The Effects of Crosslinking on Foaming of EVA

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The Effects of Crosslinking on Foaming of EVA,Doctor of Philosophy. Department of Mechanical and Industrial Engineering. University of Toronto, The effects of crosslinking on EVA foaming are studied in this thesis A fundamental. approach was applied to describe the influences of crosslinking on EVA gas viscosities gas. solubility and diffusivity in EVA EVA foaming nucleation and early stage of bubble growth. which leads to a better understanding of the plastic foaming mechanism. Although crosslinked polyolefin foaming technology has been well applied in industry. more fundamental and thorough studies are demanded to understand the mechanism which can. serve to improve the present technology The shear and extensional viscosities have been. measured for the chemically crosslinked EVA with dissolved gas which could not be found from. literature Furthermore by controlling the crosslinking agent amount the polymer melt. strength viscosity can be controlled so as to obtain optimum foam morphology The crosslinking. also has effects on the diffusivity and solubility of a blowing agent inside EVA The solubility. and the diffusivity of the blowing agent in the EVA decrease with the crosslinking degree. increases The diffusivity decrease makes more gas is utilized for the foaming rather than leak. out of the polymer matrix quickly, This thesis also presents the fundamental studies on the effects of crosslinking on cell. nucleation and early bubble growth Theoretical work and in situ visualization experimental. results indicate that partial crosslinking leads to higher cell nucleation density and slower bubble. growth both of which benefit a fine cell foam morphology generation. Last but not least an optimized foaming process was conducted to produce chemically. crosslinked EVA foams with large expansion ratios in a batch system using a chemical blowing. agent The results determine that an optimal crosslinking degree is critical for the crosslinked. EVA foaming with maximum expansion ratio Furthermore all research results not only benefit. the foaming of crosslinked EVA but also serve the better production of other crosslinked. polyolefin foams,Acknowledgments, I am deeply indebted to my supervisor Professor Chul B Park This thesis would not. have been possible without his support and guidance Prof Park offered me the opportunity and. guided me to explore the research world of cellular polymers as an engineer It is my distinct. pleasure that I express my gratitude to Professor Park for his strong support encouragement and. criticism throughout my graduate study at the University of Toronto. I would like to thank my Ph D thesis committee members Professor Hani Naguib and. Professor Jan K Spelt for their offered guidance I thank Professor Nasser Ashgriz and Professor. Salvatore Iannace for agreeing to be my external examiners. My gratitude is extended to the Department of Mechanical and Industrial Engineering at. the University of Toronto for providing the University of Toronto Doctoral Fellowship. I would like to thank all my colleagues in the microcellular plastics manufacturing. laboratory I really appreciate their help and friendship I thank Dr Jing Wang for always being. very helpful He had been my senior in the same department at my undergraduate university To. me he has always been a good example of an engineer to learn from I thank Lilac Wang for her. excellent jobs of organizing all the retreat trips for us She is always ready to help if you are in. need I thank all other past and present MPML members including Dr Jin Wang Dr Wenge. Zheng Dr Patrick Lee Dr Guangming Li Dr Qingping Guo Dr Gary Li Dr Chunmin Wang. Dr Wentao Zhai Dr Sunny Leung Hongtao Zhang Ali Rizvi Hui Wang Dr Jingjing Zhang. Dr Qingfeng Wu Mingyi Wang Yanting Guo Dr Changwei Zhu Raymond Chu Anson Wong. Dr John Lee Dr Ryan Kim Dr Kevin Lee Peter Jung Dr Yongrak Moon Dr Patrick Lee Dr. Kyungmin Lee Dr Richard Lee Sue Chang Johnny Park Alex Lee Dr Takashi Kuboki Dr. Bhuwnesh Kumar Dr Mohammed Serry Mohammad Hasan Dr Maridass Balasubramanian. Professor Wanrudee Kaewmesri Florien Gunkel Ivan Gutierrez Esther Lee April Binnie and. Marilyn Law I thank them for all their kind support. Finally I would like to express my great gratitude to my parents for their support. throughout all the years They always motivate me with their unreserved love. Table of Contents,Abstract ii,Acknowledgements iv,Table of Contents vi.
List of Tables ix,List of Figures x,List of Symbols xii. Chapter 1 Introduction, 1 1 Crosslinked Polyolefin Foams and their processing technology 1. 1 2 Research Motivation 4,1 3 General Objectives 5. 1 4 Thesis Format and Outline 6,Chapter 2 Background and Literature Review. 2 1 Plastic Foams Blowing Agents and EVA 8,2 1 1 Categories of Foams 8.
2 1 2 Blowing Agents in Plastic Foaming 9,2 1 2 1 Physical Blowing Agent in Foaming 10. 2 1 2 2 Chemical Blowing Agent in Foaming 11,2 1 3 Ethylene Vinyl Acetate 13. 2 2 Plastic Foaming 14,2 2 1 Microcellular Foam Processing 15. 2 2 2 Rheology 16,2 2 3 Solubility and Diffusivity 20. 2 2 3 1 Solubility 20,2 2 3 2 Diffusivity 21, 2 2 4 Homogeneous Nucleation and Heterogeneous Nucleation 22.
2 2 5 Cell Growth in Foaming 26,2 3 Crosslinking in Polyolefin Foam Processing 27. 2 3 1 Crosslinking 27,2 3 2 Characterization of Crosslinking 30. 2 3 3 Crosslinking in Polyolefin Foam Processing 31. 2 4 Objectives and Methodology of the Thesis 36, Chapter 3 Effects of Crosslinking on Fundamental Properties of EVA Gas Mixtures. 3 1 Introduction 39, 3 2 Methods for Characterizing Rheological Properties 40. 3 2 1 Commercial Rheometers 40, 3 2 2 The Hele Shaw Channels and The Processing System 41.
3 3 Study of Shear Rheological Properties of Crosslinked EVA and EVA Gas. 3 4 Study of Extensional Rheological Properties of Crosslinked EVA and EVA Gas. 3 5 Methods for Characterizing Solubility and Diffusivity of Blowing Agent in. Polymers 60, 3 6 Study of the Influence of Crosslinking on the Solubility and Diffusivity of. Blowing Agent in Crosslinked EVA 63,3 7 Summary 65. Chapter 4 In Situ Visualization Study on the Effects of Crosslinking on Cell Nucleation. and Early Cell Growth of EVA Foam,4 1 Introduction 67. 4 2 In Situ Visualization of Bubble Growth in the Crosslinked EVA Foaming 68. 4 2 1 Materials Experimental Apparatus and Procedure 68. 4 2 2 Results and Discussion 71,4 2 2 1 Effects of Crosslinking Agent Content 71. 4 2 2 2 Effects of Gas Content 73,4 3 Theoretical Analysis 75.
4 4 Summary 77, Chapter 5 Compression Molding of Crosslinked EVA Foams. 5 1 Introduction 78,5 2 Experimental Design 79,5 2 1 Processing Strategies 79. 5 2 2 Material Properties 80,5 2 3 Characterizations 80. 5 2 4 Foaming Processing Window 81, 5 3 Preliminary Analysis of Processing Parameters 82. 5 3 1 Effects of Temperature 82, 5 3 2 Effects of Chemical Blowing Agent Content 84.
5 3 3 Effects of Crosslinking Agent Content 85,5 3 4 Effects of Nucleating Agent 87. 5 4 Optimization of the Processing Parameters to Maximize the Expansion. of Crosslinked EVA Foam using a Chemical Blowing Agent 89. 5 5 Summary 93,Chapter 6 Conclusions,6 1 Concluding Remarks 95. 6 2 Recommendations for Future Work 97,References 99. List of Tables, Table 4 1 Experimental design of visualization batch foaming 69. List of Figures, Figure 1 1 Schematic of the foaming technology of the crosslinked plastic 4.
Figure 1 2 Basic steps of cellular plastics processing 4. Figure 2 1 EVA molecular formula 13, Figure 2 2 Relationship between maximum molecular weight and vinyl acetate content for. Figure 2 3 Schematic of cell model 56 18,Figure 2 4 The stretch of the bubble wall 19. Figure 2 5 Homogenous bubble nucleation and free energy 24. Figure 2 6 Heterogeneously nucleated bubble where is the wetting angle 25. Figure 2 7 Polymer chains and crosslinking 28,Figure 2 8 Crosslinking using peroxide 106 29. Figure 2 9 Crosslinking using peroxide 112 31, Figure 2 10 Effects of crosslinking on foaming window of polyolefin 8 32. Figure 3 1 Oscillatory shear 40, Figure 3 2 Schematic of the Extensional Viscosity Fixture 41.
Figure 3 3 Schematic of the Hele Shaw die the circles indicate the diaphragms of the. pressure transducers 80 43, Figure 3 4 Schematic of the tandem extrusion system 43. Figure 3 5 Time sweep curve for crosslinking 45,Figure 3 6 Loss tangent with time 45. Figure 3 7 Complex viscosity with varying DCP content time sweep test to 170oC 47. Figure 3 8 Complex viscosity vs DCP content 47, Figure 3 9 Rheological behavior of EVA a shear viscosity b relaxation time 49. Figure 3 10 Rheological behavior of EVA obtained from the capillary rheometer 50. Figure 3 11 Overall rheological behavior of EVA a 170oC and b 190oC 52. Figure 3 12 Effect of temperature on EVA shear viscosity 53. Figure 3 13 Effects of crosslinking on EVA shear viscosity a 170oC b 190oC 55. Figure 3 14 Effects of blowing agent on EVA shear viscosity 56. Figure 3 15 Growth curves of extensional viscosity for crosslinked EVA at a 170 C b. 190 C with 0 08 phr and 0 16 phr at various strain rates 0 01 s 1 0 05 s 1 and 0 10. Figure 3 16 Effect of crosslinking on EVA extensional viscosity 60. Figure 3 17 Schematic of overall MSB system 1 Electromagnet 2 Permanent magnet. 3 Position sensor 4 Coupling device 5 Sample holder 18 61. Figure 3 18 Schematic of PVT System 86 62, Figure 3 19 Effect of Crosslinking on EVA Swelling 64. Figure 3 20 Effect of Crosslinking on the solubility and diffusivity of N 2 in EVA. Figure 4 1 On line visualization system 102 68,Figure 4 2 Captured images of bubble growth 70.
Figure 4 3 Cell density calculations 70, Figure 4 4 Early bubble growth at 10 3MPa 170oC 71. Figure 4 5 Cell density increase with time at varying crosslinking agent amount a 6 9MPa. b 10 3MPa c 13 8MPa 73, Figure 4 6 Cell density increase with time at varying gas pressure a 0phr DCP b 0 08phr. DCP c 0 16phr DCP 75,Figure 5 1 Schematic of batch foaming process 79. Figure 5 2 Taguchi design analysis 82, Figure 5 3 Crosslinked EVA foams with varying temperatures a data graph b SEM. Figure 5 4 Crosslinked EVA foams with varying CBA contents a data graph b SEM. Figure 5 5 Crosslinked EVA foams with varying CA contents a data graph b SEM images. 170oC c SEM images 190oC 87, Figure 5 6 Crosslinked EVA foams with different nucleating sites a data graph b SEM.
Figure 5 7 Optimization of maximum expansion ratio of crosslinked EVA a expansion. ratio b cell density 90, Figure 5 8 Heat flow of partially crosslinked EVA 91. Figure 5 9 Curing percentage compared with fully crosslinked EVA 9phr DCP. Figure 5 10 EVA foams with varying crosslinking percentage a expansion ratio b cell. density 92,List of Symbols,Shear rate,Gibbs free energy. Free energy to form critical nucleus during homogeneous nucleation. Free energy to form critical nucleus during heterogeneous nucleation. Free energy difference between the bubble phase and the polymer phase. Pressure drop,Exit pressure drop,Elongation or extension or stretch rate. Shear viscosity,Zero shear rate viscosity,Viscosity at infinite shear rate. Complex viscosity,Relaxation time,Surface tension,or Shear stress.
Wall shear stress,Stress is the direction,Stress in the direction. Bubble surface area,Extensional flow parameter 0 1. Width used in various contexts,Gas concentration or. Initial dissolved gas concentration or,Diffusivity or diffusion coefficient. Gravitational constant 9 8,Elastic modulus,Storage modulus.
Loss modulus,or Height used in various contexts,Nucleation rate per unit volume of polymer. Frequency factor,Thermal conductivity,Boltzmann constant 1 38 10. Henry s Law constant,Length used in various contexts. Ratio of gas dissolved over polymer at time, Ratio of gas dissolved over polymer after infinite time. Number averaged molecular weight,Weight averaged molecular weight.
Power Law parameter,Non Newtonian index in Power Law. Cell nucleation rate during homogeneous nucleation. Cell nucleation rate during heterogeneous nucleation. Gas pressure inside a cell,System pressure,Parts per hundred resin. Volumetric flow rate,and Cylindrical coordinates,Critical radius. Molar gas constant 8 314,Temperature,Melting temperature. Glass transition temperature,Crystallization temperature.
The effects of crosslinking on EVA foaming are studied in this thesis A fundamental approach was applied to describe the influences of crosslinking on EVA gas viscosities gas solubility and diffusivity in EVA EVA foaming nucleation and early stage of bubble growth which leads to a better understanding of the plastic foaming mechanism Although crosslinked polyolefin foaming technology has

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