Front cover 1
Foreword 9
Preface 11
Acknowledgments 13
Contributors 15
Contents 17
Chapter 1 19
Solubility and Diffusivity 19
1.1 Introduction 20
1.2 Theories and Mechanisms 20
1.2.1 Glassy and Rubbery State 21
1.2.2 Other Variables Affecting Sorption 24
1.2.2.1 Structure and Degree of Crosslinking 24
1.2.2.2 Polymer Crystallinity Content 25
1.2.2.3 Plasticizers and Fillers 27
1.3 Models for Prediction 28
1.3.1 Fickian Diffusion 29
1.3.2 Non-Fickian Diffusion 30
1.4 Measurement Methods 32
1.4.1 Permeation 32
1.4.1.1 Mathematical Models 33
1.4.1.2 Experimental Apparatus 36
1.4.2 Sorption 36
1.4.2.1 Mathematical Models 37
1.4.2.2 Experimental Techniques 39
1.4.2.3 Investigated Polymer-Gas Systems 41
1.5 Impact on Foam Processing and Foam Properties 44
1.5.1 Plasticization 44
1.5.2 Solubility vs. Phase Separation 44
1.5.3 Cell Density 46
1.5.4 Nucleation and Cell Growth 47
1.5.5 Diffusion vs. Applications 48
1.6 Retrograde Behavior 49
1.7 Conclusions 52
Abbreviations 53
References 54
Chapter 2 61
Rheological Behavior Relevant to Extrusion Foaming 61
2.1 Introduction: The Role of Rheology in Foam Processing 62
2.2 Basic Rheological Concepts 63
2.2.1 Dynamic Rheology 64
2.2.2 Shear Rheology 67
2.2.3 Extensional Rheology 69
2.2.4 Rheological Models 74
2.3 Review of Extensional Behavior of Various Foamable Polymers 75
2.3.1 Polystyrene 75
2.3.2 Polyolefins 79
2.3.3 PVC 82
2.3.4 PET 85
2.3.5 Polycarbonate 87
2.3.6 Defining Appropriate Rheological Behavior for Foaming 87
2.3.7 Controlling the Strain-Hardening Feature 89
2.4 Effect of PFA on Rheological Behavior 93
2.4.1 Reduction of Shear Viscosity 93
2.4.2 Effect of Physical Foaming Agent on Extensional Rheology 99
2.5 Failure and Rupture 102
2.5.1 Homogeneous Deformation: The Consid猫re Criterion 104
2.5.2 From Liquid to Glass-Like Behavior 106
2.5.3 Effects of Temperature, Molecular Weight, and Rate of Deformation on Failure of PS Samples 108
2.7 Conclusions 115
Abbreviations 116
References 117
Chapter 3 123
Polymer Blending Technology in Foam Processing 123
3.1 Introduction 123
3.2 Fundamentals of Polymer Blending 124
3.2.1 Miscibility 125
3.2.2 Designing Polymer Blends 126
3.2.2.1 Targeting Properties 126
3.2.2.2 Methods of Blending 127
3.2.2.3 Compatibilization 128
3.2.3 Blend Characteristics 130
3.2.3.1 Morphology 130
3.2.3.2 Rheology 133
3.3 Customizing Polymer Blends for Foam Processing and Applications 135
3.3.1 Strain Hardening and Foamability 137
3.3.2 Nucleation, Growth, and Foam Density 138
3.3.3 Open/Closed Cell Content 141
3.3.4 PFA Affinity 143
3.3.5 Dimensional Stability and Expandable Bead Formulations 143
3.3.6 Other Physical and Mechanical Properties 145
3.4 Conclusions and Outlook 148
Abbreviations 152
References 154
Chapter 4 159
Research on Alternative Blowing Agents 159
4.1 Introduction 160
4.1.1 Historical Perspective 160
4.1.2 Nomenclature 163
4.1.3 General Requirements for Physical Foaming Agents 164
4.2 Physical Blowing Agents 165
4.2.1 Hydrocarbons 166
4.2.2 Inert Gases 167
4.2.3 Hydrofluorocarbons 172
4.2.4 Other PFAs 175
4.2.5 Blends of Physical Blowing Agents 177
4.3 Chemical Blowing Agents 179
4.3.1 General Properties 179
4.3.2 Foaming with CBAs 180
4.4 Pathways for PFA Validation 182
4.4.1 Monitoring of Gas-Polymer Systems 182
4.4.2 Foam Characterization 186
4.5 Blowing Agent Processing 189
4.5.1 Plasticization 189
4.5.2 Solubility 194
4.5.3 Nucleation and Expansion 197
4.6 Conclusions 205
Abbreviations 206
References 206
Chapter 5 213
Investigating Foam Processing 213
5.1 Introduction: Understanding Extrusion Foam Processsing 214
5.2 Tools for Understanding Foam Extrusion 214
5.2.1 Introduction 214
5.2.2 Solubility 215
5.2.3 Plasticization 216
5.2.4 Nucleation 217
5.3 The Ultrasonic Technique 218
5.3.1 Basics: The Propagation of Sound Waves in Polymers 218
5.3.2 Off-Line Technique 219
5.3.3 In-Line Technique 222
5.4 Applications of Ultrasounds Related to Foam Processing 223
5.4.1 Solubility 223
5.4.1.1 Apparent Effect of Flow on Degassing 225
5.4.1.2 Apparent Effect of Nucleating Agent on Degassing 226
5.4.2 Plasticization 228
5.4.3 Nucleation 231
5.4.3.1 Effect of the Rheological Properties of the Polymer 231
5.4.3.2 Heterogeneous Nucleation 236
5.4.4 Impact of Screw Configuration on PFA Dissolution 242
5.4.5 Chemical Blowing Agent Decomposition (Off-Line) 244
5.5 Conclusions - Future Perspectives? 247
Abbreviations 247
References 248
Chapter 6 253
The Relationship between Morphology and Mechanical Properties in Thermoplastic Foams 253
6.1 Introduction 254
6.2 Classical Mechanical Approach 255
6.2.1 Standard Mechanical Testing 255
6.2.2 The Classical Approach 257
6.3 Literature Review 259
6.3.1 Microcellular Foams 259
6.3.2 Regular Low-Density Foams 262
6.4 Morphological Description of Foams 266
6.4.1 Foam Density 266
6.4.2 Foam Structure 266
6.4.3 Cell Size Distribution 266
6.4.4 Foam Anisotropy 268
6.4.5 Microstructure Density Parameter 268
6.5 Morphology-Mechanical Behavior of Foams 271
6.5.1 Mechanical Behavior vs. Cell Size in a Single Parameter for Polystyrene Foams 271
6.5.1.1 Compression Testing 271
6.5.1.2 Dynamic Shock Cushioning Testing 275
6.5.1.3 Falling Dart Impact Tests 278
6.5.2 Validation of the Single Parameter Approach for Polyolefin Foams 279
6.5.2.1 Compression Testing 279
6.5.2.2 Dynamic Shock Cushioning Testing 282
6.5.3 Validation of Single Parameter Approach for Anisotropic Polyolefin Foams 283
6.5.3.1 Compression Testing 284
6.5.3.2 Correction of the Microstructural Parameter for Anisotropy 285
6.5.3.3 Dynamic Shock Cushioning Testing 288
6.5.4 Discussion 290
6.6 Summary and Conclusions 295
Abbreviations 297
References 297
Index 301
A 301
B 301
C 302
D 304
E 305
F 306
G 307
H 307
I 308
K 308
L 308
M 309
N 310
O 310
P 310
Q 313
R 313
S 313
T 315
U 316
V 316
W 317
X 317
Y 317
Z 317