(PHBV) Bioplastic for Food Packaging Applications Disse
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Natural Rubber Toughened Poly (3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) Bioplastic for Food Packaging Applications Dissertation Presented in Partial Fulfillment of the Requirements for the Degree Doctor of Philosophy in the Graduate School of The Ohio State University By Xiaoying Zhao Graduate Program in Food Science and Technology The Ohio State University 2018 Dissertation Committee Yael Vodovotz, Advisor Katrina Cornish, Advisor Dr. Kurt Koelling Dr. David Nagib 1 Copyrighted by Xiaoying Zhao 2018 2 Abstract The packaging industry is searching for bio-based alternatives. Poly-(β- hydroxybutyrate-co-valerate) (PHBV) is a promising bioplastic made from bacterial fermentation of renewable resources. It has mechanical properties similar to propylene (PP) but is more brittle. PHBV toughness and flexibility must be improved before it can be commercially used for packaging. An industrially viable and economically effective way to toughen PHBV is blending it with flexible and ductile materials. Natural rubber (NR) is a promising toughening material due to its unique combination of ductility, flexibility, and renewability. NR has various packaging applications such as films and tapes. Blends from rubber and thermoplastics, such as polyethylene and PP, with improved toughness, flexibility, and other properties have been used in packaging industry. Therefore, the objective of this work is to improve PHBV toughness and flexibility through NR incorporation, elucidate the reaction mechanism of the coagent- assisted peroxide-induced reactive extrusion of NR and PHBV, optimize the PHBV/NR blends, and evaluate their suitability for food packaging applications. In this study, 2-25 wt. %NR was incorporated into PHBV through reactive extrusion in the presence of peroxide to improve PHBV flexibility and toughness. The PHBV/NR blends had two phases with crosslinked rubber being dispersed in PHBV matrix. Rubber addition restricted PHBV crystallization and decreased its degree of crystallinity. The blend had improved flexibility, toughness, thermal stability, and melt ii strength, but decreased tensile strength than pristine PHBV. The blend performance had clear rubber loading-dependent differences. To improve rubber toughening efficiency and the PHBV/NR blend strength, a trifunctional acrylic coagent was synergistically used with the peroxide during the melt blending process. The reaction mechanism was investigated through FTIR and NMR analysis. Coagent and peroxide synergically crosslinked rubber phase and grafted PHBV onto rubber backbones. The presence of coagent improved peroxide crosslinking efficiency and suppressed peroxy-radical caused polymer degradation, leading to a homogeneous rubber dispersion, increased rubber modulus and cohesive strength, and improved PHBV-rubber compatibility. The peroxide-coagent treatment decreased PHBV crystallinity and crystal size. The new PHBV/NR blends had a 70% better impact strength than pristine PHBV, 40% better tensile strength then peroxide-only cured blend, and a broadened processing window. Mechanical properties of the peroxide-coagent treated PHBV/NR blends were optimized using a response surface methodology (RSM) with a Box-Behnken design. Ascending coagent loading led to increased toughness and tensile strength, but decreased flexibility of the PHBV/NR blends. Ascending rubber loading led to increased flexibility, decreased tensile strength, and maximal toughness at 15 wt. % loading. Peroxide had minimal effect on tensile strength and flexibility, but increased toughness. The optimal PHBV/NR blend was obtained at 15 wt. % NR, 4.2 phr peroxide, and 3 phr coagent, with a tensile strength of 28.1 MPa, notched impact strength of 27.5 J/m, flex modulus (1% secant modulus) of 8,679 MPa. The blends degraded by ~15% in 53 days in a lab-scale iii aerobic composting system at 58 °C. Trays made from the optimized PHBV/NR blend had water vapor permeability and sealability comparable to polypropylene, good stabilitywith acid food under freezing and microwave heating. Migration studies indicated that the trays were safe for food-contact applications. This research demonstrated that the bio-based and bio-degradable PHBV/NR blends potentially can be used as bio-alternatives to the petroleum-based plastic packaging materials. iv Dedication To my family, my advisors, and my faithful friends v Acknowledgments I would like to express my sincerest gratitude to Dr. Yael Vodovotz and Dr. Katrina Cornish for their endless support, patience, motivation, and immense knowledge. Your advice on my research has been invaluable. I would also like to thank my committee members, Dr. Kurt Koelling and Dr. David Nagib, for their great support and insightful suggestions. I would like to thank the Center for Advanced Processing and Packaging Studies (CAPPS) for funding this research project. I would also like to thank Polymers Center of Excellence in Charlotte, North Carolina, Progressive Packaging in Plymouth, Minnesota, and Priority Design in Columbus, Ohio for assisting in sheeting and thermoforming of the materials. I would like to thank Dr. Jose Castro for providing the Instron universal testing machine and impact tester, Dr. Tea Meulia for assisting in TEM imaging, and Dr. Ming Gao from the Liquid Crystal Institute of Kent State University for assisting in TEM sample sectioning. I would like to thank my group members in Food Science and Chemical Engineering, for assisting in extrusion, rheology, mechanical, and biodegradation testing. vi Vita 2005-2009………………...............................Bachelor, Food Science and Engineering, Jilin University, China 2009-2012…………………………………...Master, Food Science and Engineering, Jilin University, China 2012-2014…………………………………...Research Assistant, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences 2014-2018…………………………………...Graduate Research Assistant, The Ohio State University, Doctor of Philosophy Candidate Publications 1. Xiaoying Zhao, Varun Venoor, Kurt Koelling, Katrina Cornish, Yael Vodovotz. Bio-based Blends from Poly (3-hydroxybutyrate-co-3-hydroxyvalerate) and Natural Rubber for Packaging Applications. J Appl Polym Sci 2018. DOI: 10.1002/app.47334. 2. Xiaoying Zhao, Katrina Cornish, Yael Vodovotz. Synergistic mechanisms underlie the peroxide and coagent improvement of natural rubber toughened PHBV mechanical performance. Submitted. vii 3. Xiaoying Zhao, Kuihao Ji, Katrina Cornish, Yael Vodovotz. Optimal Mechanical Properties of Biodegradable Natural Rubber-Toughened PHBV Bioplastics intended for Food Packaging Applications. Submitted. 4. Yael Vodovotz, Katrina Cornish, Xiaoying Zhao, Sunny Modi. Fabrication and improved performance of poly-(3-hydroxybutyrate-co-3-hydroxyvalerate) for packaging by addition of high molecular weight natural rubber. Proceedings of the International Elastomer Conference, Pittsburgh, PA, October 10-13, 2016. Fields of Study Major Field: Food Science and Technology viii Table of Contents Abstract ............................................................................................................................... ii Dedication ........................................................................................................................... v Acknowledgments.............................................................................................................. vi Vita .................................................................................................................................... vii List of Tables ..................................................................................................................... xi List of Figures ................................................................................................................... xii Chapter 1. Introduction ....................................................................................................... 1 Chapter 2. Statement of Problem ........................................................................................ 4 Chapter 3. Literature Review .............................................................................................. 6 3.1 Bioplastics Landscape ............................................................................................... 7 3.2 Compare with Conventional Plastics ...................................................................... 31 3.3 Toughening Methods .............................................................................................. 34 3.4 Compatibilization of Polymer Blends by Reactive Extrusion ................................ 46 Chapter 4. Bio-based Blends from Poly (3-hydroxybutyrate-co-3-hydroxyvalerate) and Natural Rubber for Packaging Applications ..................................................................... 52 Abstract ......................................................................................................................... 52 4.1 Introduction ............................................................................................................. 54 4.2 Experimental ........................................................................................................... 60 4.3 Results and Discussion ........................................................................................... 65 3.4 Conclusions ............................................................................................................. 90 Chapter 5. Synergistic Mechanisms Underlie the Peroxide and Coagent Improvement of Natural Rubber