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Scale-Up of Extrusion Foaming Process for Manufacture of Polystyrene Foams Using Carbon Dioxide

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Scale-Up of Extrusion Foaming Process for Manufacture of Polystyrene Foams Using Carbon Dioxide Scale-Up of Extrusion Foaming Process for Manufacture of Polystyrene Foams Using Carbon Dioxide by Hongtao Zhang A thesis submitted in conformity with the requirements for the degree of Master of Applied Science Graduate Department of Mechanical and Industrial Engineering University of Toronto © Copyright by Hongtao Zhang 2010 Scale-Up of Extrusion Foaming Process for Manufacture of Polystyrene Foams Using Carbon Dioxide Hongtao Zhang Master of Applied Science Department of Mechanical and Industrial Engineering University of Toronto 2010 Abstract An initial evaluation of the scalability of extrusion foaming technology is conducted in this thesis. Both lab- and pilot-scale foam extrusion systems along with annular dies and flat dies were used to investigate the effects of extrusion system scale on the foam expansion. The effects of the processing conditions including die temperature and blowing agent content on the volume expansion of extruded polystyrene foams blown with carbon dioxide are presented. A systematic comparison of the effects of extrusion system scale on the expansion behavior of polystyrene foams blown with carbon dioxide at the consistent pressure-drop rate, demonstrated that the scale of the foam extrusion system does not affect the principles of the foaming process, and the effects of extrusion system size on the scale-up of foam techniques, such as shear rate and temperature uniformity, could be suppressed by tailoring the processing conditions and experimental parameters. ii Acknowledgments Throughout my graduate study at the University of Toronto, there are a multitude of people that have helped, supported, and encouraged me to make the experience a wealth. I would like to express my deep and sincere gratitude to my supervisor, Professor Chul B. Park. His valued supervision, guidance and support have made me go this far. The knowledge I have learned from him will have a great impact on my future career. I would also like to thank Professor Hani Naguib and Professor Lidan You for agreeing to join my thesis committee. My gratitude is extended to the Department of Mechanical and Industrial Engineering at the University of Toronto, for providing financial support through the University of Toronto Fellowship. I would like to thank my colleagues and fellow researchers in the Microcellular Plastics Manufacturing Laboratory for their help and friendship over the past years. I thank all present and past MPML members, including Dr. Jing Wang, Dr. Zhenjin Zhu, Dr. Changwei Zhu, Dr. Saleh Amani, Dr. Sunny Leung, Dr. Takashi Kuboki, Dr. Gary Li, Dr. Gangjian Guo, Dr. Qingping Guo, Dr. Wenli Zhu, Dr. Wentao Zhai, Dr. Richard Lee, Dr. Yongrak Moon, Nan Chen, Lilac Wang, Raymond Chu, Anson Wong, Yanting Guo, Peter Jung, Esther Lee, Marilyn Law, Qingfeng Wu, Jingjing Zhang, Mingyi Wang, Weidan Ding, Wei Wang, Mohammad Hasan, Ryohei Koyama, Davoud Alizadeh, Kamlesh Majithiya, and Reza Nofar. iii Also, I would like to acknowledge the professional technical support from Ryan Mendell, Jeff Sansome in the Machine Shop for their quality work and professional advice. My special thanks go to many staff members, including Brenda Fung, Donna Liu, Sheila Baker, and Teresa Lai. Finally, I would like to thank my family for their deep love and consistent support under any circumstance. iv Table of Contents Abstract ........................................................................................................................................................................ii Acknowledgments.......................................................................................................................................................iii Table of Contents.........................................................................................................................................................v List of Tables...............................................................................................................................................................ix List of Figures ..............................................................................................................................................................x List of Symbols..........................................................................................................................................................xiv Chapter 1 Introduction 1.1 Preamble ......................................................................................................................................................1 1.2 Thermoplastic Foams and Their Processing ................................................................................................2 1.3 Polystyrene Foams and Its Applications ......................................................................................................4 1.4 Foam Extrusion............................................................................................................................................5 1.5 Motivations of the Study..............................................................................................................................6 1.6 General Objectives.......................................................................................................................................6 1.7 Overview of the Thesis ................................................................................................................................7 Chapter 2 Theoretical Background and Literature Review 2.1 Theoretical Background on Foam Processing............................................................................................11 2.1.1 Formation of Polymer/Gas Solution..................................................................................................11 2.1.2 Nucleation .........................................................................................................................................16 2.1.3 Cell Growth and Stabilization ...........................................................................................................21 2.2 Blowing Agents..........................................................................................................................................26 2.3 Foam Extrusion..........................................................................................................................................27 2.3.1 Foam Extrusion Process ....................................................................................................................28 2.3.2 Conventional Foam Extrusion...........................................................................................................28 2.3.3 Microcellular Foam Extrusion...........................................................................................................29 2.4 Volume Expansion Mechanism in Foam Extrusion...................................................................................30 2.5 Characterization of Polymer Foams...........................................................................................................33 v 2.5.1 Volume Expansion Ratio...................................................................................................................33 2.5.2 Cell Density.......................................................................................................................................34 2.5.3 Cellular Morphology .........................................................................................................................34 2.6 Issues of Scale-Up in Foam Extrusion .......................................................................................................35 2.7 Objectives of the Thesis.............................................................................................................................36 Chapter 3 Processing Parameters and Strategies for PS foaming 3.1 System and Die Pressure............................................................................................................................45 3.2 Pressure-Drop Rate ....................................................................................................................................46 3.3 Die Temperature ........................................................................................................................................46 3.4 Contents of Blowing Agents ......................................................................................................................47 3.5 Strategies for Achieving Low-density PS Foams Using CO2 ....................................................................47 Chapter 4 Design and Construction of Experimental Equipment 4.1 Materials ....................................................................................................................................................51 4.1.1 Plastics...............................................................................................................................................51 4.1.2 Blowing Agent ..................................................................................................................................52 4.2 Lab-Scale Extrusion System ......................................................................................................................52 4.3 Set-Up of Pilot-Scale Extrusion System ....................................................................................................52 4.3.1
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