizing with alkyl ketene dimer (AKD) was

surroundings. It was also noticed that the se-

greatly dependent on the type of foaming

lection of utilized foaming aids must be done

aid used. Ionic sodium lauryl ether sulfate

together with the selection of the utilized re-

(SLES) and SDS required significantly higher

tention system. In conclusion, understanding

AKD dosage to achieve similar Mini-Cobb30

and control of fibre-foam chemistry is a key for

values to non-ionic alkyl polyglucoside

successful tailoring of final product properties.

Figure 15. Left: The effects of AKD dosage on Mini-Cobb30 value of foam- and water-formed handsheets. Right: The effects of foaming aid type and dosage on dryness after wet pressing for foam (and water) formed handsheets.

4.5 Foam forming concept and evaluations

sumptions underneath of figure 17, a 25% reduction in production costs can be expected (Figure 17). The calculations are based on the

The financial impacts and costs of adaption of

laboratory and semi-pilot scale results. Pro-

the foam technology are discussed in this sec-

duction in square metres is assumed to be the

tion. Folding box board (FBB) is used as a ref-

same, i.e., the volume of the reference water

erence case. The main changes required to re-

forming machine is 400,000 t/a and the foam

build a FBB machine are illustrated in Figure

forming machine 245,000 t/a (same speed,

16. A foam forming rebuild costs in the region

width and efficiency).

of EUR 10 million. The main changes to the system are the conversion to a closed head-

Assumptions to achieve these results are:

box (which might, in some cases, not even be

Fibre: Reduction of basis weight from 270 g/

necessary) and installation of a foam genera-

m2 to 166 g/m2. Basis weight of the middle lay-

tor for mixing and dispersing, vacuum pumps

er is reduced from 192 g/m2 to 88 g/m2. MFC is

and a vacuum line for foam removal. In addi-

considered as fibre, a dosage of 20% is used

tion, minor automation updates are expected.

in calculations. It is also assumed that MFC re-

The consistency is assumed to increase from

places chemical pulp. This results in a total fi-

1% to 2.5%, so existing tank volumes are suf-

bre cost of 496 â&#x201A;Ź/t.

ficient. Fresh water intake and outgoing water quality are assumed to remain unchanged.

Energy: Total energy consumption reduction is estimated to be 20% (per tonne). This arises

There were two main outcomes of the FFB

from higher consistency (2.5%) as lower mass

case. Firstly, significant resource savings were

flows are needed but also due to lower basis

expected for both new forming technologies,

weight needed for the final product. Use of the

especially if microcellulose was used to in-

same energy levels in forming results in higher

crease the strength properties. Secondly, the

solids content before pressing. For example, for

savings potential is realized only if the value is

the reference case an increase from 19% to 24%

calculated per unit area (â&#x201A;Ź/km2). Using the as-

is obtained using the same pulp mix (Birch/pine/

Figure 16. Foam rebuild FBB concept with changes highlighted.

CTMP). The same energy used in pressing re-

38%. Reductions are realized mainly through re-

sults in higher solids content after pressing. This

duced basis weight. For water footprint, the wa-

results in a total energy cost of 31 €/t.

ter scarcity is different in different regions of the world; in Finland, where water resources are

Water: 13 m3/t water needed for production

readily available, the water scarcity footprint is

(4€/t). This is based on forming at higher con-

low in both cases (reference and foam FBB).

sistency (2.5%) and improved retention. During the estimated 20-year lifetime of a maChemicals: Chemical cost per tonne for the

chine line, with 9% interest, the reduction in

reference are assumed to be 86 €/t. For foam-

total cost of ownership (TCO) can be about

ing chemicals the cost is assumed to be 8€/t

35%. This estimation arises from savings in

(SDS: 0.31% dosage, 2700€/t)

operating, investment, interest (shorter payback of machine when operating cost savings

For carbon footprint, the reduction is 45%, as

are assumed to be used to reduce loans fast-

shown in Figure 18. Water footprint reduction is

er), logistics and insurance costs.

Figure 17. Estimated savings potential for foam-formed folding box board.

Figure 18. Carbon (left) and water footprints (right).

5. Exploitation plan and impact of results

jects. Based on the results, we strongly believe that foam forming will lead to a new manufacturing platform for fibre-based products as it 1)

Foam forming technology can significantly im-

requires significantly less raw materials, water

prove competitiveness, reduce capital intensive-

and energy than conventional manufacturing,

ness, reduce consumption of resources and im-

2) remarkably improves many product proper-

prove the sustainability of current products. At

ties, 3) enables exploitation of new raw mate-

the same time, it paves the way for the renew-

rial combinations, 4) offers a sustainable solu-

al of the forest industry by enabling raw materi-

tion for manufacturing a wide range of products,

als to be combined in new ways, thus opening

such as paper, board, tissue, hygiene products,

up opportunities for companies to create novel

insulation materials, filters and other added val-

value chains. This will create new business op-

ue products from bio-based, long fibres and 5)

portunities for large companies as well as small

offers possibilities for both large companies and

and medium sized enterprises (SMEs). Within

SMEs to create novel value chains.

this programme the concept was demonstrated at the laboratory and semi-pilot scale. The next step â&#x20AC;&#x201C; validating the achievements at the pilot

6. Networking

scale â&#x20AC;&#x201C; has already started in one project, SMEs are seeking value-added applications in another

The research was carried out jointly by VTT

project, and several companies are also taking

and Finnish forest cluster companies. Table 3

active steps in this area through their own pro-

presents the research partners and their roles.

Table 3. Partner organisations and their research roles.

Partner

Role

VTT Technical Research centre of Finland, Fibre Process Knowledge Centre

Foam forming research, demo products manufacturing, fibre network modelling and concept evaluation

Metso Paper

Process knowhow, demo products specifications, commercialization perspective

MetsĂ¤ Board

Demo products specifications, concept evaluation, commercialization perspective

Stora Enso

Demo products specifications, concept evaluation, commercialization perspective

UPM-Kymmene

Demo products specifications, concept evaluation, commercialization perspective

SP Technical Research Institute of Sweden (former YKI)

Foam chemistry research, understanding of basic mechanisms related to fibre-foam chemistry, foamability and stability

7. Publications and reports Publications:

Hellén, E., “Lightweight fibre materials through

Al-Qararah, A. M., Hjelt, T., Kinnunen, K., Be-

dustrial Applications –seminar, Espoo, 2013.

foam technology”, Biomaterials - Towards Inletski, N., Ketoja, J. A., Exceptional pore size distribution in foam-formed fibre networks.

Hellén, E., “Renewal by combining novel form-

Nordic Pulp Paper Res. J. 27, 226-230 (2012).

ing technologies with advanced raw materials”, EffFibre&EffNet Workshop, 2012.

Al-Qararah, A. M., Hjelt, T., Koponen, A., Harlin, A., Ketoja, J. A., “Bubble size and air content

Hellén, E., “Beyond paper and board - Leap

of wet fibre foams in axial mixing with macro-

in resource-efficiency with nanocellulose and

instabilities, Colloids and Surfaces A: Physic-

new forming techniques”, Forestcluster Annu-

ochemical and Engineering Aspects, Volume

al seminar, 2011.

436, 5 September 2013, Pages 1130-1139. Hjelt, T., Kinnunen, K., Lehmonen, J., Beletski, Lappalainen, T. and Lehmonen, J., “ Determi-

N., Hellén, E., Liljeström, V., Serimaa, R., Miet-

nations of bubble size distribution of foam-fi-

tinen, A., and Kataja, M., ”Intriguing structur-

bre mixture using circular Hough transform”,

al and strength behaviour in foam forming”,

Nordic Pulp and Paper Research Journal, 2012,

PPPS 2011, Graz.

Vol 27, no. 5, 930-939. Lehmonen, J., Jetsu, P., Kinnunen, K. and Lehmonen, J., Jetsu, P., Kinnunen, K. and

Hjelt, T., ”Potential of microfibrillar cellulose in

Hjelt, T., “Potential of foam-laid forming tech-

water-laid and foam-laid papers” 2013 Tappi

nology in paper applications”, approved to

International Conference on Nanotechnology

Nordic Pulp and Paper Research Journal.

for Renewable Materials.

Kinnunen, K., Lehmonen, J., Beletski, N., Jet-

Mira, I., Andersson, M., Boge, L., Blute, I.,

su, P. and Hjelt, T., “Benefits of foam technol-

Salminen, K., Lappalainen, T., Kinnunen, K.,

ogy and its applicability in high MFC addition

“Foaming behaviour of cellulose pulp fibre-

structures”, approved to FRC.

surfactant systems used for novel production of fibre-based materials”, Formula VII, 1 July 13 - 4 July 2013, Université de Haute Alsace, Mul-

Presentations:

house, France.

Al-Qararah, A. M., Hjelt, T., Kinnunen, K., Belet-

Poranen, J., Kiiskinen, H., Salmela, J., Asi-

ski, N., Ketoja, J. A., “Exceptional pore size distri-

kainen, J.,Keränen, J., Pääkkönen, E., “Break-

bution in foam-formed fibre networks”, Int. Pa-

through in papermaking resource efficiency

per Physics Conf. 2012, Stockholm, Sweden.

with foam forming”, PaperCon, Atlanta, 2013.

Hellén, E., ”Resource efficiency with foam

Poranen, J., “Resource efficiency with foam

forming”, Tissue World, Barcelona, 2013.

forming”, EffFibre & EffNet Seminar, 2012.

Posters: Lappalainen, T., Salminen, K., Kinnunen, K., Järvinen, M., Mira, I., Boge, L., Andersson, L., M. and Carlsson, G. ”Laboratory scale investigation of foam forming”, EffFibre & EffNet Seminar, 20.11.2012. Lehmonen, J., Kinnunen, K., Hjelt, T., “Significant process improvements using foam forming”, Forestcluster Annual seminar, 2011. Kinnunen, K., Lehmonen, J., Hjelt, T., Jetsu, P., “Foam forming facilities and demonstrations”, EffFibre & EFFNet Seminar, 2012. Kinnunen, K., Hjelt, T., Lehmonen, J., Jetsu, P., Hellén, E., Kiiskinen, H., Poranen, J., ”Foam forming - renewal of fibre products”, SHOK Summit, 2012. Salminen, K., Lappalainen, T., Kinnunen, K., Andersson, M., Isabell, M., ”Foam chemistry”, EffFibre & EFFNet Seminar, 2012.

Fibre-based

products for new applications

c o n ta c t p e r s o n Erkki HellĂŠn, erkki.hellen@vtt.fi

pa r t n e r s VTT Aalto University Helsinki University Kemira Stora Enso Tampere University of Technology UPM

effnet Programme report

Abstract Demonstrations of new fibre-based products focussed on utilizing microfibrillated or microcrystalline celluloses in various applications and determining the potential of foam forming technology to manufacture value-added products. Filler-MFC composites were shown to offer a cost-effective substrate for printed electronics applications with a superior temperature tolerance that only special plastics can compete with. The performance of four different demonstrators printed on the composite were comparable to those printed on plastic reference substrates: conductors by inkjet, a LC resonator by screen printing, a near field communication RFID tag by screen printing, and transistors by flexo printing. Lightweight structures (densities 8-26 kg/m3; bulk 38-120 cm3/g) having thermal conductivities comparable to commercial mineral and stone wool insulation materials were made from basic papermaking raw materials using foam forming. Similar structures were also shown to perform well as lightweight, sustainable sound absorption materials at challenging low frequencies (~500Hz). The best structures were comparable to commercial sound insulation materials with a density as low as 20 kg/m3. Finally, it was demonstrated that a new type of microcellulose, namely carboxymethyl cellulose grafted microcrystalline cellulose, can act as an efficient strength additive in paper. Foam forming clearly has the highest value creation potential of the concepts studied in this section. Foam forming opens the way for a new manufacturing platform for fibre-based products, as it 1) enables exploitation of unprecedented raw material combinations 2) offers a sustainable solution for the manufacture of a wide range of products like paper, board, tissue, hygiene products, insulation materials, filters and other added value products from bio-based, long fibres, and 3) offers possibilities for both large companies and SMEs to create novel value chains. The substrate for printed electronics also shows good value creation potential but, although the market potential for printed electronics is high, the market itself is still most probably too small for large companies to enter. The same applies to the other demonstrations, which, however, may offer viable market opportunities for small and medium size enterprises. Overall, these demonstrations show that it is possible to manufacture value-added products from wood fibres.

Keywords printed electronics, MFC, foam forming, sound absorption, lightweighting, thermal insulation

effnet Programme report

1. Background

3. Research approach

The main driver behind the work is renewal:

The starting point for new product demonstra-

finding ways to generate new business from

tions has been the unique properties of micro-

sustainable raw materials. This directly sup-

fibrillated celluloses and the novel possibili-

ports the Research Strategy of the Finnish For-

ties provided by foam forming. The properties

est Cluster, which says “…The objective is to

of microfibrillated celluloses range from high-

double the value of the forest cluster’s prod-

stretch packaging applications to transparent

ucts and services by 2030. Half of this value

barrier films and thermally stable and smooth

would come from new products…”. These new

substrates for electronic applications. For ex-

products are seen to arise by developing new

ample, it is possible to make 1) transparent,

products utilizing a wide raw material base,

non-porous films, 2) paper-like, flexible sub-

especially microfibrillated celluloses, and new

strates, and 3) plastic-like, hard plates from

production technologies such as foam forming.

the same raw material just by changing the

The actions described here are largely based

processing conditions. This is far beyond what

on the research started within the Re-Engi-

can be achieved with ordinary fibres. Here we

neering Paper (REP) project during the first

have modified microcelluloses for paper appli-

two years of the EffTech programme. The

cations as well as for superabsorbents. When

REP project originally aimed at developing re-

making substrates for printed electronics, MFC

source-efficient paper production by utiliz-

has been used to glue cheap filler particles to a

ing microcelluloses and developing advanced

flexible sheet. Foam forming has been used to

multi-scale models to support this aim. Based

manufacture low-density structures from tra-

on discussions with industrial partners, the

ditional papermaking raw materials at unpar-

experimental focus was extended to identify

alleled high performance/weight ratios.

the potential of microcelluloses also in other

To decrease product development costs and

applications than paper, both from the product

speed up development times, we started to

and process point of view. This section out-

develop multi-scale modelling and simulation

lines the main achievements.

tools to examine new resource-efficient paper structures and different ways that they can be produced. The modelling tools were developed

2. Objectives

collaboratively by several top research teams. Here, the aim was to elevate to an entirely new level the way microscopic structures are de-

To demonstrate product concepts and technol-

picted and to utilize several models togeth-

ogies to replace current, non-fibre-based prod-

er. However, covering in detail all the relevant

ucts. The target is to develop 2-4 new prod-

scales and phenomena related to MFC pro-

uct concepts outside the existing business of

cesses and applications proved too challeng-

paper and board making companies. To pro-

ing within a single research programme. The

vide microfibrillated celluloses (MFCs) for pro-

developed models were therefore used to help

gramme partners and develop modelling tools.

in interpreting experimental results. The models also led to important findings beyond current experimental capabilities.

4. Results

Thermogravimetric analysis (TGA) showed that the substrates can tolerate short exposure to

4.1 Cheap, temperature-tolerant substrates for printed electronics

temperatures up to 270째C and over 12 h exposure to 230째C. These temperatures are much higher than the current substrates for printed

Filler-MFC composites have been shown to of-

electronics, enabling, for example, high sintering

fer a cost-effective substrate for printed elec-

temperatures and increased production speeds.

tronics applications at high temperatures that only very special plastic films can nowadays

Four demonstrations were successfully print-

withstand (see Figure 1). The composites con-

ed on the substrates: The above-mentioned

sist typically of 80% filler and 20% MFC. The

conductors by inkjet, an LC resonator by screen

properties of the substrates can be varied with-

printing, a near field communication RFID tag by

in a relatively large range by the selection of

screen printing, and transistors by flexo print-

raw materials and their relative propositions.

ing. In all cases the components performed as well as on plastic reference substrates.

The substrates performed well in printing tests. The conductivity values of patterns were simi-

The LC resonator was screen-printed using

lar to those printed on PET film (Mylar A). The

silver-microparticle paste for bottom and top

best conductivity was obtained with silver na-

conductors and UV-cured dielectric paste (Fig-

noparticle patterns, which were inkjet printed on

ure 2). The obtained resistivity of the printed

kaolin-based sheets. Most interestingly, curing

pattern complies closely with the ink manu-

temperatures as high as 220 째C could be used

facturer specifications. However, the printed

without causing any damage to the sheets.

resonator did not provide the needed func-

Figure 1. Filler-microcellulose composites (yellow) offer a cost-effective substrate for printed electronics applications with a superior temperature tolerance that only special plastics can compete with. Plastic film mylar A (PET 1), electronic grade paper substrate (PEL) and polyimide Kapton film (PI).

tionality. This is not due to the substrate mate-

nent to be processed on filler-MFC substrates.

rial, but rather the need for optimization of the

OFETs fabricated on the filler-MFC substrate

printing process.

were compared to ones fabricated on selected plastic substrates (polyimide) and on a “Lumi-

The functional near field communication RFID

Press Art” coated paper substrate provided by

demo consisted of an antenna screen printed

Stora Enso. Transistors made on the smoothed

with silver ink on a filler-MFC sheet and a com-

paper substrate showed excellent output char-

mercial RFID chip (strap) attached using silver

acteristics (Figure 3). Only the gate leakage

epoxy. The tags for near-field communication

current was slightly high. Transistors made on

are a more sophisticated version of the infor-

a polyimide plastic substrate had similar per-

mation previously stored in bar codes. This

formance, as well as those printed on MFC-

information is readable using many smart-

kaolin substrates. However, with MFC-kaolin

phones and, for example, in consumer goods

substrates the transistors could be made in air

they can be used for gathering information

at 240°C (even with flexographic printed base

about products or for making payments. The

coat), whereas for the other substrates mul-

DC resistance of the printed antenna, 33Ω (33

tiple coating layers were needed and the Lu-

m Ω /sq sheet resistance), is similar to those

miPress Art paper could be processed only at

printed on PET film (30-45Ω depending on the

200°C and in N2 conditions.

sintering temperature) and lower than those printed on copy paper. Benefits of the filler-

Upscaling the production. Several methods

MFC substrate include better temperature tol-

to upscale the production of MFC-filler sub-

erance compared to PET film. This enables

strates were tested. Optimizing the drying

the use of higher sintering temperatures and

conditions proved to be of extreme impor-

opens the way towards achieving even lower

tance. Quick drying of the filler-MFC web re-

resistance levels. When compared to copy pa-

sulted in cracks and the dried structure was

per, the filler-MFC substrate is less sensitive to

hard and brittle. Slow drying at room temper-

moisture changes.

ature resulted in a smooth and more flexible structure. The best results were obtained by

Organic field-effect transistors (OFET) were

pressing the formed web before/during dry-

chosen as the most challenging test compo-

ing. The smoothest surface was obtained by

Figure 2. Demonstrators made on filler-MFC substrates. Left: An LC resonator. Right: A RFID tag, hotlaminated into a plastic pocket. The content of the tag can be read with a mobile phone supporting the near-field communication technology. Both demos have been screen printed.

Figure 3. Example of an organic transistor printed on coated paper â&#x20AC;?LumiPress Artâ&#x20AC;? (left), which shows excellent output characteristics (right).

oven drying under pressure. Interestingly, ex-

ed cellulose (MFC) and is formed by vacuum fil-

cess water can be easily pressed out of the

tration, dried under pressure and calendered.

structure, which clearly speeds the drying pro-

These assumptions result in a total produc-

cess. Pressing also further improved the flex-

tion line cost of about EUR 10 million with a

ibility of the formed structure.

production capacity of 3000 t/a, whereas PET film production lines typically cost EUR 40-75

Techno-economic feasibility of the sub-

million and produce 10,000-20,000 t/a. New

strate for printed electronics. The following

product opportunities and markets can be

assumptions based on the experiments have

captured through the use of filler-MFC sub-

been made in the analysis: The substrates are

strates for printed electronics applications.

printable with inkjet, flexo and screen printing

However, this concept still requires develop-

at good enough quality for low-cost applica-

ment and drying conditions, in particular, are

tions. The structure consists of 80% pigment

critical. The environmental performance of

filler (e.g.CaCO3, kaolin) and 20% microfibrillat-

these products is excellent (Figure 5), based

Figure 4. Production cost estimates of printed electronics substrates.

Figure 5. Environmental performance screening for the substrates of printed electronics: Carbon (left) and water scarcity (right) footprints.

on evaluations using the standardized LCA approach, including fossil greenhouse gases

4.3 New microcelluloses for increasing the tensile strength of paper

(CO2, CH4 and N2O), expressed as carbon dioxide equivalents (CO2 eq). No water consump-

Laboratory tests showed that carboxymethyl

tion data were available for the reference

cellulose (CMC) can be produced from micro-

product.

crystalline cellulose (MCC) using the chloroacetic acid method. Although the product is slightly

4.2 Conductive materials for fuel cells, sensors and indicators

yellowish and contains some fibre flocks, it is a technical grade. Within this study, CMC was made from 1) MCCs produced from softwood

The carbon-containing sheets were formed

bleached pulp with degrees of polymerization

using a similar method as for preparing filler-

(DP) of 300, 400, 500 and 2) MCC produced

MFC sheets, and calendered. The sheets con-

from eucalyptus bleached pulp with DP 500. By

tained 80% carbon (Printex carbon black or

varying the DP of the MCC it is possible to affect

G1 graphite) and microfibrillated cellulose was

the properties of CMC, making MCC an interest-

used to form a network that binds the carbon

ing raw material for CMC production.

particles into the structure. The surface re-

sistivity of the printed carbon black contain-

Microcrystalline cellulose was modified to pro-

ing sheet was at same level as that of a print-

duce different kinds of microreticulated cellu-

ed current collector (~1 Ohm). Benefits of the

loses (MRCs), see Figure 6 for an example. The

substrate include high porosity, high surface

MCC was produced via acid hydrolysis of Kraft

area, flexibility, low cost and biodegradability.

pulp at the pilot scale at Kemira using cook-

These are properties desirable for, e.g., biofu-

ing times of 20 and 120min, and further refined

el cells and sensors. However, the conductivity

with varied setups to produce MRCs. Scan-

turned out to be sensitive to moisture content.

ning electron microscope (SEM) imaging and

This issue was not further studied. Moisture

viscosity measurements clearly indicated that

sensitivity could, however, be overcome by

different kind of MCCs and MRCs were suc-

pre-treatment of cellulose fibrils. On the oth-

cessfully produced. Longer-cooked MCC had

er hand, moisture sensitivity offers potential

smaller particle size, and refining of MCC par-

uses for the substrates as intelligent seals or

ticles caused more fibrillated and smaller parti-

moisture indicators.

cles. The differences in viscosity between MRCs

produced from 120 min cooked MCCs were neg-

in bulk with CMC was around 1%. Interesting-

ligible. Addition of CMC to refining seemed to

ly, the smaller particle size 120 min cooked

cause a more fibrillated and loosened structure

and grafted MCC gave better drainage than

compared to refining without CMC.

20 min cooked and grafted MCC, even though it is known that smaller particle size normally

The potential to increase the tensile strength

causes longer drainage times. The dosage of

of paper using these new celluloses was test-

the MCC (5%) responds to 1 kg/t of pure CMC.

ed using a dosage of 50 kg/t. Pure MCC did not increase tensile strength notably. A 10% increase in tensile strength with MRC was ob-

4.4 Thermal insulation and sound absorption materials by foam forming

tained when the refining was done at pH 7, but at the same time the drainage time increased.

Lightweight structures were prepared at labo-

The best increase in tensile strength was ob-

ratory scale from basic papermaking raw ma-

tained with MRCs or MCCs that were graft-

terials with target grammages of 200, 400 and

ed with CMC. The highest increase in tensile

800 g/m2 using foam forming (Table 1, Figure 7).

strength was obtained with 20 min cooked

The density of the samples varied from 8 kg/m3

CMC grafted MCC that was refined once at

to 30 kg/m3 (bulk 34â&#x20AC;&#x201C;126 cm3/g). Compressibil-

pH 7. However, while the tensile strength in-

ity and reversibility were measured to under-

creased by 32%, the drainage time increased

stand the response to external load. Samples

by more than 30%.

were compressed to 50% initial thickness and the maximum load was measured. Thicker 800

The best combination of strength, drain-

g/m2 sheets showed much higher compression

age and bulk was obtained with non-refined,

loads than thinner 200 and 400 g/m2 sheets.

CMC grafted MCC, see Figure 6 (right). The 120

Pure pine pulp sheets seemed to have higher

min cooked CMC grafted MCC increased ten-

compression strength, but also better revers-

sile strength by over 29% and had a negligi-

ibility than CTMP sheets. Microcellulose made

ble effect on drainage time (5% increase). Bulk

the structures a lot less compressible, especial-

decreased by 2.6%. For comparison, a 4 kg/t

ly for CTMP-based structures, and also greatly

dosage of pure CMC increased tensile strength

improved their reversibility. The results showed

by 25%, but at the same time the drainage

that all foamed samples reversed quite well

time increased by nearly 20%. The decrease

after compression (62â&#x20AC;&#x201C;83%) and, after 1 min,

Figure 6. Left: SEM image of a microreticulated cellulose. Right: Carboxymethyl cellulose grafted microcrystalline cellulose significantly increases tensile strength and decreases drainage time.

they had reversed by a further 3â&#x20AC;&#x201C;6%. Thus, the

tion do not show as good thermal conductiv-

bulky structure is maintained well even if some

ity as stone or mineral insulation, but slightly

external load exists.

better conductivity than, e.g., flax insulation. The thermal conductivity of pure CTMP sheet

The thermal conductivity values of foam-

is slightly high, but still comparable with some

formed sheets were compared to commer-

flax insulation. Naturally, there are other re-

cial thermal insulators (Table 2). The thermal

quirements for insulation materials than mere-

conductivities of pure pine pulp sheets, CTMP

ly thermal conductivity, but other application

with 20% microcellulose addition and CTMP

areas, such as packaging, could also be con-

with 20% PCC addition seem very promis-

sidered for these kinds of foamed, low-density

ing. The values are comparable to mineral and

materials.

stone wool insulation materials of similar density. CTMP sheets with 50% pine pulp addi-

The lightweight, foam-formed structures also

Table 1. Basic properties of foam-formed sheets. The values for typical Styrofoam are shown for reference.

Sample

Grammage Thickness Density Bulk

[g/m2] [mm] [kg/m3] [cm3/g] 100 CTMP

800

100 Pine pulp

885

80/20 CTMP/MFC

820

80/20 CTMP/PCC

760

50/50 CTMP/pine

845

80/20 CTMP/PCC(1 720 87 8 120 Commercial Styrofoam

530

(1 Water and surfactant was foamed at the 1st stage, and fibres and other substances were added at the 2nd stage.

Figure 7. Left: Foam-formed, low-density pine pulp sheets. Right: Structures made from different wood fibres: 200 and 400g/m2 samples shown on the left and 800g/m2 samples on the right.

act as good sound absorbers. The results in-

the values for the commercial products varied

dicate that thicker samples with a grammage

from 0.1 to 0.6. Interestingly, the absorption co-

of 800 g/m2 had a much higher sound absorp-

efficient measured from the denser side of a

tion coefficient than thinner 200 g/m2 sheets.

CTMP sheet gave the highest value, 0.5, of the

Pine pulp sheets, CTMP with 20% MFC addition

foamed structures at 500 Hz frequency.

and 50/50% mixture of CTMP/pine, had the best overall absorption coefficient in all meas-

A potential production line for making low-

ured (0, 10 and 30 mm) air spaces. At the chal-

density sound insulation materials with foam

lenging 500 Hz frequency, the absorption coef-

forming is shown in Figure 8. The concept is

ficient of the foamed samples was 0.3, whereas

still web-like, although the super-bulky and

Figure 8. Concept line for making low-density foam-formed sound insulation materials.

Table 2. Comparison of foam-formed sample with commercial thermal insulators (source: TM Rakennusmaailma 06/2012). U-values were calculated.

Trade name

Material

Density Thermal

U-value 1

conductivity kg/m3

10 W/(m路K)

Commercial

Isover KL-33

glass

21.8

0.033

0.66

glass and stone

Ursa Lasivilla lambda 37 glass

18.3

0.035

0.70

wool insulators

Knauf Space Slab 035

glass

23.1

0.035

0.70

Paroc eXtra

stone

31.1

0.035

0.70

Rockwool Flexi-Batts

stone

34.5

0.035

0.70

Commercial

Hunton Flex

wood

62.2

0.038

0.76

natural fibre

Ekovilla

paper

38.6

0.038

0.76

insulators

Konto

peat+wood 54.2

0.037

0.74

Foam-formed

Foamed pine

pine pulp

0.035

0.71

28.0

1 Calculated value: U = 1/R, where R = d/位. Thickness (d) of the samples was 50 mm. For foamformed sample also 50 mm thickness value was used and expected that thermal conductivity is same than with 31.5 mm sample.

Figure 9. Environmental performance screenings for foam-formed, low-density sound absorption materials at 800 gsm: carbon (above) and water (below) footprints.

thick materials would most likely be formed

in sound absorption applications as, without

using non-continuous processes. The cost of

any optimization of the structure, they showed

such a line is estimated to be approximately

mediocre results compared to commercial

EUR 20-30 million (15 000 t/a) with a width of

products on the market. For thermal insulation

1.5m, speed of 30m/min and annual produc-

applications, the production of bulky struc-

tion of 20 km2/a. The production cost is esti-

tures economically enough, i.e., drying them

mated to be about 1.7 â&#x201A;Ź/m2, whereas compet-

in a manner that preserves their bulk, should

ing products are in the order 9-14 â&#x201A;Ź/m2. When

be addressed as well as their flammability and

comparing this, e.g., with cylinder drying used

water absorption properties.

for a typical folding box board machine, more energy is needed (increase 200%) due to through air drying and as no press water re-

4.5 Modelling of material interactions, rheology and structure

moval is made. Water usage is at the same level, chemical costs increase by 20% (more

New models describing the basic properties

binding chemicals) and investment is assumed

of cellulose nanofibrils and their product ap-

to cost 170% of the original, mainly due to the

plications were developed at several different

longer dryer section requirement.

scales, as indicated in Figure 10. With the help of modelling, it is possible to re-think the be-

The environmental performance of foam-

haviour of MFC in very short time and spatial

formed sound insulation materials is better

scales. Although the process size is huge, the

than that of competing products (Figure 9)

short time and spatial scales often drive mac-

based on standardized LCA evaluation, includ-

roscopic behaviour. For example, amorphous

ing fossil greenhouse gases (CO2, CH4 and N2O)

nano-scale regions in elementary fibrils domi-

expressed as carbon dioxide equivalents (CO2

nate the macroscopic viscoelastic properties of

eq). No water consumption data were availa-

not only MFC films, but also those of wood fi-

ble for the reference product.

bre networks and thus conventional paper. As a second example, fibril floc formation within

In conclusion, the results indicate that foam-

microseconds affects the rheology of MFC sus-

formed structures could have great potential

pensions and the macroscopic strength prop-

Figure 10. Modelling groups and topics related to MFC in the EffNet programme. The operation scales of the models are indicated on the horizontal axis.

erties of MFC re-enforced materials. There are

pected based on the very high elastic modu-

also rheological and structural properties, such

lus of 120-150 GPa of a single cellulose crystal.

as plug flow in pipes or optimal composition of

This discrepancy could be caused either by im-

a multi-layer structure, that can be understood

perfections in the fibrils or by the inability of

only by looking at sufficiently large, sometimes

the fibrilsâ&#x20AC;&#x2122; networks to utilize the full strength

even macroscopic scales.

potential of individual fibrils. Thus, it is important to systematically investigate the effect of

It is impossible to comprehensively cover all

various structural factors on different scales

relevant scales and phenomena related to

to gain a fuller understanding of the causes of

MFC processes and applications within a sin-

the observed mechanical behaviour. Atomis-

gle research programme. Therefore, the ini-

tic simulations provide great insight into the

tial multi-scale modelling objective, in which

dominant molecular-level factors that may

models developed by different groups would

drive macroscopic behaviour. Previous atom-

be combined into a coherent analysis package,

istic molecular dynamics simulations of cel-

was too challenging. However, the developed

lulose have focused on its crystal structure

models not only helped in interpreting the ex-

and elastic behaviour, whereas in the EffNet

perimental results, but also led to important

programme this approach was extended to

findings beyond current experimental capabil-

non-crystalline regions formed within the fi-

ities. A few key examples of such findings are

bril in zones where a large part of the cellulose

given in Figure 10.

chains were broken (Figure 11). X-ray diffraction data suggests such regions to be common

Viscoelastic behaviour of elementary fibrils

in cellulose fibrils, with up to 50% of the mate-

affects the stiffness of MFC films

rial being in an amorphous state.

Experimental studies have shown that micro-

The simulated elastic modulus for crystal cellu-

cellulose films are not as stiff as could be ex-

lose compared well with the values obtained ex-

perimentally. However, non-crystalline regions

by 4 GPa for each additional connecting chain.

were found to decrease the modulus significant-

The molecular dynamics simulations are closely

ly. Different numbers of connecting chains be-

related to the fibril network simulations of Ku-

tween the crystallites were examined, and it was

lachenko et al. (2012, Cellulose 19, p. 793). Our at-

found that the elastic constants, inelastic defor-

omistic simulations confirmed a number of their

mations, and strength of the fibril depended on

speculations on the role of non-crystalline re-

this number. For example, the elastic modulus

gions in fibril stiffness.

for the whole fibril can be estimated to increase Microrheology of nanocellulose suspensions is dominated by consistency and fibril length Nanocellulose fibres in suspension/gel states are known to have complex structures, depending on, for example, concentration and ionic strength. These complex structures pose both opportunities and challenges: creating novel functional structures is challenged due to the difficult rheology and processability of MFC suspensions. To better assess the chemical and rheological impacts on the formation of nanocellulose structures, a novel particlebased method based on smoothed dissipative particle hydrodynamics was developed. This Figure 11. Relative sliding of cellulose chains within an amorphous region, leading finally to breakup of the fibril at high tensile stress. The images are snapshots of fibril structure in atomistic molecular simulations at different phases of straining.

numerical approach treats both fluid and solid phases in a unified way. The fluid and solid phases are described as a set of particles exchanging momentum and/or interacting through Derjaguin-Landau-Verwey-Overbeek (DLVO) potentials. Furthermore, nanocellulose fibres are represented as strings of solid particles connected through extensional/bending springs. This model was used to simulate the microrheology of MFC suspensions. The simulations were carried out for the Couette geometry with a gap of 1 Îźm. The goal was to determine the effect of various properties of cellulose nanofibre and its interaction strength on forming micro-flocs and on local viscosity. The parametric effects on the micro scale are

Figure 12. Dependence of simulated viscosity on various model parameters. In each case, the other model parameters were fixed at the values shown in the middle of each block (consistency 1.0%, length 0.30Âľm etc.).

expected to be reflected in the observed macroscopic flow behaviour, as this behaviour depends critically on the local aggregation dynamics. In the simulations, at very large shear rate 0.3 106 1/s floc formation was seen to take

place very rapidly, within microseconds. Moreover, due to slippage, the local shear rate be-

5. Exploitation plan and impact of results

comes higher than average close to the walls. Thus, the effective viscosity has a higher val-

The achievements directly support the goal of

ue in the central region of the flow compared

demonstrating new types of products that can be

to the boundary regions. As regards the varied

produced from wood-fibre based materials and

parameters, suspension concentration and fi-

that expand the current product portfolio offered

bril geometry (especially length) appear to have

by forest cluster companies. Micro- and nanofi-

much stronger effects on viscosity and floc

brillated cellulose raw materials will have a high

formation than fibril interaction (double layer

impact on the future paper- and board-making

thickness) or bending stiffness (Figure 12).

industry through the introduction of new products. Filler-MFC composites show good potential

Surface pore structure underlies conductivity of

for low-cost printed electronics substrates, but

printed lines on filler-microcellulose substrates

market penetration will require investment in developing the production technology.

Composites made from cellulose microfibres and inorganic filler particles can be applied as

Foam forming clearly has very high value cre-

substrates for printed electronics. The struc-

ation potential as it can both considerably in-

tural properties of these substrates have been

crease the competiveness of current fibre

studied both experimentally at VTT and with

products and offer a sustainable solution for

a particle-level modelling approach developed

manufacturing a large range of value-added

at Helsinki University. The model describes

products. This opens opportunities for both

the skeleton structure formed by pigment

large companies and SMEs to create novel val-

particles of varied shape and size distribu-

ue chains. The examples of lightweight struc-

tion. Microcellulose is assumed to fill voids of

tures demonstrated in this section represent

the structure. In order to compare the mod-

only the tip of the iceberg. Good sound ab-

el results with experiments, it was important

sorbance properties achieved with lightweight

to also simulate the profilometer measure-

structures made from sustainable raw materi-

ment of surface roughness. The model simu-

als is an intriguing combination to be addressed

lations predict quite well the relative changes

further. Similarly, the microcrystalline cellulose

in measured density, porosity and roughness

applications show potential both as superab-

for kaolin and precipitated calcium carbon-

sorbent polymers and strength additives in pa-

ate (PCC) pigments. Small-scale roughness

permaking. The modelling results can be ap-

turned out to be higher for kaolin than for PCC.

plied, for example, when tailoring micro- and

However, the measured conductivity of print-

nanocelluloses for specific applications.

ed lines on kaolin surfaces was higher than on PCC surfaces. The simulations reveal a more open surface pore structure for PCC than for kaolin, which leads to stronger absorption of the silver ink, and thus explains the differences in the measured conductivities. These results have been published by Penttil채 et al. (2013, Cellulose 20, pp. 1413-1424).

6. Networking

Solid Mechanics at the Royal Institute of Technology (Sweden) has assisted VTT in the devel-

The research was carried out jointly by re-

opment of the advanced fibre network model.

search organisations and Finnish forest cluster companies. Table 3 presents the partners

The Tampere university of Technology group

and their role in the research.

has collaborated with the Royal Institute of Technology (KTH, Stockholm) on coarse grain-

VTT has collaborated with FPInnovations (Can-

ing of cellulose nanofibril systems using the

ada) on modelling the rheological properties of

Martini model. The modelling work of the Bio-

micro/nanocellulose suspensions and forming

logical Physics and Soft Matter team are also

micro-scale fibre networks. The Department of

coupled to the ESF network SIMBIOMA in terms

Table 3. Partner organisations and their research roles.

Partner

Role

Aalto University, Complex

Simulations of the flocculation of microcellulose, also in the

Systems and Materials,

presence of filler particles. Investigation of the mechanical

Prof. Alava

properties of particle-MFC packings.

Helsinki University,

Optical simulations and particle packing simulations in the virtual

Department of Physics,

product development environment.

Penttil채 Helsinki University,

Specialized in structural characterization of materials and

Department of Physics,

products using X-rays. Team responsible for x-ray scattering and

Prof. Serimaa

x-ray microtomography measurements of cellulose microfibers and structures.

Kemira

Evaluating both the quality and properties of microcellulose, focusing on P&P applications.

Stora Enso

NFC processing and fractionation, substrates for printed electronics.

Tampere University of

Development of atomistic, molecular and coarse-grained models

Technology, Biological Physics

for nanocellulose.

and Soft Matter, Prof. Vattulainen UPM

Microcellulose polymer interactions in water suspensions.

VTT Technical Research

Production of microcelluloses, demonstration of new product

Centre of Finland

concepts, implementation of virtual product model environment and coordination of networking activities.

of developing coarse-graining techniques and

Torvinen, K., Sievänen, J., Hjelt, T., Hellén, E.,

coarse-grained models for complex biomolecu-

“Smooth and flexible filler-nanocellulose com-

lar systems. In addition, the research benefits

posite structure for printed electronics appli-

from the ESF network FUNCDYN, the objective

cations”, Cellulose 19, Issue 3, pp 821-829. doi:

of which is to link detailed models to large-scale

10.1007/s10570-012-9677-5

networks for the examination of functional dynamics in complex chemical systems. The team

Conference presentations and posters:

also belongs to the Norforsk-funded networks “Refining Lignocellulosics to Advanced Poly-

Hellén Erkki., “Filler-nanocellulose composite

mers and Fibers” (headed by Maija Tenkanen,

as a substrate for printed electronics”, Indus-

Finland) and “Nordic Network of Soft Matter

trial Biomaterials seminar, November 22, 2012.

Physics (headed by Jon-Otto Fossum, Norway).

Espoo, Finland.

7. Publications

Illa, X., Puisto, A., Mohtaschemi, M., Lehtinen, A., and Alava, M. J., “Simple rheological models and fluidization in complex fluids”, 2nd Edition

Illa, X., Puisto, A., Mohtaschemi, M., Alava, M. J.,

on Materials Deformation: Fluctuations, Scal-

Transient shear banding in time-dependent flu-

ing, Predictability, February 17-22 2013, Les

ids. Phys. Rev. E 87, 022307 (2013).

Houches, France.

Paavilainen, S., Róg, T., and Vattulainen, I.,

Illa, X., Puisto, A., Mohtaschemi, M., and Ala-

Analysis of Twisting of Cellulose Nanofibrils

va, M. J., “Transient Shear Banding in Attractive

in Atomistic Molecular Dynamics Simulations.

Colloids”, The 2nd Workshop on Fluctuations

The Journal of Physical Chemistry B, 2011, 115,

in Materials Properties: Physics, Geoscience

3747-3755

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Microcelluloses and their characteristics

c o n ta c t p e r s o n Heli Kangas, heli.kangas@vtt.fi

pa r t n e r s VTT Aalto University Andritz Oy Kemira Stora Enso University of Oulu University of Helsinki UPM

Abstract

Different types of microcelluloses were produced in a quality-controlled way, characterized and distributed to programme partners. MicroFracon showed promise as a method for analysing the amount of nanomaterial in microcelluloses, although further development of the method is needed. Analysis methods suitable for routine quality control of microcelluloses, namely low shear viscosity and transmittance measurements, were harmonized and can now be used routinely in different laboratories. A method to determine both the retention and distribution of microcelluloses in the final product in real papermaking process conditions was developed and successfully demonstrated at pilot scale trials. Deeper understanding of the rheological properties of suspensions of microfibrillated celluloses was gained. Together with the results on the processability, i.e. pumping and mixing, and dewatering of microfibrillated cellulose suspensions, this information can help in designing future industrial processes. Up-to-date information on progress in research, legislation and recommendations related to product safety of microcelluloses was gathered, and REACH requirements for microcelluloses were clarified. International and national cooperation was established related to both the characterization and product safety of nanocelluloses.

Keywords microcellulose, nanocellulose, fibrillated celluloses, characterization, product safety, processability, pumping, mixing, rheology, dewatering

1. Background

very closely related to accurate and reliable characterization of raw materials used. The

The overall goal of the EffNet research pro-

safety of bio-based nanomaterials depends

gramme has been the development of re-

on many still poorly understood factors, as

source-efficient

technologies

well as on the exposure route (via respiratory,

through the renewal of production processes

gastronomic track, skin or eye). The size and

and by developing new unit processes based

shape of the particles, their aggregation prop-

on advanced raw materials and desired end-

erties, degree of branching and specific sur-

product characteristics. Bio-based nanoma-

face properties, among others, may affect the

terials are promising candidates for improv-

interactions of bio-based micro- and nanoma-

ing the performance of many products in the

terials with cells and living organisms.

production

near future due to their unique properties and to the fact that they originate from renewa-

It is known that the rheological properties of

ble resources. Among the most abundant and

suspensions containing micro- and nanocel-

sustainable nanomaterials are micro- and na-

luloses differ a great deal from those in to-

nocelluloses, which have a wide industrial ap-

day’s papermaking operations. In order to pro-

plication potential, including, for example,

cess these suspensions, their rheology must

novel composites and construction materi-

be known. In addition, due to their high swell-

als, new kinds of porous materials, biomedical

ing, micro- and nanocelluloses are inherent-

materials, value-added paper and board prod-

ly difficult to dewater. Up-scaling will require

ucts, intelligent packages, barrier materials, as

re-thinking of the whole papermaking process

well as functional surfaces and additives.

from wet end to drying of the porous structure. Therefore, unit operations involved in the

As with any new materials, proper characteri-

processing of micro- and nanocelluloses, such

zation of micro- and nanocelluloses is critical,

as pumping, mixing and dewatering, need to

both for their trade and for their safety assess-

be carefully studied.

ment. However, characterization, especially of fibrillated celluloses, is challenging due to their heterogeneous nature and the fact that

2. Objectives

they mostly consist of long, slender fibrils with a high degree of branching. Research in this

The objectives were to gain information about

area is very actively pursued in several re-

the characteristics of microcelluloses with

search projects around the world, but despite

variable properties as well as their behaviour

the characterization work done already, there

in different processing environments. Activi-

is still a need to find new methods and develop

ties related to the product safety of microcel-

existing ones in order to better describe mi-

lulose, such as research projects and guide-

cro- and nanocelluloses and their distribution

lines given by the authorities, were actively

in web-like end-product or composite struc-

followed to obtain up-to-date information. The

tures. In particular, reliable characterization

specific objectives of the work were:

methods are needed to determine the quality of micro- and nanocelluloses. Validation of

• Preparation of tailored raw materials

the characterization methods to enable com-

• To achieve a leading role in the product

parison of material properties is also a key factor. In addition, product safety is an essential aspect when developing new products and is

safety and characterization of micro- and nanocelluloses • To ensure the safety of new materials,

processes and product concepts based on

for quality control and safety assessment of

microcellulose

micro- and nanocelluloses. As a result, viscos-

• To evaluate the effects of microfibrillated

ity and transmittance measurement methods

cellulose on forming and dewatering

were harmonized and can now be used in dif-

characteristics

ferent laboratories to obtain comparable re-

• To gain deeper understanding of the

sults. An estimate of the size distribution of

rheological properties of microfibrillated

particles in microcelluloses can be obtained by

cellulose suspensions, in order to have

fractional analysis.

necessary knowledge for eventual scaleup of MFC processes; production, paper

Product safety is an essential part of the de-

manufacture, etc.

velopment of new products and very closely related to accurate and reliable character-

3. Research approach

ization of the raw materials used. As there were many national and EU FP7 projects related to safety issues of microcelluloses al-

For successful research on the characteristics

ready on-going at the beginning of the pro-

and safety aspects of microcelluloses, as well as

ject, their activities were intensively followed

on their behaviour and performance during pro-

in order to avoid parallel research in the field

cessing, the production of the studied materials

as well as to gain state-of-the-art knowledge

must be performed in a quality-controlled way.

on product safety. In addition to this, relevant

The fundamental issues critical to the produc-

and up-to-date information on the product

tion of micro- and nanocelluloses were therefore

safety of micro- and nanocelluloses was con-

studied. As a result, seven different types of mi-

tinuously collected by following the develop-

crocelluloses were successfully made, charac-

ment of legislative requirements and recom-

terized and delivered to partners.

mendations given by authorities, scientific advisory bodies, and international organiza-

Based on the results from the first phase of

tions in EU member states and North Ameri-

the programme, characterization of the mi-

ca. The REACH requirements for nanomateri-

crocelluloses was considered both essen-

als were clarified and simplified based on the

tial and challenging. Identification of suitable

new RIP-oNs (Reach Implementation Project

methods was therefore required. A survey of

on Nanomaterials) guidelines and ECHA (Eu-

published micro- and nanocellulose charac-

ropean Chemicals Agency) recommendations.

terization methods was performed to gain in-

In addition, application-specific requirements

formation on their most important properties

for nano- and microcelluloses were evaluated.

and state-of-the-art characterization meth-

Information needed for material safety data

ods. Active discussion with the industrial part-

sheets (MSDS) for micro- and nanocelluloses

ners of EffNet led to proposals both for materi-

was gathered, and the main knowledge gaps

al specification and a classification scheme for

identified. International cooperation was es-

micro- and nanocelluloses. Start-up work for

tablished in the field of nanomaterial safety,

standardization included participation in the

for example with COST action FA0904 and the

preparation of a standardization workshop and

Canadian research centre FPInnovations. Na-

allowed us to contribute to the roadmap for in-

tional cooperation between two SHOKs (Finn-

ternational standardization of cellulose nano-

ish strategic centres for science, technology

materials. Method development was success-

and innovation), FIBIC’s EffNet programme

fully performed in areas considered important

and CLEEN’s MMEA programme was practiced

under the title “Environmental management

4. Results

and sustainable use of nanocellulose”. The lished in a public report.

4.1 Production and characteristics of microcelluloses

In studying the processability of microcel-

Production of microcelluloses

luloses, the main aim was to clarify the pro-

Different types of microcelluloses were either

cessability of high-water binding furnishes in-

acquired or produced for research purposes in

cluding rheological properties, pumping and

EffNet. The microcelluloses used in the project

mixing with the applied chemistry. The behav-

are described as follows:

discussions of a two-day workshop were pub-

iour of suspensions of microcelluloses at different consistencies between 1% and ~20%

• Daicel MFC (Celish KY-100G) According to

was studied, including studies of both UHC (ul-

current knowledge, Celish KY-100G consists

tra-high consistency) and foam suspensions.

of dissolving pulp with high cellulose

Suspension rheology was measured with

content. The dissolving pulp is originally

state-of-the-art devices and the studies on

from softwood. The material was delivered

flow rheology at various chemical conditions

at 10% consistency.

were supported by simulations. The effect of

• VTT coarse and fine MFC: Both VTT grades

microcellulose quality was analysed with new

are made of bleached hardwood kraft pulp.

meso-scale models for colloidal interactions,

They are ground to different coarseness

which was applicable even at very high con-

levels having a viscous structure higher

sistencies. Simulations were used to extrap-

than other grades. These grades also

olate the process operating window beyond

have the highest transmittance levels. The

laboratory scale, for example by simulating a

material was delivered at 3% consistency

faster process, which would be impossible experimentally. This supports the design of scalable forming concepts.

unless otherwise stated. • P-1 MFC: Pilot-scale microfibrillated material consisting of stiff fibre fragments and fibrils, having medium viscosity compared

In the dewatering studies, the target was to determine the limitations of initial dewater-

to the other available grades. • P-2 MFC: Pilot-scale microfibrillated

ing and press dewatering for microcellulose-

material consisting of a wide selection of

containing furnishes. The material behaviour

unfibrillated and fibrillated material and

in dewatering operations was studied at lab

having medium viscosity compared to the

scale with a moving belt former. The effect of

other available grades.

furnish type was studied based on the water

• MCC and MRC: Microcrystalline cellulose

removal efficiency of the furnish recipes, the

(MCC) is produced via acid hydrolysis of

main variables being furnish composition, re-

kraft pulp cellulose polymer. The produced

tention control, and type and amount of micro-

MCC is refined with varied setups to

cellulose. The effect of papermaking additives

produce microreticulated cellulose (MRC).

and fines on dewatering was also studied.

The samples have relatively low viscosity and MRC has smaller reticulated particle size compared to MCC.

Basic characterization

for evaluating the product quality of microfibril-

The basic characteristics of the microcellulos-

lated celluloses. In order for the results to be

es were defined using the following methods:

comparable regardless of the place of measurement or type of sample, efforts towards

• Optical microscopy (OM) – visual inspection

harmonization of these measurement methods

of microcellulose sample type (coarse/fine)

were made. The harmonization included both

and assessment of homogeneity.

the sample preparation and the measurement

• Scanning electron microscopy (SEM) –

procedure. The methods were then tested with

evaluation of detailed fibril structure.

the same samples between different labora-

Thickness and branching of the fibrils.

tories. The introduced viscosity measurement

• Low-shear viscosity – evaluation of gel

method is now routinely used in at least six lab-

strength and flow behaviour as a measure

oratories and the transmittance measurement

of product quality and processability.

method in three laboratories.

• Transmittance – evaluation of the amount of larger-size fibrils in the suspension.

Strength potential of microcelluloses As part of their characterization, the strength

• Stability analysis – transmission measurement combined with measurement

potentials of the EffNet microcelluloses were

of the specific volume of sedimentation

evaluated. The strength measurements were

at a certain time frequency, providing

done both for 100% microcellulose films and

information about the stability of

for blend sheets, in which microcellulose addi-

the system (e.g. phase separation,

tion levels of 0, 1 and 5% and two different fur-

sedimentation).

nishes, spruce CTMP (CSF=570 ml) and chemical pine (19 °SR), were used. The results for

The basic characteristics of the EffNet mi-

100% microcellulose films showed that the

crocellulose samples are summarized in Ta-

type of microcellulose has an impact on the

ble 1 and their optical microscopy images are

strength potential of the films, as do the film

shown in Figure 1.

forming and drying procedures. The elastic modulus of the films increased with density,

Low shear viscosity and transmittance meas-

but for fine microcellulose grades, the brittle

urements were both considered good methods

structure of the films with no plastic behaviour

Table 1. Basic characteristics of the EffNet microcelluloses.

Shear viscosity, Transmittance, Stability analysis mPa·s % Sedimentation volume, (10 rpm, 1.5%) (800 nm, 0.1%) mm

Transmittance of sediment, %

Daicel MFC

15 777

8.1

VTT coarse MFC

23 176

34.3

7.5

VTT fine MFC

22 502

60.2

P-1 MFC

2 784

24.9

P-2 MFC

3 654

26.2

11.5

MCC NA 0.2 9

MRC

400 0.5 32

Figure 1. Optical microscopy images of the EffNet microcelluloses. Scale bar: 200 Âľm.

resulted in low tensile values. For handsheets

the particles are separated axially so that

with microcellulose addition, the effect of mi-

the largest ones accumulate at the front end

crocellulose type was insignificant. A 1% ad-

of the flow plug and the smallest ones at the

dition of microcellulose did not notably influ-

rear end. In MicroFracon, a defined quantity of

ence the wet and dry strength properties of

sample is mixed with water flowing through a

the handsheets. However, with 5% microcel-

long tube wound onto a wheel. The pulp sam-

lulose addition, a substantial increase in tensile index was observed for CTMP, even 73% with VTT coarse (Figure 2). In addition, the zdirectional strength increased for both pulps and the increase in wet tensile strength was remarkable in both pulps. Fractional analysis Fractional analysis of microcelluloses was performed at the University of Oulu with a MicroFracon device (Metso Automation, Finland), which utilises a tube flow fractionation principle (Figure 3). In the tube flow technique,

Figure 2. Tensile index for CTMP handsheets with microcellulose addition.

ple is fractionated into different size catego-

centages of the fractions were determined

ries as it flows through the tube, and when the

by filtration (in the presence of flocculent) on

pulp-water mixture exits the long tube, it is di-

a membrane, followed by precision weighing

vided into size fractions according to the setup

(Table 2). The largest particles in the fraction-

of the device. The different fractions can then

ated particle-water suspension were visual-

be analysed, for example with image analysis

ised with a high definition camera unit. How-

software or various microscopic methods.

ever, the sensitivity of the image analysis is around 1 µm, and particles with dimensions

The EffNet microcellulose samples were frac-

smaller than that could not be reliably meas-

tionated into four different fractions according

ured. The aspect ratio (AR) of particles – the

to their size, primarily according to the long-

relation of the longest dimensions (LD) and

est dimension of the particles. The fractions

the shortest dimensions (SD) – were obtained

obtained were FR1 (largest particles), FR2, FR3

from optical image analysis (fractionation im-

and FR4 (smallest particles). The mass per-

ages) (Table 3).

Figure 3. Principle of tube flow fractionation. Table 2. Mass percentages of the EffNet microcelluloses in different fractions.

FR1 [%]

FR2 [%]

FR3 [%]

FR4 [%]

Daicel MFC

31.4

53.6

13.7

1.3

VTT coarse MFC 27.0

59.7

9.8

3.5

VTT fine MFC

63.8

29.7

4.8

P1-MFC 46.0

50.9

3.2

0.0

P2-MFC 57.2

23.2

1.8

14.9

4.7

MCC 48.0 35.8

12.0

4.2

MRC 5.5

13.6

3.7

77.2

Table 3. Dimensional data of fractions from EffNet microcelluloses. * not enough particles for MicroFracon image analysis (see mass percentages in Table 2).

LD FR1 LD FR2 LD FR3 SD FR1 SD FR2 SD FR3 AR AR AR [µm] [µm] [µm] [µm] [µm] [µm] FR1 FR2 FR3

Daicel MFC

141

4.5

2.1

1.5

31.3

26.2

13.3

VTT coarse MFC 34

2.2

1.5

1.3

15.5

12.7

8.5

VTT fine MFC

2.7

1.2

1.1

18.1

10.9

8.2

P1-MFC

41 22 * 3.0 1.7 * 13.7 12.9 -

P2-MFC

178

4.5

1.7

1.2

39.6 10

MCC

139

10.3

2.5

1.7

13.5 6.8 6.5

MRC

3.4

2.9

1.6

6.2 10 6.3

6.7

Direct measurement of MFC retention and distribution in paper by labelling Detection of individual MFC fibres in paper is difficult using any measurement method available because the density and chemical composition of the pulp and MFC fibres are the same. A method to increase the average density of MFC using a selective labelling method was therefore developed, enabling the detection of the spatial distribution of MFC and providing a method to study its retention in paper. The labelling method is based on attaching Iron-Cobalt-nanoparticles onto the surface of the MFC. The spatial distribution of the MFC can be evaluated from the X-ray microtomographic images and the retention can be studied by scanning electron microscope (SEM), energy-dispersive X-ray spectroscopy (EDS) analysis and inductively coupled plasma optical emission spectrophotometry (ICP-OES) measurements (Figure 4). Tests showed that labelling does not change the strength properties of the samples. The concept was tested in pilot-scale SUORA trials with good success. The trial showed that is possible to directly measure the effect of MFC addition on paper strength properties, as well as monitor retention and distribution in real papermaking process conditions. Structural analysis The research group at the Department of Physics, University of Helsinki, is specialized in structural analysis of soft materials using xrays, especially synchrotron radiation based methods. In this project, the structure of cellulosic materials, including microcelluloses, was studied using x-ray scattering and microtomography. Specifically, the preferred orientations of cellulose fibres were determined using both x-ray microtomography and x-ray diffraction, and similar results were obtained. Wide-angle x-ray scattering (WAXS) was used for determining the crystallinity and size of

Figure 4. Visualization of paper cross sections by SEM (a, b) and X-ray microtomography (c). In image a) dense, labelled MFC was thresholded from the image and denser areas are emphasized with red colour. In image b) (reference with original MFC), the contrast between fibres and MFC cannot be seen. Image c) illustrates four paper samples with different amounts of labelled MFC and d) shows the distribution of MFC in a paper produced in the SUORA environment.

cellulose crystallites in the studied samples

Following the start-up work on standardiza-

(Figure 5). In addition, WAXS gave information

tion in EffNet, the international standardiza-

on the crystal structure (cellulose I, II). Small-

tion regarding nano- and microcelluloses is

angle x-ray scattering (SAXS) was found to be

being currently managed by Kemesta ry (For-

useful in studies of nanometre range porosity

est and Chemical Industry) and METSTA (Na-

and short range order of cellulose microfibrils.

notechnology).

Standardization of micro- and nanocelluloses

4.2 Product safety aspects of microcelluloses

At the beginning of the project, standardization of micro- and nanocelluloses was considered important both in Finland and internationally,

As product safety is an essential part of new

and preparatory work for standardization was

product development, the safety aspects of

included in the project plan. First, the most im-

nano- and microcelluloses must be taken into

portant aspects for the industrial programme

account as early as possible. During EffNet,

partners were clarified and a suggestion/road-

the current knowledge on the safety of nano-

map for continuation of the standardization

materials was reviewed as well as the current

was drafted. Internationally, a proposal to the

regulations related to nanomaterials.

ISO to form a nanocellulose task group under TC-229 nanotechnologies, which would coor-

At present, there are no detailed regulations re-

dinate ISO standardization of nanocelluloses,

garding nanomaterials, and nanocelluloses are

was made. In addition, participation in organiz-

regulated as bulk cellulose. Any nanomaterial is

ing an international Workshop on Internation-

thus required to fulfil current regulations, such

al Standards for Nanocellulose, held in Wash-

as REACH, occupational health related instruc-

ington DC on June 9, 2011, was accomplished.

tions, and regulations based on its intended use, such as regulations related to food contact materials (FCM), food legislation, cosmetics, etc. However, authorities worldwide are currently evaluating the existing regulations in order to determine whether they are applicable or adequate for nanomaterials, or whether there is a need for further nanomaterial-specific rules. It remains to be seen whether such specific regulations will be announced and if they will be applied also to nano- and microcelluloses. Some scientific opinions and guidelines have already been published, such as the OECD’s Guidance Manual for the Testing of Manufactured Nanomaterials and the REACH Implementation Project on Nanomaterials (RIP-oNs). Based on the

Figure 5. Crystallinity of VTT fine and coarse MFC, measured from 100% microcellulose films. Crystallinity of VTT fine MFC was 42±3% and that of VTT coarse MFC 40±3%. The crystal width (200 reflection in Iβ) was 4.4±0.1 nm for VTT fine MFC and VTT coarse MFC 4.5±0.1 nm.

extensive RIP-oN reports, the European Chemicals Agency (ECHA) has released the Guidance on Information Requirements and Chemical Safety Assessment on nanomaterials, providing endpoint-specific guidance for registrants preparing REACH dossiers on nanomaterials.

The guideline is relevant to physico-chemical

The main question regarding legislation re-

and ecotoxicological endpoints. In addition,

quirements on micro- and nanocelluloses in

guidelines on the characterization of dose-

the future will be whether they are considered

response for human health and the environ-

nanomaterials according to the Commission

ment, and occupational exposure estimation

definition 2011/696/EU (Figure 6). Today cellu-

are given by the ECHA. The main guideline is

lose pulp is exempted from the registration re-

now in hearing by CARACAL (an expert advi-

quirements based on Article 2(7)a; Annex IV, if

sory group to the European Commission and

not chemically modified, and as there are no

ECHA on questions related to REACH and CLP

specific requirements for nanomaterials, cel-

(Classification, Labelling and Packaging) of sub-

lulose micro- and nanomaterials are exempted

stances and mixtures) and in all likelihood will

also. However, there is a possibility that this will

be included in the EU’s chemical legislation in

change, since REACH is currently under revision

the near future. In addition, specific applica-

and new guidance documents and possibly

tion areas have specific requirements that the

amended annexes will be published after June

materials applied should fulfil, for example the

2013. Chemical modification may also bring mi-

European Food Safety Authority (EFSA) has re-

cro- and nanocelluloses under the REACH reg-

leased guidance on risk assessment concern-

ulation and under registration requirements.

ing potential risks arising from applications of nanoscience and nanotechnologies to food and

Published studies of the health effects of mi-

feed, and in the USA the Food and Drug Admin-

cro- and nanocelluloses as well as their envi-

istration (FDA) has published guidelines for the

ronmental effects and occupational health is-

food and food packaging industry. The require-

sues were first reviewed in the research report

ments also vary depending on the application

“Characterization and safety aspects of nano-

area, such as food, food contact materials, cos-

celluloses” and, more recently, in the Hand-

metics, etc. For example in the US, the FDA has

book of Green Materials; Processing Technolo-

published guidelines for industry on the safety

gies, Properties and Applications (Chapter 12,

of nanomaterials in cosmetic products.

Toxicity and health issues). The results pub-

Is the nanocellulose nanomaterial according definition?

Is the nanocellulose chemically modified?

Registration requirements apply

New recommendations published by ECHA

Registration with additional nanomaterial specific requirements

Registration requirements apply

Registration with current rules

Current REACH regulations stands

No registration

Figure 6. Current status of nanocellulose and possible future vision.

lished so far indicated that nano- and micro-

The environmental behaviour of microcellulos-

celluloses do not pose risk to human health

es is important when considering both their fu-

or to the environment, but more research and

ture production and the utilization of products

toxicity tests are needed to guarantee their

based on them. Therefore, the biodegradation

safety, especially if the finest particles will be

of two EffNet microcelluloses, VTT fine MFC

applied in high concentrations. In addition,

and P-2 MFC (produced at laboratory scale),

even though there is no related safety con-

was studied according to OECD test methods

cern, these materials cannot be considered in-

commonly used in chemical testing. The ready

ert either, since inflammation reactions have

biodegradability was determined according to

been observed in many cases.

OECD 301 B Ready Biodegradability CO2 Evolution (Modified Sturm Test) measuring CO2 pro-

As mentioned above, more research and toxic-

duced during the test (28 days). The criterion

ity tests are needed to guarantee the safety of

of ready biodegradability is 60% ThCO2 within

nano- and microcelluloses, especially if the fin-

10 days. Based on the results, VTT fine MFC is

est particles will be applied in high concentra-

readily biodegradable. P-2 MFC did not reach

tions. In order to also guarantee the safety of

the criterion for ready biodegradation, but can

the finest particles, their amount in microfibril-

be considered as rapidly biodegradable. The

lated cellulose (MFC) was studied, along with

difference in the biodegradability was proba-

their properties and health effects as part of the

bly due to the finer structure of VTT fine MFC.

safety assessment. VTT fine MFC was fractionated with MicroFracon into 4 fractions of differ-

The most critical product safety, environmen-

ent size. The two smallest fractions (FR3+FR4)

tal efficiency and regulation challenges of MFC

were collected and subjected to toxicity testing.

production and its use were identified in a

Using In vitro toxicity testing, the effect of the

pre-study “Environmental management and

fractions (FR3+FR4) on human cervix carcino-

sustainable use of nanocellulose”. The Finn-

ma (Hela229) cells was studied. Cytotoxicity was

ish national study was jointly conducted by

assessed by short-term studies including esti-

the EffNet programme of the Forest Cluster/

mates of highest tolerated dose (HTD) and to-

Finnish Bioeconomy Cluster (FIBIC) and the

tal protein content (TPC). Sublethal toxicity was

Measuring, Monitoring and Environmental as-

assessed by RNA inhibition testing, and geno-

sessment (MMEA) programme of the Cluster

toxicity was evaluated by the Ames test. By In

for Energy and Environment (CLEEN). In the

vivo toxicity testing, the effect of the fractions

study, information needs and possible obsta-

(FR3+FR4) was studied on a living organism. The

cles to utilization of nanocelluloses were iden-

test was performed with the Nematode Caeno-

tified. The main issues identified were the lack

rhabditis elegans as an egg-laying assay. The

of and confusion over regulation for nanoma-

results showed no indication of toxicity in the

terials; risk for over-regulation, especially for

majority of the tests. Slight indication of cyto-

natural, unmodified materials; and challenges

toxicity was observed in the TPC test with the

in the communication chain. However, pro-ac-

highest sample concentration. However, the cy-

tive regulation was found to be a possible tool.

totoxicity test result should be considered only

The report “Piecing together research needs:

indicative, since the toxicity test results should

safety, environmental performance and regu-

always be addressed in relation to the other tox-

latory issues of nanofibrillated cellulose (NFC)”

icity test results, which showed no indication of

was published in June 2012.

toxicity. Most importantly, there was no indication of toxicity in the in vivo test.

Guidance documents relevant to the safety of nanomaterials:

• U.S. Food and Drug Administration (FDA). Draft Guidance for Industry. Safety of Nanomaterials in Cosmetic

• Guidance Manual for the Testing of

Products. Available in Internet (8.10.2012):

Manufactured Nanomaterials: OECD’s

http://www.fda.gov/Cosmetics/

Sponsorship Programme. First Revision,

GuidanceComplianceRegulatoryInformation/

02-Jun-2010, Series on the Safety of

GuidanceDocuments/ucm300886.htm

Manufactured Nanomaterials 25 (2012). Available in Internet (21.12.2012): http:// search.oecd.org/officialdocuments/

4.3 Processability and preservability of microcelluloses

displaydocumentpdf/?cote=env/jm/ mono(2009)20/rev&doclanguage=en • REACH Implementation Project on

Pumping and mixing characteristics of microfibrillated cellulose

Nanomaterials (RIPoN) final reports

The objective of this study was to clarify the

(RIPON2 and RIPON3). Available in

behaviour of MFC grades in mixing and pump-

Internet (17.12.2012): http://ec.europa.eu/

ing through pipes. It was found that mixing

environment/chemicals/nanotech/

of MFC (into pulp) is difficult with a tradition-

• European Chemical Agency (ECHA).

al tank mixer. Due to the shear thinning flow

Guidance on information requirements and

behaviour of MFC a fluidized cavity is formed

chemical safety assessment. Available in

around the impeller, while the material near

Internet (8.10.2012): http://echa.europa.

the tank walls remains stationary. With the

eu/guidance-documents/guidance-on-

tested centrifugal pump, the characteristic

information-requirements-and-chemical-

curves of MFC grades were identical to those

safety-assessment

of water, but, due to the high loss in MFC flow,

• European Food Safety Authority (EFSA).

there was an upper limit to the consisten-

Guidance on the risk assessment of

cy at which centrifugal pumps may be used.

the application of nanoscience and

Screw pumps, on the other hand, are favour-

nanotechnologies in the food and feed

able when pumping high-consistency MFC at

chain, 10 May 2011. EFSA Journal 9(5): (2011)

low or moderate flow rates, as shown by the

2140, 36 pp. DOI:10.2903/j.efsa.2011.2140

red patch in Figure 7.

Available in Internet (21.12.2012): http:// www.efsa.europa.eu/en/efsajournal/

In a pipe flow, MFC has two distinct flow re-

pub/2140.htm

gimes. At low flow rates, MFC undergoes lami-

• U.S. Food and Drug Administration (FDA). Draft

nar, shear thinning flow with high energy loss

Guidance for Industry: Assessing the Effects

as compared with water flow. At high flow

of Significant Manufacturing Process Changes,

rates the flow of MFC is very similar to turbu-

Including Emerging Technologies, on the Safety

lent water flow, i.e. it is in fluidized state, as il-

and Regulatory Status of Food Ingredients

lustrated by the green patches in Fig. 7. Due to

and Food Contact Substances, Including Food

various flow-induced instabilities that may be

Ingredients that are Color Additives. Available in

present in the shear thinning flow, the fluidized

Internet (8.10.2012): http://www.fda.gov/Food/

regime is preferable while pumping MFC with a

GuidanceComplianceRegulatoryInformation/

centrifugal pump. Thus the experimental data

GuidanceDocuments/

presented here provides a simple tool in de-

FoodIngredientsandPackaging/ucm300661.

signing pipe flow systems for MFC.

htm

Preservability of microfibrillated cellulose Experimental laboratory and semi-pilot scale studies were carried out to evaluate the preservability properties of microfibrillated cellulose and to demonstrate the effects of material spoilage on its quality and usability. The main focus was to study the effects of MFC spoilage in papermaking applications. At startup, the batch of VTT coarse MFC used in the study was clean (aerobic and anaerobic bacteria counts were less than 10 cfu/ml); the batch was then contaminated by diluting it with process water to 1% consistency.

Figure 8. Evolution of redox potential (continuous on-line data), anaerobic bacteria count (samples), and filtration time (samples) during the preservability trial of VTT coarse MFC.

The results indicate that microbes can easily utilize MFC as a nutrient. Microbial activi-

housekeeping, including storage and trans-

ty caused spoilage of MFC within a few days

portation, as well as a carefully planned bioc-

of storage. This spoilage can be detected as

ide strategy should be applied to ensure opti-

changes in chemical parameters (e.g. pH and

mal performance for MFC.

redox potential drop) as well as increase in microbial counts (Figure 8). The spoilage of MFC

Laboratory-scale processability of MFC at

directly affected its performance: phenome-

various consistencies

na such as dewatering and bonding were af-

Information on the laminar, mixed, or turbulent

fected, causing deterioration in viscosity and

suspension flow behaviour is typically used as

strength properties.

initial data for equipment design and process engineering. To that end, MFC and kraft pulp

Biocide treatment can inhibit the microbi-

mixing and turbulence tests were performed.

al growth. However, the recovery of spoiled

The measurements were carried out with a

MFC using biocides is difficult. Therefore, good

medium-consistency laboratory mixer. The relationship between power consumption and rotor speed provides the basis for determining the processability of MFC. Mill-produced northern SW kraft pulp (NBSK) was used as a reference pulp for the measurements. In the MFC tests, VTT coarse and VTT fine MFC grades were used as the raw materials. In the tests, each sample exhibited three distinct phases: laminar flow with minor power dissipation at low speeds, mixed flow with temporal fluctuations at moderate speeds, and finally a turbulent flow with high power dissipation at high speeds. The power dissipa-

Figure 7. Operating window graph showing preferable flow rates and pump types.

tion increases with increasing consistency. At 1% consistency, both MFC and SW kraft pulp

behave like water but, already at 2% consist-

aging methods were combined with rheome-

ency, the power dissipation in MFC is higher

try. Firstly, the floc structure in different shear

than in the pulp. At 3% consistency, the differ-

conditions was studied by photographing the

ence between MFC and SW pulp is clear (Fig-

suspension under shear. The results showed

ure 9). MFC requires significantly higher ener-

that the floc size is dependent on the flow rate

gy in the mixing process than SW kraft pulp

above the apparent yield stress of the mate-

(50% more at 3% consistency), and there is no

rial. On the other hand, certain polymers can

major difference between the VTT coarse and

be used to prevent flocculation, whereas ex-

VTT fine grades. Moreover, after the suspen-

cess ions in the suspension enhance floccula-

sion has been mixed using high dissipation en-

tion, in a similar manner to pulp suspensions.

ergy, the suspension properties are equal to

Secondly, in collaboration with VTT, optical co-

those of pulp.

herence tomography (OCT) was employed to analyse the flow in the rheometer gap. These

Dynamic rotational rheometer as a tool to

studies revealed the occurrence of wall deple-

identify and characterize MFC suspensions

tion, which has to be taken into account when

MFC as a heterogeneous fibre material is chal-

analysing the rheological data from this kind

lenging to characterize with conventional dy-

of measurement. Contrary to flow measure-

namic rotational rheometers. MFC also has a

ments, the oscillation measurements are not

tendency to flocculate depending on, for ex-

as prone to wall depletion, since the materi-

ample, the flow conditions. As such, measur-

al is analysed at very low stresses and defor-

ing its rheology must be performed carefully,

mations. Oscillation measurements, such as

as many errors may occur during measure-

amplitude sweep or frequency sweep, proved

ment, such as wall slip or wall depletion, shear

to be a good characterization method for the

localization, or other heterogeneities in the

MFC suspensions, giving information about

flow profile. These phenomena are a problem

the gel strength of different kinds of MFC sus-

in flow measurements, in particular. To study

pensions. An example of this is given in Figure

and overcome these problems, different im-

10, where different size fractions of the same

Figure 9. Power consumption of MFC and NBSK at 3% consistency as a function of mixer rpm.

MFC (VTT coarse MFC) give different storage

gregate size distribution. This clearly demon-

moduli, which can be considered as the gel

strates that the time-dependent behaviour of

strength of the material. The finest fraction

these unstable suspensions can be easily con-

had the highest storage modulus, whereas the

fused with an elastic response of the material.

coarsest fraction had the lowest storage mod-

However, the difference between the two cas-

ulus. This can be attributed to the denser net-

es, although both appear during shear tran-

work of fibrils in the finest suspension.

sients, is from the model point of view clear. In the experiments it might be difficult, or even

Models for the rheology of MFC suspensions

impossible, to distinguish between the two.

Traditional continuum rheological models are suitable when simulating the steady-state

The role of MFC swelling in the rheology and

flow of complex fluids, which can exhibit, for

dewatering of high-consistency furnishes

example, shear thinning, shear thickening or

The studied microfibrillated cellulose suspen-

yield stress. However, these models offer no

sions and furnishes were evaluated in the con-

information on more complex flow behaviour,

sistency ranges of 1–2%, 3%, and 5–15% with

such as thixotropy, rheopexy, or other flow

the Åbo Akademi gravimetric dewatering de-

transients. More advanced structural models

vice (ÅA-GWR) and MCR 300 rheometer ac-

have to be used to describe the real physical

companied with and an immobilization cell

microscopic processes underlying these mac-

(IMC). The furnish composition was 70% fill-

roscopically observed rheological phenomena.

er, 20–30% VTT coarse MFC or P-2 MFC, and

Of such models, a colloidal aggregation model

0–10% cellulose fibres. All labels followed the

was used to simulate the flow of MFC suspen-

notation: ratio of pigment / ratio and type of

sions under various conditions. In this model,

MFC / ratio of pulp / consistency. The surface

the collisions of particles lead to growth of ag-

charge of the fibrillated cellulose was found

gregates, thus increasing the flow resistance,

to influence the rheological and dewater-

i.e. viscosity. Forcing the flow, on the other

ing properties of the evaluated suspensions

hand, tends to break the aggregates, thus de-

and furnishes due to its impact on swelling

creasing the viscosity. Using the model, an ad-

and effectively bound water; the higher sur-

equate reproduction of experimental rheology data measured for MFC was obtained (Figure 11a). A plausible reason for the differences between the model and the experiments may be heterogeneous shearing during the experiments, which was not explicitly taken into account in the model. To that end, the model was solved in conjunction with a flow solution in the Couette geometry, and the results indicate that the heterogeneous flow can indeed cause problems in the experimental setting. During the shear transients, the aggregation model showed stress overshoots (Figure 11b). These transients are typical for viscoelastic fluids, and the origins of such a phenomenon were traced to the delayed response of the ag-

Figure 10. Frequency sweep for the VTT coarse MFC suspension and its fractions at a concentration of 0.5% (weight/weight). G’ is the storage modulus and G’’ the loss modulus.

Figure 11 a) The steady shear rheology of MFC water suspensions with different concentrations as reported in experiments (dots) and predicted by the model (lines). b) The transient shear response of the model showing stress overshoots related to the delayed response of the aggregate size distribution.

face charge of P-2 MFC resulted in lower stor-

on the rheological properties of high-consist-

age modulus (G`) and higher WRV due to the

ency microfibrillated cellulose (VTT coarse MFC

more swollen fibrillated cellulose particles. The

and P-2 MFC) based furnishes can be utilized for

flow curves of both the VTT coarse MFC and

improving dewatering. It was found that when

P-2 MFC suspensions and furnishes showed a

the studied furnishes were dewatered under

gel-like structure and shear thinning behav-

vacuum conditions, the final solids content was

iour, and had a high yield stress. All the fur-

increased with the application of shear, which

nishes showed shear thinning behaviour with

was applied between oscillation intervals with

the power law exponent n ≈ -1; the actual fit-

the application of vacuum dewatering. The im-

ted exponents varied between -1.02 and -0.94.

plementation of rotation cycles between oscil-

The yield stress, as an indicator of the floccu-

lation vacuum cycles was found to increase the

lated network strength, was found to increase

final solids content of the samples. Complex vis-

with the consistencies, following the increase

cosity (η*) in an oscillation cycle had a non-linear

in elastic moduli (G`), which indicated a gel-like

dependency on the solids content of the furnish

strongly flocculated matrix of VTT coarse MFC

cake, shear thinning during the rotation interval,

and P-2 MFC.

shearing history in previous oscillation cycles, and the Weissenberg effect (Figure 12). A minute

Complex systems, such as the materials used in

difference in final solids content was obtained

this study, i.e. microfibrillar and nanofibrillar cel-

with respect to the MFC type and the presence

luloses as well as colloidal particulates, undergo

of cellulose fibres (Figure 13).

multiple structural configurations during dewatering. A modified method for determination of immobilization times was developed. The meth-

4.4 Dewatering of microcelluloses

od is based on a rheological analysis, adopt-

ing the rate of change in viscoelastic loss factor

Forming and dewatering analysis with the

(tan δ) over time, as first and second zero of d

Moving Belt Former

(tan δ). It was shown that it is possible to char-

The target of this study was to show how mi-

acterize the immobilization of these materials

crofibrillar cellulose and fines material from

(VTT coarse MFC and P-2 MFC) without a direct

TMP pulp affect forming and dewatering of

measure of MFC surface swelling. Information

mechanical pulp furnishes. A dynamic form-

ing device, the Moving Belt Former (MBF), was used to form the sheets under pulsating vacuum dewatering. An important research question was how fibrillated celluloses and fines interact during vacuum-assisted pulsating dewatering. The furnish components were TMP long fibres mixed with different amounts of TMP fines (0, 10 and 20%) and MFCs (VTT coarse and fine, 1 and 3%). The retention components and additives used were cationic-PAM (7 mil. g/mol 1meq/g , 600 g/t, added 10 s prior to dewatering) and starch (Raisamyl 50021, addition 1% from dry matter). A fractional factorial design with 34 trial points was carried out. The following measurements were taken during the forming process: dry solids after forming, total retention, vacuum levels during forming, surface level curves from the forming chamber (dewatering speed), dewatering time (both initial and high-vacuum dewatering) and apparent thickness of the wet fibre mat.

Figure 12. Development of dynamic and complex viscosities during measurement of 5% consistency P2-MFC-furnish without cellulose fibres, subjected to a rotation rate of 200 s-1 during the CSR cycle.

The effects of different factors on dewatering time are summarized in Table 4. Effect of papermaking additives and fines on dewatering The objective of this set of experiments was to clarify how different types of MFCs affect drainage when different papermaking additives are present in the system. The main focus was on studying how the amount of fines affects dewatering when MFC is used in combination with different retention aids. Dewatering was studied with the Åbo Akademi Gravimetric Water Retention (ÅAGWR) and Dynamic Drainage Analyser (DDA) devices. With the ÅAGWR device, the purpose was to evaluate how different MFC properties influence water holding capacity and how the addition of different polyelectrolytes affects this. In addition, the effect of fines on dewatering was

Figure 13. Solid content increase, ∆φ, for different dewatering schemes vs. shear rates in CSR intervals 0, 40 and 200 s-1, and the flow index K for all furnishes.

studied. With the DDA device, the purpose was

to study how dewatering of the pulp changes

fined VTT coarse MFC had no significant ef-

when different MFCs are added to the system

fect on dewatering. The effect was emphasized

in the presence of polyelectrolytes and fines.

when a higher amount of fines was present in the pulp. Dewatering of the pulp could be im-

Dewatering of the MFC was significantly

proved by adding high molecular weight cati-

changed when different polyelectrolytes were

onic polyacrylamide (CPAM) (Figure 14b). When

added to the MFC suspension. With low mo-

the amount of MFC increased, a higher amount

lecular weight cationic polyelectrolyte, dewa-

of CPAM was also needed to improve dewater-

tering of the MFC was improved, while addition

ing, especially with the more refined VTT fine

of high molecular weight polyelectrolyte led to

MFC grade.

deteriorated drainage, the biggest effect being observed with high molecular anionic polyelectrolyte. The amount of fines also had a significant effect on dewatering: as the amount of

5. Exploitation plan and impact of results

fines increased, pulp dewatering deteriorated significantly (Figure 14a). In addition, the MFC

Micro- and nanocelluloses are among the most

grade used had an effect on dewatering. The

important developments in the forest cluster

more refined VTT fine MFC deteriorated dewa-

in recent years. Current research in this field is

tering to a large extent, whereas the less re-

vast and conducted mostly outside of the pre-

Table 4. Effect of different factors on dewatering time.

Factor

Initial dewatering

High vacuum dewatering

Fraction of long fibres increases

Decrease (---)

Slight decrease (-)

Fraction of TMP fines increases

Increase (+++)

Amount of added CPAM increases

Slight decrease (-)

Interaction of fines x MFC amount

Clear increase (++)

Interaction of fines x starch

Slight increase (+)

Figure 14. Effect of a) MFC amount and fines content and b) addition of CPAM on dewatering.

sent programme. As companies begin com-

6. Networking

mercializing these products, issues of product safety, environmental efficiency, regulato-

The research was carried out jointly by re-

ry challenges and the need for standardiza-

search organisations and Finnish forest clus-

tion are becoming centre stage. Knowledge of

ter companies. Table 5 presents the research

the general properties of microcelluloses and

partners and their roles.

suitable characterization methods will help the industry to plan its own analytical procedures. Harmonized viscosity and transmittance measurements are ready to be used for quality control purposes. This programme has created several new networks, both national and international, to support these themes. Understanding the rheological properties of microcellulose suspensions and their processability and dewatering characteristics will help in up-scaling unit operations and in designing industrial processing. The manufacturer is always responsible for the safety of its products. The product safety information gathered here helps companies to plan and realize appropriate and sufficient safety testing programmes for their future products, and could thus accelerate the placement of future products on the market.

Table 5. Partner organisations and their research roles.

Partner

Role

VTT Technical Research Centre of Finland

Production of EffNet microcelluloses and their basic characterization, product safety aspects of microcelluloses, organizing the harmonization of viscosity and transmittance measurements, startup work for standardization, assessment of safety aspects of microcelluloses, engineering studies on the flow behaviour, pumping, mixing, and storage of MFC suspensions

Stora Enso

Participation in the activities for harmonization of viscosity and transmittance measurements

UPM

Participation in the activities for harmonization of viscosity and transmittance measurements, participation in biodegradability and toxicity testing

University of Oulu,

Method development and fractional analysis of

Fibre and Particle Engineering Laboratory

EffNet microcelluloses

University of Helsinki,

X-ray scattering and microtomography measure-

Department of Physics

ments of cellulose samples

Kemira

SEM imaging of EffNet microcelluloses, production of MCC and MRC samples, method development and characterization of MCC and MRC samples, participation in the activities for harmonization of viscosity and transmittance measurements

Andritz Oy

Laboratory-scale processability of MFC at various consistencies

Aalto University, Polymer Technology

Rheology and flocculation of MFC suspensions at low concentrations

Aalto University,

Aggregation models of MFC suspensions

Complex systems and Materials

Aalto University,

Forming and dewatering analysis with the Moving

Paper Converting and Packaging

Belt Former

Aalto University,

Dewatering methodology of high consistency

Bio-based Materials Technology

furnishes

7. Publications and reports

Book chapters:

Scientific journals:

Kangas, H., Cellulose nanofibrils – a material

Leppänen, K., Pirkkalainen, K., Penttilä, P.,

tial applications. In: Production and Applica-

Sievänen, J., Kotelnikova, N., Serimaa R.,

tions of Cellulose Nanomaterials. M.T. Postek,

Small-angle x-ray scattering study on the

R. Moon, M. Bilodeau, A. Rudie (Eds.), June

structure of microcrystalline and nanofibril-

2013. Accepted.

with unique properties and numerous poten-

lated cellulose. Journal of Physics: Conference Series, 247 (2010):012030, doi:10.1088/1742-

Pitkänen, M., Kangas, H., Vartiainen, J., Chap-

6596/247/1/012030.

ter 12. Toxicity and health issues. In: Handbook of Green Materials; Processing Technologies,

Mohtaschemi, M., Karppinen, A., Saarinen,

Properties and Applications. Vol 1. Bio Based

T., Puisto, A., Lehtinen, A., Illa, X., Alava, M.,

Nanomaterials: Separation Processes, Char-

Shear Banding and Colloidal Models, Annual

acterisation and Properties. Accepted.

Transactions of the Nordic Rheology Society 20 (2012):113-116.

Conference presentations/posters:

Puisto, A., Illa, X., Mohtaschemi, M., Alava, M.J.,

Forsström, U. and Hellén, E., Finland’s opin-

Modeling the viscosity and aggregation of sus-

ion: Standardization of micro- and nanocellu-

pensions of highly anisotropic nanoparticles,

loses. Oral presentation in Workshop on Inter-

Eur. Phys. J. E 6 (2012) 35:

national Standards for Nanocellulose, June 9, 2011, Washington DC (Arlington VA), USA.

Puisto, A., Illa, X., Mohtaschemi, M., and Alava, M.J., Modeling the viscosity and aggre-

Forsström, U. and Harlin, A., International

gation of suspensions of highly anisotrop-

co-operation for the standardization of nano-

ic nanoparticles, Nordic Pulp Paper Res. J.

scale cellulose materials. Oral presentation in

27(2):277-281 (2012).

2011 TAPPI International Conference on Nanotechnology for renewable Materials, June 6-8,

Rämänen, P., Penttilä, P.A., Svedström, K.,

2011, Washington DC (Arlington VA), USA.

Maunu, S.-L., Serimaa, R., The effect of drying method on the properties and nanoscale

Jäsberg, A., Gorshkova, E., Kiuru, J., Kouko, J.,

structure of cellulose whiskers. Cellulose

Lampinen, H., Liukkonen, J., Luukkainen, V.-M.,

19(3):901-912, 2012.

Tukiainen, P., Salmela, J., Syrjänen, J., Processability of nanocelluloses. Oral presentation in

Saarinen, T., Karppinen, A., Seppälä, J., Evolu-

EffFibre&EffNet Seminar 2012, Nov. 20, 2012,

tion of Floc Structure as Function of Time. An-

Helsinki.

nual Transactions of the Nordic Rheology Society 20 (2012): 113-116.

Jäsberg, A., Kouko, J., Luukkainen, V-M., Salmela, J., Processability of microfibrillated cellulose. Proceedings of Papercon 2012. Tappi, Apr. 22 – 25, 2012, New Orleans, LA, USA. Jäsberg, A., Kouko, J., Luukkainen, V.M., Processing of nanocellulose. Poster presentation in Forestcluster Ltd’s Annual Seminar 2011, November 16, 2011, Helsinki.

Laitinen, O., Niinimäki, J., Fractional analysis

Kangas, H., Pitkänen, M., Hellén, E., Micro-

and characterization of microfibrillated cellu-

and nanofibrillated celluloses – Characteriza-

lose. Accepted for oral presentation in 2013

tion, classification and safety. Poster presen-

Tappi International Conference on Nanotech-

tation in Forestcluster Ltd’s Annual Seminar

nology for Renewable Materials, June 24-27,

2011, November 16, 2011, Helsinki.

Stockholm, Sweden. Peltonen K., Vehmaa J., Henriksson, A., and Leppänen, K., Lucenius, J., Immerzeel, P., Mel-

Tirri, T., Laboratory scale processability of na-

lerowicz, E., Fagerstedt, K., Saranpää, P., Seri-

nocellulose in various consistencies, compar-

maa, R., Effect of moisture on cellulose structure

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nanostructured polymeric materials for food

27 – 29, 2010, Espoo, Finland.

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on Nanotechnology for Renewable Materials,

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FILE=5350&name=file

ed cellulose films - environmentally safe alternative. International workshop, COST Action FA0904, Development of new safe PNFP, Workshop WG1, 7 - 8 February, Prague, Czech Republic, Book of Abstracts (2013), 20.

Resource-efficient

papermaking

c o n ta c t p e r s o n Juha Salmela, juha.salmela@vtt.fi

Pa r t n e r s VTT Aalto University Metso Paper University of Jyv채skyl채

Abstract

This research was aimed at achieving radical improvements in the resource efficiency of papermaking. Specifically, the goals were to reduce papermaking raw material consumption by 25% and to improve the energy, water and raw-material efficiency of paper- and board-making processes. Novel production concepts for printing paper, fine paper and for board grades were developed and demonstrated. All concepts show good potential for improving resource efficiency and profitability. In all cases, the research was done from laboratory scale to pilot scale and end products were tested for all relevant properties, including print quality where necessary. Optimal use of raw materials is key to the global competitiveness of the Finnish papermaking industry. Reduced basis weight, increased filler content, and optimized dewatering offer the potential to decrease product costs and improve product properties significantly. The cost savings of the printing paper concept were calculated to be ~23% and the use of advanced fillers may improve this further. An optimized dewatering profile will save energy in the forming, press and in drying sections. The cost savings for a typical LWC paper machine between traditional and optimized dewatering are around EUR 500,000 per year for the dryer section alone, representing ~0.3% of total production costs with a 1.5% increase in dryness after the press section.

Keywords: Resource efficiency, printing paper, board, layering, dewatering, fillers

1. Background

and novel surface treatment methods that will provide the functional product properties re-

This part of EffNet programme is focused on

quired for the existing marketplace of consum-

radical improvement of the resource efficien-

er applications with radically less material. The

cy of papermaking. The main goals are to re-

main research topics and their motivation are:

duce papermaking raw material consumption by 25% and to improve the energy, water and

• Fractionation and layering of fibres

raw-material efficiency of paper- and board-

• stiff fibres to produce bulky layer

making processes. Traditionally, paper has

• fines for smooth printing surface

been sold by weight, but future paper pricing

• Optimized dewatering and retention

will change from weight- to area-based. Area-

• Novel filler particles

based pricing enables production of lighter pa-

• Optimization of surface and printing

per or board grades that meet current paper

process

demands. This, together with increased use of novel fillers, will enable radical savings in material costs. Future paper and fibre compos-

3. Research approach

ite products will involve much more sophisticated integration of mineral and fibrous and

The project utilized a unique research chain in

polymeric material compared to today’s filled

which the initial research hypothesis was first

papers. Savings will also come from optimiz-

demonstrated and then improved at VTT’s re-

ing de-watering and from reduced drying and

search laboratories. The laboratory-scale re-

pumping costs. Another important goal is to

sults were verified in VTT’s SUORA environ-

find optimal means for forming section and

ment and produced samples were calendered

press section cooperation. Improved dryness

(Metso / Kemira), finished (VTT, Espoo) and

after the press section requires optimization

printed (KCL). From each of these unit pro-

of the forming section de-watering profile so

cesses feedback was collected and new reci-

that paper solid content is maximized after

pes and technologies were tested at the labo-

press section. Modelling of these processes is

ratory scale before the next pilot-scale round.

also included in this study.

Up to five test loops were required to achieve a good-quality novel printed paper product from

2. Objectives

KCL pilot printing tests. Material efficiency was achieved by reducing

The main goal is to reduce raw material con-

LWC paper grammage by using stiff, long-fibre

sumption by 25% and to improve the energy,

TMP furnish to produce bulky base paper and by

water and raw-material efficiency of paper-

replacing LWC coating with layering of TMP fines

making processes. For fine paper grades, the

on the surface of the bulky base paper at the

goal is to find a viable solution to increase fill-

end of the forming section.

er content by 5% (thus reducing variable costs

by 10%) and to integrate inorganic components

Developing the binding of MFC-PCC aggregates

and organic material to produce novel fillers.

and starch-based biominerals raises the pos-

Together with these goals, product properties

sibility to increase the filler content of papers.

should also be either retained or improved. This

The research hypothesis for high-binding fillers

calls for the development of new raw materi-

was that they have better filler and MFC reten-

al concepts, advanced web forming techniques

tion and high shear resistivity. The optimal ag-

gregate size distribution was studied to obtain

ly better possibilities for validating dewatering

sufficient strength and printing properties. The

models than the conventional methods based

developed new material combinations also of-

on measuring various bulk properties (e.g. total

fer possibilities outside paper applications.

pressure loss and average volume fraction of fibres in a filtrated cake).

To study dewatering efficiency, an improved version of the laboratory-scale experimental 1D filtration device was developed. Using

4. Results

this method, it is possible to determine optimal dewatering conditions in terms of ener-

4.1 Dewatering modelling and efficiency

gy consumption (i.e. water removal efficiency) for different furnish types. Experiments with a

Filtration models for fibre suspension in the

dynamic wet pressing simulator indicated that

paper machine former section have to include

increased solid content achieved using opti-

the effects of air in addition to fibres and water.

mal initial dewatering conditions remains also

Thus, a three-phase (water+fibre+air) model

after wet pressing. Based on the filtration re-

has been developed. The model has been for-

sults, a novel phenomenological model for the

mulated as a generalization of the two-phase

time-evolution of sheet flow resistivity during

model, such that model parameters found in

filtration was developed.

the filtration device could be exploited as much as possible. The model developed by the Uni-

At the University of Jyväskylä, a two-phase

versity of Jyväskylä has been successfully used

(water + fibre) volume-averaged model for the

for simulating fibre consolidation in VTT’s fibre

filtration of fibre suspensions has been devel-

suspension filtration device (Figure 1).

oped. The model includes a novel viscoelastic sub-model for structural stress in the consoli-

Knowledge gained from the laboratory experi-

dating fibre network. The model was first ap-

ments was successfully applied in VTT’s SUO-

plied to simulation of dewatering in the wet

RA environment to develop an optimal initial

pressing section of VTT’s SUORA environment

dewatering profile for maximizing solids con-

with relatively accurate results. Secondly, the

tent after the press section. Overall, our new

model has been used for simulating fibre con-

concept can be used for improving the effi-

solidation in VTT’s fibre suspension filtration

ciency of the forming and press sections. The

device, resulting in plausible estimates of the

detailed results have been published by Ko-

dynamic behaviour of the fibre suspension.

ponen et.al (PaperCon, 2012).

The filtration device itself has been improved

The effect of vacuum profile on dewatering ef-

such that it can be used to accurately deter-

ficiency was studied using a modified filtration

mine parameters for the model. The modifica-

device. Figure 2 shows how an optimal dewa-

tions include, e.g., fitting a new set of ultrasound

tering profile can be found for any paper fur-

Doppler anemometer sensors and refurbished

nish at the laboratory scale. Dewatering was

control and analysis software. The device can

shown to be up to three times more efficient

now produce repeatable experimental results

after optimization.

on the temporal evolution of local velocity, volume fractions and stresses of fibre and liquid

Dewatering profile can be expressed as the to-

phases inside the consolidating network during

tal impulse of the vacuum on the web. Figure 3

the filtration process. This provides significant-

shows at pilot scale how an optimal dewatering

Figure 1. Fibre pathlines in a filtration experiment where the flow has been stopped between 8.5 and 12.5 s. Solid lines represent measured results; dashed lines are given by the mathematical model. Colours represent the pathlines of fibres from different initial positions.

Figure 2. Left: Water removal efficiency E of LWC furnish for different dewatering profiles. Here efficiency E=C/Wend where C is final sheet consistency and Wend is the total pressure work during the filtration process. Right: An example of a measured and modelled time-evolution of the paper sheet resistivity K during the filtration process. The water flow rate v through the sheet is v=P/Kb, where P is pressure loss, b is basis weight and K is resistivity (Filtration device, LWC furnish, grammage 80 g/m2).

Figure 3. Left: Impulse on the fourdrinier forming board and total impulse on the forming section together with the consistency after the forming section for different dewatering profiles. Right: Solid content after the press section for different dewatering profiles. The results resemble those acquired at the laboratory scale: the highest pressure impulse does not necessarily give the highest dewatering efficiency (SUORA environment, OCC furnish, grammage 90 g/m2).

Figure 4. Relative web solid content before the hybrid unit for different NFC addition amounts. Values are scaled according to the reference case solids content. Smaller values represent lower solids.

pressure profile and impulse gives the highest

was finally fulfilled at the end of the project. In

solid content also after the press section.

the concept development, an iterative research process from laboratory scale to pilot produc-

In the SUORA dewatering trials it was found

tion and printing was employed (Figure 5).

that addition of MFC decreases the initial dewatering rates (as indicated by many labora-

The research was divided into three tasks: base

tory-scale tests), but as the solid content in-

paper recipe, surface layer recipe and surface

creases in the forming section MFC actually

layer application method. The novel printing

improves dewatering and increases the final

paper concept study started with a laborato-

solid content after the forming section and

ry-scale study of the paper recipe. Based on

press section (see Figure 4).

4.2 Novel printing paper In the novel printing paper study, the potential of the layered structure concept to achieve the assigned target of 25% raw material savings was investigated. Initially, TMP pulp was separated into fines and coarse fractions. The base paper was produced from the coarse fractions and the surface layers from a mixture of fines and pigments. The coarse furnish of the base paper increased the bulk and the fines smoothened the surfaces to meet the quality demands. The object was to verify the potential of the novel printing paper concept by producing one-side coated reels in the SUORA environment and printing them at KCL on a heatset web offset (HSWO) printing press. This object

Figure 5. Iterative research process used in the novel LWC concept study.

the laboratory-scale results, the initial surface

The results showed that surface treatment

layer recipe for the SUORA trial was:

with SOS polymer also had potential to enhance print gloss and diminish mottling.

– Base paper 35 g/m2: 95% coarse fraction of TMP & 5% MFC – Surface 5 g/m2: 60% TMP fines & 40% calcined clay pigment and binder chemicals

In pilot scale studies, on-line fractionation of the coarse fraction and fines gave good results. Initially, application of fines to the surface was done by spraying with tongue-type

One interesting avenue studied was the use of

nozzles. The nozzles are shown in Figure 7.

SOS (self-organizing structure) polymers to increase surface strength and print quality. The

Paper samples produced with this technique

polymers were synthesized from native pota-

were calendered at Metso Järvenpää and their

to starch (Periva, Kokemäki) at VTT Rajamäki.

paper properties were tested. The roughness and

Native potato starch was modified using vari-

bulk behaviour of the novel LWC paper and the

ous functional groups (acetate group, hydroxy-

IGT strength results are presented in Figure 8.

propyl group, carboxymethyl group and octenyl succinate groups). The emphasis was on low or

In the following lab and pilot trials, the focus

moderate degree of substitution of the select-

was on improving the surface properties of the

ed substituent in order to keep the modifica-

paper. An improved recipe with good surface

tion as simple as possible. Six different water-

strength and optical properties was eventual-

soluble modified potato starches were selected

ly achieved. Cationic starch and SB-latex com-

and synthetized, using know-how and meth-

binations gave the best IGT surface strength

ods developed in other projects. The most suit-

(Figure 9) and use of GCC together with cal-

able SOS starch at the laboratory scale was se-

cined clay gave the most even ink transfer.

lected for pilot-scale testing. Selected octenyl succinate starch polymer with a low degree of

The new surface layer recipe:

substitution (0.1) is anionic and hydrophobic and was synthesized as described in the patent application by Kataja et al. (2007) in order to achieve water-soluble derivatives.

– Raw materials: 60% TMP fines, 20% calcined clay pigment & 20% carbonate pigment – Binders: 3% starch & 6% SB-latex of solids

SOS polymers were tested with respect to im-

content of surface

proved surface strength. They increased IGT

surface strength by over 300% in laboratory-

To further improve surface coverage, the

scale tests (Figure 6). At the pilot scale, SOS

tongue nozzles were replaced with air-atom-

treatment increased the surface strength by

izing nozzles. Four reels of the novel printing

106% or 41%, depending on the used base pa-

paper were successfully produced and HSWO

per and polymer amount. The amount of pol-

printed. Although visual observations of the

ymer was notably lower at the pilot scale to

paper were very promising, SEM images re-

prevent an excessively hydrophobic surface

vealed the surface layer coverage to be slight-

for offset printing. It should be noted that the

ly uneven (Figure 10). The sprayed particles

surface layer recipe was changed during the

have filled the pores between the fibres, but

project, whereas the SOS polymer was not

have not attached to the fibres. Surface lay-

changed. The fundamentals of SOS polymer

er application, and probably also grammage,

selection are described by Anttila et al. (2012).

need further optimization.

Figure 6. Effect of SOS polymer on the novel LWC surface strength.

Figure 7. Five tongue-type nozzles in operation during SUORA trials

Figure 8. Left: Roughness and bulk development of the novel LWC paper with sprayed surface during Gekko calendering test. Right: IGT surface strength of the novel LWC compared with the commercial LWC gloss paper. Both surface layer application methods, spraying and water forming, are presented.

Figure 9. IGT surface strength results of two surface layer recipe optimization series.

Figure 10. SEM images of the novel LWC base paper and layered novel LWC paper.

Table 1. Target and achieved values for critical properties of the unprinted novel LWC paper.

The achieved paper properties are present-

ergy are striven for by increasing the filler con-

ed in Table 1 together with the target values.

tent of the studied paper grades. The research

The roughness and thickness were almost at

hypothesis is to create mechanically stable

the target level in the trial, despite the limit-

and durable aggregates or biominerals that si-

ed calendering conditions of the narrow web.

multaneously enhance dry and wet strength

The tensile, z-directional and surface strength

properties, filler retention and dewatering

properties of the novel LWC paper are also at

compared to traditional fillers. By developing

acceptable levels. It should be noted, howev-

the binding MFC-PCC aggregates and starch-

er, that in this trial MFC was not used in the

based biominerals it is possible to increase the

base paper, only cationic starch was added to

filler content of papers. The new developed

the coarse fibres as a strength additive. The

material combinations also open up possibili-

bending stiffness of the product was relatively

ties beyond paper applications.

low. Optical properties can be improved by using better quality TMP raw material. For bet-

PCC-MFC aggregates

ter gloss, optimization of pigment quality is re-

Promising results were achieved using the

quired; varnishing is one option for improving

MFC-PCC aggregates in high filler (40%) con-

the gloss of the novel LWC paper.

tent PGW-based SC laboratory handsheets, and also at the semi-pilot scale (KISU envi-

Print quality of the novel LWC was general-

ronment). The final content of VTT fine MFC

ly lower compared to commercial LWC gloss.

in the sheets was approximately 2-2.5% de-

The printed gloss of the novel LWC was sig-

pending on the retention. Calendered sheet

nificantly lower and the surface was rougher

dry strength properties, optical properties and

after printing. The print density was lower due

predicted printing properties (density, print

to deeper penetration or greater spread of ink

gloss and wet pick) improved when aggregates

on the novel LWC. Performance of the novel

were used compared to the reference PCC. The

LWC paper web was nevertheless fairly good

RPA (retention process analyzer) device was

in printing, with HSWO runnability and print-

used to study the fibre and ash retention and

ability at acceptable levels. The print quality of

also dewatering of PCC-MFC aggregates in the

the novel LWC can be further enhanced by op-

SC paper furnish. Use of either dispersed or

timization of surface layer material spreading,

undispersed PCC was observed to be the most

adding surface layer on both sides, optimiza-

important variable affecting both ash reten-

tion of the surface layer recipe, and applying

tion and fibre retention. With undispersed cat-

surface varnish after or during printing.

ionic PCC, both ash and fibre retention were remarkably better than with dispersed anionic

Overall, the layered novel LWC concept seemed

PCC. The effect of the PCC-MFC aggregation

to be a potential option for producing printing

was slightly negative for retention and uncer-

paper using 25% less raw material and with

tain with respect to ash retention compared

15% lower production costs.

to direct dosage of the same materials to the furnish. With the finest VTT fine MFC ash re-

4.3 High filler content papers

tention was the lowest, and with the roughest P2-MFC ash retention was the best with the

The aim of this task was to develop the bind-

tested MFC types. The RPA laboratory-scale

ing properties of fillers by using microfibrillat-

tests showed no significant advantages relat-

ed cellulose (MFC), starch and other bio-based

ed to ash and fibre retention from using PCC-

materials. Savings in costs, materials and en-

MFC aggregates. Furthermore, in the laborato-

Figure 11. All main properties of printing papers can be improved with the use of filler-MFC aggregates. Results from the KISU environment semi-pilot scale tests. The strength properties are scaled to 30% filler content. MFC dosing amount was ~2.8% of total product.

Figure 12. Left: IGT surface strength WS results for different filler contents; Right: Scott Bond results for different filler contents. The mill reference sample was included in the calendering trials.

100

ry handsheet tests no significant improvement

surface strength and other relevant papermaking

in dry strength properties were obtained using

properties (See Figures 11 and 12). The finer VTT

PCC-MFC aggregates compared to direct dos-

fine MFC provided better strength potential than

age of raw materials in TMP-based SC paper.

the courser P2-MFC grade, especially Scott Bond

Because of these results, a new research di-

and IGT surface strength increased remarkably.

rection was needed and a larger floc size hy-

The finer MFC has more specific surface area and

pothesis was developed in cooperation with

the potential to form suitable flocs and microfilms

VTT and Aalto University.

between filler agglomerates and fibres.

The semi-pilot trials (KISU environment) were

The SUORA environment pilot-scale trials were

done with on-line PCC-MFC aggregates and

run successfully. The main goal of the trials

starch dosing, which was a different approach to

was to verify on-line dosing of aggregates and

any previous off-line aggregate dosing. With on-

the benefit of using them when the filler con-

line dosing significant improvements were ob-

tent of SC paper was increased. Possible bottle-

tained in strength properties, ash retention, IGT

necks were also investigated. Based on knowl-

edge from the semi-pilot trials, the selected trial

was conducted at the laboratory scale with a

points were chosen for the pilot-scale tests. The

4-litre adiabatic reactor with suitable control

long paper rolls were reeled for pilot calendering

system. A major focus of the project was on

and heatset web offset (HSWO) printing tests.

combining existing low-cost raw materials in new ways. Thus, besides simulated flue gas

All of the most critical properties, i.e. strength,

and commercial lime, natural starch, cationic

retention, dewatering, formation, smoothness,

and anionic starches and carboxymethyl cel-

optical and predicted printing properties, either

lulose were used in many experiments. Some

improved or achieved similar levels compared

experiments were conducted with microfibril-

to the reference PCC in the pilot SUORA trials.

lated cellulose and with chitosan, which are

In particular, IGT surface strength and Scott

not common commercial additives for paper.

Bond improved significantly when aggregates

The main technical approaches were:

were used. This gives the possibility to raise the filler content from 30% to 40% or even more. No major bottlenecks occurred in the trials.

1. To precipitate calcium carbonate on top of a polymer. The purpose of the polymer was to a) help direct the morphology of the

The high filler content SUORA SC paper reels

pigment and b) form a polymer reinforced

were pilot-calendered at Metso Paper. The

microcomposite with desirable properties.

calendered paper rolls were HSWO printed at

The crystallization conditions were

KCL. These full-scale printed novel SC papers were compared to mill reference paper, which

explored in some detail. 2. The surface treatment of commercial

was also pilot-calendered with the same pilot

PCC with polymer and polymer/calcium

machine and also to commercial production-

carbonate complexes. In this case, the

scale SC paper. The performance of the novel

problem was to increase the polymer

SC papers in HSWO printing was quite good,

adsorption beyond the natural monolayer

no breaks or picking occurred and accept-

levels so that a significant improvement in

able runnability and printability levels were

sheet bonding potential could be realized. It

achieved. No significant differences occurred

is known that when pigments are added to

between the SUORA reference and the aggre-

paper the elastic modulus (thus stiffness,

gate trial points in print gloss, printed smooth-

strength) is lowered because ordinary

ness, print trough, dot gain or print density.

pigments interrupt the fibre-fibre hydrogen

Print trough, dot gain and print density were of

bonds. In this work we attempted to

similar levels compared to the commercial SC

counteract this affect by clever adsorption

paper. Sight mottling and graininess tendencies were observed in aggregate trial points in

of polymers and polymer/PCC complexes. 3. In some experiments, the use of

some measured colour areas, but, in general,

microfibrillated cellulose as a substrate for

no significant differences were observed com-

calcium carbonate growth was explored.

pared to the reference samples. Calendering

The target was to improve both optical and

with higher nip pressure reduced the mottling.

strength properties simultaneously, which is difficult to do in polymer systems. In

4.4 Biominerals

other experiments, precipitation of calcium carbonate was used to reduce swelling

An experimental framework for starch-PCC bi-

and improve the dewatering properties of

ominerals was built around coprecipitation of

microfibrillated cellulose.

calcium carbonate from milk of lime and supersaturated carbon dioxide systems. The work

101

Calcium carbonate on top of polymer

6. Both the value proposition and the

The experiments involved the precipitation of

technical feasibility warrant further pilot-

PCC on top of starch(es), CMC, chitosan and

and full-scale research of this concept.

cmc/cationic starch complexes. The crystallization conditions were varied so that crystalliza-

Surface treatment of PCC

tion was done under acid and alkali conditions,

Commercial PCC bonding characteristics were

at different concentrations and temperatures.

studied using a couple of novel routes. In one

Extensive particle analysis and handsheet ex-

pathway, a technique for precipitating CMC onto

periments were carried out for each of the bi-

the pigment surface under high Ca++ concentra-

ominerals produced. The main conclusions are:

tion was developed. In a second pathway, starch (cationic/anionic/natural corn) was adsorbed to

1. Composite pigments were produced

the pigment. A technique was developed for co-

with pigment structures (particle size,

precipitating the unadsorbed starch from the

distribution, surface area, morphology,

solution. Thus, the starch adsorption could be

pigment strength) that would be hard to

increased and the wet end kept clean even at el-

achieve with classical pigment synthesis

evated starch levels. The main results are:

routes. In particular, it was possible to engineer higher-order structural levels

cationic starch gave desirable strength,

work showed that by altering both the

stiffness and other properties consistent

crystallization conditions and polymer

with a 5-7% filler content increase. It is

chemistry it was possible to engineer paper

notable that in many experiments with CMC

properties in new beneficial ways.

optical properties were improved compared

2. The aggregates, being polymer-reinforced microcomposites, were quite strong and

to reference or starch-based treatments. 2. Natural starch and cationic starch surface

capable of withstanding wet-end shear

treatment also increased strength

conditions (in simulated lab measurements),

significantly. The results show that

contrary to classical filler flocculation

paper properties can be manipulated

systems, which are sensitive to electrostatic

in a non-obvious way by changing the

interactions and shear conditions.

coprecipitation conditions. For example, by

3. Several pigments were found that led to superior paper strength properties and bulk/strength relationship compared to the reference pigments and thus could be used to increase filler content. 4. The improved paper strength was believed

changing the pH of coprecipitation, very different improvements to different paper strength properties could be achieved. 3. Starch adsorption was found to be improved by cooking the starch in a pigment slurry. It was also found that while natural

to derive from the aggregate structure, as

starch has higher adsorption under some

the added polymer was mostly covered with

conditions, under other conditions cationic

PCC and not available for hydrogen bonding.

starch had the best adsorption. Cationic

5. Low light scattering was somewhat problematic, especially for the starch-based pigments. This was due to the formation of an undesirable amorphous PCC morphology.

102

1. PCC surfaces treated with CMC and CMC/

by precipitating in polymer solutions. The

starch is probably the most feasible surface treatment polymer considering performance, cost and wet-end behaviour. 4. The results show that by using the

This problem should still be solved before

right combination of starch chemistry,

full- scale implementation, at least with

adsorption conditions and coprecipitation

natural corn starch as a substrate.

it is possible to increase the starch content,

strength properties and filler content of

4.5 Calcium silicate hydrates on PCC surface

paper (by 5-7%) in a cost effective manner. 5. The technology opens opportunities for

The nucleation effect on the PCC surface was

increased filler content in various printing

also demonstrated. This concept originated from

and writing grades of paper, eliminating the

concrete production, in which concrete reacts

size press, as well as other potential board

with water to produce calcium silicate hydrate

applications. The technology is untested

(CHS), which provides the concrete its strength,

in large scale, but there are no major

and CSH is formed on the concrete surface.

roadblocks to scale-up.

The same treatment was done with PCC, and the treated PCCs were then formed into hand-

Microfibrillated cellulose/PCC complexes

sheets. Raw materials used in the treatment

Experiments were conducted to determine

method were Ca(OH)2 (calcium hydroxide) and

whether microfibrillated cellulose could be a

SiO2 (silica). As a result, calcium hydrate â&#x20AC;&#x153;hairsâ&#x20AC;?

useful substrate on which to grow PCC. Oth-

(CSH) were obtained, the length of which can be

er experiments were done to determine if the

altered by adjusting the reaction time and condi-

swelling of oxidized MFC could be altered by

tions. As a Figure 13 shows, nanoscale CHS par-

coprecipitation of PCC. The results were:

ticles were grown on the PCC surface.

1. MFC/PCC gave good strength, retention, low

Calcium silicate hydrate (CSH) pigments were

roughness and also good light scattering

studied with chemical cement coating treat-

and appears to be an excellent substrate for

ment and additional cement coating treat-

building PCC/cellulose biominerals.

ment. VTT fine MFC was also added to these

2. A small amount of PCC precipitated to

treatment processes. The best growth of CHS

the surface of oxidized microfibrillated

on the filler surface was observed with 1% dos-

cellulose could reduce its swelling from 40

age of cement. The higher dosages produced

ml/g to 8 ml/g, showing that dewatering of

competitive reactions and less desirable CSH

microfibrillated cellulose can be improved

growth. Treatment of the fillers required vig-

using biomineral systems. This is important

orous mixing and careful addition of cement

in several fibrillated cellulose applications.

when adjusting the length of growth. Ten-

Figure 13. Nucleation treatment of PCC filler. Left: Treated CSH nucleated PCC; Right: Reference nontreated PCC.

103

Figure 14. Strength properties of calendered SC sheets improved with cement-treated CSH fillers and with VTT fine MFC. The figure shows how pigment treatment intensity influences the modulus of elasticity.

sile index and modulus of elasticity improved

This work directly supports the goal of the EffNet

with cement addition, but not with chemical

programme of developing radically new produc-

treatment in calendered SC sheets (Figure 14).

tion systems that make the best use of resources

Strain at break decreased linearly as pigment

and are energy-efficient so as to reduce capital

treatment intensity increased. Interaction with

intensiveness and improve the entire cluster's ef-

MFC was good, with both treatments improv-

ficiency and flexibility. The expected impacts on

ing the mechanical properties significantly.

the forest cluster companies include:

Further optimization of process variables is required in the CSH cement coating of fillers.

• Novel layered printing paper and folding box board products will give substantial

5. Exploitation plan and impact of results

competitive advantage • Improved forming section de-watering profile will change the way paper machine forming section de-watering is done and

Optimized dewatering may change the way initial dewatering is carried out on paper machines,

• De-watering modelling will improve

and lowered vacuums may enable the use of

possibilities to predict needed changes

blowers instead of vacuum pumps. This, togeth-

in de-watering elements when furnish

er with more gradual water removal rates will

properties are modified

decrease the cost of de-watering substantially.

• Bindable MFC-PCC aggregates and starch-

Development of the de-watering model will in-

based biominerals enable the filler content

crease the efficiency of trial planning and, in fu-

of papers to be substantially increased.

ture, also enable forming section development.

104

bring vacuum system cost savings

Expected scientific impacts:

6. Networking

• Effect of furnish properties on de-watering

The research was carried out jointly by re-

• Effect of pulsation on filtration process

search organisations and Finnish forest clus-

dynamics and web consolidation • Novel information on web consolidation and

ter companies. Table 2 presents the research partners and their roles.

structure during the filtration process • MFC distribution in paper structure • New understanding of how microfibrillated cellulose fibres increase paper strength • Improved forming section and press section de-watering models • Potential to replace vacuums with blowers Majority of the results indicated that savings in both energy and raw material consumption can be achieved. The novel layered printing paper concept will reduce costs by 23%. New NFC filler aggregates may further decrease energy consumption of different pumping operations. The novel surface layer spraying technique may be used in several applications in the near future.

Table 2. Partner organisations and their research roles.

Partner

Role

VTT

Dewatering research, high filler content papers, novel printing paper research

Metso Paper

Dewatering research, dynamic wet pressing, finishing and calendering

University of Jyväskylä

Modelling of dewatering

Aalto University

Biomineral development

105

7. Publications and reports Presentations:

Master Thesis:

Haavisto, S., Liukkonen, J., Jäsberg, A., Ko-

Ahonen, M., “Measurement of elastoplastic

ponen, A., Lille, M., Salmela, J., “Laboratory-

parameters of fibre networks “, University of

scale pipe rheometry: A study of a microfibril-

Jyväskylä

lated cellulose suspension”, PaperCon 2011, Vol. 1 (2011), 357-370, Covington, KY, 1 - 4 May 2011

Ghosh. I., “Starch adsorption onto PCC”, 6/2013, Aalto university

Koponen, A., Haavisto, S., Salmela, J., Liukkonen, J., “Optimization of paper machine ini-

Juusela. L., “Starch modification to increase

tial dewatering”, Papercon 2012. New Orleans,

filler content of paper”, 10.8.2011, Aalto

LA, USA, 22 - 25 Apr. 2012. Tappi. New Orleans,

University

LA, USA (2012) Koski, R., "Kontrastin lisääminen puukuidun Salmela, J., Ruusuvirta, L., “MFC Labelling, Re-

rakenteen selvittämiseksi ja paikallistamiseksi

tention and Distribution in Paper”, 2013 TAPPI

paperiarkista röntgentomografialla", 2011,

International Conference on Nanotechnology

University of Jyväskylä

for Renewable Materials, 24-27 June, Stockholm, Sweden.

Ruusuvirta, L., “Microfibrillated cellulose – structure, properties and interactions with

Torvinen, K., Helin, T., Kiiskinen, H., Hellén, E., Hohenthal, C. and Ketoja, J., “Nano fibrillated cellulose as a strength additive in filler-rich SC paper”, 2011 TAPPI International Conference on Nanotechnology for Renewable Materials, 6-8.6. Arlington, USA. Torvinen, K., Vehmas, T., Kronlöf, A., Hellén, E., ”Binding fillers for paper applications using nanoscale calcium silicate hydrate coating and nanofibrillated cellulose” 2013 TAPPI International Conference on Nanotechnology for Renewable Materials, 24-27 June, Stockholm, Sweden.

106

metals “, 2012, University of Jyväskylä

107

image-based measurements

c o n ta c t p e r s o n Risto Ritala, risto.ritala@tut.fi

pa r t n e r s Tampere University of Technology Kemira Lappeenranta University of Technology Metso Automation University of Eastern Finland University of Helsinki University of Jyv채skyl채 University of Oulu UPM

108

Abstract In order to support the quality management of current and future products, imagingbased measurements of fibrous network structures were developed. A device capable of measuring surface topography on-line based on photometric stereo was developed. The device is also capable of measuring surface fibre/floc orientation. The illumination and imaging geometry were optimized for topography inference. The measurement was validated based on X-ray tomography measurements that provide high-resolution 3D information about the fibre network in laboratory conditions. Optical coherence tomography was shown to be a promising technique for a reference measurement as it is much faster than X-ray tomography. Varying the wavelength of illumination, in particular in near infrared, enables the planar distribution of material components on the paper surface to be examined. It was also shown that current web defection imaging systems can be used to assess CD/MD variation of the web for control and monitoring purposes. It was found that with such measurements CD profile estimation is speeded up considerably, which allows some room for improvement in controller performance. The main limiting factor in further control performance improvement is the long delay from actuators at the headbox to measurements at the dry end. New image-based technology was studied and applied to the monitoring of chemistry in papermaking. For enhancing tissue production and improving tissue quality, two new image analysis methods were developed and tested. The image-based measurement system for tissue structure and quality provides a means to enhance the creping process and production rate in tissue production. For monitoring and controlling chemistry in water streams a new particle analysis method was developed and tested at laboratory and full scale. The method automatically detects particles from images and continuously analyses their properties, such as size, count, shape and type. It also provides distributional information on particle types. When moving towards higher added value products, papermaking is facing increasingly strict requirements on the uniformity of quality. With current products and production systems, incomplete quality information leads to non-optimal use of raw materials due to â&#x20AC;&#x153;safety marginsâ&#x20AC;?. Measurability and controllability affect how new production system concepts should be designed and, hence, the new image-based methods add degrees of freedom to the design. Keywords: imaging, fibre network structure, topography, orientation, surface composition, printability, tomography, near infrared, web-wide imaging, 2D control

109

1. Background

- Sub-formation scales of surfaces affecting printing; mottling effects, deep surface

EffNet has developed production system concepts for producing the functional property combinations of present products more efficiently by reducing raw material costs, use of energy and water, and capital expenditure, and with present or reduced carbon and water

pores in uncoated surfaces - Formation scale structure, including fibre orientation - Web-wide structures at high resolution (sub mm) - Fast web-wide temporal structures

footprint. EffNet research is providing means

(residual variation at resolution of 10 cm...1

for achieving this by developing new raw mate-

m in machine direction and 1 mm in cross-

rial concepts, advanced web generation techniques, novel surface treatments, and studying optimal roles of paper surface preparation and

direction) - Slow web-wide temporal structures (MD and CD profiles)

printing. However, for these methods to be applicable in large-scale production, the uniform-

This characterization will be based on digital

ity of the functional properties of printed prod-

imaging, which has been the most rapidly de-

ucts must be managed. It is well-known that

veloping area of electronics in the last decade.

current production systems must operate with

Inference based on images will be supported

considerable and costly safety margins as qual-

by advanced use of structural models and oth-

ity variations would otherwise lead to process-

er prior information according to the principle

ing problems and poor consumer-perceived

of inverse and Bayesian methods. The man-

quality. Furthermore, many key characteristics

agement of uniformity will consist of a com-

cannot be measured on-line; e.g. surface to-

bination of feedback control and diagnostics.

pography and mottling tendency are crucial for print quality, and surface orientation and for-

QVision-project generated an idea to utilize

mation are critical for out-of-plane mechanics

imaging techniques for evaluating properties

(curl and cockling). As the development of new

of tissue paper and water & pulp quality. Cur-

production system concepts has been largely

rently, measurements on quality properties

based on using more tailored material compo-

specific to tissue are scarce, which is a ma-

nents and fractions and more delicate surface

jor limiting factor for quality management. Im-

treatments, the benefits will be limited by how

age-based measurement techniques for char-

uniform the material composition and structure

acterizing web structure may provide new

are in large-scale operation.

quality measurement opportunities in tissue production, as they have provided in other pa-

The research on image-based measurements

per manufacturing applications. New imaging

continues the work initiated in EffTechâ&#x20AC;&#x2122;s Qvision

techniques together with novel analytical and

project. The objective of this study was to pro-

computational methods can generate deeper

vide means for managing the uniformity of web

understanding needed for improved chemistry

material in the macro scale, in particular, so that

control in papermaking.

bulk and surface microstructure are consistently produced over time and machine-wide. Until very recently â&#x20AC;&#x201C; mostly due to the work of Qvision â&#x20AC;&#x201C; wide ranges of product variability have been unobservable. The web needs to be characterized and managed at the following scales:

110

2. Objectives

to what accuracy (varying illumination and imaging geometry and wavelength of

The objectives of the study were to develop

light)? The ground truth of the fibre network

new on-line characterization methods for web

structure was assumed to be provided by

structure and to develop image technology based chemistry control concepts to manage wet end chemistry and tissue paper properties.

X-ray tomography. 2. Which image-based measurements can be implemented on-line with CD scanning? Which measurements can be implemented

The specific objectives were to:

web-wide with time-wise snapshot sampling? Which measurements can be implemented

- Develop on-line measurements for topography and surface orientation, - Analyse the feasibility of on-line surface orientation measurement, and to identify

web-wide continuously in time? 3. To what extent do such measurements improve the performance of CD/MD control?

opportunities for spectral surface imaging in paper surface chemistry applications - Develop continuous web-wide imaging as a

In particular, the following structural properties were considered:

variability analysis tool in all relevant length scales, and to assist scanner-based quality

1. Surface topography (photometric stereo)

control by optimizing the scanner path

2. Orientation (on surface and through the

based on transmittance variability - Study methods of 2D control based on continuous web imaging, supported by scanner measurements - Develop a crepe bar analyser for tissue paper structure and an analysis method for

web) 3. Basis weight variation in scales relevant for CD/MD control 4. Small-scale basis weight variations 5. Surface composition (NIR illumination) 6. Web shrinkage

evaluation of tissue softness - Apply and evaluate new imaging

The main outcomes were:

technologies for improving papermaking chemistry and process efficiency

1. A device capable for simultaneous surface topography and surface orientation

3. Research approach

measurement on-line has been constructed and applied on webs at realistic production speeds.

The research hypothesis was that many highly

2. Measurement setup (illumination angle,

relevant structural properties of fibre networks

number of lights) and computational

can be inferred from images of paper. As a rap-

methods (gradient methods, curvelets,

id-response measurement method, imaging can

SIFT) for surface topography/orientation

be applied on-line and web-wide and can im-

have been analysed and optimized.

prove the performance of on-line quality control.

3. Traceability from X-ray tomography to imaging surface measurements has been

The research questions were:

established. 4. Optical coherence tomography provides a

1. Which structural properties of the fibre network can be inferred by imaging and

fast reference measurement for structural measurements. The measurement results

111

provide required accuracy with well-

The work was organized into five tasks as

stabilized laser.

follows:

5. Spectral imaging is feasible for analysis of small-scale variations in surface composition. 6. New set of web-wide mill data was collected and analysed for quality variations and actuator responses. Although the data set was rather limited due to production problems at the site, overcoming the realtime and huge data flow requirements has been proved feasible. 7. Comprehensive diagnostics functions for 2D transmittance variation have been

• Characterization methods of paper structure aiming at scanning or point-wise measurements. • Characterization of web-wide variability of optical transmittance. • Management of functional web properties with control and chemicals. • Image analysis for enhancing tissue production • Image analysis method for water and pulp quality

implemented. 8. A method for extracting actuator step responses from image data has been

4. Results

developed. 9. Dynamics of 2D control has been analysed to analyse the importance of dead time as the leading limiting factor in control

4.1 Paper structure characterization methods based on scanning or pointwise measurements

performance based on 2D quality measurement.

Measurements for surface topography and sur-

10. Simulations to validate the performance

face orientation were developed; improvements

improvements of 2D control using web-

in bulk formation and orientation measurements

wide measurements were continued and

were made; the feasibility of surface chemical

a new multiple-property controller was

composition measurement was analysed; and

developed and tested.

dot gain measurement concepts were proposed.

11. Formation measurement and control opportunities explored in the SUORA

The general goal was to develop a tracea-

environment.

ble measurement chain from first-principles

12. Two new image analysis methods for

structural laboratory measurements to im-

enhancing tissue production and improving

aging measurements made at full speed on-

tissue quality were developed and tested. A

line. Tomography measurements are consid-

developed new image-based measurement

ered the ground truth. At present, tomography

system for tissue structure and quality

measurements are X-ray based and are highly

opens opportunities for enhancing the

accurate but time-consuming. Simultaneous-

creping process and tissue production rate.

ly sub-micron resolution spectral domain op-

13. For monitoring and controlling chemistry

tical coherence tomography (OCT) has been

in water streams, a new particle analysis

developed. OCT measurement provides meas-

method was developed and tested in

urement speeds of 1-140 kHz, which is suffi-

laboratory and full scale.

cient for fast laboratory measurements and may even have on-line potential. However, spectral OCT requires more advanced data analysis and signal processing. Spatial meas-

112

urements were initially noisier than the time

measurement method for image-based struc-

domain method. The new measurement setup,

tural measurements of paper.

based on spectral domain analysis, was developed and the resolution was confirmed. Sensi-

An on-line device (see Figure 2) capable of

tivity problems were solved towards the end of

measuring surface topography and orien-

the project by a new laser. The laser is sealed

tation was designed, built and installed to

and thus not sensitive to environmental vari-

measure at speeds corresponding to the re-

ations. EffNet samples were measured with a

alistic web speeds of new production system

measurement time of 1-2 seconds per sample,

concepts. The measurement area is 1 cm x 1

see Figure 1. The penetration depth was 40

cm and pixel size roughly 10 ď m. The method

um. The data is of the order of 40 MB. The de-

is based on simultaneously illuminating the

velopment of OCT continues in other projects.

sample with three different wavelengths and

OCT appears to be a good and fast reference

imaging it so that the main response of each

Figure 1. Reconstruction of paper structure using OCT. Measurement area 1 mm x 1 mm x 1.4 mm.

Figure 2. Structure of the on-line surface orientation and topography measurement device.

Figure 3. Surface topography of a sample. Left: Reconstruction using photometric stereo. Right: Reconstruction using X-ray tomography. The correspondence is good, although X-ray tomography (ground truth) has higher spatial resolution.

113

light has its own response channel in a redgreen-blue (RGB) camera.

A pentagon arrangement was found to be better than a three-light arrangement. - A method for floc orientation was

Topography reconstruction using the optical

developed and compared with fibre

method (photometric stereo) and X-ray tomog-

orientation results. The effect of scale on

raphy were compared, see Figure 3. The corre-

floc orientation was analysed.

spondence is quite good and has been further characterized by 2D spectral coherence analysis. The laboratory optical method is based on

- Bulk orientation angle can be estimated even from standard resolution formation images.

a large number of different illumination angles.

- The response of a wavelength to surface

With the on-line device only a few illumination

gradient depends on the wavelength (the

angles are used, but the effect of varying the

shorter the wavelength the larger the

number of illuminations has been analysed and

response). This needs to be taken into

the on-line structure has been found to provide

account in particular in surface orientation

good correspondence to the true surface, as

analysis. A computational correction for

evaluated by tomography.

dealing with these problems was developed and implemented.

Orientation and formation were analysed both at the surfaces and in the bulk. The main

Surface composition was analysed using IR

observations are:

spectral means. Kaolin, water and paper have specific absorbencies as functions of wave-

- Several efficient methods for extracting

length. In Figure 5, examples of paper and

orientation distribution were developed.

kaolin absorbencies are shown as spectra

These include Fourier-based, gradient-

measured with a PerkinElmer Lambda 1050

based, curvelet and Scale Invariant Feature

spectrophotometer and two spectral bands

Transform (SIFT) methods. The Fourier and

ď Ź=1600 nm and ď Ź=2208 nm of a Specim N25E

gradient-based methods were implemented

spectral camera (spatial resolution 30 Âľm and

in the prototype.

real dimension 10 x 32 mm), where the Metso

- The number of lights and the illumination

logo is hand-drawn with kaolin on paper. Ka-

angle were analysed and optimized as

olin peaks at wavelength 2208 nm are clear-

measurement parameters, see Figure 4.

ly shown. Hence, measuring the uniformity of

Figure 4. Left: The effect of inclination angle on orientation distribution observed; Right: The effect of number of lights on orientation distribution and its repeatability.

114

Figure 5. (Left) Absorbance of kaolin and paper in near infrared. The Metso logo was drawn by hand with kaolin on the surface of the paper. (Middle) at spectral band 1600 nm the logo cannot be observed, but at 2208 nm (right) it is clearly visible.

kaolin is feasible by comparing the images at

was rather poor due to production problems

different wavelengths. Similarly, measuring

at the site of data collection. The data collec-

the distribution of water (moisture) in the sur-

tion was planned for the start-up of the line.

face was shown to be feasible.

However, the start-up was delayed and not all data specified could be obtained. The follow-

4.2 Characterization of web-wide variability of optical transmittance

ing data was obtained: - Calibration measurements for identifying

The Qvision project and the EffNet programme planned two mill data collection campaigns of web-wide measurements, carried them out on

uneven illumination effects and geometric disturbances - Two sets of line data of duration 10 min

a full-scale paper machine, and pre-processed

each; including step response tests

and analysed the data in order to assess the

- Some reference paper samples for the

possibilities to estimate basis weight varia-

Tapio web analyser

tions. Such studies need to be carried out in a full-scale environment as real-time issues

Due to practical limitations caused by the de-

and huge data flows are important technologi-

layed start-up of the line, no full image data

cal challenges of such systems. The data was

or data in which the reference scanner meas-

analysed with tools developed earlier to clas-

urements were stationary were obtained. The

sify and diagnose the 2D variations in the Qvi-

analysis focussed on on-line data. Line data

sion project and in EffNet. Unfortunately, the

required considerable preprocessing. In par-

quality of the data from the second campaign

ticular, the alignment needed considerable

115

correction compared to the image metadata.

Simulations with a simplified process mod-

Preliminary indication of actuator respons-

el show that imaging measurements may in-

es was observed, but response identification

crease the dynamic bandwidth of the cross

from the data was not possible.

direction control system substantially. It can also be expected that errors in actuator re-

A method for identifying actuator step respons-

sponse identification and shrinkage estima-

es from web-wide images was developed based

tion can be decreased. It was found that the

on principal component analysis (PCA) and test-

imaging measurements may provide means

ed with simulated data, see Figure 6. Response

for removing cross direction profile distur-

forms can be obtained from far shorter tests

bances with wavelengths larger than 400 s,

than at present with scanners. The method re-

whereas with scanner-based control, all dis-

quires a scanner for response gain identification.

turbances with wavelengths under 1000 s are practically uncontrollable. With perfect model

4.3 Management of functional web properties with control and chemicals

knowledge and measurements, the limit is almost an order of magnitude smaller than with the more practical case simulated with the

This study sought to assess the potential for

scanner measurements. Also, higher sampling

quality improvement if continuous 2D imaging

rates and shorter control intervals provided by

is used as the primary measurement signal in

the imaging measurements indicate that actu-

CD/MD control. At present, it is conjectured that

ator dynamics will not necessary be an unim-

the limiting dynamic factor of CD/MD control is

portant factor in paper machine control, espe-

the scanner measurement and CD/MD estima-

cially if the dynamic part of CD profiles is to be

tion of the scanned signal. This limitation would

controlled. The results also indicate the impor-

be obviously removed if the 2D image data

tance of accurate approximation of time delay

gave perfect quality information, primarily on

in order to maximize control performance.

basis weight. Then, the dynamic limits would be set by the dead time from actuator to measure-

The results presented underscore the impor-

ment and the actuator speed.

tance of developing new sensing techniques in paper machines and, hence, call for continued development. We assumed rather fast CD profile changes to be present in the paper machine. Therefore, it should be examined whether such dynamic patterns in cross direction variation really exist. A large number of control algorithms for CD problems can be found from literature and, with minor changes, these might be applicable also with faster measurements. The controller structure applied in this paper showed good computational performance, which surely is an important, perhaps even limiting factor when bring-

Figure 6. (Left) Simulated step response on the mill web-wide transmittance data. The CD response identified for a number of durations (10â&#x20AC;&#x201C; 60s) of response test.

116

ing the sampling and control interval from one scan time closer to one second. Analysis of the potential of 2D control with im-

aging measurements has continued with dy-

considerable limitations so that dynamics

namic response modelling only, thus enabling

faster than, say, 300s cannot be affected. The

control performance to be determined across

results are in accordance with the 2D simula-

a wide frequency range, with different actua-

tor results. This comparison justifies our use of

tor scenarios and with varying quality of the es-

the simpler SISO models in the analysis.

timated model. The control loop is constructed using the estimated process model in the

Successful web-wide measurements make it

controller, but then simulated with a â&#x20AC;&#x153;trueâ&#x20AC;? re-

possible to extend the CD control strategy to

sponse model as a process model. The estima-

multiple property control, i.e. to combine the

tion process is modelled as the difference be-

control of several paper properties and sever-

tween the true and the estimated response,

al actuators in an optimal control strategy that

including the dead time difference. Two types

takes the interactions into account. This kind of

of simulated actuators are studied, one with

new control strategy has been tested by simu-

sufficiently fast response dynamics and anoth-

lations. The results show that as the benefits

er with slower response. These actuators can

of multiple-property CD control we can expect

be considered as the dilution valve and slice lip

more uniformity when observing all properties

used in basis weight control in a paper machine.

of interest and with less actuating energy. The

The simulated dead time remains the same, as

controller presented is a computationally ef-

the actuator position with respect to the meas-

ficient option and is expected to be a feasible

urement position is not changed. The time con-

control method for use with the higher sam-

stant and the delay of the control model are al-

pling frequencies provided by imaging meas-

tered in order to demonstrate how the quality

urements. The automated tuning procedure

of the image-based estimate may affect the

developed offers a way to avoid severe input

achievable control potential, see Figure 7.

saturation, although further development and analysis of the method is required.

The results show that, mainly due to dead time, but partly also due to actuator speed

The web-wide measurements enable coordi-

and to the mismatch between true response

nation of CD actuators effectively also in MD

dynamics and estimated dynamics, there are

control. Simulations indicate that a substantial

Figure 7. Limiting disturbance wavelength as a function of control model dynamics, in s, when the estimated model and true model differ. Estimated models are (1-a)z-d/(z-a)). Results are given as functions of a and d. On the left, with fast actuator (true model: 0.6916z-10/(z-0.3084)). On the right, with slow actuator (true model: 0.1z-10/(z-0.9)).

117

Figure 8. MD control performance for disturbance rejection. (a) MD profiles, (b) Power spectrum. The dotted line is disturbances, the gray dashed line is image-based control and solid line is CD assisted control.

performance increment in MD control, both in

moving element vacuums were changed, the in-

disturbance rejection and setpoint following,

terpretation of the results is somewhat cum-

could be expected if CD assistance is taken

bersome due to numerous other parameters, in

into action (Figure 8). The variance of the MD

particular basis weight, changing at the same

profile is decreased 55% compared to conven-

time. Moderate correlations were found between

tional PI control and Smith predictor by using

the image features and reference values. The

scanner-based estimation. The effect of im-

effect of retention chemicals on formation ap-

age-based estimation solely is more moder-

peared to be small.

ate, at around 12% degradation in variance. In order to analyse the MD control opportunities

4.4 Image analysis for enhancing tissue production

of features extractable from image-based measurements, data was collected from the VTT SUO-

Tissue structure analysis

RA environment in experiments in February 2011.

For analysing the crepe structure of tissue pa-

The correspondence between on-line and off-line

per, an image-based measurement system

image analysis was studied (see Figure 9), reveal-

was developed. The system captures four re-

ing on-line and off-line measurement to be close-

flectance images and one transmittance im-

ly comparable. Although formation changes were

age from tissue paper. In the reflectance imag-

observed when the jet-to-wire ratio or water re-

es the light sources were located at an angle to the tissue surface. The optimum angle between the light source and the tissue surface was found to be 55 degrees. An example image and mechanical drawing from the off-line measurement system are shown in Figure 10. The 3D surface and gradient fields were reconstructed from four reflectance images based on photometric stereo. The gradient field estimates the steepness of ascent and decent from the tissue paper, and the 3D surface estimates the shapes and height of the crepes in millimetres. The crepe bar distributions from

Figure 9. Comparison of on-line and off-line imaging results (standard deviation of illumination).

118

reflectance, gradient field and 3D surface images were computed. Computation of crepe

Figure 10. Off-line image-based measurement system.

Figure 11. Image-based estimation of tissue properties.

density from gradient field in MD was found to

obtained. Figure 11 illustrates how the tissue

be the most robust method.

properties were estimated from the images.

The crepe length distribution in CD was stud-

To validate the tissue analyser, several tissue

ied from the gradient fields and the amount

samples were analysed. Cross-dimensional

of defects from the reflectance images was

samples were collected from the top of a ma-

119

chine reel, each sample consisting of one ply.

estimated to be higher. These areas do not in-

Basis weight data was collected with an online

clude crepe folds, which increases the crepe

quality control system. The scanner measured

frequency value computed from such image.

basis weight, moisture and dry weight. The off-

It appears that high basis weight increases the

line and on-line profiles were aligned uniformly

probability of uncreped areas.

in CD according to maximized correlation. The crepe frequency profiles of bath tissue The CD samples were measured with the im-

were also measured. The profiles are shown in

age analyser, which captures light reflectance

Figure 14. The samples were cut from the same

images from the Yankee side of the tissue web.

reel with an approximately 10-metre MD sam-

The most important property evaluated was

pling interval. It can be seen that the amount of

crepe frequency, which describes the number

crepe folds per mm varies between 2.9 and 3.3.

of crepe folds per unit length. An ideal creping mechanism would generate uniform crepe

The crepe frequencies computed from the

frequency profiles in CD. However, with real

bath tissue grade are much lower than the

tissue samples it can be seen that the crepe

napkin grade. The image pair captured at CD

frequency is not constant in CD. Figure 12 also

locations 900 mm and 1900 mm is shown in

shows the basis weight profiles computed

Figure 15. The crepe frequency values at these

from the same reels from which the crepe fre-

locations were 2.85 and 3.33 crepes/mm, re-

quency profiles were measured.

spectively. The images show a visually observable difference in crepe frequency value,

Figure 13 shows a pair of images captured from

as indicated by the crepe frequency estimate,

the first reel at the CD locations 300mm and

as opposed to the presence of uncreped areas,

2700mm. The crepe frequency values computed

which caused the crepe frequency difference

at these locations were 4.1 and 4.6 crepe folds/

with the napkin samples.

mm, respectively. As the images show, some areas are not creped. Furthermore, the share of

It was observed that the crepe frequency varies

such areas is much higher at the 2700mm CD

in CD on tissue machines. The main reasons for

location, at which the crepe frequency had been

the crepe frequency profile are the condition of

Figure 12. Basis weight and crepe frequency profiles from consecutive reels.

120

Figure 13. Images captured from napkin tissue at CD locations 300mm and 2700mm.

Figure 14. Crepe frequency profiles measured from bath tissue.

Figure 15. Images captured from bath tissue at CD locations 900mm and 1900mm.

121

the blade and CD variation of web properties

ment of surface softness is not straightforward.

such as bulk and basis weight. It was observed

One factor influencing surface softness is the

that the basis weight and crepe frequency pro-

fibers extending from the surface of the paper.

file correlate significantly. It was conjectured that the variation in basis weight profile pro-

To detect the amount of such fibers in tissue

duces variations in the crepe frequency profile.

paper, a novel imaging method was developed (Figure 16). The method is based on the detec-

Ordinary measurement devices on tissue ma-

tion of shadows caused by free fibre ends. The

chines are not able to detect crepe frequen-

shadows cannot be detected directly from the

cy or other properties related to the struc-

reflectance image due to the rough and wavy

ture of crepe folds or the creping mechanism.

surface of tissue paper. Therefore, the surface

Thus, there is a need for optical measurement

normals of the tissue paper were first estimat-

devices for measuring and controlling crep-

ed based on the photometric stereo method.

ing. Although the method developed here has

The reflectance intensities of the surface were

been tested for tissue only under laboratory

then reconstructed based on the surface nor-

conditions, it is based on technology that has

mals and the result was subtracted from the

been proven in other applications to be direct-

original reflectance intensities. The shadows

ly transferable to on-line applications at web

were then detected from the difference image.

speeds of up to 30 m/s.

The paper surface can be divided roughly into specular and diffuse based on the surface re-

122

Free fibre end (softness) analysis

flection. The photometric stereo method as-

For the end user, softness is among the most

sumes that the surface reflection is diffuse. The

desired properties of tissue paper. Tissue soft-

surface of paper is nearly diffuse. The unwant-

ness can be divided into bulk softness and sur-

ed effect of specular reflection was reduced by

face softness. Bulk softness can be measured

passing the light through two linear polarizers

quite reliably by measuring the thickness and

positioned at 90 degrees to each other, one in

elasticity of the sheet. However, the measure-

front of the LED light source and one in front

Figure 16. The polarizers block the specularly reflected light from the sample surface.

Figure 17. Close-up of the original image (a), reconstructed image (b), difference between the images (c) and the processed image in which shadows are amplified (d).

of the camera. The light which passes the first

systems, one for laboratory use and one for

polarizer is blocked at the second polarizer if

on-line mill tests. The systems contain a flow-

the light is specularly reflected. Both polariz-

through cuvette, a CCD camera equipped with

ers were attached to a supporting arm, so that

a high-magnification objective achieving mi-

the polarizer in front of the camera lens rotated,

crometer resolution per pixel, and back-light

thus keeping the orientation between the po-

illumination (Figure 18). The software in sys-

larizers constant during measurement.

tems automatically analyses the morphological properties of particles with a size range

The shadows caused by the fibres can be seen

from micrometres to millimetres.

as faint dark curves in the difference image. Detection of the shadows is based on line detection

The method automatically detects particles

in all orientations across the image. The shadow

from images and continuously analyses their

lengths vary depending on the angle and exten-

properties, such size, count, shape and type.

sion from the paper surface of the free ends of

It also provides distributional information on

the fibres, which are usually shorter than the ac-

particle types.

tual fibre length. Figure 17 illustrates the differShape properties describe the morphology

ent steps in the image processing.

of particles. These properties are aspect raThe number of free fibre ends in three tissue

tio, roundness, and coarseness. Aspect ratio is

grades was estimated with the new imaging

computed as the ratio between the major and

system. The fibres were counted from the side

minor axes of the particle image. The princi-

of tissue paper which had been in contact with

pal axes are computed from the particle image

the Yankee cylinder.

with principal component analysis (PCA). The aspect ratio of an infinitely thin line goes to in-

Average Std

Grade 1

Grade 2

Grade 3

finity, whereas a sphereâ&#x20AC;&#x2122;s aspect ratio is one.

36.3

40.1

64.5

Roundness determines how circular the par-

6.1

5.4

2.7

ticle is. Round objects have 100% roundness,

Table 1. Free fibre end count estimated with the novel imaging system

and the roundness percentage decreases with increasing the complexity of the particle shape. Roundness thus indicates the degree

Based on the results, significant differences in

to which a particle outline deviates from a cir-

free fibre end count were observed between

cle. Coarseness is computed as the sum of

each tissue grade tested. The standard devia-

discrete curvatures along the perimeter di-

tion of the fibre counts was small, which indi-

vided by the length of the outline (degrees/

cates good repeatability of the measurement.

pixel). Only the discrete curvatures of spikes

The result of this research provides a good

(i.e. rapid turns) are counted in the coarseness

starting point for development of off-line or

computation. Therefore, coarseness increases

on-line softness measurement systems.

with the increasing number density and sharpness of spikes along the perimeter. Bubbles,

4.5 Image analysis method for water and pulp quality

droplets and other blobs have low coarseness values, whereas fibres and flocs have higher coarseness values.

An image analysis method was developed for monitoring particles in water suspension. The

Particles can be classified as fibres, flocs or oth-

method was implemented as two prototype

er particles based on measured size, roundness

123

Figure 18. The flow-through cuvette with optical setup and CCD camera.

Figure 19. Images of water and pulp suspensions.

Figure 20. Examples of images from pulp treatment tests.

124

and coarseness values. Flocs are distinguished

count by bridging them with larger flocs and

based on their high coarseness value. Fibres

with fibres. Polymer B forms smaller flocs by

have a low roundness value and a correspond-

neutralizing the surface charge of particles.

ingly high aspect ratio. Other particles are more

The choice of chemical depends on the appli-

or less round and have smooth outlines.

cation and target quality.

Laboratory test results

Another chemical treatment example is pre-

Image analysis was applied to measure the

sented in Figures 21 and 22. In this example,

quality of various water and pulp samples from

the original water sample contains only a small

paper mills as well as a number of samples from

amount of particles. At low chemical dosage

high-filler and printing house trials. Figure 19

the particle count increases due to the precipi-

shows some example images from the analysis.

tation of dissolved substances. Flocculation of particles starts at higher chemical doses. The

The effect of chemical treatment of pulp in a

size and coarseness of particles increase and

laboratory-scale system is illustrated in Fig-

the particle count decreases as the chemical

ure 20. The original pulp sample contains a

doses increase. The performance of the chem-

lot of small colloids and fibres. The sample

icals also differs with, for example, better floc

was treated with two different types of cati-

formation achieved with chemical A.

onic polymer (A&B). The reaction mechanisms of the two polymers are different, as can be

On-line prototype test results

discerned from the images. Polymer A has a

The on-line prototype was tested in a paper

longer chain length and decreases the colloid

mill. Three different types of water sample

Figure 21. Example water treatment analysis using the image analysis method: particle count and mean size as a function of chemical dose.

Figure 22. Example water treatment analysis using the image analysis method: particle coarseness and floc count as a function of chemical dose.

125

were measured: white water and two filtrates

production concepts for printed products, and

(pulp, water circulation). The white water

the methods developed are imperative when

and pulp filtrate samples required dilution of

the concept analysis is extended to include the

the sample flow. An automatic cleaning sys-

optimization between functionalities generat-

tem was also required to prevent fouling and

ed at the paper machine and printing press.

blocking of the system. Image-based measurement system for tissue The first successful mill test result is presented

structure and quality opens a way to enhance

in Figure 23. The results from a three-month

the creping process and production rate in tis-

test period revealed that circulation water

sue production. Today, the crepe ratio is con-

quality varies considerably. Mean particle size

trolled on the basis of unreliable, subjective and

varied in the range 4-10 Âľm and the maxi-

slow measurements. New image analysis based

mum particle count was 600 pc/image. Circu-

measurement provides fast and accurate infor-

lation water includes several water streams,

mation for optimizing the creping process.

the quality of which can vary significantly. In this case one stream brings varying amount of

One important goal in the creping process is to

small particles to the water circulation. There-

achieve the desired sheet quality with the low-

fore the particle count increases and average

est possible crepe ratio. In addition, the frequen-

size decreases cyclically in water circulation.

cy of creping blade changes has a direct impact on the production rate of tissue machines. The

Chemical response tests were carried out in the

novel image analysis method enables the effect

mill to investigate how to reduce colloidal par-

of chemicals on the creping process to be evalu-

ticles in the water circulation. A clear chemi-

ated, leading to a radical improvements in pro-

cal response was seen with respect to particle

cess efficiency in tissue production.

counts. The tests showed that chemical treatment could be improved by controlling chemi-

The image-based analyser can provide spe-

cal doses using the new image-based analyser.

cific information on particles in water and pulp suspensions for chemical testing, anal-

5. Exploitation and impact of results

ysis and optimization of chemical treatments in papermaking. By utilizing this new methodology more specific chemistry and phenomena based information can be provided ei-

The developed technologies can be implemented

ther to develop new chemical products or to

in existing production systems with appropriate

improve papermaking process performance

cooperation between end users, large automa-

through more optimal selection of chemicals.

tion suppliers and SMEs specializing in imaged-

The image analysis system can also be used

based measurements and machine vision.

to improve colloidal chemistry in papermaking. Current commercial systems and sensors are

Radically improved management of the materi-

more or less indirect (e.g. turbidity, cationic de-

al flow of webs â&#x20AC;&#x201C; achieved through continuous

mand) and not feasible for efficient chemistry

transmittance imaging and 2D control support-

management. This new approach facilitates

ed by it â&#x20AC;&#x201C; is expected to be a component of the

the direct observation of colloids by imaging.

management in all concepts considered in the

126

EffNet programme. Surface characterization

For immediate utilization of image-based

for printing is obviously of importance for all

measurements, EffNet actively pursued the

involvement of partner SMEs in the project.

6. Networking

LabVision was included in all project activities to develop laboratory-level technologies for

The research was carried out jointly by re-

current production systems. Metso is active-

search organisations and Finnish forest clus-

ly analysing opportunities for commercializing

ter companies. Table 2 presents the research

the technologies developed, both scanning

partners and their roles.

image based surface property measurement, and continuous web imaging based on technology acquired from Viconsys, a partner in the earlier Qvision project.

Figure 23. Particle count and size in circulating water during mill tests.

127

Table 2. Partner organisations and their research roles.

128

Partner

Role

Tampere University of Technology, Department of Automation Science and Engineering

Imaging for topography, surface orientation and dot gain measurement. Diagnostic analysis methods for web-wide images. Image-based measurement technology in tissue structure analysis and control of tissue machine.

Kemira

Image-based measurement technology for water and pulp quality analysis and control of chemistry. Image-based measurement technology in tissue structure analysis and tissue machine control.

Lappeenranta University of Technology, Information technology

Imaging and analysis methods for topography, surface orientation and formation. Imaging for online control of formation/orientation.

Metso Automation

Development of on-line scanning image-based measurements for topography and surface orientation/formation. Web inspection systems for web-wide imaging solutions.

University of Eastern Finland, Optics

Spectral imaging for surface chemistry applications.

University of Helsinki, Department of Mathematics

Inverse methods and wavelet transforms for surface orientation measurements. Inverse methods in estimation for diagnostics and control.

University of Jyv채skyl채, Department of Physics (P), Department of Information Technology (IT)

(P:) X-ray tomography measurements as references for paper structure measurements. Wavelet and related methods for surface orientation analysis. (IT:) Image correction, calibration and stitching methods for web-wide imaging solutions. Feature extraction methods for diagnostics based on webwide images.

University of Oulu, Control (C), Optoelectronics (O) UPM

(C:) 2D control methods and their performance (O:) Optical tomography measurements as references for paper structure measurements. Providing a case for full-scale studies of web-wide imaging.

7. Publications Ihalainen, H., Marjanen, K., Mäntylä, M., Ko-

Seppänen, J., Utilizing Online topography

sonen, M.J., Developments in camera-based

Measurement on LWC papermachine, Master’s

measurement of paper, presented as an invit-

thesis, University of Oulu, 2013

ed paper in Control systems 2012 conference in New Orleans, USA, April 2012.

Raunio, J.-P., Ritala, R. and Mäkinen, M., (2012): Variability of crepe frequency in tissue

Isokangas, A., Leiviskä, K., Analysis of forma-

paper; relationship to basis weight profiles, In-

tion and flock size on the basis of optical trans-

ternational Control systems Program 2012,

mittance. Report series A, Control Engineering

New Orleans, USA, 2012.

Laboratory, University of Oulu. Raunio, J.-P. and Ritala, R., (2012): Simulation Kälviäinen, H., "Machine vision based quality

of creping pattern in tissue paper, Nordic Pulp

control from pulping to papermaking for print-

and Pap. Res. J., Vol. 27, No. 2, pp. 375-381.

ing", Presentation as an invited speaker in 10th International Conference on Pattern Recogni-

Raunio J.-P., Tirronen, V., Lehtoranta, I. and

tion and Image Analysis (PRIA-20-2010), St.

Ritala, R., (2013): Web-wide imaging of paper;

Petersburg, Russian Federation, and accept-

Analyzing the potential of on-line light trans-

ed to Pattern Recognition and Image Analysis.

mittance measurement in quality control and diagnostics of paper, Nordic Pulp and Pap.

Mettänen, M., Jukola, M., Miettinen, A.,

Res. J., Vol. 28, No. 1, pp. 137-146.

Ihalainen, H., ” Comparison of registered paper surface representations from microto-

Raunio, J.-P. and Ritala, R., (2013): Potential of

mography and photometric stereo”, accepted

full-web imaging in measuring web structure

to 2011 Paper Physics Seminar, Graz, Austria,

on-line, J-For, Vol. 3, No. 1, pp. 6-12.

5-8.9.2011. Raunio, J-P. and Ritala R., (2013): Method for deOhenoja, M., "Application feasibility study of

tecting free fiber ends in tissue paper, accepted

2D control methods", Report series A, Control

to Measurement Science and Technology.

Engineering Laboratory, University of Oulu. Takalo, J., Timonen, J., Sampo, J., Siltanen, S., Ohenoja, M., Leiviskä, K., Multiple property con-

and Lassas, M., “Evaluation of the areal mate-

trol in cross direction in a sheet-forming process,

rial distribution of paper from its optical trans-

Journal Modelling, Identification and Control.

mission image”, Eur. Phys. J. Appl. Phys. 55 (2011) 20701.

Ohenoja, M., Leiviskä, K., Potential of imaging measurements in paper machine control. Control systems 2012 conference in New Orleans, USA, April 2012. Pant, P., Mutanen, J., Mankki, A., Hauta-Kasari, M., Parkkinen, J., Spectral Analysis and Classification of Dirt Particles in Pulp, Nordic Pulp & Paper Research Journal, 2012, pp.577–589.

129

Expanded operating window for printing process enabling

efficient use of newly engineered fibre web substrate c o n ta c t p e r s o n Markku Parola, markku.parola@vtt.fi

Pa r t n e r s VTT Sanoma News Stora Enso UPM

130

Abstract This research explored the key printing materials and press adjustments affecting press runnability and productivity through finite element modelling, laboratory work and printing trials. Finite element modelling enables the prediction of the operating window in a heatset press: how the key paper and printing material parameters affect press runnability. With the help of modelling and measurements in the laboratory and in printing presses, the web tension formation mechanism between printing units was determined for the first time. This helps both papermakers and printers to achieve better productivity. Here, printing blankets and nip loads play a crucial role in affecting the web strain between printing units. The most important paper property affecting web tension is tensile stiffness. Accumulation build-up (piling) starts with the interaction between the ink and the printing plate. A slight increase in fountain solution feed in the printing press decreases build-up tendency. The use of novel topography measurement in the printing press helps the printer to optimize washing cycles and leads to better press productivity. Key paper parameters of novel webs regarding printing are: surface strength, absorption, tensile stiffness and hygroexpansion. Accurate selection of press material combinations and optimized press settings enabled printability of the novel webs produced in EffNet. A novel printing concept in which the web is varnished after printing was studied. Laboratory varnishing tests gave promising results, as varnished uncoated and printed SC papers gave as good printed gloss levels as the reference LWC paper.

Keywords: heatset printing, runnability, web tension, accumulation, blanket, web release, novel web, varnishing, build-up, piling

131

1. Background

of the current printing process to accommodate cost efficient printing of novel webs.

The push towards efficiency enhancement and cost reduction continues to dominate the printing industry. Good print quality is also no

2. Objectives

longer a competitive asset, but a bare necessity. Common runnability problems faced in-

The main objective of the printing research

clude, for example, material accumulation on

was to maintain the newly engineered fibre

the blanket (piling) and problems related to

web properties throughout the printing phase,

web tension. Blanket accumulation, in turn,

thus increasing the efficiency of the whole val-

results in vanishing dots, ghosting and de-

ue chain. Furthermore, the aim was to identi-

creased print density. In addition, short wash-

fy in which phases of the value chain actions

ing intervals decrease press productivity, and

towards efficient production could be feasibly

web tension variations through the press af-

taken, and whether the printing process could

fect printed waste, web breaks, colour register,

replace certain fibre web manufacturing phas-

web movements, web release in the nip area,

es (e.g. surface treatment). The research thus

waviness, fluting, etc.

contributes to overall optimization of the whole value chain, from paper making to printing.

VTT has conducted extensive research on printing process interactions and runnability.

The research focussed on heatset web off-

Studies have focussed on a specific stage (e.g.

set printing because demanding process con-

drying) or phenomenon (e.g. accumulation,

ditions apply high stresses on the fibre web

web tension) at a time. Printing research with-

during printing. As the newly engineered fibre

in EffNet summarizes the knowledge gained

products require a new approach to the print-

in earlier studies and clarifies in further detail

ing process, the printing research concentrat-

those phenomena that are expected to be the

ed on how different components of the print-

most significant when optimizing the efficien-

ing process influence the fibre web. One goal

cy of the heatset printing process.

was also to expand the operating window of the current printing process to accommodate

The overall goal of the Efficient Networking To-

the novel webs, drawing on the valuable con-

wards Novel Products and Processes (EffNet)

tribution of the graphic industry and its suppli-

programme is to improve the competitiveness

ers. Furthermore, the novel webs and new im-

of the whole forest cluster by developing rad-

age-based measurement method developed

ically new energy and resource efficient pro-

in EffNet Programme enabled exploration of

duction technologies and by finding means

the printing process.

to reduce capital intensiveness. The printing component of the EffNet programme studied

The knowledge gained from the printing research

the critical interactions between the fibre web,

and the validated characterization methods can

printing materials and the press in order to op-

be turned into services, sharing the knowledge

timize the printing process for novel fibre webs

throughout the value chain of printed products,

developed in EffNet Programme. In addition,

and thus increasing competitiveness.

possibilities to perform surface finishing of the fibre web with existing technologies during the printing stage were explored. One important goal was to expand the operating window

132

The objectives of the printing research were to:

to ink build-up on printing blankets (accumulation). Finite element modelling was successful-

• Study the printability of the newly

ly used to model the effect of the printing nips

engineered fibre web substrates

on the paper web. The papers, inks and print-

• Optimize the printing process for new substrates (operating window of presses)

ing blankets were characterized in laboratory studies. Commercial materials were used in

• Increase knowledge of the interactions

the study: six paper grades, two inks and four

between the fibre web and the printing

different printing blankets. Printing trials and

process

measurements were carried out on the KCL

• Clarify the key paper and printing parameters affecting runnability and

heatset press and on two commercial printing presses (Hansaprint and Sanomapaino).

accumulation in printing • Predict the effects of material changes on

Furthermore, the aim was to identify the stag-

runnability and printability => efficiency

es in the value chain in which actions towards

throughout the value chain

efficient production of printed end products

• Predict whether the printing process can

could be feasibly implemented, and whether

replace some fibre web manufacturing

the printing process could replace certain fibre

phases

web manufacturing phases (e.g. surface treat-

• Create practical tools and services for

ment). As part of the novel printing concept,

improving printing productivity and for

the influence of varnishing on the printed sur-

future implementations

face was also studied.

3. Research approach

4. Results

The printing research was considered essential

4.1 Modelling printing nips and the paper web

for the development of novel paper concepts for the printing market. Better understanding of the printing process, especially printing nip

The novel webs developed under the EffNet pro-

phenomena, is needed to determine how nov-

gramme have different structure and bulk com-

el fibre webs should be printed and how the re-

pared to currently used paper grades. It is there-

quired print quality can be achieved. The printing

fore essential to determine how these novel

research within the EffNet programme focussed

structures perform during printing, especially

on heatset web offset printing, because the de-

under high nip loads. Nip phenomena are, how-

manding process conditions of HSWO printing

ever, not yet well understood, and no definitive

apply high stresses on the fibre web during print-

results have been reported in the literature.

ing. The newly engineered fibre products require a new printing approach; the study therefore fo-

The goal of this study was to increase our un-

cussed on how different printing process com-

derstanding of the stresses occurring in the

ponents affect the fibre web.

printing nip and how they affect web tension formation by means of modelling. The model-

The research set out to clarify two important

ling was carried out using the finite element

aspects of heatset printing: the web tension

method with the Abaqus software.

formation between printing units and inside the printing nips, and the mechanisms leading

The two-dimensional finite element model

133

consists of four printing units. Each printing

structure. The surface and compressible lay-

unit consists of two rubber-covered cylinders

ers were modelled as hyperelastic material,

through which the paper web passes (Figure 1).

whereas the bottom fabric layer was modelled

The web tension was kept constant before the

as linearly elastic material. For the compress-

first unit. The paper web and rubber blankets

ible middle layer, the elastomeric foam mate-

were considered to be in plane strain state. The

rial model was used.

friction between contact surfaces was modelled using Coulombâ&#x20AC;&#x2122;s friction law, with a con-

The actual simulation consists of three steps. In

stant coefficient of friction. In all simulation

the first step, a tractive infeed tension is creat-

cases, the radius of the cylinders was 100 mm

ed. At this stage, the cylinders are not touching

and the thickness of the blanket 2 mm. The be-

the paper web. In the second step, the oppos-

haviour of the web was assumed to follow the

ing printing cylinders are pressed together to

orthotropic linearly elastic constitutive law.

generate the nip. In the final step, the printing process is activated by rotating the cylinders at

Rolling contact is a well-investigated area.

a prescribed angular velocity. The cylinders are

Rolling contact with respect to multi-layered

rotated until a steady state is attained.

cylinders has been reported in the literature mainly with regard to strains and stresses in

The forces and strains acting inside the print-

the nip area. In the present study, the rubber

ing nip were modelled to analyse how the nips

blankets were represented as a three-layer

affect the web tension. Figure 2 presents an

Figure 1. The printing nip and different blanket layers used in the modelling.

134

Figure 2. Modelled velocity fields in printing blankets in a printing nip.

example modelling result, in this case the ve-

ing the finite element method (FEM). The fig-

locities (MD direction) of the blankets inside

ure shows the simulated stress-strain test re-

the printing nip are modelled.

sult for a network in which the bonds do not break (blue line), and for a network modelled

The nip modelling results are presented in the

with spring-like bonds that can fail (red line).

next chapter together with web tension results. It can be seen that a network with spring-like Further on, the modelling has been pushed

bonds gives quite a realistic stress-strain curve.

forward to analyse the fibre network behaviour under loading inside the printing nip. The

The developed modelling allows adjustment of

finite element method was used to create the

the fibre shape and orientation, as well as ap-

fibre network, with the bonds between differ-

plication of a coating layer on the surface of

ent fibres modelled as springs that can fail.

the network.

Figure 3 presents a fibre network created us-

Figure 3. Left: A fibre network created with FEM. Right: Results of the modelled stress-strain test for a network in which the bonds do not break (blue line) and for a network modelled with spring-like bonds that can fail (red line).

135

4.2 Web tension

stresses and strains in different directions build up inside a printing nip, as they cannot

Comprehensive understanding of web tension

be measured on line. In this study, three dif-

formation in the heatset offset printing pro-

ferent blankets types with different feeding

cess facilitates the introduction of novel webs

properties were used: neutral (n), negative (N)

into the printing process. The web tension for-

and positive (P) feeding. Trials were carried out

mation mechanisms and the key parameters

on the KCL press with three different blanket

affecting them were studied through model-

combinations, n-n-n-n; n-P-N-n and n-N-P-n,

ling and measurements both in the laborato-

where n-P-N-n means that the printing units

ry and on actual printing presses (KCL press

had neutral, positive, negative, and neutral

and a commercial press). Figure 4 presents the

blankets, respectively. In this way, all blanket

measurement setup at the KCL heatset press.

combinations could be studied.

Web tensions were measured with weighing

Modelling revealed that different blankets affect

rollers between all printing units. Web tension

the strains between the printing units, leading to

was also measured at the infeed unit, before

tension changes between printing units. Figure

the dryer and before the folder.

5 presents the modelled strains and modelled and measured web tensions on the KCL press

The results show that press draw adjustments

with different blanket configurations.

explain a large part of the tension formation before and after the printing nips. These ad-

As the figures show, the measurements and

justments include the infeed control, chilling

the modelling results correlate well. It was

roller and folder draws.

concluded that tension changes are due to strain differences, and that the degree of pa-

As the web tension formation between the

per tensile stiffness determines the magni-

first and last printing units is complex, mod-

tude of the change. Figure 6 presents the ten-

elling is needed to support its analysis. Mod-

sion and tensile stiffness measurements for

elling was especially used to understand how

the studied paper samples.

Figure 4. Web tension and other measurement locations in the web tension trial run on the KCL press.

136

Figure 5. Left: Modelled strains of the paper web through the printing units; Right: Modelled (blue line) and measured web tensions (green spots). The blankets sets are marked above the figures, n-P-N-n above and n-N-P-n below.

As the figure shows, the n-P-N-n blanket set in-

ing nip load, and drying temperature. As

creases the draw between the 1st and 2nd print-

expected, increased fountain solution feed de-

ing units (neutral â&#x20AC;&#x201C; positive blanket). It can also be seen that the tensile stiffness of the different paper grades (violet line) correlates with the web tension change. Between the 2nd and 3rd printing units (positive â&#x20AC;&#x201C; negative blanket), the blankets decrease the draw. In this case, the web tension drops more when tensile stiffness is higher, as indicated by the green columns. The measured tension changes and their correlation with paper tensile stiffness also strongly suggest that strain changes occur between printing units, thus verifying the modelling results. The other key parameters affecting web tension were: fountain solution feed level, print-

Figure 6. Effect of tensile stiffness of paper (blanket set n-P-N-n) on web tension between printing units 1 and 2 and between printing units 2 and 3.

137

creased web tension, but the effect was quite

mulation, register errors and on web handling.

small. Nip load has a clear effect on web ten-

Poor web release also leads to high release

sion as it affects the feeding property of the

forces, which, in turn, lead to a higher surface

blanket. Within the operating window of heat-

strength requirement of the paper. The web

set printing, dryer temperature changes had

release angle was measured after the fourth

only a small effect on web tension.

printing unit in the KCL press trials (Figure 7).

High web tension peaks were measured during

The results showed that the release angle in-

printing press start-ups. Such tension peaks can

creases with higher ink tack and higher nip

lead to web breaks during start-up. The peaks

load. Conversely, increased fountain solution

are most likely due to the start-up sequence, in

feed lowers the release angle: a higher amount

which the paper is first run without ink and foun-

of fountain solution in the ink emulsion low-

tain solution during warm-up of the dryer.

ers the internal cohesion of the ink, leading to easier emulsion splitting at the nip exit and to

Web tension is not normally measured be-

easier web release.

tween the last printing unit and the chilling rollers. However, with heatset presses it is rec-

Blanket manufacturer has developed easy-

ommended that web tension should also be

release blankets. The release property of the

measured (after the dryer and before 1st chillig

blankets is controlled by surface chemistry (po-

roller) and controlled in this part of the press in

larity) and/or by controlling the surface rough-

order to avoid start-up problems.

ness of the blanket. Test results showed that the easy-release blankets achieved a lower

Trials were also carried out on Sanomapaino

web release angle compared to normal release

and Hansaprint presses. These results were in

blankets. Figure 8 presents the effect of blanket

line with the results of the KCL press.

type, paper and ink type on web release angle.

4.3 Web release

The results are in line with the laboratory measurements, in which easy-release blan-

Web release from the printing blankets was

kets achieved lower release forces than nor-

studied in the laboratory and with on-line

mal release blankets. The easy-release blan-

measurements on the KCL press. Web release

kets also produced less lint and dust than the

has an effect, for example, on dot gain, accu-

normal blankets. In general, the paper grade determined the level of release angle: in all printing material combinations and press settings LWC gloss had the biggest, and LWC matt lowest release angles. It is yet not clear what is behind this phenomenon as there are many paper properties affecting release angle. It is presumed that the high ink setting speed, high surface smoothness and low porosity (small pore size distribution) of LWC gloss paper leads to a

Figure 7. Measured and calculated points for determining release angle.

138

large contact area between the inked blanket and paper surface in the nip, thus leading to a

higher force needed to separate the inked pa-

ly between every one or two hours in heatset

per from the blanket surface.

web printing, leading to high printed waste and lowered printing productivity.

4.4 Accumulation build-up The accumulation mechanism was studied in The accumulation build-up of ink and paper

heatset printing trials at KCL and in a commer-

particles on the printing blanket, leads to de-

cial press using on-line devices including a mi-

teriorated print quality. This accumulated ma-

croimaging system and various IR and UV-VIS

terial has to be washed from blankets typical-

measurements. A high-resolution colour cam-

Figure 8. Effect of blanket release property, paper and ink tack on release angle in the KCL press trial. Release angles at 300 N/m web tension.

Figure 9. On-line instrumentation and additional measurements for studying build-up tendency on KCLâ&#x20AC;&#x2122;s HSWO press.

139

era was used to take still images from the ro-

trapping image areas transfers to the plate by

tating plate and blanket cylinder surface during

micro-toning or by migration. These ink impu-

printing. On-line measurement systems were

rities are then transferred to, and accumulated

used to monitor the amount of water, ink binder

on, the non-image areas of the blankets of the

and ink pigment on the rotating blanket cylinder.

next printing units.

Figure 9 shows the used on-line instrumentation

The image area accumulation build-up took

during the piling trial on the KCL press. The addi-

place at the edges of the images. Uneven

tional off-line analyses are also listed in Figure 9.

splitting of emulsion in the printing nip induces ink tailing at the edges of the image area

Samples from the fountain solution and cyan

on the printing plate. These ink tails transfer

and magenta emulsions were taken during the

to the blanket, increasing the accumulation on

accumulation trial and analysed in the lab. Lint

the trailing edges of the image areas (Figure

and dust were measured from adhesive tape

11). Nip pressure further enriches the amount

samples taken from the blanket surface of the

the accumulation on the leading and trailing

first printing unit. The composition of the accu-

edges of the image areas in both the ink trans-

mulated material was analysed using scanning

fer and back-trapping areas.

electron microscope/energy dispersive spectroscopy (SEM/EDS) and pyrolysis gas chroma-

It was found that the distribution of accumulat-

tography/mass spectrometry (GC/MS) meth-

ed material between image and non-image ar-

ods from blanket samples cut after printing.

eas depends on the printed paper grade. With coated grades the ink transfer areas are clean,

Microimaging results showed that non-image

while the non-image areas are covered with

area accumulation starts from the printing

accumulated material. Accumulated material

plate conditions; impurities originating from

at the edges of the images areas forms sharp

fountain solution cycle as well as uneven split-

dense edges that prevent efficient ink transfer,

ting of emulsion between the plate and blanket

leading to reduced dot size and vanishing dots

cylinder cause ink transfer to non-image are-

on the printed paper. With uncoated grades

as on the printing plate and further on to the

accumulation is detected on non-image areas

blanket (Figure 10). Moreover, ink from back-

and, in some cases, even on image areas. This

Figure 10. Formation of non-image area accumulation; Left: Microimage showing ink spots on the nonimage area of a printing plate; Right: Microimage from non-image area accumulation on a printing blanket (magenta).

140

Figure 11. Formation of edge accumulation. Left: Ink tails on halftone dots on the plate. Middle: Accumulation build-up around halftone dots on the blanket. Right: Illustration of accumulation build-up around halftone dots on the blanket.

is especially noted on back-trapping halftone

sis was carried out using SEM/EDS equipment.

areas. However, with uncoated grades the ac-

Analysis of the printing materials, i.e. papers,

cumulated material contains sparse fibrous

inks and blankets, was carried out using the

material, thus allowing sufficient ink transfer.

IR method. Both studied inks contained small amounts of clay and calcium carbonate, which

It was found that a slight increase in fountain

are also common compounds in paper coating

solution feed is beneficial for heatset print-

and fillers. According to EDS elemental map-

ing productivity (Figure 12). Higher fountain

ping, the accumulated material in magenta ink

solution feed decreases accumulation build-

transfer areas contained both clay (Al, Si) and

up and eases web release, leading to longer

calcium carbonate (Ca). The calcium carbon-

washing cycles. A minor increase in fountain

ate and clay are located mainly between dots,

solution feed has no notable influence on web

indicating that slightly more accumulation oc-

tension, drying efficiency or print quality.

curs on the non-image areas. Figure 13 shows an example of an EDS measurement from a

Analysis of the accumulated inorganic materi-

blanket. As all of these materials are present

al composition was carried out from the blan-

in both ink and in paper it is impossible to iso-

ket samples cut after printing of the coated

late the origin of the detected elements.

and uncoated papers. The elemental analy-

Figure 12. On-line images from the printing plate. Left = more fountain solution feed. Right = less fountain solution feed

141

Figure 13. SEM/EDS elemental maps of blanket samples cut after coated paper printing from 15% halftone area. Accumulation of cyan ink. Left: SEM image showing the accumulation topography on the blanket. The elemental maps to the right show the distribution of aluminium (Al), silicon (Si) and calcium (Ca).

Figure 14. Material components and accumulation composition at different trial points. KP 1 is a SC paper, KP 3 a LWC paper. Reference points are measurements of used materials (left). The measured composition of the accumulation is presented on the right.

Figure 15. Accumulation measured from the printing blanket topography (LabVision Technologies Oyj). C15 is Cyan in 15% dot field (see also figure above). M is magenta and K is Black. 100 mean compact ink field. Y-axis is in micrometres.

142

The composition of the accumulated organ-

improved printed quality could be achieved for

ic material was studied using the methylation

uncoated papers in the heatset offset printing

pyrolysis GC/MS method. The method shows

process. As a result, the concept of paper var-

the organic structure of the accumulation, but

nishing after the last printing unit was select-

does not give quantitative results for the ac-

ed for closer examination.

cumulated components. Figure 14 reveals the composition of the used materials and accu-

Laboratory-scale trials were carried out with

mulation components at different trial points.

the Prüfbau printing apparatus. A SC paper and improved news samples were printed with cyan

The analysis showed that the accumulated ma-

ink and varnished with an oil-based commercial

terial consists of components from both ink and

varnish wet on wet. LWC reference paper was

paper. The results show that the accumulated or-

also printed with compact cyan ink. The print-

ganic material consists mainly of fatty and resin

ed gloss was then measured (Figure 16). The

acids, originating most likely from the used inks.

amount of varnish used with SC paper was between 3.5 and 3.9 g/m², which is considerably

Topography

measurements

LabVision

more than in commercial sheetfed offset press,

Technologies Oyj clearly show how the accu-

where varnish levels are typically about 2 g/m².

mulation occurs in different areas of printed web. Figure 15 shows the accumulation buildup on three printed paper rolls.

4.6 Micro-scale analysis of paper structural properties for printability prediction

Topography measurement enables the optimization of washing intervals in heatset printing.

This research evaluated the mill performance of a new on-line paper quality sensor that con-

4.5 Varnishing the paper web

tinuously measures paper surface topography from the moving web (Figure 17). The results

Background research (literature review and in-

clearly indicate that the measurement appli-

terviews) was carried out to determine how

cation reliably predicts printability and pro-

Figure 16. The effect of varnishing on printed gloss; printed with Prüfbau apparatus at laboratory scale. The results are quite promising, as the printed gloss of the varnished SC paper is quite near to that of the reference LWC papers.

143

Figure 17. The on-line topography measurement principle: RGB photometric stereo imaging.

vides real-time information for process control and troubleshooting purposes. The state-of-

the-art imaging system, developed by Metso Automation, is based on topography measurement and includes a novel image analysis technology integrated into the process quality control system.

5. Exploitation plan and impact of results

• • • •

Less printed waste Fewer web breaks Fewer colour register problems Quicker printing start-ups

Increased printing efficiency will also lead to a smaller carbon footprint. Varnishing of the printed web substantially improves the printed quality. Varnishing (after the printing units) can be used in the printing of papers developed in EffNet programme as

The printing study defined the operating window for novel webs in heatset web offset printing, thus supporting the introduction of novel webs to the printing market.

well as in traditional printing. The research results can also be beneficially used in other web applications, such as papermaking and printed electronics. Cooperation

The results revealed the crucial press and paper parameters affecting runnability in heatset printing. The results have already been successfully used by papermakers in troubleshooting customer problems in printing presses, leading to financial benefits through increased paper orders. The results suggest that printing press runnability can be increased significantly and systematic exploitation of the results would lead to remarkable cost savings in heatset printing. These savings include, for example:

with printed electronics manufacturers has already started. In printed electronics, the register accuracy between different printed layers remains a key challenge to be resolved.

6. Networking The research was carried out jointly by research organisations and Finnish forest cluster companies. Table 1 presents the research partners and their roles.

• Longer washing cycles due to better process knowledge and novel topography measurements

144

Table 1. Partner organisations and their research roles.

Partner

Role

UPM

Contribution of expertise and materials; BALAS modelling of heatset press; adhesion study and trial run on a commercial press to examine the effect of press materials and settings on web release and piling.

Sanomapaino

Contribution of printing expertise; printing trials on the Sanomapaino printing press; financing of materials, machine time and man-hours.

Stora Enso

Contribution of expertise and materials; verification of results in sheet-fed offset press; financing of separate rotogravure study for testing the new Labvision imaging systems ability to predict missing dots.

VTT Technical Research Centre of Finland

Responsible for the majority of printing research and reporting.

LabVision Technologies

Conducting and reporting on-line surface topography and on-line dot measurements.

ContiTech AG

Delivery of printing blankets; expertise in blankets and printing; laboratory analyses of printing blankets.

7. Publications and reports Parola, M., Sorvari, J., Ketoja, J., Web tension

Passoja, S., Sneck, A., Hakkila, O., Monitoring

formation and web deformation in printing

heatset performance to control accumulation,

process; presented at the 16th International

Tappi Papercon, April, 2013, Atlanta, USA

Coating Science and Technology Symposium, September 9-12, 2012, Atlanta, USA.

Sneck, A., Passoja, S., Monitoring heatset performance to control accumulation; presented

Parola, M., Sorvari, J., Web deformations in

at PTS Imaging Symposium – Paper and Imag-

printing; presented at the 2012 International

ing (20.–21.11.2012, Munich)

Conference on Flexible and Printed Electronics, September 2012, Tokyo, Japan

Sneck, A., Passoja, S., Web release in heatset web offset printing, PTS Coating Conference,

Parola, M., Sorvari, J., Web tension forma-

Germany, September 2013

tion in heatset printing; presented at PTS Imaging Symposium - Paper and Imaging (20.–

Sorvari, J., Parola, M., Effect of printing nips on

21.11.2012, Munich)

web tension formation in offset printing; presented at the 6th European Congress on Com-

Parola, M., Sorvari, J., Modeling web behaviour

putational Methods in Applied Sciences and

in printing press and in printed electronics,

Engineering (ECCOMAS) in Vienna, Austria,

IWEB 2013, International Web Handling Con-

September 2012.

ference, USA, June 2013

145

Optimizing structures and operation of entire production systems

c o n ta c t p e r s o n Risto Ritala, risto.ritala@tut.fi

Pa r t n e r Tampere University of Technology Aalto University University of Eastern Finland University of Jyv채skyl채 VTT Technical Research Centre of Finland

146

Abstract

A general methodology for concurrently designing processes and their operational practices under several conflicting objectives was developed. The six-stage procedure is based on dynamic modelling of the process, developing a parameterized operational practice and then, by using multi-objective optimization methods, finding the trade-offs between the objectives as functions of operational parameters, process dimensions and structures. The objectives are evaluated in dynamic simulations corresponding to process operation of months to years. The solution is computationally highly intensive. Thus, the design optimization first produces a vast amount of design data, and then makes a computationally light surrogate model to be used in interaction with the design decision maker. The final design candidate is then further analysed with the simulator â&#x20AC;&#x201C; first to determine the corresponding design parameters and then to analyse the sensitivity of the choice to the simulation model parameters. Finally, the design is validated with a more detailed simulator. This design methodology was applied to two of the concept cases. The finescoated LWC and the binding filler concept (of fine paper rather than SC, which was studied by other WPs). The studies were on retrofit designs, analysing the trade-off between buffer volumes and tolerance to process upsets and nonstationary operating conditions. Due to rather limited degrees of freedom in the cases, the trade-offs involved investment differences of only a few millions of euros. A simulation model and operational optimization were also developed for the foam-formed folding boxboard case. The studies emphasized the importance of efficient management of the foaming chemical in long circulation if a foam headbox is implemented as a retrofit in existing mills.

Keywords: process design, control design, optimization, Pareto optimal, validation, LWC, fine paper, folding boxboard, foam forming.

147

1. Background

and the reallocation of tasks between papermaking and printing must be considered as a

Large capital employed and inflexibility of pro-

design degree of freedom.

duction systems are the core business challenges of forest-based chemical industries.

Best-practice chemical engineering methods

Design of production systems has been consid-

for the integrated design of process structure

ered from the point of view of material equilib-

and control have been developed, but not ap-

rium at operating points and with convention-

plied in pulp and paper. Furthermore, recent

al processing tasks for players in the supply

developments in biorefinery and its integra-

chain, most notably for papermakers and print-

tion into conventional pulping and papermak-

ers. The design of production system dynam-

ing have opened up possibilities to radically

ics has been based on rather coarse analyses

rethink material flows and to seek completely

of production disturbances. Buffer volumes be-

different process structures.

tween production departments and mechanisms for attenuating disturbances have been designed accordingly, but only after the main

2. Objectives

production system structures have been determined. Control and operational decision sup-

Objectives of optimizing structures and oper-

port systems have thus had minimal degrees

ation of entire production systems research

of freedom in their design and, as a result, dy-

area with in EffNet was to develop multi-ob-

namic behaviour and capital efficiency are sub-

jective design optimization methodology ad-

optimal: many operations that could be dealt

dressing the structural and operations design

with by information, computational and con-

on the basis of results in EffTech programme.

trol means are implemented with capital-intensive process equipment. Implementing the

Specific objectives of the research:

management of disturbances with equipment has led to long transition times between oper-

• Optimize the structure, dimensioning,

ating points – i.e. poor flexibility. These factors

dynamics and operation of conceptual

have resulted in production systems that have

cases defined by EffNet. Two categories of

high performance when analysed in the steady

design cases are foreseen: one for retrofit

state, but when dynamics and operational is-

renewal of current process concepts and

sues are included, their performance is severely deteriorated. The effects of poor dynamical

another for entirely new process concept. • Multi-objective design optimization

performance can vary greatly between produc-

methodology addressing structural and

tion system structures and concepts, resulting

operational design developed further based

in pure steady-state analyses incorrectly prior-

on EffTech results. In particular, scalability

itizing certain concepts as investment targets.

issues and multi-objective operational

Optimization of production system structures

design were addressed.

has also been constrained by the conventional

• Work flow and business model for the

task descriptions of papermakers and printers.

joint design of process structures and

As the EffNet programme seeks major changes

operations developed to draft level.

to – or entirely new – production system con-

148

cepts throughout the value chain, design com-

The design cases were updated during the re-

parisons must be based on concepts that in-

search with discussions on concept cases in the

clude both structural and operational issues,

entire programme. Two cases – the fines-coated

LWC concept and the high binding filler content

Initially, the scope was planned to include

fine paper concept – were selected for detailed

two case studies: retrofitting new unit pro-

analysis, and one case, foam-formed folding

cess technology in a current mill layout, and

boxboard, was examined with simulations. All

designing a radically new process structure

cases studied analyse the entire mill concepts.

(green field). However, in practice, all three of the studied concepts fell into the retrofit cat-

3. Research approach

egory. Furthermore, the additional third case study was not carried out as a complete design optimization, but rather as a dynamic

The research hypothesis was that by integrat-

simulation study.

ing the design of process structure and operation, the cost of ownership can be reduced

The main outcomes of the work are the

considerably.

following:

The research questions were:

1. The design methodology was developed and tested in the case studies. The

1. How can the design of process equipment and

methodology is feasible and generic. As

process operation, measurement and control

the method relies heavily on the process

be integrated so that the life-time performance

models and their parameterizations, the

of the production system is enhanced from

critical point in the analysis is the quality of

the conventional practice of layout design preceding operational/control design? 2. How can design decisions be based on life-

models available for the analysis. 2. The service business model was analysed and outlined. The methodology combines

time performance data obtained through

knowledge in the application domain,

time-consuming dynamic simulations?

modelling and simulation, and multi-

3. How should multiple contradictory design

objective optimization. Thus, the challenge

objectives be dealt with, and how should

for the service business is to acquire

the trade-offs be presented to the decision

the right combination of people with the

maker?

required knowledge areas and to arrange

4. Can the model-based, multi-objective

their communication, which most probably

design methodology be implemented as

requires “an integrator” with adequate

commercially viable service business?

background in all these fields. Furthermore, due to costs and response times, the

These methodological questions were

service is seen as viable for studies of novel

studied through case analyses, the design

process systems rather than as a tool for

problems being derived from the envisaged

“standard cases”.

novel concepts in EffNet. In particular, the three cases studied were:

3. The results of the case studies were encouraging, but indecisive regarding benefits with respect to cost of ownership.

1. LWC paper with a fractionated TMP fines based coating. 2. Fine paper with a high content of filler with binding capability. 3. Folding boxboard with a foam-formed centre ply.

This is firstly because the cases studied had a rather narrow scope of optimization, and secondly because the effects of model uncertainties could not be assessed in detail as no process implementations were made. The model and parameter uncertainties are

149

the main limitation for the credibility of the

Given a set of performance criteria, find the

design optimization results.

process

structure,

dimensioning,

control

structure and tuning so that the life-cycle perThe work was organized into three tasks as

formance of the system under a set of busi-

follows:

ness scenarios is Pareto optimal.

Development of methods for multi-objective

As there are several performance criteria,

conceptual design. Conceptual design address-

the design problem includes an important

ing both structures and operation in a multi-ob-

communication task:

jective way is an area of research about which rather little literature and methodology exists.

To effectively present the Pareto optimal designs and their trade-offs to the decision

Concept optimization. A set of concepts to be

maker(s) so that person(s) with expertise in

optimized can be defined as a process super-

the process/business domain but not in the

structure, indicating the potential components

modelling/optimization methods are able to

of the concept and their structural and para-

make justified design decisions based on the

metric options. Multi-objective optimization

data produced during the mathematical analy-

considers performance criteria set at both the

sis of the design problem.

life-cycle level and the operational level. The design methodology developed in EffNet Work flow and IT infrastructure analysis. The

consists of the following main steps:

current work flow in conceptual design results from the conventional design practice of first

1. Mathematical problem formulation. This

choosing the process structure and only then

step translates the process description,

tackling operability. This study first analyses

objectives and constraints, degrees of

the current work flow and attitudes of present

freedom, reference process information

players towards concurrent structural and op-

and long-term business and technology

erational design, and then specifies new ways

environment scenarios from verbal

of working towards concurrent design, pre-

information into mathematical expressions

senting this as the basis for service provider

that can be used in the mathematical

business planning.

4. Results

(multi-objective) design optimization. 2. Constructing the dynamic process (superstructure) model that allows assessment of the life-time performance of

This section first describes the methodology,

any production system within the scope of

then the results of the three concept case stud-

degrees of freedom.

ies and, finally, the business model analysis.

3. Implementing operational optimization in the dynamic process model. In this step the

4.1 Methodology for designing process structures and dynamics with multiple contradictory design objectives

control degrees of freedom are included in the analysis. Each production system performance is compared when optimally operated, although the exact form of

The problem of concurrent design of process structure, dynamics and operation can be stated as follows:

150

optimal operation may depend on the system structure and parameters. 4. Multi-objective design and presentation

of the decision alternatives to the

options; the critical requirement is that

decision maker. At this stage the life-

the computation time must be 1/100000

time performance of the system is assessed in order to generate “trade-off

of real time. (iii) Model for operational optimization;

surfaces” for the design objectives. This

simplified – typically a linearized version

is computationally extremely demanding.

of the nominal model – nests inside

Presenting the options to the decision

the nominal model and is used at each

maker is therefore an important part of the

time step to find the optimal sequence

methodology.

of actions over time horizons of hours;

5. Robustness/sensitivity analysis examines

the critical requirement is the speed

the extent of the changes imposed on the

of computation, which must be such

performance of the chosen design when

that the nominal model including this

the parameters in the dynamic process

model satisfies the requirements for

model are varied within their uncertainty

computational time.

range. 6. Validation implements the chosen design

Operational optimization is a dynamic pro-

with a more detailed process simulator in

gramming problem which, for nonlinear mod-

order to safeguard against phenomena

els, has been solved using the receding hori-

neglected in the model used in the

zon model-predictive control approach.

computationally heavy design optimization. In multi-objective design, the task is to obtain The problem formulation includes specifying

a process structure with good performance

first verbally and then mathematically the fol-

in the long-term in all respects. In papermak-

lowing:

ing, the processes considered are dynamic and, due to web breaks, stochastic. As the

(i) Process description

evolution of the process states is stochastic,

(ii) Metrics for process performance,

the process performance over a time period

including constraints and other limitations

is a random variable. In design optimization,

(iii) Degrees of freedom

the process performance is evaluated based

(iv) Reference process information

on long-term simulations with the nominal

(v) Long-term scenarios

model with nested operational optimization that includes the prediction model. In an ideal

Models are constructed at three levels:

case, the process is simulated over the entire life time; in practice, simulations span a peri-

(i) Validation model; detailed description

od of months up to a year. Thus each simula-

of the final design candidate, usually

tion provides a sample vector of the process

implemented on a platform such as

performance. The performance of the process

APROS; the critical requirement is that it

is calculated as the mean of the performance

must support both process and control/

samples from the design simulations.

operations modelling. (ii) Nominal model; somewhat simplified

In order to solve optimization problems while

process model (e.g. tank dynamics,

taking into account multiple objectives, multi-

separations with constant retention

objective optimization methods have to be ap-

parameters, etc.) used in estimating the

plied. These can be classified as a priori, a pos-

performance of a large number of design

teriori, interactive and no-preference methods

151

based on the time when the preference infor-

sists of three stages. The stages are classified

mation is taken into account. The interactive

as the pre-decision making stage, the decision

methods for solving multi-objective optimiza-

making stage, and the post-decision making

tion problems are very useful as they involve

stage. The decision maker is directly involved

the decision maker in the solution process

only in the decision making stage, whereas all

and enable learning about the problem. These

computationally intensive tasks are carried

methods elicit preference information from the

out in the pre- and post-decision making stag-

decision maker progressively. At each itera-

es. The stages along with their main compo-

tion, the decision maker is presented with one

nents and the dependences among them are

or more designs and asked to express prefer-

illustrated in Figure 1.

ences relative to them. Interactive methods facilitate comparing performance trade-offs.

In the pre-decision making stage an a poste-

However, in simulation-based optimization

riori method is applied to the multi-objective

and in design optimization in general, it is

design optimization problem to produce a set

time-consuming to compute new solution(s)

of Pareto optimal decision vectors that are

and the decision maker cannot be realistically

used to define the surrogate problem. In the

expected wait for the next results. Therefore,

decision making stage, the computationally

the multi-objective computationally intensive

inexpensive surrogate problem is tackled: the

problem was replaced by a surrogate problem

decision maker identifies the preferred per-

with the same performance objectives. The

formance vector. In the post-decision making

surrogate problem must be computationally

stage, the original multi-objective design opti-

inexpensive in order to eliminate waiting times

mization problem is solved in a scalarized form

in the interactive process. The use of a surro-

to project the objective vector (of the surro-

gate problem for real-life decision making con-

gate problem) preferred by the decision maker

Figure 1. A solution approach consisting of three stages (MO: multi-objective, SO: single objective).

152

to the Pareto optimal set of the original design

The Pareto optimal solutions should be pre-

optimization problem.

sented in a convenient and understandable way to reduce the cognitive load on the de-

The three-stage solution allows fluent interac-

cision maker when considering the trade-offs.

tion with the decision maker regardless of the

Therefore, the decision maker has to select the

computational intensiveness of the simulation

most comfortable visualization.

model. The solution process is motivated by the PAINT method to create a surrogate prob-

Interactive methods require active participa-

lem for decision making, and by the availability

tion of the decision maker. An example inter-

of multi-objective optimization methods such

active method is the NIMBUS method, which

as ParEGO and SMS-EGO that provide a finite

is implemented in the IND-NIMBUS software.

approximation to the Pareto optimal set of a

The graphical user interface of the NIMBUS

multi-objective optimization problem.

method is presented in Figure 4.

The decision maker requires visualization sup-

After selecting the design candidate, the ro-

port to deal with multiple conflicting objec-

bustness of the performance of the chosen

tives in their search for a preferred solution.

candidate with respect to the model simplifi-

For example, simple pairwise projections of

cations and parameter values used must be

the Pareto optimal solutions can be provided

analysed. Robustness describes the modelâ&#x20AC;&#x2122;s

to the decision maker, as shown in Figure 2.

ability to operate in different conditions where

The solutions for a problem with four objec-

the chosen model parameters are not exactly

tives can be presented as a 3D figure in which

correct. The robustness of the chosen opera-

the fourth objective is represented by different

tional optimization is examined by simulating

colours depending on its value (see Figure 3).

the process using different parameter values

Figure 2. Pairwise projections of objective functions

153

Figure 3. 3D Pareto optimal solutions representation, with fourth objective value shown in different colours.

in the simulator (nominal model) than in the

For example, a nominal quality value may have

operational optimizer (prediction model). The

been defined as a starting point for the design

parameter values are cross-studied in the sim-

analysis. This is achieved by a combination of

ulator and optimizer.

material property parameters. If the parameters are varied one at a time, the reference

The robustness of the design is studied by var-

point changes. Instead, they must be varied so

ying the nominal model parameters slightly and

that the nominal quality value is maintained.

studying the corresponding changes in performance. The degree of the â&#x20AC;&#x153;slight variationâ&#x20AC;? re-

Sensitivity analysis assumes linearity of the pro-

flects the uncertainty of the parameter. When

cess performance with respect to the param-

varying the parameters, it should be recog-

eters in the analysis range. A typical nominal

nized that there are constraints between them.

model for the design analysis includes 30-300 parameters, preventing the analysis of cross effects, which scales as the square of the number of parameters. In the paper production system, the parameters of the break probability model are based on rather vague assumptions. Thus, its robustness with respect to the break model parameters needs to be studied carefully. The nominal model used in the design optimization is based on approximations of the real system, thus it might contain certain inaccuracies. The validation model is as realistic a

Figure 4. Screen shot of the graphical user interface of the NIMBUS method in the IND-NIMBUS software.

154

model as possible, including more features of the real process. The objective of the validation model is to test with the final design how

sensitive the process performance estimates

The main dynamic control challenge is that, due

are to these finer details of the process.

to fractionation, there are two parallel material flow lines of TMP that need to be balanced

4.2 Concept cases

in dynamic conditions caused by, for example, web breaks and/or a variable amount of broke

Fines-coated LWC (concept case 1, CC1)

used in the base paper furnish. The material flow vector was divided into 17 components indicat-

The first concept studied was based on applying

ing the proportions of furnish components in the

a TMP fines fraction as a coating for LWC paper.

base paper and surface layers. A dynamic operational optimization was implemented with ob-

A dynamical model for CC1 was drawn up

jectives related to quality and constraints relat-

on the basis of the diagram shown in Fig-

ed to tower overflows/running empty.

ure 5. The economic performance assessment shows that radical improvements can

The dimensioning of the fractionation was giv-

be achieved only if the content of fines in the

en fixed. Structurally, one open question was

coating is high, e.g. 40%. As there is currently

where to direct the overflow from the fines

no unit process technology available for this,

chest, the options including the broke chests,

the unit process development must be accom-

mixing chest, TMP proportioning chest or TMP

panied with concept optimization.

tower. After initial assessments, the TMP tow-

Figure 5. Model for concept case 1. The key elements are fractionation of the TMP so that the fines fraction can be applied to the surface, and surface preparation with the fines-based â&#x20AC;&#x153;coating colourâ&#x20AC;?. Balancing the two parallel TMP lines (fibres and fines) in dynamic conditions (breaks, variable dosage of broke) are the main operational challenges, which also necessitate new chests in the system.

155

er was chosen due to the high consistency of

- Volume of a clear filtrate tower

the fines fraction and the consistency uniform-

- Short-term risk of tower overflow

ity problems presented by the other locations.

- Relative weighting of quality variations in operational optimization

The design was given five objectives:

Over 300 non-dominated solutions were gen- Investment costs (min)

erated in the simulations (stage 1, Figure 6).

- Average proportion of time spent in

Each simulation was run till first tower over/

uncoated breaks (min)

underflow or, at most, to a time correspond-

- Average time till volume overflows/empty (max)

ing to approximately 9 months of process op-

- Average deviation of light scattering

eration. Each design was simulated 80 times

coefficient from target value (min)

and the averages of the objective values were

- Average deviation of strength coefficient from target value (min)

computed for each design to determine nondominated solutions. The parallelized computation took some 13 days on a grid consisting

The design degrees of freedom were

of 160 computers (Kivikasa grid, University of

four tower volumes and two operational

Jyv채skyl채) using the parallelized Matlab com-

parameters:

putation tool. Illustrating the non-dominated points in a five-dimensional space of objec-

- Volume of a white water tower

tives is somewhat challenging. However, Fig-

- Volume of an uncoated broke tower

ure 6 gives these in projections to planes of

- Volume of a coated broke tower

two objectives at a time.

Figure 6. Projections of the non-dominated solutions to the planes of two objectives at a time.

156

The set of non-dominated solutions was used

selected by the decision maker over the non-

to create a surrogate problem using the PAINT

dominated solution set of the original problem.

method, which was solved by the NIMBUS method implemented in IND-NIMBUS soft-

The results were discussed, but no actual de-

ware. With NIMBUS the decision maker can

cision-making exercise was carried out. The

search for the most favourable design by ex-

following three points of criticism were raised:

pressing their preferences, by indicating the desired trade-off among the objectives (as in

- The non-dominated solutions do not have

Figure 4). When the most favourable design

the expected property that the sum of

in the objective space (of the surrogate prob-

water volumes would equal the sum of

lem) is found, then the closest objective vec-

broke volumes. This is probably because

tor of the original problem can be sought in

there was no constraint on water intake/

two senses: either the closest by to one of the

outflow from the balance area. This

non-dominated designs or closest by to the

emphasizes the importance of setting the

interpolated set of non-dominated solutions.

objectives at the design and at operational

The first option readily gives the design pa-

level so that they cover all aspects.

rameters corresponding to the objective vec-

- The designs were based on average values

tor of the surrogate problem selected by the

of objectives. As Figure 7 shows, the

decision maker, whereas the second requires

distributions of the objective values are

further simulations to find the projection of

rather wide. Therefore, a more appropriate

the objective vector of the surrogate problem

design would probably be based on a

Figure 7. Distribution of the objectives for a non-dominated design, 80 simulations. Wide distributions suggest that designs should be considered also from the x worst-case percentile approach.

157

percentile basis: if x percentage of the

increasing the filler content of fine paper from

worst cases are first eliminated from the

the current 30% to 40%. In the analysis it is as-

analysis, what is the remaining worst case.

sumed that the retention of binding filler in the

- The design aspects were focussed on issues

short circulation is 0.6 (corresponding typical-

of, at most, moderate economic interest (a

ly 0.25..0.3 first pass retention) and that all fill-

few million euros). This is because the degrees

ers leaving the short circulation area lose their

of freedom given were rather narrow, e.g.

binding capacity. A critical issue in this concept

the volume of the fractionation was fixed. In

is runnability. The break tendency was assumed

practical decision making, the main issue in

to be such that with a nominal (all filler binding)

CC1 would be the technical feasibility of the

recipe, the time spent in breaks is 3%, whereas

application of fines on the paper surface; this

with a realistic (non-binding filler recovered and

could not be analysed with the techniques

reused) recipe the figure is 7% on balance.

used in the optimization study. The analysis is based on a conventional fine A more general concern expressed was that as

paper mill layout. The degrees of freedom in

the approach hinges on process models, the ac-

the study were the buffer volume (broke and

curacy/reliability of the models should be as-

clear filtrate), disc filter capacity, and opera-

sessed and the sensitivity to the key model pa-

tional parameters. Either clear filtrate or white

rameters should always be analysed in detail.

water can be used for broke dilution. The main

Sensitivity analysis shows the most critical pa-

objectives were to minimize:

rameters to be those related to the break model. - Capital employed High filler content fine paper

- Loss of production time due to breaks - Variations in filler content

The second concept studied was based on fillers manipulated to form binding structures for

- Solids lost through the broke system (insufficient capacity)

Figure 8. Process model for the high filler content fine paper concept case. Two options for broke dilution are indicated.

158

A dynamic process model for seven material

The performance of the design alternatives was

components at 10 min time step was devel-

studied through simulations corresponding to

oped for process alternatives, see Figure 8.

one year of mill operation. The simulations were repeated ten times and the average was taken as

The operations were developed as dynamic

the performance vector. Initial sets consisting of

optimization, characterized by three param-

125/133 (dilution with clear filtrate/white water)

eters related to the aggressiveness of broke

Pareto optimal solutions were constructed for

volume management. Figure 9 shows two ex-

a range of performance values, see Table 1. The

treme ways of operation.

range was further narrowed on the basis of these

Figure 9. Two extreme ways to manage broke dosage. Top 4 curves: aggressive control causing variations but helping to manage volumes. Bottom 4 curves: conservative control, no variations but volume management problems.

159

results and 948/551 Pareto optimal solutions

If retention in the short circulation falls below

were constructed for a range of performance val-

0.6 (and fillers leaving short circulation lose

ues, see Table 2. Pairwise comparisons of these

their binding capacity), managing the quality

are presented in Figure 2 and a three-dimension-

and runnability of the system becomes very

al presentation with the fourth objective colour

difficult, even with large investments in buff-

coded in Figure 3 as examples of the methodol-

ering volumes and internal water purification.

ogy. The results can be analysed either by rotating the 3D presentation or through a surrogate

Folding boxboard with foam-formed middle ply

model and decision maker interaction through

The task was to design a production line for

the NIMBUS programme (Figure 4).

folding box board in which the middle ply is formed using a foam forming technique. Be-

The main observations are that at investments

cause there is no reference case of mill-scale

above EUR 9 million, operability becomes quite

foam forming, the technique was applied to a

good in all respects, whereas with invest-

mill with a traditional water forming process

ments below EUR 6 million good compromises

with the middle ply section modified to corre-

can be reached, but not completely problem-

spond to foam forming. Technical information

free operation. The results also show that with

of the reference line was provided by Mets채

constant investment the system with clear fil-

Board. Parameter information of the foam

trate dilution performs better than that with

forming technique was based on the laborato-

white water dilution.

ry and semi-pilot scale trials conducted at VTT Jyv채skyl채 as part of EffNet. As the study was initially resourced for only two application studies, the third case study was an add-on and thus not all steps of the methodology were worked through in detail. The case study developed a process model and operational optimization suited for design analysis, but no systematic construction of Pareto optimal designs was made.

Table 1. The initial performance range studied.

Figure 10 presents the process structure. The process corresponds to a normal threeply board line. The most significant revisions are made to the approach system of the middle ply and to the water system. The foaming chemical is mixed with the stock just before the forming section. The chemical retains its foaming capacity after the forming section, with most of the chemical ending up in the water system. To avoid foaming in the water towers, defoamer is used in the disc filter feed. However, defoamer in the water cir-

Table 2. Narrowed performance space, limited to EUR 5.5-7.5 million investment.

160

culation also decreases foaming capacity in the forming section. In the model, any single

Figure 10. Process model for the folding boxboard concept with foam-formed middle ply.

flow may include only either foaming chemi-

foaming chemical, defoamer and process vol-

cal or defoamer, i.e. the reaction between the

umes and retentions in separation processes.

chemicals is assumed to be complete. Foam-

istic time constant of 30 minutes.

4.3 Workflow in conceptual process design based on modelling and multiobjective optimization

As the phenomena and possibilities of the

The bi-level multi-objective optimization (BLMOO)

foam forming were partly unknown, the dry

method in EffNet WP9 was applied to the design

solids content after the forming section can be

of paper manufacturing facilities. This subsec-

parametrically tuned in the model to anything

tion proposes a business process guideline for

between 8% and 25%.

a business process in a real-scale business en-

ing chemical is dosed before the forming section using a simulated control loop with a real-

vironment. The proposed business process was In the model, each flow was defined as a flow

evaluated by expert interviews and critical suc-

vector of fifteen elements: water, CTMP, MFC,

cess factors based on the concept case projects.

filler, pigment, foaming chemical, defoamer, broke (two pulps, CTMP, MFC), broke filler and

The conventional process plant design process

broke pigment. The dynamic process model

is described with the linear waterfall model.

was based on a steady-state model in which

The design process consists of problem anal-

the nominal state was defined.

ysis, conceptual design, detailed engineering and construction. The BLMOO method mainly

The simulator can easily be modified to incor-

addresses the conceptual design phase.

porate future changes in the model and operational control. Figure 11 shows a simulation case

Current practice in forest industry process en-

study. This model and the operational optimi-

gineering is almost solely based on engineering

zation within it can be used to compare differ-

experience. Mass and energy balances of oper-

ent process parameterizations, both concerning

ating points can be defined with steady-state

161

Figure 11. An example of simulated dynamics of the folding boxboard case.

Figure 12. BLMOO design adds the optimization and modelling organization to the conventional design organization consisting of the end user and engineering. BDM = business decision maker, TDM = technology decision maker, BC = business consultant, D = designer, A = analyst, VM, M1, M2, M3 = modellers.

162

simulation. Dynamic simulation is used in the

concepts are designed simultaneously, which

design of unit processes, but less in the design

leads to more systematic trade-offs.

of the process as whole. The process structure is designed in general first and the operation of

The BLMOO method introduces a new element

the plant after that. BLMOO studies the options

to the engineering organization, the optimi-

more widely and may consider various busi-

zation and modeling organization (Figure 12).

ness possibilities in the design. Plant-wide sim-

In particular, the key role of the analyst (A) is

ulation enables the validation of process struc-

added. Furthermore, as the optimization task

ture and control concepts before an investment

requires additional nominal and predictive

decision and therefore reduces risks. In BLMOO

models, two modellers are added (M2 and M3).

method, both the process structure and control

It should be noted that whereas the designer

Figure 13. Workflow in BLMOO design.

163

mostly communicates with the technical deci-

For technical and economic credibility of the

sion maker and the business consult with the

multiobjective bilevel design methodology in-

business decision maker, the analyst must be

cluding both structural and operational as-

proficient in both technical and business mat-

pects is crucial for its rapid uptake. The con-

ters in order to form the optimization task and

cept case studies within EFFNet serve three

communicate the results. The iterative na-

exploitation/impact purposes. Firstly, the con-

ture of the design process cannot be avoided,

cept is expected to be essentially improved

which leads to close cooperation between the

by such an analysis, and made more rapidly

designer, analyst and modellers. These can

transferable to the implementation stage as

then share common knowledge about process

operational aspects are addressed early on.

design, mathematical formulation, modelling

Secondly, the case studies demonstrate the

and optimization, which constitutes a critical

benefits of the approach to the end users and

requirement for the BLMOO as business; in

hence create markets for the design method-

particular as the changes in the interface be-

ology as a service. Thirdly, the concept analy-

tween the customer organization and engi-

sis is closely monitored in order to define the

neering organization need to be kept minimal

work flows and practices involved in the de-

in order to be able to compete with engineer-

sign approach, thus creating the way of work-

ing organizations offering traditional design.

ing and business model for provision of the

The workflow of the BLMOO method is de-

model-based design optimization as a service.

scribed in Figure 13. This further emphasizes the role of the Analyst as being capable

Furthermore, the design methodology is quite

of communicating about business, process,

generic and can be applied not only to the de-

modelling and optimization issues.

sign of papermaking systems but also to pulp production and biointegrates. Cooperation be-

The organizational structure and workflow pre-

tween all FIBIC programmes related to new

sented here provide the basis for a business

production systems is a further exploitation

model for BLMOO consultancy as a service. It is

avenue to be examined.

therefore concluded that the main customer of the service business is the engineering organi-

The design methodology has been of practical

zation, which may be a consultant to the end

importance also when paving the way for the

customer or, in some cases, the engineering or-

uptake of new process technology. The meth-

ganization within the end customer.

od reveals the key issues of concern when implementing new technologies in new environ-

5. Exploitation plan and impact of results

ments, thus guides the research to cover all relevant aspects. The operational optimization methodology can be readily implemented on existing production systems.

This study addresses the key economic challenge of the forest-based chemical industries â&#x20AC;&#x201C; capital intensiveness. The results are considered essential to the renewal of the industry and are expected to contribute strongly to the selection of future production concepts and their unit process technology.

164

6. Networking The research was carried out jointly by research organisations and Finnish forest cluster companies. Table 3 presents the research partners and their roles.

Table 3. Partner organisations and their research roles.

Partner

Role

Tampere University of Technology,

Work Package Manager. Task Leader for concept case

Department of Automation Science and

studies. Formulation of the design optimization prob-

Engineering

lem and the related operational optimization problem, participation in solving the case design problems.

Aalto University, Information

Task Leader for work flow analysis. Design work flow

Technology in Automation

analysis and development of a new work flow for model-based multi-objective, optimized conceptual design.

University of Eastern Finland,

Modelling for the design case studies, participation in

Paper Physics

solving the case design problems.

University of Jyv채skyl채,

Task Leader in multi-objective optimization methods,

Industrial Optimization

formulation and solvers. Participation in solving the design case problems.

VTT Technical Research Centre of

Modelling for the design case studies, participation in

Finland, Systems Dynamics

solving the case design problems, design validation.

165

7. Publications and reports

Ropponen, A., Ritala, R., Pistikopoulos, E.N., “Optimization issues of the broke manage-

Linnala, M., "Optimization and simulation

ment system in papermaking”, Computers &

tools in paper machine concept design", PaP-

Chemical Engineering, 35, 2510-2520 (2011)

SaT/FPIRC Annual Seminar, 22.-24.8.2011, Lappeenranta, Finland

Ropponen, A., Rajala, M., Ritala, R., "Multiobjective optimization of the pulp/water stor-

Linnala, M., Hämäläinen, J., "Improvement of

age towers in design of paper production sys-

the cost efficiency in papermaking with opti-

tems", ESCAPE-21 conference, Thessaloniki,

mization tools", was presented at PAPTAC Pa-

Greece, June 2011.

per week, 2011. Ropponen, A., Ritala, R., "Multiobjective opLinnala, M., Hämäläinen, J., "Improvement of

timization of process design and operation: a

the cost efficiency in papermaking with op-

case study on paper production", 21st Interna-

timization tools", The Journal of Science and

tional Conference on Multiple Criteria Decision

Technology for Forest Products and Process-

Making, 13-17.6.2011, Jyväskylä, Finland

es, 1(2), 71-76, 2011. Ropponen, A., Ritala, R., "Specifying risk levLinnala, M., Hämäläinen, J., "Model-based op-

el for constraint violation in stochastic system

timization in papermaking process design",

- a case study on papermaking" ESCAPE-22,

Progress in Paper Physics Seminar, 5.-8.9.2011,

London, UK, June 2012.

Graz, Austria Ropponen, A., Ritala, R., "Operational optimiLinnala, M., Hämäläinen, J., "Bi-level optimi-

zation of flow management in papermaking”,

zation in papermaking process design", Nordic

Control Systems 2012, April 2012, New Orleans,

Pulp and Paper Research Journal, 27(4), 774-

USA.

782, 2012. Ruuska, S., Miettinen, K., Wiecek, M., "ReforLinnala, M., Madetoja, E., Ruotsalainen, H.,

mulations for Bilevel Multiobjective Optimiza-

Hämäläinen, J., "Bi-level optimization for a dy-

tion", 21st International Conference on Multiple

namic multiobjective problem", Engineering

Criteria Decision Making, 13-17.6.2011, Jyväsky-

Optimization, 44(2), 195-207, 2012.

lä, Finland

Miettinen, K., Steponavice, I., and Ruuska,

Ruuska, S., Miettinen, K., Wiecek, M., "Con-

S., Challenges of Multiobjective Optimization

nections between Single-level and Bilevel

in Integrated Design and Control: Case Study

Multiobjective Optimization", Journal of Opti-

in Paper Making, 17th International Confer-

mization Theory and Applications, 153(1), 60-

ence on Mathematical Modelling and Analysis

74, 2012

(MMA2012), Tallinn, Estonia, June 6-9, 2012 Ruuska, S., Miettinen, K., Constructing EvoRajala, M., Ropponen, A., Ritala, R., "Multi-ob-

lutionary Algorithms for Bilevel Multiobjec-

jective supervisory control of furnish flows",

tive Optimization, in "Proceedings of the 2012

presented at PAPTAC Paper week, 2011

IEEE World Congress on Computational Intelligence", IEEE Press, 374-380, 2012.

166

Ruuska, S. and Miettinen, K., Constructing

Steponavice, I., Ruuska, S., and Miettinen, K.,

Evolutionary Algorithms for Bilevel Multiobjec-

Decision making in a multi-objective paper mill

tive Optimization, 2012 IEEE Congress on Evo-

design problem, 25th European Conference

lutionary Computation (CEC 2012), Brisbane,

on Operational Research (EURO2012), Vilnius,

Australia, June 10-15, 2012

Lithuania, July 8-11, 2012.

Savolainen, J., "Global Sensitivity Analysis of a

Steponavice, I., Ruuska, S., and Miettinen,

Feedback Controlled Stochastic Process Mod-

K., On Challenges in Simulation-based Multi-

el", Simulation Practice and Theory, vol. 36,

objective Optimal Design with an Application

August 2013, pp. 1-10.

in Paper Industry, submitted for publication in Computer-Aided Design

Savolainen, J., Linnala, M., "Modelling issues in multiobjective bi-level optimization of pro-

Strömman, M., Seilonen, I., Koskinen, K., “Chal-

cess design and operations", 21st International

lenges in Applying Optimization in the Design

Conference on Multiple Criteria Decision Mak-

of Continuous Processes – Case: Collaborative

ing, 13-17.6.2011, Jyväskylä, Finland.

Optimizing Design of Pulp Fractionation Process”, SIMULTECH 2012 (2st International Con-

Savolainen, J., Saarela, O., Lappalainen, J. and

ference on Simulation and Modeling Method-

Kaijaluoto, S., 2011, "Assessment method of dy-

ologies, Technologies and Applications. Rome,

namic, stochastic process models with an appli-

Italy 28-31, July 2012

cation to papermaking", Nordic Pulp and Paper Research Journal, vol. 26, no. 3, pp. 336-348.

Strömman, M., Seilonen, I., and Koskinen, K.,”Collaborative optimization based design

Steponavice, I., Miettinen, K., “On Multiob-

process for process engineering,” in Simula-

jective Robustness for Simulation-Based Op-

tion and Modeling Methodologies, Technolo-

timization”, 21st International Symposium on

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Efficient Networking Towards Novel Products and Processes (EffNet) is one of FIBICÂ´s research programmes. The focus of the EffNet programme is on developing radically new energy- and resource-efficient web production technologies and designing nanocellulose-based production concepts and novel, innovative products. The overall goal of the EffNet programme was to develop sustainable solutions to ensure the leading position of the Finnish forest cluster in the large-scale production of fibre-based printed and packaging products.