Foam extrusion: principles and practice

FOAM EXTRUSION: Principles and Practice......Page 1
Contents......Page 4
Foreword......Page 8
Preface......Page 9
Acknowledgments......Page 11
List of Contributors......Page 12
1.1 THERMOPLASTIC FOAM......Page 14
Table of Contents......Page 0
1.2 FOAM EXTRUSION......Page 19
1.3 RECENT DEVELOPMENTS......Page 23
1.4 OUTLINE OF THE BOOK......Page 25
1.5 REFERENCES......Page 26
2.1 INTRODUCTION......Page 28
2.2 THERMODYNAMICS......Page 29
2.3.1 THE VAPOR......Page 30
2.3.2 THE CONDENSED PHASE: SINGLE CONSTITUENT......Page 31
2.3.3 THE CONDENSED PHASE: MULTICONSTITUENT......Page 33
2.3.4 THE FREE ENERGY OF THE MIXTURE......Page 34
2.5.1 COMPARISON BETWEEN EXPERIMENT AND THEORY......Page 35
2.5.2 INFLUENCE OF EQUATION OF STATE PARAMETERS FOR CO2......Page 38
2.5.3 SOLUBILITY COMPUTATIONS WITH OTHER STATISTICAL-THERMODYNAMIC MODELS......Page 41
2.7 NOMENCLATURE......Page 44
2.8 REFERENCES......Page 45
3.1 INTRODUCTION: THE IMPORTANCE OF RHEOLOGY IN FOAMING PROCESSES......Page 47
3.2.1 RHEOMETRICAL CONSIDERATIONS......Page 48
3.2.2 EFFECT OF THE BLOWING AGENT ON THE SHEAR VISCOSITY......Page 51
3.2.2.1 Apparent Plasticizing Effect Evaluated at Constant Rate......Page 54
3.2.2.2 Apparent Plasticizing Effect Evaluated at Constant Stress......Page 56
3.2.3.1 Theory for Concentrated Polymer Solutions......Page 58
3.2.3.1.1 Increase of the Free Volume and Decrease of the Glass Transition Temperature......Page 59
3.2.3.1.2 Dilution Effects......Page 60
3.2.3.2.1 Computation of the Glass Transition Temperature......Page 62
3.2.3.2.2 Effect of the Pressure on the Viscosity......Page 66
3.2.3.2.3 Vapor-Liquid Equilibrium......Page 69
3.2.3.3 Case for Semicrystalline Polymers......Page 71
3.2.4.1 Effect of Shear on the Cell Nucleation......Page 74
3.2.4.2 Shear Viscosity of the Foam Phase......Page 75
3.3.1 DEFINITIONS......Page 77
3.3.2 METHODS AND RHEOMETERS......Page 81
3.3.3 ELONGATIONAL RHEOLOGY OF POLYMERS......Page 82
3.3.3.1 Polyolefins......Page 83
3.3.4 ELONGATIONAL RHEOLOGY OF BLOWING AGENT-CHARGED POLYMERIC SYSTEMS......Page 87
3.4 CONCLUSION......Page 88
3.5 REFERENCES......Page 89
4.1 INTRODUCTION......Page 93
4.2 EQUILIBRIUM CONSIDERATIONS......Page 95
4.3.1 HOMOGENEOUS NUCLEATION......Page 99
4.3.2 MODIFIED NUCLEATION THEORIES......Page 106
4.3.3 HETEROGENEOUS NUCLEATION......Page 111
4.4 CAVITATION......Page 114
4.5 FOAM EXTRUSION NUCLEATION......Page 120
4.6 SUMMARY......Page 128
4.7 NOMENCLATURE......Page 131
4.8 REFERENCES......Page 133
5.1 INTRODUCTION......Page 137
5.3.2 CELL MODEL (1984–1998)......Page 138
5.3.2.1.1 Arefmanesh and Advani Model......Page 139
5.3.2.2.1 Ramesh, Lee, Malwitz Model......Page 145
5.4 FOAM GROWTH EXPERIMENT......Page 146
5.5 FOAM GROWTH MODELING......Page 147
5.6 FOAM GROWTH EQUATIONS......Page 148
5.7 BOUNDARY CONDITIONS......Page 149
5.8 COMPARISON OF THEORY WITH EXPERIMENT......Page 153
5.10 NOMENCLATURE......Page 154
5.11 REFERENCES......Page 155
6.1 INTRODUCTION......Page 157
6.2.1 NUCLEATION MODEL......Page 158
6.2.2 BUBBLE GROWTH MODELS......Page 159
6.2.3 INFLUENCE VOLUME......Page 161
6.2.5 SIMULATION RESULTS AND DISCUSSIONS......Page 164
6.2.5.1 Effect of Pressure Releasing Rate on the Bubble Size and Density......Page 165
6.2.5.2 Effect of Dissolved Gas Concentration on the Bubble Size and Density......Page 166
6.2.5.3 Interaction between Homogeneously Nucleated and Heterogeneously Nucleated Bubbles [24]......Page 167
6.3.1 VISUAL OBSERVATION......Page 170
6.3.2 FOAM MODELS IN THE SHEAR FIELD......Page 171
6.3.3 SIMULATION AND EXPERIMENTAL RESULTS......Page 173
6.4 CONCLUSIONS......Page 174
6.5 NOMENCLATURE......Page 175
6.6 REFERENCES......Page 176
7.1 INTRODUCTION......Page 177
7.2 HIGH-DENSITY STRUCTURAL FOAM PROCESS......Page 178
7.2.1.1.2 Barrel Zone 1......Page 179
7.2.1.1.3 Downstream Barrel Zones......Page 180
7.2.2.1 Setting Operating Conditions for Twin-Screw Extruders......Page 181
7.3 LOW-DENSITY FOAM PROCESS......Page 183
7.3.2 SETTING OPERATING CONDITIONS FOR THE PLASTICATING EXTRUDER......Page 184
7.3.4 COOLING EXTRUDER SCREW DESIGN FOR LOWDENSITY FOAM......Page 185
7.4 DIE DESIGN PROCEDURES FOR FOAM EXTRUSION......Page 188
7.4.1.1 Free-Foaming Method......Page 192
7.4.1.2 Constrained Foaming Method......Page 194
7.4.2 DIE DESIGN FOR LOW-DENSITY FOAM PRODUCTS......Page 195
7.5 REFERENCES......Page 199
8.1 PREFACE REGARDING EXTRUDERS FOR FOAMING......Page 200
8.2.1 SIMILARITIES TO CONTINUOUS MIXERS......Page 201
8.2.2 OTHER BASIC PROPERTIES OF SINGLE-SCREW AND TWIN-SCREW EXTRUDERS AND DIFFERENCES FROM INTERNAL MIXERS......Page 203
8.2.3 SINGLE-SCREW VERSUS TWIN-SCREW EXTRUDERS IN FOAM PROCESSES......Page 205
8.2.4 LIMITATIONS OF TWIN-SCREW FOAM EXTRUDERS......Page 206
8.2.5 SOME DISCUSSIONS ABOUT FREE VOLUME AND SCREWS’ TORQUE......Page 207
8.2.6 OVERVIEW OF USING THE EXTRUDER......Page 209
8.3 BASIC UNIT OPERATIONS IN FOAM PROCESSES......Page 210
8.3.1 POLYMER SYSTEM FEEDING......Page 211
8.3.2 MELTING AND COMPOUNDING......Page 213
8.3.3 DYNAMIC SEALING......Page 214
8.3.5 HIGH-RATE DISTRIBUTIVE MIXING......Page 215
8.3.6 COOLING......Page 216
8.3.7 PUMPING......Page 217
8.3.9 DIE FORMING......Page 218
8.4.1 CLASSICAL EXTRUDER TYPES AND EFFICIENCY......Page 219
8.4.2 MAKING TWIN-SCREWS MORE EFFICIENT IN FOAMING PROCESSES......Page 220
8.4.3 WHICH TYPE OF TWIN-SCREW EXTRUDER?......Page 221
8.4.4 WHERE TO PUT SUBPROCESSES WHEN THE EXTRUDER CANNOT DO THEM......Page 222
8.5 GENERAL EXTRUDER OBSERVATIONS......Page 223
8.6 REFERENCES......Page 224
9.1 INTRODUCTION......Page 225
9.2 THERMOPLASTIC FOAM EXTRUSION PROCESSES......Page 226
9.2.1 HIGH-DENSITY FOAM PROCESS......Page 227
9.2.2 LOW-DENSITY FOAM PROCESS......Page 228
9.3 MIXING—THEORIES AND EXPERIMENTS......Page 229
9.3.1.1 Laminar Mixing......Page 230
9.3.1.2.1 Interfacial Area Growth in Simple Shear......Page 231
9.3.1.2.2 Reorientation in Changing Flow Field......Page 232
9.3.1.2.4 Distribution of Mixing......Page 233
9.3.1.3 Experimental......Page 235
9.3.1.4.1 Corotating Twin-Screw Extruder (CoTSE)......Page 237
9.3.1.4.2 Nonintermeshing Twin-Screw Extruder (NITSE)......Page 238
9.3.2 DISPERSIVE MIXING......Page 239
9.3.2.1 Relationship of Dispersive and Distributive Mixing......Page 240
9.3.2.2 Liquid-Liquid Mixing......Page 241
9.3.2.2.1 Viscoelastic Effects......Page 242
9.3.2.4 Solid-Liquid Breakup......Page 244
9.4.1 MIXING SECTIONS IN SINGLE-SCREW EXTRUDERS......Page 245
9.4.2 MIXING SECTIONS IN COROTATING INTERMESHING TWIN-SCREW EXTRUDERS......Page 247
9.4.3 MIXING SECTIONS IN COUNTERROTATING INTERMESHING TWIN-SCREW EXTRUDERS......Page 250
9.4.4 MIXING SECTIONS IN COUNTERROTATING NONINTERMESHING TWIN-SCREW EXTRUDERS......Page 251
9.5.1 INJECTION AND MIXING OF PHYSICAL BLOWING AGENTS......Page 252
9.5.2 EXTRUDER COOLING......Page 254
9.6 SUMMARY......Page 256
9.8 REFERENCES......Page 257
10.2 PHYSICAL FOAMING AGENTS......Page 261
10.3 CHEMICAL FOAMING AGENTS......Page 267
10.3.1 AZODICARBONAMIDE [13]......Page 268
10.3.2 ACID/CARBONATE BLEND......Page 269
10.4 REFERENCES......Page 272
11.1 INTRODUCTION......Page 273
11.2 PREVIOUS STUDIES ON BATCH AND SEMICONTINUOUS MICROCELLULAR PROCESSING......Page 275
11.3 BACKGROUND ON MICROCELLULAR PLASTICS PROCESSING......Page 276
11.4.1 ESTIMATION OF GAS SOLUBILITY IN POLYMERS AT ELEVATED TEMPERATURES AND PRESSURES......Page 278
11.4.3 BASIC CONCEPT OF CONVECTIVE DIFFUSION: MIXING AND DIFFUSION......Page 280
11.4.4 ANALYSIS OF A CONVECTIVE DIFFUSION PROCESS......Page 282
11.5 MICROCELLULAR NUCLEATION CONTROL......Page 284
11.5.1 EFFECT OF THE PRESSURE DROP RATE ON NUCLEATION......Page 286
11.5.2 ANALYSIS OF THE PRESSURE DROP RATE IN A FILAMENTARY DIE......Page 290
11.6 SUPPRESSION OF CELL COALESCENCE......Page 293
11.7.1 PREVIOUS STUDIES OF LOW-DENSITY EXTRUSION FOAM PROCESSING USING AN INERT GAS......Page 295
11.7.2 STRATEGY FOR CONTROL OF VOLUME EXPANSION......Page 296
11.8 EXPERIMENTAL SET-UP......Page 297
11.9.1.1 Effect of Gases on Cell Nucleation......Page 298
11.9.1.3 Effect of the Injected Gas Amount on Cell Nucleation......Page 299
11.9.1.4 Effect of the Pressure Drop Rate on Cell Nucleation......Page 301
11.9.2 CELL COALESCENCE EXPERIMENTS......Page 305
11.9.3 EXPANSION EXPERIMENTS......Page 308
11.10 SUMMARY AND CONCLUSIONS......Page 311
11.11 NOMENCLATURE......Page 312
11.12 REFERENCES......Page 313
12.1 INTRODUCTION......Page 316
12.2. REVIEW OF PET CHEMISTRY AND PROCESSING CHARACTERISTICS......Page 318
12.3.1 CHEMICAL MODIFICATION OF PET FOR LOW-DENSITY EXTRUSION FOAMING......Page 320
12.3.1.3 Post-Reactor Modification by Reactive Extrusion......Page 321
12.3.2 RHEOLOGICAL CHARACTERISTICS OF FOAMABLE PET RESINS......Page 324
12.3.3.1 General......Page 326
12.3.3.1.1 Example I......Page 329
12.3.3.1.3 Example III......Page 331
12.3.3.1.4 Example IV......Page 332
12.3.3.2.1 Extrusion for High-Density Thermoformable Trays......Page 334
12.3.3.2.2 Extrusion for Low-Density Thermoformable Trays......Page 335
12.4.1 GENERAL......Page 337
12.4.2 EXTRUSION FOAMING OF PET......Page 338
12.4.2.1 Parameters Affecting PET Foaming—Laboratory Scale......Page 339
12.4.2.2 Parameters Affecting PET Foaming—Large Scale......Page 340
12.5 CONCLUDING REMARKS......Page 344
12.7 REFERENCES......Page 345