Thermoplastic Foam Processing: Principles and Development (Polymeric Foams Series)

This book is part of a series entitled Polymeric Foams and is a companion to the volume, Foam Extrusion: Principles and Practices (2000). It addresses new topics such as polymer blends and mechanical properties and develops other topics that have only been overviewed in Foam Extrusion. Written by experts, the book presents the latest research in foam extrusion and foaming polymer blends with a strong focus on polymeric materials interaction in foaming process. Thermoplastic Foam Processing: Principles and Applications gives the reader a clear understanding of the current trends in R & D and an up-to-date review of the current knowledge in thermoplastic foam processing. THERMOPLASTIC FOAM PROCESSING: Principles and Development 1 POLYMERIC FOAMS SERIES 2 Dedication 5 Foreword 6 Preface 8 Acknowledgments 10 Contributors 11 Contents 12 Contents -1 THERMOPLASTIC FOAM PROCESSING: Principles and Development 13 Chapter 1 Solubility and Diffusivity 13 1.1 Introduction 14 1.2 Theories and Mechanisms 14 1.2.1 Glassy and Rubbery State 15 1.2.2 Other Variables Affecting Sorption 18 1.2.2.1 Structure and Degree of Crosslinking 18 1.2.2.2 Polymer Crystallinity Content 19 1.2.2.3 Plasticizers and Fillers 21 1.3 Models for Prediction 22 1.3.1 Fickian Diffusion 23 1.3.2 Non- Fickian Diffusion 24 1.4 Measurement Methods 26 1.4.1 Permeation 26 1.4.1.1 Mathematical Models 27 1.4.1.2 Experimental Apparatus 30 1.4.2 Sorption 30 1.4.2.1 Mathematical Models 31 1.4.2.2 Experimental Techniques 33 1.4.2.3 Investigated Polymer - Gas Systems 35 1.5 Impact on Foam Processing and Foam Properties 38 1.5.1 Plasticization 38 1.5.2 Solubility vs. Phase Separation 38 1.5.3 Cell Density 40 1.5.4 Nucleation and Cell Growth 41 1.5.5 Diffusion vs. Applications 42 1.6 Retrograde Behavior 43 1.7 Conclusions 46 Abbreviations 47 References 48 Chapter 2 Rheological Behavior Relevant to Extrusion Foaming 55 2.1 Introduction: The Role of Rheology in Foam Processing 56 2.2 Basic Rheological Concepts 57 2.2.1 Dynamic Rheology 58 2.2.2 Shear Rheology 61 2.2.3 Extensional Rheology 63 2.2.4 Rheological Models 68 2.3 Review of Extensional Behavior of Various Foamable Polymers 69 2.3.1 Polystyrene 69 2.3.2 Polyolefins 73 2.3.3 PVC 76 2.3.4 PET 79 2.3.5 Polycarbonate 81 2.3.6 Defining Appropriate Rheological Behavior for Foaming 81 2.3.7 Controlling the Strain- Hardening Feature 83 2.4 Effect of PFA on Rheological Behavior 87 2.4.1 Reduction of Shear Viscosity 87 2.4.2 Effect of Physical Foaming Agent on Extensional Rheology 93 2.5 Failure and Rupture 96 2.5.1 Homogeneous Deformation: The Consid¿re Criterion 98 2.5.2 From Liquid to Glass- Like Behavior 99 2.5.3 Effects of Temperature, Molecular Weight, and Rate of Deformation on Failure of PS Samples 101 2.7 Conclusions 108 Abbreviations 109 References 111 Chapter 3 Polymer Blending Technology in Foam Processing 116 3.1 Introduction 116 3.2 Fundamentals of Polymer Blending 117 3.2.1 Miscibility 118 3.2.2 Designing Polymer Blends 119 3.2.2.1 Targeting Properties 119 3.2.2.2 Methods of Blending 120 3.2.2.3 Compatibilization 121 3.2.3 Blend Characteristics 123 3.2.3.1 Morphology 123 3.2.3.2 Rheology 126 3.3 Customizing Polymer Blends for Foam Processing and Applications 128 3.3.1 Strain Hardening and Foamability 130 3.3.2 Nucleation, Growth, and Foam Density 131 3.3.3 Open/ Closed Cell Content 134 3.3.4 PFA Affinity 136 3.3.5 Dimensional Stability and Expandable Bead Formulations 136 3.3.6 Other Physical and Mechanical Properties 138 3.4 Conclusions and Outlook 141 Abbreviations 145 References 147 Chapter 4 Research on Alternative Blowing Agents 151 4.1 Introduction 152 4.1.1 Historical Perspective 152 4.1.2 Nomenclature 155 4.1.3 General Requirements for Physical Foaming Agents 156 4.2 Physical Blowing Agents 157 4.2.1 Hydrocarbons 158 4.2.2 Inert Gases 159 4.2.3 Hydrofluorocarbons 164 4.2.4 Other PFAs 167 4.2.5 Blends of Physical Blowing Agents 169 4.3 Chemical Blowing Agents 171 4.3.1 General Properties 171 4.3.2 Foaming with CBAs 172 4.4 Pathways for PFA Validation 174 4.4.1 Monitoring of Gas Ò Polymer Systems 174 4.4.2 Foam Characterization 178 4.5 Blowing Agent Processing 181 4.5.1 Plasticization 181 4.5.2 Solubility 186 4.5.3 Nucleation and Expansion 189 4.6 Conclusions 197 Abbreviations 198 References 198 Chapter 5 Investigating Foam Processing 204 5.1 Introduction: Understanding Extrusion Foam Processsing 205 5.2 Tools for Understanding Foam Extrusion 205 5.2.1 Introduction 205 5.2.2 Solubility 206 5.2.3 Plasticization 207 5.2.4 Nucleation 208 5.3 The Ultrasonic Technique 209 5.3.1 Basics: The Propagation of Sound Waves in Polymers 209 5.3.2 Off- Line Technique 210 5.3.3 In- Line Technique 213 5.4 Applications of Ultrasounds Related to Foam Processing 214 5.4.1 Solubility 214 5.4.1.1 Apparent Effect of Flow on Degassing 216 5.4.1.2 Apparent Effect of Nucleating Agent on Degassing 217 5.4.2 Plasticization 219 5.4.3 Nucleation 222 5.4.3.1 Effect of the Rheological Properties of the Polymer 222 5.4.3.2 Heterogeneous Nucleation 227 5.4.4 Impact of Screw Configuration on PFA Dissolution 233 5.4.5 Chemical Blowing Agent Decomposition ( Off- Line) 235 5.5 Conclusions - Future Perspectives? 238 Abbreviations 238 References 239 Chapter 6 The Relationship between Morphology and Mechanical Properties in Thermoplastic Foams 243 6.1 Introduction 244 6.2 Classical Mechanical Approach 245 6.2.1 Standard Mechanical Testing 245 6.2.2 The Classical Approach 247 6.3 Literature Review 249 6.3.1 Microcellular Foams 249 6.3.2 Regular Low- Density Foams 252 6.4 Morphological Description of Foams 256 6.4.1 Foam Density 256 6.4.2 Foam Structure 256 6.4.3 Cell Size Distribution 256 6.4.4 Foam Anisotropy 258 6.4.5 Microstructure Density Parameter 258 6.5 Morphology- Mechanical Behavior of Foams 261 6.5.1 Mechanical Behavior vs. Cell Size in a Single Parameter for Polystyrene Foams 261 6.5.1.1 Compression Testing 261 6.5.1.2 Dynamic Shock Cushioning Testing 265 6.5.1.3 Falling Dart Impact Tests 268 6.5.2 Validation of the Single Parameter Approach for Polyolefin Foams 269 6.5.2.1 Compression Testing 269 6.5.2.2 Dynamic Shock Cushioning Testing 272 6.5.3 Validation of Single Parameter Approach for Anisotropic Polyolefin Foams 273 6.5.3.1 Compression Testing 274 6.5.3.2 Correction of the Microstructural Parameter for Anisotropy 275 6.5.3.3 Dynamic Shock Cushioning Testing 278 6.5.4 Discussion 280 6.6 Summary and Conclusions 285 Abbreviations 287 References 287 Solubility and DiffusivityRheological Behavior Relevant to Extrusion FoamingPolymer Blending Technology in Foam ProcessingResearch on Alternative Blowing AgentsInvestigating Foam ProcessingThe Relationship between Morphology and Mechanical Properties in Thermoplastic FoamsIndexContributors: Martin N. BureauIndustrial Materials Institute, National Research Council of Canada, QuebecMichel F. ChampagneIndustrial Materials Institute, National Research Council of Canada, QuebecRichard GendronIndustrial Materials Institute, National Research Council of Canada, QuebecA. Victoria NawabyInstitute for C "In the midst of new research for alternative, environmentally friendly foaming agents, Thermoplastic Foam Processing: Principles and Development gives the reader a clear understanding of the current trends in R & D and an up-to-date review of the state of the art in thermoplastic foam processing. This book provides useful tools for the development and validation of innovative physical foaming agent and polymer combinations for current and future research."--Jacket As researchers seek replacements for banned, ozone-depleting foaming agents, the authors of Thermoplastic Foam Processing: Principles and Development strive to develop a better understanding of foaming processes and find solutions for day-to-day practice. This book presents the latest research in foam extrusion and physical foaming agents with a st Plastics play a major role in our everyday lives, ranging from basic commodity goods to more sophisticated cellular structures for drug delivery systems [1,2].