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©2020 Yu Sun All Rights Reserved ©2020 YU SUN ALL RIGHTS RESERVED VULCANIZATION AND DEVULCANIZATION OF RUBBER A Dissertation Presented to The Graduate Faculty of The University of Akron In Partial Fulfillment of the Requirement for the Degree Doctor of Philosophy YU SUN August, 2020 VULCANIZATION AND DEVULCANIZATION OF RUBBER YU SUN Dissertation Approved: Accepted: _____________________________ _____________________________ Advisor Department Chair Dr. Li Jia Dr. Tianbo Liu _____________________________ _____________________________ Committee Chair Interim Dean of the College Dr. Toshikazu Miyoshi Dr. Ali Dhinojwala _____________________________ _____________________________ Committee Member Acting Dean of the Graduate School Dr. Gary R. Hamed Dr. Marnie Saunders _____________________________ _____________________________ Committee Member Date Dr. Junpeng Wang _____________________________ Committee Member Dr. Kevin Cavicchi ii ABSTRACT The research in this dissertation includes two parts: vulcanization of isobutylene- isoprene rubber (IIR) containing geminal vinylidene-acrylate groups and surface devulcanization of ground rubber particles (GRPs) for rubber recycling. In Chapter 2, EIIR was synthesized by grafting ethyl propiolate to IIR via EtAlCl2- catalyzed Alder-ene reaction. Methods for crosslinking EIIR using dicumyl peroxide (DCP) with m-Phenylene-N,N’-bismaleimide (BMI) as a coagent were investigated. The strength, extensibility, and overall toughness of the peroxide-cured EIIR significantly exceed those of previously reported peroxide-cured IIR derivatives. A wide range of stiffness can be realized without sacrificing the strength. The crosslinking density achieved using such curatives is indexed as a function of DCP/BMI ratio, and the curing efficiency of peroxide as a function of DCP/BMI ratio and DCP loading. The role of the geminal vinylidene-acrylate moiety in curing was studied by model reactions, which suggest that the geminal vinylidene-acrylate moiety undergoes both radical addition and hydrogen abstraction. Coagent trimethylolpropane trimethacrylate (TMPTMA) was studied to replace BMI due to high toxicity of BMI. Low degrees of crosslinking (~50%) were found in all vulcanizates cured by DCP and TMPTMA, likely because of a mismatch between the reactivities of DCP and TMPMTA. Benzoyl peroxide (BPO) was then used in conjunction with TMPTMA. EIIR was successfully cured with BPO and TMPTMA to give iii high stress and strain at break, and toughness exceeding those achieved with DCP and BMI as the curing agents. Atomic force microscopy and transmission electron microscopy indicate that phase-separated nanodomains presumably of polymers or oligomers of TMPTMA are present in the continuous rubber phase. These domains are likely also responsible for achieving the observed superior mechanical properties. The combination of BPO and BMI are also capable to sufficiently cure EIIR, but the resultant vulcanizates have tensile properties somewhat worse than those cured by DCP and BMI. In Chapter 3, recycling of GRPs was studied. Poor interfacial bonding and interfacial modulus contrast were identified as two inherent causes for the inferior mechanical properties of vulcanizates containing GRPs in comparison to vulcanizates of fresh rubber. The poor interfacial bonding is caused by limited depth of mixing and molecular contact between the polymer chains in the GRPs and fresh rubber. The interfacial modulus contrast is caused by diffusion of curatives from the fresh rubber to the GRPs. Surface devulcanization of GRPs gives rise to strong interfacial bonding equal to the cohesive strength of the rubber but only improves the tensile properties of vulcanizates containing GRPs to a limited extent. When the interfacial modulus contrast is erased, the tensile strength of vulcanizates containing GRPs become equal to that of the fresh rubber vulcanizate. This study also shows that oxidative aging harms the interfacial bonding more than it does the bulk properties. When the surface devulcanization method was applied to GRPs, the vulcanizates containing aged GRPs display similar tensile properties to those of the vulcanizates containing GRPs without aging. iv ACKNOWLEDGEMENT I would like to give my sincere and deep gratitude to my advisor, Dr. Li Jia, for his guidance and support throughout the duration of my stay in the research group. It is a great opportunity for me to work with Dr. Jia. He is a true scientist. I have learnt lots of things from him in research and the way of thinking. Besides of my advisor, I would like to thank Dr. Gary Hamed for helping me with the research and providing me many papers related to rubber science and technology. I would also like to thank Dr. Toshikazu Miyoshi, Dr. Junpeng Wang and Dr. Kevin Cavicchi for being on my committees and giving me valuable comments and suggestions. My sincere thanks also goes to Chengkai Fan, Junyi Chen, Xuesong Yan, Yihong Zhao, Xin Tan, Honghe Liang, Nathan Schmitz, Yiwei Dai, Mengsha Qian and all the other group members for their help and support. I must thank Dr. Jiansheng Feng for helping me on AFM and nano-indenter. I also want to thank Dr. Crittenden Ohlemacher and Yaohong Pang for their help during my research. Furthermore, I must thank Dr. Georg Bohm for helping me with the research. Finally, I must thank my family and Ye Xiao for their love and support. They always stand by me through the good times and bad. In the end, I want to say, “I came; I saw; I conquered”. v TABLE OF CONTENTS Page LIST OF TABLES ............................................................................................................. ix LIST OF FIGURES ........................................................................................................... xi LIST OF SCHEMES......................................................................................................... xv CHAPTER I. GENERAL INTRODUCTION AND BACKGROUND ............................................... 1 1.1 Introduction of Rubbers ........................................................................................ 1 1.1.1 Butyl Rubber and Halogenated Butyl Ruber .............................................. 2 1.1.2 Polybutadiene Rubber ................................................................................. 4 1.2 Vulcanization of Rubbers ..................................................................................... 5 1.2.1 Vulcanization by Sulfur and Accelerators .................................................. 7 1.2.2 Vulcanization by Phenolic Compounds .................................................... 12 1.2.3 Vulcanization by Peroxide-coagent System ............................................. 18 1.3 Recycling of Rubbers .......................................................................................... 29 1.3.1 Reclaiming of Vulcanizates by Physical Reclaiming Processes ............... 33 1.3.2 Reclaiming of Vulcanizates by Chemical Reclaiming Processes ............. 35 II. VULCANIZATION OF BUTYL RUBBER CONTAINING GEMINAL VINYLIDENE-ACRYLATE GROUPS ........................................................................... 51 2.1 Introduction ......................................................................................................... 51 vi 2.2 Experimental ....................................................................................................... 53 2.2.1 Material ..................................................................................................... 53 2.2.2 Chemical Structure Characterization ........................................................ 54 2.2.3 Synthesis of Ethyl Propiolate Grafted Butyl Rubber (EIIR) ..................... 55 2.2.4 Synthesis of Ethyl 4,5-dimethyl-(E-2),5-hexdienoate (EDHEX) ............. 55 2.2.5 Rubber Compounding ............................................................................... 56 2.2.6 Compositions of EIIR Compounds ........................................................... 56 2.2.7 Vulcanization Kinetics .............................................................................. 59 2.2.8 Vulcanization ............................................................................................ 59 2.2.9 Stress Relaxation ....................................................................................... 59 2.2.10 Tensile Test ............................................................................................. 59 2.2.11 Swelling Test for Crosslinking Density .................................................. 60 2.2.12 Reactions of EDHEX with DCP and N-Phenylmaleimide (PMI). .......... 62 2.2.13 Microscopic Characterization ................................................................. 62 2.3 Results and Discussion ....................................................................................... 63 2.3.1 EIIR Compounds Cured by DCP-BMI ..................................................... 63 2.3.2 EIIR Compounds Containing TMPTMA .................................................. 87 2.4 Conclusion ........................................................................................................ 107 III. SURFACE DEVULCANIZATION OF GROUND RUBBER PARTICLES FOR RUBBER RECYCLING ................................................................................................. 109 3.1 Introduction ....................................................................................................... 109 3.2 Experimental ....................................................................................................
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