Micro and Nanostructured Epoxy / Rubber Blends

Epoxy resins are polymers which are extensively used as coating materials due to their outstanding mechanical properties and good handling characteristics. A disadvantage results from their high cross-link density: they are brittle and have very low resistance to crack growth and propagation. This necessitates the toughening of the epoxy matrix without impairing its good thermomechanical properties. The final properties of the polymer depend on their structure. The book focuses on the microstructural aspects in the modification of epoxy resins with low molecular weight liquid rubbers, one of the prime toughening agents commonly employed.

The book follows thoroughly the reactions of elastomer-modified epoxy resins from their liquid stage to the network formation. It gives an in-depth view into the cure reaction, phase separation and the simultaneous development of the morphology. Chapters on ageing, failure analysis and life cycle analysis round out the book.

PrefaceXV

List of ContributorsXVII

1 Introduction1
Raju Thomas, Christophe Sinturel, Sabu Thomas, and Elham Mostafa Sadek El Akiaby

1.1 Epoxy Resin – Introduction 1

1.2 Cure Reactions 1

1.3 Curing Agents 2

1.3.1 Catalytic Cure 3

1.3.2 Co-reactive Cure 3

1.4 Different Curing Methods 7

1.4.1 Thermal Curing 7

1.4.2 Microwave Curing 8

1.4.3 Radiation Curing 10

1.5 Curing of Epoxy Resins: Structure–Property Relationship 12

1.6 Toughening of Epoxy Resin 13

1.6.1 Different Toughening Agents 13

1.7 Rubber-Modified Epoxy Resin: Factors Influencing Toughening 16

1.7.1 Concentration Effects 16

1.7.2 Particle Size and Distribution of Rubber 16

1.7.3 Effect of Temperature 17

1.7.4 Effect of Rubber 17

1.7.5 Interfacial Adhesion 18

1.8 Toughening Mechanisms in Elastomer-Modified Epoxy Resins 18

1.8.1 Particle Deformation 18

1.8.2 Shear Yielding 19

1.8.3 Crazing 20

1.8.4 Simultaneous Shear Yielding and Crazing 21

1.8.5 Crack Pinning 22

1.8.6 Cavitation and Rumples 22

1.9 Quantitative Assessment of Toughening Mechanisms 23

1.10 Introduction of Chapters 24

References 25

2 Liquid Rubbers as Toughening Agents31
Hanieh Kargarzadeh, Ishak Ahmad, and Ibrahim Abdullah

2.1 Introduction 31

2.2 Toughening of Thermoset Resins 31

2.3 Fracture Behavior of Rubber-Toughened Thermosets 32

2.4 Natural Rubbers 35

2.4.1 Preparation Method of LNR 36

2.5 Liquid-Toughening Rubber in Thermoset Resins 43

2.6 Concluding Remarks 49

References 50

3 Nanostructured Epoxy Composites53
Yuan Meng and Xinghong Zhang

3.1 Introduction 53

3.2 Preparation Methods of the Nanostructured Epoxy Thermoset 54

3.3 Morphology of the Nanostructured Epoxy Thermoset 56

3.3.1 Parameters Controlling the Morphologies 56

3.4 Microphase Separation Mechanism 60

3.4.1 Self-Assembly Mechanism 61

3.4.2 Reaction-Induced Microphase Separation Mechanism 63

3.5 Mechanical and Thermal Properties 65

3.5.1 Fracture Toughness 65

3.5.2 Glass Transition Temperature 67

3.6 Conclusions and Outlooks 67

References 68

4 Manufacture of Epoxy Resin/Liquid Rubber Blends73
Sahrim Bin Hj Ahmad, Mimi Azlina Abu Bakar, Ying Yi, and Qi Qin

4.1 Introduction 73

4.2 Comparison of Hardeners 74

4.3 Rubber-Toughened Epoxy Resins 77

4.4 Cure Reaction Analysis 79

4.5 Conclusions 79

References 80

5 Cure and Cure Kinetics of Epoxy-Rubber Systems83
Humberto Vázquez-Torres

5.1 Introduction 83

5.2 Cure Analysis 83

5.3 Curing Kinetics 84

5.3.1 Kinetics Analysis 85

5.3.2 Autocatalytic Model 85

5.3.3 Activation Energies 86

5.4 Diffusion Factor 88

5.5 Differential Scanning Calorimetry 88

5.5.1 Dynamic DSC 89

5.5.2 Isothermal DSC 90

5.6 FTIR Spectroscopy 92

5.7 Dielectric Spectroscopy Thermal Method 94

5.8 Pressure–Volume–Temperature (PVT) Method 96

5.9 Dynamic Mechanical Analysis (DMA) and Rheological Methods 97

5.10 Conclusions 101

Acknowledgments 101

References 101

6 Theoretical Modeling of the Curing Process105
Nicolas Boyard, Vincent Sobotka, and Didier Delaunay

6.1 Introduction 105

6.2 Modeling of the Curing Kinetics 106

6.2.1 Mechanistic Approach 107

6.2.2 Phenomenological Models Describing the Reaction 109

6.2.3 Rheological Models 118

6.2.4 Effect of Vitrification (Tg ) on the Reaction Rate 119

6.3 Applications of the Empirical Models 120

6.4 Conclusion 122

References 123

7 Phase-Separation Mechanism in Epoxy Resin/Rubber Blends127
Vattikuti Lakshmana Rao and Bejoy Francis

7.1 Introduction 127

7.2 Thermodynamics of Phase Separation 128

7.2.1 Nucleation and Growth Mechanism 130

7.2.2 Spinodal Decomposition 130

7.3 Phase Separation in Uncured Epoxy Resin/Liquid Rubber Blends 131

7.4 Phase-Separation Mechanism in Cured Blends 133

7.5 Conclusion 144

References 144

8 Morphology Analysis by Microscopy Techniques and Light Scattering147
Daohong Zhang, Junheng Zhang, and Aiqing Zhang

8.1 Introduction 147

8.2 Developments of Morphology Analysis in Rubber-Modified Epoxies 147

8.2.1 Optical Microscopy (OM) 148

8.2.2 Scanning Electron Microscopy (SEM) 150

8.2.3 Atomic Force Microscopy (AFM) 153

8.2.4 Transmission Electron Microscopy (TEM) 155

8.2.5 Small-Angle Light Scattering (SALS) 159

8.3 Different Types of Morphologies 160

8.3.1 Phase-Separation Morphology of Epoxy/Rubbers Blends 160

8.3.2 Morphology of Hybrids 161

8.3.3 Homogeneous Morphology 163

8.4 Morphology of Toughening and Reinforcing Effects 165

8.4.1 Conventional Additives 165

8.4.2 Hyperbranched Polymers 167

8.5 Conclusions 171

Acknowledgments 172

References 172

9 Pressure–Volume–Temperature (PVT) Analysis179
Didier Delaunay, Nicolas Boyard, and Vincent Sobotka

9.1 Introduction 179

9.2 Generalities on the Behavior of the Polymers 180

9.3 Measurement Techniques 184

9.4 PvT Measures on Epoxies 187

References 190

10 Rheology of Rubber-Toughened Structural Epoxy Resin Systems193
Richard A. Pethrick

10.1 Introduction 193

10.2 Epoxy Resin Chemistry 194

10.2.1 Basic Epoxy Chemical Reactions 195

10.2.2 Kinetics of Cure 196

10.2.3 Epoxy Reactivity 198

10.3 Modeling of the Cure Process 198

10.4 Rheological Implication of Differences in Reactivity 201

10.4.1 Modeling Rheological Behavior 202

10.4.2 Connection between Rheology and Cure 203

10.5 Rheological Studies of Cure 206

10.6 Toughened Epoxy Resins 209

10.6.1 Carboxy-Terminated Butadiene Acrylonitrile (CTBN) 210

10.6.2 Polyethersulfone (PES) 211

10.6.3 Nano Clay Toughening of Epoxy Resins 213

10.6.4 Toughening with Nano Carbon and Silica Nano Particles 213

10.6.5 Plasticization 213

10.7 Concluding Comments 214

Acknowledgments 214

References 214

11 Viscoelastic Measurements and Properties of Rubber-Modified Epoxies219
Yingfeng Yu

11.1 Introduction 219

11.1.1 State Transitions from Liquid to Solid 220

11.1.2 Viscoelasticity of Cured Materials 222

11.2 Viscoelastic Behavior Below and Near Gel Point 224

11.2.1 Liquid-Rubber-Modified Epoxies 224

11.2.2 Core–Shell Rubber-Modified Epoxies 224

11.2.3 Ternary Systems with Fillers 228

11.3 Viscoelasticity of Cured Materials 228

11.3.1 Dynamic Mechanical Study 228

11.3.2 Dielectric Measurement 231

11.4 Other Remarks 233

11.5 Conclusion 234

References 234

12 Light, X-ray, and Neutron Scattering Techniques for Miscibility and Phase Behavior Studies in Polymer Blends239
Chikkakuntappa Ranganathaiah

12.1 Introduction 239

12.2 Brief Theoretical Considerations of Scattering 240

12.3 Light Scattering Experiment 242

12.4 X-ray Scattering 251

12.5 Neutron Scattering 261

12.5.1 Small-Angle Neutron Scattering (SANS) 261

12.6 Conclusions and Future Outlook 267

Acknowledgments 267

References 267

13 Mechanical Properties271
Shinu Koshy

13.1 Introduction 271

13.2 Morphology and Mechanical Properties of Rubber-Modified Epoxies 272

13.2.1 Influence of Rubber Concentration 273

13.2.2 Influence of Initial Cure Temperature 276

13.2.3 Influence of Curing Agent 278

13.2.4 Influence of Acrylonitrile Content 279

13.2.5 Influence of Strain Rate 280

13.2.6 Kerner Equation 281

13.3 Fracture Toughness 281

13.3.1 Effect of Concentration on Fracture Toughness 282

13.3.2 Effect of Strain Rate on Fracture Toughness 284

13.3.3 Effect of Curing Agent on Fracture Toughness 285

13.4 Conclusion 285

References 286

14 Thermal Properties289
Vincent Sobotka, Didier Delaunay, Nicolas Boyard, Sabu Thomas, and Poornima Vijayan P.

14.1 Specific Heat 289

14.2 Thermal Conductivity 292

14.2.1 Main Methods of Characterization 292

14.2.2 Classical Model to Describe Thermal Conductivity as a Function of Temperature and Degree of Cure 296

14.3 Thermogravimetric Analysis of Rubber/Epoxy Systems 297

14.4 Kinetic Study from TGA 300

References 301

15 Dielectric Properties of Elastomeric Modified Epoxies305
Yerrapragada Venkata Lakshmi Ravi Kumar, Swayampakula Kalyani, and Nidamarthy Vasantha Kumar Dutt

15.1 Introduction 305

15.2 Dielectric Study in Rubber/Epoxy Systems 306

15.2.1 Dielectric Constant () 306

15.2.2 Volume Resistivity (VR) 308

15.2.3 Conductivity () 310

15.2.4 Combined Studies on Dielectric Constant, Volume Resistivity, and Conductivity 311

15.3 Summary 312

References 312

16 Spectroscopy Analysis of Micro/Nanostructured Epoxy/Rubber Blends315
Xiaojiang Wang and Mark D. Soucek

16.1 Introduction 315

16.2 Fourier Transform Infrared (FTIR) and Raman Spectroscopy 316

16.2.1 DGEBA Epoxy/Rubber Blends 316

16.2.2 Other Epoxy/Rubber Blends 320

16.2.3 FTIR Image and Raman Spectroscopy 322

16.3 Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) 323

16.3.1 Acid-Terminated Rubber/DGEBA Epoxy Blends 323

16.3.2 Hydroxyl-Terminated Rubber/DGEBA Epoxy Blends 326

16.3.3 Neutral Rubber/DGEBA Epoxy Blends 329

16.3.4 Other Type Epoxy/Rubber Blends 331

16.4 Other Spectroscopy 333

16.5 Summary 333

Abbreviations 334

References 334

17 Applications339

17.1 Applications of Toughened Epoxy Resins339
Richard A. Pethrick

17.1.1 Introduction 339

17.1.2 Aerospace Adhesive Applications 339

17.1.3 Rubber-Modified Resins 340

17.1.4 Composites 341

17.1.5 Epoxy Resin Modification 342

17.1.6 Thermoplastic Modification 343

17.1.7 Nanoparticle Modification 343

17.1.8 Other Areas of Application 343

17.2 Thermoset-Based Materials for Optical Applications Containing Azobenzene Choromophores344
Luciana M. Sáiz, Antonela B. Orofino, María José Galante, and Patricia

A. Oyanguren

17.2.1 Introduction 344

17.2.2 Synthesis and Optical Properties of Cross-linked Azo Polymers 345

17.2.3 Photoaddressable Networks Containing Alkyl Compounds 354

17.2.4 Conclusions 358

References 360

18 Comparison of Epoxy/Rubber Blends with Other Toughening Strategies: Thermoplastic and Hyperbranched Modifiers363
Gianluca Cicala

18.1 Epoxy/Thermoplastic Blends: Development and Properties 363

18.2 Epoxy/Hyperbranched Polymer Blends: Development and Properties 375

18.3 Novel Toughening Approaches for Liquid Molding Technologies 378

18.4 Rubbers as Tougheners: Comparison with Thermoplastics and Hyperbranched Modifiers 383

18.5 Conclusions 387

References 388

19 Reliability Testing391
Marius Bâzu and Titu Bãjenescu

19.1 Introduction 391

19.2 Reliability Tests Used in Micro/Nanotechnologies 392

19.3 Behavior in Real Applications and Aging Studies of Epoxy/Rubber Blends 394

19.3.1 Epoxy/Rubber Blends Used in Packaging of Active Electronic Components 394

19.3.2 Epoxy Matrix Used in Nanocomposites 399

19.4 Conclusions 402

References 402

20 Failure Analysis405
Marius Bâzu and Titu Bãjenescu

20.1 Introduction 405

20.2 Methods for Failure Analysis of Epoxy/Rubber Blends 405

20.3 Typical Failure Modes and Failure Mechanisms of Epoxy/Rubber Blends Used in Micro and Nanotechnologies 405

20.3.1 Mechanical Damages 409

20.3.2 Ion Contamination 414

20.4 Self Healing 416

20.5 Conclusions 417

References 418

21 Life Cycle Assessment (LCA) of Epoxy-Based Materials421
Jyotishkumar Parameswaranpillai and Dhanya Vijayan

21.1 Introduction to Life Cycle Assessment (LCA) 421

21.2 Significance of Life Cycle Assessment (LCA) 422

21.2.1 Goal and Scope Definition 422

21.2.2 Life Cycle Inventory Analysis 423

21.2.3 Life Cycle Impact Assessment 423

21.2.4 Life Cycle Result Interpretation 424

21.3 Life Cycle Analysis of Epoxy Systems 424

21.3.1 Life Cycle Analysis of Epoxy Resins Produced Based on Propylene and Glycerin 424

21.3.2 Life Cycle Analysis of Epoxy Resin Containing Carbon Nanotubes 426

21.3.3 Life Cycle Assessment of Wind Turbine Blade Materials 426

21.3.4 Life Cycle Assessment in Automotive Application 428

21.3.5 Life Cycle Assessment in Aerospace Application 429

21.3.6 Life Cycle Assessment of a Novel Hybrid Glass-Hemp/Thermoset Composite 429

21.3.7 Natural Fiber-Reinforced Epoxy Composites 430

21.4 Conclusion 430

References 431

Index433