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Processing and Characterization of Polycarbonate Foams with Supercritical PROCESSING AND CHARACTERIZATION OF POLYCARBONATE FOAMS WITH SUPERCRITICAL CO2 AND 5-PHENYL-1H-TETRAZOLE Thomas Cloarec, B.S. Thesis Prepared for the Degree of MASTER OF SCIENCE UNIVERSITY OF NORTH TEXAS May 2015 APPROVED: Witold Brostow, Major Professor Samir Aouadi, Committee Member Nandika A. D’Souza, Committee Member Richard F. Reidy, Committee Member Cloarec, Thomas. Processing and Characterization of Polycarbonate Foams with Supercritical Co2 and 5-Phenyl-1h-Tetrazole. Master of Science (Materials Science and Engineering), May 2015, 100 pp., 11 tables, 59 figures, references, 5 titles. Since their discovery in the 1930s, polymeric foams have been widely used in the industry for a variety of applications such as acoustical and thermal insulation, filters, absorbents etc. The reason for this ascending trend can be attributed to factors such as cost, ease of processing and a high strength to weight ratio compared to non-foamed polymers. The purpose of this project was to develop an “indestructible” material made of polycarbonate (PC) for industrial applications. Due to the high price of polycarbonate, two foaming methods were investigated to reduce the amount of material used. Samples were foamed physically in supercritical CO2 or chemically with 5-phenyl-1H-tetrazole. After thermal characterization of the foams in differential scanning calorimetry (DSC), we saw that none of the foaming methods had an influence on the glass transition of polycarbonate. Micrographs taken in scanning electron microscopy (SEM) showed that foams obtained in physical and chemical foaming had different structures. Indeed, samples foamed in supercritical CO2 exhibited a microcellular opened-cell structure with a high cell density and a homogeneous cell distribution. On the other hand, samples foamed with 5-phenyl-1H- tetrazole had a macrocellular closed-cell structure with a much smaller cell density and a random cell distribution. Compression testing showed that polycarbonate foamed physically had a compression modulus a lot greater. Then, XLPE mesh 35 or 50 and wollastonite were added to the polymeric matrices to enhance the foaming process and the mechanical properties. DSC experiments showed that the addition of fillers changed the thermal properties of polycarbonate for both foaming methods by inducing a shift in glass transition. SEM revealed that fillers lowered the average cell diameter and increased the cell density. This phenomenon increased the compression modulus for polycarbonate foamed in supercritical CO2. However, mechanical properties decreased for samples foamed with 5-phenyl-1H-tetrazole due to their relative brittleness and the propagation of microcracks. Copyright 2015 by Thomas Cloarec ii ACKNOWLEDGMENTS First, I would like to express my sincere gratitude to my adviser, Dr. Witold Brostow, who gave me the opportunity to investigate polymers during my studies toward a Master degree in Materials Science and Engineering. His guidance, knowledge and support through funding and tuition waivers were with no doubt an immeasurable chance that made my research a once in a lifetime experience. Next, I would like to thank my colleague and friend Zachary Hoyt and Dr. Richard F. Reidy for their support, help and many discussions throughout my research. Finally, I would like to thank and acknowledge Dr. Nandika A. D’Souza, Dr. Marcus Young and the Center for Advanced Research & Technology (CART) from the University of North Texas for allowing me use their equipment, without which I could not have done my research. Most importantly, I would like to thank my family, my lovely fiancé Hollye Cody and my sweet little Finn for their love, encouragement and support during my education. iii TABLE OF CONTENTS ACKNOWLEDGEMENTS…………………………………………………………………………………………………………3 LIST OF TABLES……………………………………………………………………………………………………………………..7 LIST OF FIGURES……………………………………………………………………………………………………………………8 Chapter 1………………………………………………………………………………………………………………………….…12 INTRODUCTION……………………………………………………………………………………………………….12 1.1 Polymeric foams………………………………………………………………………………………………..12 1.2 Polycarbonate foams…………………………………………………………………………………………13 1.3 Scope………………………………………………………………………………………………………………..14 1.4 References………………………………………………………………………………………………………..16 Chapter 2……………………………………………………………………………………………………………………………17 PROCESSING AND CHARACTERIZATION OF POLYCARBONATE FOAMS WITH SUPERCRITICAL CO2 ……………………………..………………………………………………………………………………………………….17 2.1 Literature review……………………………………………………………………………………………….17 2.1.1 Supercritical fluids……………………………………………………………………………….17 2.1.2 Physical foaming via supercritical CO2 ……………………………………………….. 20 2.2 Materials for supercritical foaming in CO2 ……………………………………………………….. 25 2.3 Experimental……………………………………………………………………………………………………..25 2.3.1 Samples preparation……………………………………………………………………………25 2.3.2 Foaming process………………………………………………………………………………….25 2.3.3 Characterization methods…………………………………………………………………...27 iv 2.4 Results and discussion……………………………………………………………………………………….29 2.4.1 Differential Scanning Calorimetry (DSC)………………………………………………29 2.4.2 Scanning Electron Microscopy (SEM)…………………………………………………..33 2.4.3 Compression testing……………………………………………………………………………39 2.5 Conclusions……………………………………………………………………………………………………….42 2.6 References………………………………………………………………………………………………………..43 Chapter 3…………………………………………………………………………………………………………………………...45 PROCESSING AND CHARACTERIZATION OF POLYCARBONATE FOAMS WITH CHEMICAL FOAMING AGENT 5-PHENYL-1H-TETRAZOLE……………………………………………………………45 3.1 Literature review………………………………………………………………………………………………45 3.1.1 Chemical foaming agents……………………………………………………………………45 3.1.2 Foaming via extrusion………………………………………………………………………..46 3.1.3 Foaming via injection molding……………………………………………………………48 3.2 Materials for chemical foaming in with 5-phenyl-1H-tetrazole…………………………50 3.3 Experimental…………………………………………………………………………………………..…….…51 3.3.1 Samples preparation…………………………………………………………………..….….51 3.3.2 Foaming process…………………………………………………………………………...…..52 3.3.3 Characterization methods…………………………………………………..……………..53 3.4 Results and discussion……………………………………………………………………………………...54 3.4.1 Differential Scanning Calorimetry (DSC)……………………………………………..54 3.4.2 Scanning Electron Microscopy (SEM)………………………………………………….55 3.4.3 X-ray tomography micro-CT………………………………………………………………..63 3.4.4 Compression testing……………………………………………………………….……….….65 3.5 Conclusions……………………………………………………………………………………………………….68 v 3.6 References……………………………………………………………………………………………………….69 Chapter 4………………………………………………………………………………………………………………………….71 PROCESSING AND CHARACTERIZATION OF POLYCARBONATE FOAMS WITH FILLERS………..71 4.1 Literature review……..…………………………………………………………………………………….71 4.2 Materials for physical and chemical foaming………………………………………………….72 4.3 Experimental………………………………………………………………………………………………….72 4.3.1 Samples preparation and foaming………………………………………………..…72 4.3.2 Characterization methods……………………………………………………………….73 4.4 Results and discussion…………….……………………………………………………………………..76 4.4.1 Fillers characterization……………………………………………………………………76 4.4.2 Polycarbonate mixes foamed in supercritical CO2 ………………………….82 4.4.3 Polycarbonate mixes foamed chemically with 5-phenyl-1H- tetrazole…………………………………………………………………………………………………96 4.5 Conclusions……….…………………………………………………………………………………………107 4.6 References……………………………………………………………………………………………………108 Chapter 5…………………………………………………………………………………………………………………….109 CONCLUSIONS……………………………………………………………………………………………………………..109 vi LIST OF TABLES Table 1: General properties of supercritical fluid, gas and liquid…………………………………………18 Table 2: Critical point of common solvents………………………………………………………………………….18 Table 3: Saturated solubility and diffusion coefficient of CO2 in PC for various temperatures and pressures…………………………………..…………………………………………………………………………………23 Table 4: Overall properties of PC foamed in supercritical CO2 …………………………………………….34 Table 5: Density and porosity for PC foamed in supercritical CO2 ……………………………………….38 Table 6: Percentage as a function of 5-phenyl-1H-terazole………………………………………………….52 Table 7: Overall properties for PC foamed with 5-phenyl-1H-terazole…………………………………61 Table 8: Porosity of chemically foamed samples obtained in micro-CT……………………………….64 Table 9: Overall properties for PC mixes foamed in supercritical CO2 …………………………………91 Table 10: Density and porosity for PC mixes foamed in supercritical CO2 …………………………..93 Table 11: Overall properties for PC mixes foamed chemically……..……………………………………103 vii LIST OF FIGURES Figure 1: Chemical reaction for the synthesis of polycarbonate…………………………………………..13 Figure 2: General phase diagram for a supercritical fluid…………………………………………………….19 Figure 3: Phase diagram of CO2 ………………………………………………………………………………………….20 Figure 4: DSC curves for samples foamed in supercritical CO2 …………………………………………….30 Figure 5: DSC curves for different saturation times in supercritical CO2 after depressurization ……………………………………………………………………………………………………………………………………………32 Figure 6: DSC curves for different saturation times in supercritical CO2 after erasing the stress and the thermal history…………………………………………………………………………………………….32 Figure 7: SEM micrographs for PC foamed in supercritical CO2 for 24 h with magnification 100x (A), 300x (B) and 1000x (C)………………………………………………………………………………………….33 Figure 8: SEM micrographs for PC foamed in supercritical CO2 for 48 h with magnification 100x (A), 300x (B) and 1000x (C)………………………………………………………………………………………….35 Figure 9: SEM micrographs for PC foamed in supercritical CO2 for 72 h with magnification 100x (A), 300x (B) and 1000x (C)………………………………………………………………………………………….36
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