Table Of ContentChemistry and Technology
of Epoxy Resins
Chemistry and Technology
of Epoxy Resins
Edited by
BRYAN ELLIS
Department of Engineering Materials
University of Sheffield
m
SPRINGER-SCIENCE+BUSINESS MEDIA, B.V.
First edition 1993
© Springer Science+Business Media Dordrecht 1993
Originally published by Chapman & Hali in 1993
Softcover reprint ofthe hardcover lst edition 1993
Typeset in 1O/12pt Times by EJS Chemical Composition, Bath
ISBN 978-94-010-5302-0 ISBN 978-94-011-2932-9 (eBook)
DOI 10.1007/978-94-011-2932-9
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Preface
Epoxy resins have been commercially available for about 45 years and now
have many major industrial applications, especially where technical
advantages warrant their somewhat higher costs. The chemistry of these
resins is fascinating and has attracted study by many very able scientists. The
technological applications of the epoxy resins are very demanding and there
are many new developments each year.
The aims of the present book are to present in a compact form both
theoretical and practical information that will assist in the study, research
and innovations in the field of epoxy resin science and technology. The
literature on epoxy resins is so vast that it is not possible to be encyclopaedic
and that is not the function of the present text. It is the editor's hope that the
selection of topics discussed will provide an up-to-date survey. There is some
overlap in the chapters but this is minimal and so each chapter is essentially
self contained.
As with all chemicals there are toxicological and other hazards. These are
not dealt with in this text since a little knowledge can be dangerous, but
material supplied can provide information regarding any safety precautions
that may be necessary. However, often these precautions are not onerous
and epoxy resins, or more specifically the hardeners, can be handled readily.
It is hoped that this text will provide an up-to-date outline of the science
and technology of epoxy resins and stimulate further research into unsolved
problems and assist further technological developments.
Bryan Ellis
Acknowledgements
As editor, I would like to thank all my co-authors for their contributions
without which there would be no textbook. I am grateful to the secretarial
staff of the Department of Engineering Materials, University of Sheffield
for their assistance. Finally, but not least, to the editorial staff of Blackie
who have transformed the manuscripts into a very well produced book.
B.E.
Note
For ease of reference a general index and a separate index of curving agents and hardeners
are provided.
Contents
1 Introduction to the chemistry, synthesis, manufacture and
characterization of epoxy resins 1
B. ELLIS
1.1 Epoxy resins 1
1.2 The chemistry of the epoxy group 7
1.3 The synthesis and manufacture of epoxy resins 14
1.3.1 Synthesis of epoxy compounds 14
1.3.2 Epoxy resins manufactured from epichlorohydrin 16
1.3.3 Oxidation of unsaturated compounds 26
1.4 Characterization of uncured epoxy resins 29
1.4.1 Chemical analysis 29
1.4.2 Quantitative analysis 30
1.4.3 Molecular structure 32
1.4.4 Physical properties 33
References 35
2 Curing agents for epoxy resins 37
W.R. ASHCROFf
2.1 Introduction 37
2.2 Nitrogen-containing curing agents 38
2.2.1 Aliphatic amines and derivatives 38
2.2.2 Cycloaliphatic polyamines and derivatives 51
2.2.3 Aromatic polyamines and derivatives 54
2.2.4 Catalysts and co-curing agents 56
2.2.5 Hydrazine and hydrazides 60
2.3 Oxygen-containing curing agents 60
2.3.1 Carboxylic acids and anhydrides 60
2.3.2 Phenol formaldehyde resins 65
2.3.3 Amino formaldehyde resins 66
2.4 Sulphur-containing curing agents 67
2.4.1 Polysulphides 68
2.4.2 Polymercaptans 68
2.5 Miscellaneous curing agent types 68
2.5.1 Amine-boron trihalide complexes 68
2.5.2 Quaternary phosphonium salts 69
2.5.3 Cationic salts 69
2.6 Summary 70
References 70
3 The kinetics of cure and network formation 72
B. ELLIS
3.1 Cure of epoxy resins 72
3.2 Gelation, network structure and glass transition temperature 74
viii CONTENTS
3.2.1 Branching theory 75
3.2.2 The glass transition 81
3.3 Techniques for monitoring cure 83
3.3.1 Monitoring cure 83
3.3.2 Direct assay of the concentration of reactive groups 84
3.3.3 Thermal analysis 86
3.3.4 Rheological changes during cure 87
3.4 Kinetics of cure 89
3.4.1 Introduction 89
3.4.2 Amine-curing agents 90
3.4.3 Carboxylic acid anhydrides 98
3.4.4 Diffusion control 99
3.5 Effect of cure on mechanical and related properties 102
3.5.1 Introduction 102
3.5.2 Glassy moduli 104
3.5.3 Stress-strain curves and visco-elastic behaviour 106
3.5.4 Visco-elastic properties 109
3.5.5 Physical ageing 110
References 113
4 Additives and modifiers for epoxy resins 117
S.J. SHAW
4.1 Introduction 117
4.2 Diluents 117
4.2.1 Non-reactive diluents 118
4.2.2 Reactive diluents 118
4.3 Fillers 120
4.3.1 Physical/mechanical properties 121
4.3.2 Thermal characteristics 122
4.3.3 Shrinkage 124
4.3.4 Electrical conductivity 124
4.3.5 Viscosity 124
4.3.6 Toughness 125
4.4 Resinous modifiers 126
4.5 Flexibilisers/plasticising additives 128
4.5.1 Plasticisers 128
4.5.2 Reactive flexibilising additives 128
4.6 Elastomeric modification 131
4.6.1 Types of elastomeric modifiers 131
4.6.2 Compatibility and morphology 132
4.6.3 Toughening mechanisms 137
4.6.4 The hybrid modification approach 138
4.7 Thermoplastic modification 138
4.8 Miscellaneous additives 140
References 142
5 Fracture behaviour of epoxy resins 144
W.J. CANTWELL and H.H. KAUSCH
5.1 Introduction 144
5.2 Linear elastic fracture mechanics (LEFM) 145
5.2.1 The G approach 146
5.2.2 The K approach 149
5.2.3 Crack opening displacement 150
5.3 Deformation mechanisms 150
CONTENTS ix
5.4 Modes of crack propagation 152
5.4.1 Stable brittle propagation 153
5.4.2 Unstable brittle propagation 154
5.4.3 Stable ductile propagation 156
5.5 Effect of test conditions 156
5.5.1 Temperature 156
5.5.2 Loading rate 158
5.6 Microstructural effects 159
5.7 Fractography of epoxy resins 161
5.8 Toughening strategies for epoxy resins 165
5.8.1 Mineral filler-modified epoxies 165
5.8.2 Thermoplastic-modified epoxies 166
5.8.3 Rubber-modified epoxies 167
5.8.4 Effect of particle size and volume fraction 169
5.8.5 Hybrid systems 171
5.9 Conclusions 172
References 172
6 Electrical properties of epoxy resins 175
G.P. JOHARI
6.1 Introduction 175
6.2 Physical changes during the epoxy curing 176
6.3 Theoretical formalism for electrical properties 177
6.4 Dielectric effects of sol-gel-glass conversion 182
6.5 Ionic conductivity and sol-gel conversion 189
6.6 Time and temperature evolution of the dielectric properties 191
6.7 Chemical kinetics and dielectric behaviour 194
6.8 Curing and the high-frequency relaxation process 196
6.9 Ageing effects on electrical properties 200
6.10 Electrical applications of epoxy resins 203
References 204
7 Epoxy resin adhesives 206
S.J. SHAW
7.1 Introduction 206
7.2 Theories of adhesion and wetting phenomena 207
7.2.1 Theories of adhesion 208
7.2.2 Wetting 210
7.3 Substrates and surface pretreatments 213
7.3.1 Solvent cleaning 214
7.3.2 Mechanical abrasion 214
7.3.3 Chemical pretreatment 215
7.3.4 Primers 217
7.4 Methods oftest 218
7.4.1 Conventional test techniques 219
7.4.2 Fracture mechanics approach 221
7.4.3 Environmental testing 222
7.5 Epoxy adhesive formulation 225
7.6 Properties of adhesive joints 228
7.6.1 Bulk properties of epoxy adhesive 229
7.6.2 Adhesive joint mechanical properties 233
7.7 Environmental effects 238
7.7.1 Introduction 238
7.7.2 Moisture-related effects 239
x CONTENTS
7.7.3 Failure mechanisms 240
7.7.4 Approaches to improved durability 243
7.7.5 Other hostile environments 251
7.8 Applications 252
References 253
8 Composite materials 256
F.R. JONES
8.1 Introduction 256
8.2 Fibre reinforcements 256
8.2.1 Manufacture of carbon fibres from polyacrylonitrile (PAN) precursors 259
8.2.2 Aramid fibres 263
8.2.3 Glass fibres 265
8.3 Fabrication of composites 267
8.3.1 The reinforcement form 267
8.3.2 Prepreg mouldings 267
8.3.3 Matrices for fibre composites 269
8.4 Mechanical properties of unidirectional laminates 276
8.4.1 Longitudinal modulus, E, 276
8.4.2 Longitudinal tensile strength, alll 277
8.4.3 Transverse modulus, E 280
t
8.4.4 Transverse strength, a 281
tll
8.4.5 Off-axis properties 283
8.5 Failure process in laminates 284
8.5.1 Crossplylaminates 284
8.5.2 Constraint cracking 287
8.5.3 Epoxy resin matrix failure strain 287
8.5.4 Thermal strains in crossply composites 287
8.5.5 Poisson-generated stresses and longitudinal splitting 289
8.5.6 Angle ply laminates 289
8.5.7 Discontinuous fibre composites 290
8.6 Effect of moisture on the performance of epoxy resins 290
8.6.1 Moisture absorption kinetics 291
8.6.2 Effect of resin structure 293
8.6.3 Effect of moisture on thermal residual strains 295
8.6.4 The combined effect of humidity and thermal excursions 296
8.6.5 Thermal spiking 297
8.7 Selection principles 298
8.8 Conclusions 298
8.9 Glossary of symbols 299
References 300
9 Coatings and other applications of epoxy resins 303
X.M. CHEN and B. ELLIS
9.1 Introduction 303
9.2 Surface coatings 308
9.2.1 Introduction 308
9.2.2 Surface preparation and primer 310
9.2.3 Solution coatings 311
9.2.4 Dip coats 313
9.2.5 Epoxy emulsions and other water-based coatings 314
9.2.6 Powder coatings 316
CONTENTS Xl
9.3 Industrial and related applications 318
9.3.1 Tooling 318
9.3.2 Civil engineering 319
9.3.3 Moulding compounds 321
9.3.4 Embedding 322
9.3.5 Miscellaneous 323
References 324
Index 327
