Paper Chemistry
To Lesley Joy and Jennifer Anne
PAPER CHEMISTRY
Edited by
J.e. ROBERTS
Head of Department of Paper Science
University of Manchester Institute of Science and Technology
Blackie
Glasgow and London
Published in the USA by
Chapman and Hall
New York
Blackie & Son Ltd.
Bishopbriggs, Glasgow G64 2NZ
and
7 Leicester Place, London WC2H 7BP
Published in the USA by
Chapman and Hall
a division of Routledge, Chapman and Hall, Inc.
29 West 35th Street, New York, NY 10001-2291
© 1991 BI!\ckie & Son Ltd
First published 1991
Softcover reprint of the hardcover 1st edition 1991
All rights reserved.
No part of this publication may be reproduced.
stored in a retrieval system. or transmitted.
in any form or by any means-graphic,
electronic or mechanical, including photocopying,
recording. taping-without the
written permission of the Publishers
British Library Cataloguing in Publication Data
Paper chemistry.
1. Paper. Production
I. Roberts, J.e.
676.2
ISBN-13:978-94-011-6476-4
Library of Congress Cataloging-in-Publication Data
Paper chemistry ! edited by J.e. Roberts.
p. cm.
Includes bibliographical references and index.
ISBN-13:978-94~0l1~47_6-4 e-ISBN-13: 978-94-011~474-0
DOl: lO.l07/978-94-011~474-0
1. Papermaking-Chemistry. I. Roberts, J.e. (John Christopher)
TS1120.P37 1991
676'.2-dc20 90-27806
CIP
Typesetting by Thomson Press (India) Ltd, New Delhi
Preface
Although the title of this book is Paper Chemistry, it should be considered as a
text about the chemistry of the formation of paper from aqueous suspensions
of fibre and other additives, rather than as a book about the chemistry of the
raw material itself. It is the subject of what papermakers call wet-end
chemistry. There are many other excellent texts on the chemistry of cellulose
and, apart from one chapter on the accessibility of cellulose, the subject is not
addressed here. Neither does the book deal with the chemistry of pulp
preparation (from wood, from other plant sources or from recycled fibres), for
there are also many excellent texts on this subject.
The formation of paper is a continuous filtration process in which cellulosic
fibres are formed into a network which is then pressed and dried. The
important chemistry involved in this process is firstly the retention of colloidal
material during filtration and secondly the modification of fibre and sheet
properties so as to widen the scope for the use of paper and board products.
As is the fashion these days, each chapter is written by an internationally
recognised expert in the field, and my thanks are extended to all of the
contributors. for their hours of patient and unseen research during the
preparation of their manuscripts.
The introductory chapters on the surface chemistry and electrokinetics of
the papermaking system are designed to lay the foundation for the under-
standing oflater chapters in which surface chemistry and colloidal phenomena
are of central importance. The subsequent chapters deal with retention aid
chemistry and our current understanding of the mechanism of action of
polyelectrolytes and with paper modification by chemical addition. The
principles of the chemical systems available for wet- and dry-strength
improvement, the chemistry of control of water penetration (sizing) in both
acidic and basic conditions, dyeing and optical brightening, and pigment
particle addition for the modification of optical properties are discussed. The
measurement and control of the chemical processes is the subject of the
penultimate chapter, and the final chapter deals with practical applications of
paper chemistry under real conditions.
The book is designed to accentuate the chemical principles involved in the
papermaking system rather than to be a compendium of additives and, as
such, it should be useful to the paper-mill chemist and to students and
researchers in the field. Those chemical industries supplying the paper
industry should find the book a useful reference source.
J.C.R.
vi PREFACE
Acknowledgement
The editor wishes to acknowledge the contributions made to this book by Ms
E.W. Hughes (editorial assistance), and Mrs E. Rodgers and Mr Z. Yajun (for
assist~nce with some of the diagrams).
Contributors
Dr CO. Au Paper Chemicals Division, Eka Nobel Ltd, Blackburn,
Lancashire BB1 5RP, UK
Dr R. Bown English China Clays Research Centre, St. Austell
Cornwall PL25 4DJ, UK
Dr N. Dunlop-Jones International Business Sector - Paper, Sandoz
Chemicals Ltd, Horsforth, Leeds LS18 4RP, UK
Dr J.M. Gess Weyerhauser Company, Tacoma, Washington 98477,
USA
Dr D. Horn Department of Polymer Physics, Polymer Research
Division, BASF, 6700 Ludwigshafen, Germany
Dr T. Lindstrom Mo Och Domsjo AB, MoDo Development Centre,
Ornskoldsvik, Sweden
Dr F. Linhart Applications Department Paper, Marketing Colorants
and Process Chemicals, BASF, 6700 Ludwigshafen,
Germany
Dr J. Marton Consultant and Adjunct Professor, State University of
New York, Syracuse, USA
Dr S.G. Murray International Business Sector - Paper, Sandoz
Chemicals Ltd, Horsforth, Leeds LS18 4RP, UK
Professor F. Onabe Division of Pulp and Paper Science, University of
Tokyo, Bunkyo-ku, Tokyo 113, Japan
Dr G.A.F. Roberts Department of Chemistry and Physics, Nottingham
Polytechnic, Nottingham, UK
Dr J.C Roberts Department of Paper Science, UMIST, PO Box 88,
Manchester M60 1QD, UK
Contents
1 Applications of paper chemistry 1
J.C. ROBERTS
1.1 Introduction 1
1.2 Paper chemical use in specific product grades 3
1.2.1 Newsprint 4
1.2.2 Printing and writing grades 4
1.2.3 Tissue and sanitary 5
1.2.4 Packaging and board 5
1.3 Trends in paper chemical use 6
1.3.1 Deinking chemicals 6
1.3.2 Defoamers 6
1.3.3 Retention and drainage aids 7
1.3.4 Dry-strength additives 7
1.3.5 Sizing 7
1.3.6 Wet-strength additives 8
1.3.7 Wet-end chemistry control 8
References 8
2 Accessibility of cellulose 9
G.A.F. ROBERTS
2.1 Introduction 9
2.2 The concept of accessibility 9
2.3 Determination of crystallinity/accessibility of cellulose 12
2.3.1 Physical methods 13
2.3.2 Chemical methods 15
2.3.3 Sorption methods 17
2.3.4 Comparison of results from different techniques 19
References 22
3 Electrokinetics of the papermaking industry 25
T. LINDSTROM
3.1 Introduction 25
3.2 The electrical double layer 25
3.3 Origin of the charge on papermaking fines, fibres, mineral pigments and
fillers 28
3.4 The classical coagulation theory, DLVO theory 30
3.5 Electrophoresis and electrokinetic phenomena - calculation of the zeta
potential 32
3.6 Some experimental methods of determining the zeta potential 34
3.6.1 Microelectrophoresis 34
3.6.2 Electro-osmosis 37
3.6.3 Streaming potential 38
3.7 Polyelectrolyte titrations 39
x CONTENTS
3.7.1 General principles 39
3.7.2 Determination of surface charge of solids by means of colloid
titration 40
3.7.3 Instrumentation of colloid titration 42
References 42
4 Retention aids 44
D. HORN and F. LINHART
4.1 Introduction 44
4.2 The chemical nature of retention aids 45
4.2.1 Inorganic retention aids 45
4.2.2 Retention aids based on natural, organic raw materials 46
4.2.3 Synthetic, water-soluble organic polymers 46
4.3 Mode of action of retention aids 51
4.3.1 Characterisation of retention aids 52
4.3.2 Adsorption on interfaces 53
4.3.3 Electrokinetic effects of polymer adsorption 55
4.3.4 Polymer-induced flocculation 55
4.4 Concluding remarks 59
References 60
5 Dry-strength additives 63
J. MARTON
5.1 Introduction 63
5.2 Cationic starch 65
5.2.1 Use of the starch adhesive 65
5.2.2 Cationic starch preparations 65
5.2.3 Mechanism of strength development 66
5.2.4 Highly filled papers 66
5.2.5 Adsorption of starch 67
5.2.6 Adsorption of cationic starch on furnish components 69
5.2.7 Distribution of cationic starch in the furnish 70
5.3 Vegetable gums 72
5.3.1 Mechanisms 72
5.4 Polyacrylamide resins 73
5.4.1 Mechanisms 74
References 75
6 Wet-strength chemistry 76
N. DUNLOP-JONES
6.1 Introduction 76
6.2 Mechanisms of wet-strength development 77
6.3 The chemistry and application of commercial wet-strength resins 77
6.3.1 Urea-formaldehyde resins 78
6.3.2 Melamine-formaldehyde resins 80
6.3.3 Epoxidised polyamide resins 82
6.3.4 Glyoxalated polyacrylamide resins 85
6.3.5 Comparison of properties of the predominant commercial resins 89
6.3.6 Polyethylenimine resins 89
6.3.7 Dialdehyde starch 90
6.3.8 Other wet-strength resins 92
6.4 Testing of wet-strength papers 92
CONTENTS xi
6.5 Assessing the efficiency of wet -strength resins 93
6.6 Future trends 94
References 95
7 The sizing of paper with rosin and alum at acid pHs 97
J.M. GESS
7.1 Introduction 97
7.2 Background 97
7.2.1 Sizing 97
7.2.2 History of rosin in papermaking 97
7.2.3 The forms of rosin used in papermaking 98
7.3 Sizing theories 102
7.3.1 Structural considerations in sizing 102
7.3.2 The interaction between rosin and cellulose fibres leading to sizing 104
7.3.3 Implications of the strong bond/weak bond theory 109
7.4 Summary 111
References 112
8 Neutral and alkaline sizing 114
J.C. ROBERTS
8.1 Introduction 114
8.2 Reasons for changing to neutral sizing 118
8.3 Alkyl ketene dimers 118
8.3.1 Synthetic development 118
8.3.2 Emulsion preparation and retention 119
8.3.3 Reactivity 120
8.3.4 Practical considerations 123
8.4 Alkenyl succinic anhydride 124
8.4.1 Synthetic development 124
8.4.2 Emulsification 125
8.4.3 Hydrolytic stability 125
8.4.4 Practical considerations 128
8.5 Comparisons between AKD and ASA sizing 128
References 130
9 Dyes and fluorescent whitening agents for paper 132
S.G. MURRAY
9.1 Introduction 132
9.2 Basic concepts of colour 133
9.2.1 Light absorption and reflection 133
9.2.2 Colour and constitution 134
9.3 Classification of dyes and pigments 136
9.3.1 Colour index classification 136
9.3.2 Classification by chemical structure 144
9.4 Dyes and pigments for paper 146
9.4.1 Development of paper dyes 146
9.4.2 Special requirements for paper dyes 146
9.5 Application of dyes and pigments to paper 149
9.5.1 Theory of attractive forces between dyes and cellulose molecules 150
9.5.2 Influences <;lfvarious factors used in the colouration of paper stock 151
9.5.3 Common problems and possible causes and cures 153
xii CONTENTS
9.5.4 Printing of paper 155
9.6 Fluorescent whitening agents (FW As) 155
9.6.1 Concepts of fluorescence ISS
9.6.2 Chemical constitution of FWAs 156
9.6.3 Structure and fluorescence 157
9.6.4 Application of FWAs to paper 158
References 161
10 Physical and chemical aspects of the use of fillers in paper 162
R. BOWN
10.1 Introduction 162
10.2 Filler properties 163
10.2.1 Particle size and shape 163
10.2.2 Surface chemistry 167
10.3 Retention 170
10.3.1 Mechanical entrapment 170
10.3.2 Electrokinetic effects 171
10.4 The effect of filler on paper properties 177
10.4.1 Interaction between filler and fibre 179
10.4.2 The intrinsic properties of fillers 187
10.5 General summary 194
References 196
11 Measurement and control 198
F.ONABE
11.1 Introduction 198
11.2 Current status of wet-end chemistry measurement 199
11.3 Problems in measurement and control in wet-end chemistry 200
11.3.1 Colloid chemistry factors 200
11.3.2 Sensor technology factors 200
11.3.3 Control technology factors 200
11.4 On-line wet-end chemistry instrumentation 201
11.4.1 Dissolved inorganics 202
11.4.2 Dissolved organics 202
11.4.3 Flow rates 202
11.4.4 Solid consistency measurements 202
11.4.5 Other measurement techniques 203
11.5 Process control in wet-end chemistry 204
11.6 On-line retention monitoring systems 207
11.6.1 Kajaani RM-200 system 207
11.6.2 Chemtronics 4000 system 208
11.7 Monitoring of on-line surface charge 210
11.8 Methodology for complete automatic retention control 211
11.8.1 Design of control loops for retention control 211
11.8.2 Selection of monitoring systems and sensors 213
11.8.3 Development of computerized retention control systems 213
11.9 Applicability of new sensing devices and techniques 214
11.9.1 Flow visualisation techniques 214
11.9.2 Opto-electric sensing devices 214
11.9.3 Ultrasonic sensing devices 214
11.9.4 Magnetic sensing devices 215
11.9.5 Ion-electrode sensing devices 215
11.1 0 Concluding remarks 215
References 215
CONTENTS xiii
12 Practical applications of paper chemistry 217
c.o. AU
12.1 Introduction 217
12.2 Retention 217
12.3 Starch 219
12.4 Sizing 223
12.5 Deposit control 224
12.6 Difficulties and limitations of practical applications 227
References 228
Index 231
