Rubber to Rubber Adhesion

Readers will get helpful ideas and in-depth knowledge about various aspects of rubber to rubber adhesion with particular reference to theory and practice.

This book covers various aspects of rubber to rubber adhesion which is important theoretically, as well as having practical implications. Rubber is a polymer whose glass transition temperature is well below the room temperature and hence the chains are very mobile at room and higher temperatures, making the material very versatile. Rubber is used in a large number of applications ranging from underground mining to tire to space vehicles. In all these cases, compounded rubbers are used in laminates and joined. The higher the adhesion, the higher will be the joint strength. The principles taught in adhesion science and technology are extensively used to prepare better joints and more useful products.

The book serves to satisfy a wide range of disciplines (polymers, materials, chemical, chemistry, mechanical, etc.) and starts with an introduction on rubber, then characterization of rubber, rubber surface and joints and, finally, other chapters on rubber to rubber adhesion. Scientific aspects to understand the technology are highlighted. It gives a comprehensive treatment on adhesion between unvulcanized elastomers, self-healing of elastomers, adhesion between compounded elastomers by co-crosslinking, adhesion between partially vulcanized compounded rubber and partially vulcanized compounded rubber, adhesion between vulcanized rubber and unvulcanized rubber- or partially vulcanized rubber, and adhesion between vulcanized rubber and vulcanized rubber.

Audience The book will be used by academicians in polymer science, materials science, chemical and mechanical engineering, chemistry, R & D personnel, industry people, as well as rubber and adhesion practitioners.

Dr. Dinesh Kumar Kotnees is currently working as an Assistant Professor in Department of Metallurgical and Materials Engineering at Indian Institute of Technology Patna (IIT Patna). Before joining IIT Patna he was working as a Research Scientist in General Electric Company (GE Plastics) Bangalore, India. Dr. Kotnees holds a Ph.D. degree in Rubber Science and Technology from IIT Kharagpur. His broad research interests are adhesion science and technology, polymer blends and alloys, development of hybrid nanofillers and polymer nanocomposites. He has published a number of papers and has been teaching and consultant to companies in these disciplines.

Professor Anil K. Bhowmick is currently at the Department of Chemical and Biomolecular Engineering at the University of Houston and a former Professor of Eminence, IIT Kharagpur, India. He was previously associated with the University of Akron, Ohio, USA, London School of Polymer Technology, London and Tokyo Institute of Technology, Japan. He has more than 550 peer-reviewed international publications in these fields, 35 book chapters and 7 books. He holds twenty-one patents, including three US, three Japanese and one German patents.
His main research interests are: Adhesion and Adhesives, Failure and Degradation of Polymers, Sustainable Materials, Nanocomposites, Rubber-Filler Interaction, Thermoplastic Elastomers and Polymer blends, Polymer modification, and Rubber Technology. He was the 2002 winner of the Chemistry of Thermoplastic Elastomers award, the 1997 winner of the George Stafford Whitby award of the Rubber Division, American Chemical Society for innovative research, 2019 SPE Fred E. Schwab Education Award of the Society of Plastics Engineers and 2001 K.M. Philip award of the All India Rubber Industries Association for outstanding contribution to the growth and development of rubber industries in India.

Foreword xv

Preface xvii

1 Introduction to Rubber 1

1.1 History 1

1.2 What is a Rubber? 3

1.3 What is the Structure of Rubber? 5

1.4 Why is Rubber Chosen Over Other Materials? 9

1.5 Brief Outline of Preparation of Rubber 10

1.6 Types of Rubber 13

1.6.1 Natural Rubber (NR) 14

1.6.2 Styrene - Butadiene Rubber (SBR) 14

1.6.3 Polybutadiene Rubber (BR) 15

1.6.4 Nitrile Rubber (NBR) and Hydrogenated Nitrile Butadiene Rubber (HNBR) 15

1.6.5 Ethylene Propylene Rubber (EPDM/EPM) 16

1.6.6 Chloroprene Rubber (CR) 16

1.6.7 Butyl Rubber (IIR) 16

1.7 Compounding of Rubbers 17

1.7.1 Rubbers 17

1.7.2 Vulcanizing Agents 20

1.7.3 Accelerator and Accelerator-Activators 21

1.7.4 Age Resistors 21

1.7.5 Fillers 23

1.7.6 Processing Aid 23

1.7.7 Miscellaneous Ingredients 24

1.8 The Processes of the Rubber Industry 25

1.9 Why is Adhesion Important in Rubber Science? 28

References 29

2 Important Physical Properties for Understanding Rubber Adhesion and Measurements of Rubber Adhesion 31

2.1 Molecular Weight of Polymer 33

2.1.1 Definition 33

2.1.1.1 Number Average Molecular Weight (M_n) 33

2.1.1.2 Weight Average Molecular Weight (M_w) 34

2.1.1.3 Z-Average Molecular Weight (M_z) and Viscosity Average Molecular Weight (M_v) 34

2.1.1.4 Molecular Weight Distribution (MWD) 35

2.1.2 Determination of Molecular Weight and MWD 36

2.1.2.1 GPC 36

2.1.2.2 Viscosity and Light Scattering Methods 37

2.1.2.3 Use of 1H NMR Spectroscopy in Polymer Molecular Weight Analysis 38

2.1.3 Relationship Between Adhesion and Molecular Weight in Unvulcanized Rubber 39

References 40

2.2 Glass Transition Temperature 41

2.2.1 Introduction and Definition 41

2.2.2 Glass Transition and Thermodynamics 42

2.2.3 Factors on Which T_g Depends 44

2.2.3.1 Chain Flexibility 44

2.2.3.2 Bulky Side Group 44

2.2.3.3 Polar Effect 44

2.2.3.4 Monomer Structure and T_g 44

2.2.3.5 Configurational Effect 45

2.2.3.6 Effect of Crosslinks 46

2.2.3.7 T_g and Plasticizer 46

2.2.4 Determination of T_g 46

References 49

2.3 Solubility Parameter, Interaction Parameter and Interface 50

2.3.1 Solubility Parameter 50

2.3.2 Interaction Parameter 52

2.3.3 Interface 55

References 59

2.4 Spectroscopic Techniques 60

2.4.1 Introduction 60

2.4.2 Principle of FTIR Spectroscopy 61

2.4.3 Principle of Nuclear Magnetic Resonance (NMR) Spectroscopy 64

2.4.4 Principle of X-Ray Photoelectron Spectroscopy (XPS) 66

2.4.5 Chemical Groups and Adhesion 70

References 71

2.5 Microscopy 73

2.5.1 Optical or Light Microscopy 73

2.5.2 Scanning Electron Microscopy (SEM) 74

2.5.2.1 Principle of SEM 74

2.5.2.2 Sample Preparation and Measurements 76

2.5.3 Transmission Electron Microscopy (TEM) 79

2.5.4 Atomic Force Microscopy (AFM) 80

2.5.4.1 Principle 81

2.5.4.2 Operational Modes 82

2.5.4.3 Detection Method 83

2.5.4.4 Imaging and Analysis 84

References 89

2.6 Contact Angle, Surface Energy and Surface Roughness 91

2.6.1 Contact Angle 91

2.6.1.1 Concepts 91

2.6.1.2 Measurements 92

2.6.2 Surface Energy 93

2.6.3 Work of Adhesion and Spreading Coefficient 99

2.6.4 Theoretical Adhesion and Practical Adhesion 101

2.6.5 Surface Roughness 101

2.6.5.1 Concepts 101

2.6.5.2 Measurements 103

References 108

2.7 Rheological Properties of Rubber 110

2.7.1 Definition 110

2.7.1.1 Shear Viscosity 110

2.7.1.2 Shear Stress 111

2.7.1.3 Shear Rate 111

2.7.1.4 Viscous and Elastic Components 111

2.7.2 Measurement of Viscosity and Elasticity 113

2.7.2.1 Capillary Viscometer/Rheometer 113

2.7.2.2 Rotational Rheometry/Viscometry 116

2.7.2.3 Oscillatory Rheometry 117

References 120

2.8 Curing and Crosslinking of Rubber 121

2.8.1 Concepts and Definitions 121

2.8.2 Measurements 123

2.8.3 Determination of Crosslink Density 126

2.8.3.1 Chemical Method 126

2.8.3.2 Physical Method 128

2.8.4 Relationship Between Adhesion Strength and Crosslinking 128

References 129

2.9 Mechanical Properties 131

2.9.1 Tensile Properties 131

2.9.1.1 Unvulcanized Rubber 131

2.9.1.2 Vulcanized Rubber 132

2.9.2 Tearing Energy/Tear Strength 134

2.9.3 Fatigue, Stress Relaxation and Creep of Rubber 137

References 142

2.10 Dynamical Mechanical Analysis (DMA) 144

2.10.1 Introduction 144

2.10.2 Operating Principles 145

2.10.3 Temperature Sweep Test Using DMA 148

2.10.4 Frequency Sweep Master Curves from Time-Temperature Superposition (TTS) Using DMA 150

2.10.4.1 Terminal Relaxation Time ( t_e) from Plateau and Terminal Zone 153

2.10.4.2 Self-Diffusion Coefficient (D) 154

2.10.4.3 Onset of Transition Zone Relaxation Time ( t_r) 154

2.10.4.4 Monomer Friction Coefficient, MFC (ζ₀) from Transition Zone 154

References 155

2.11 Diffusion and Adhesion 157

2.11.1 Concepts 157

2.11.2 Diffusion Theory of Adhesion 158

2.11.3 Methods to Identify Diffusion Across the Interface 158

2.11.4 Self-Diffusion Coefficient 159

2.11.5 Concept of Tack, Diffusion and Viscosity 161

2.11.6 Models Related to Diffusion of Polymers 164

2.11.6.1 Reptation Model 164

2.11.6.2 Model Theory of Crack Healing 165

References 168

2.12 Test Methods for Rubber to Rubber Adhesion and Self-Healing 171

2.12.1 Unvulcanized Rubber Test 171

2.12.2 Vulcanized Rubber Test 178

2.12.3 Tests for Self-Healing 187

References 189

3 Adhesion Between Unvulcanized Elastomers 193

3.1 Introduction 193

3.2 Autohesive Tack 195

3.2.1 Autohesive Tack Criterion 196

3.2.2 Theories Related to Autohesive Tack 197

3.2.2.1 Diffusion Theory 197

3.2.2.2 Contact Theory 199

3.2.3 Factors Affecting Autohesive Tack Bond Formation Process 201

3.2.3.1 Effect of Contact Time 201

3.2.3.2 Effect of Contact Pressure 204

3.2.3.3 Effect of Contact Temperature 204

3.2.3.4 Effect of Surface Roughness 206

3.2.4 Factors Affecting Autohesive Tack Bond Destruction Process 207

3.2.4.1 Effect of Test Rate 207

3.2.4.2 Effect of Test Temperature 207

3.2.4.3 Effect of Bond Thickness 208

3.2.5 Effect of Molecular Properties on Autohesive Tack 209

3.2.5.1 Effect of Molecular Weight 209

3.2.5.2 Effect of Microstructure 209

3.2.5.3 Effect of Crystallinity 210

3.2.5.4 Effect of Polar Groups 211

3.2.6 Environmental Effects on Autohesive Tack 212

3.2.6.1 Effect of Surface Oxidation 212

3.2.6.2 Effect of Humidity 212

3.2.7 Effect of Compounding Ingredients on Autohesive Tack 213

3.2.7.1 Effect of Processing Oil 213

3.2.7.2 Effect of Tackifiers 213

3.2.8 Effect of Fillers 247

3.2.8.1 Effect of Carbon Black and Silica on Autohesive Tack of Elastomers Used in the Rubber Industry 247

3.2.8.2 Effect of Nanoclay on Autohesive Tack of Elastomers Used in the Rubber Industry 250

References 260

4 Self-Healing of Elastomers 269

4.1 Introduction 269

4.2 Examples 272

4.2.1 Hydrogen Bonding 272

4.2.2 Thermo Reversible Diels-Alder Chemistry 275

4.2.3 Ionic Bonding 279

4.2.4 Coordination Complexes 284

4.2.5 Exchange of Disulfide Bonds 286

4.2.6 Other Reactions 287

4.3 Reactions on Various Rubbers 287

4.4 External Healing Agents 294

4.5 Self-Healing in Tire Industry 294

4.6 Summary of Self-Healing System 295

References 297

5 Adhesion Between Compounded Elastomers by Co-Crosslinking 305

5.1 Introduction 305

5.2 Co-Crosslinking 306

5.2.1 Adhesion Between Unvulcanized Rubber (Filled with Crosslinking Agents) and Unvulcanized Rubber (Filled with Crosslinking Agents) by Co-Crosslinking 310

References 329

6 Adhesion Between Partially Vulcanized Rubber and Partially Vulcanized Rubber 331

6.1 Introduction 331

6.2 Experiments of Chang and Gent 331

6.3 Experiments of Bhowmick and Gent 335

6.4 Experiments of Chun and Gent 340

6.5 Experiments of Sarkar and Bhowmick 345

6.6 Experiments of Gent and Lai 349

6.7 Experiments of Ruch, David and Vallat 352

References 355

7 Adhesion Between Vulcanized Rubber and Unvulcanized Rubber or Partially Vulcanized Rubber 357

7.1 Introduction 357

7.2 Adhesion Between Vulcanized Rubber and Unvulcanized Rubber (Filled with Crosslinking Agents) 360

7.3 Adhesion Between Vulcanized Rubber and Partially Vulcanized Rubber (Filled with Crosslinking Agents) 386

References 389

8 Adhesion Between Vulcanized Rubber and Vulcanized Rubber 391

References 413

Index 415

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