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(PHBV) and Poly(Lactic Acid) (PLA) Blends Were Studied

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Assessing the Feasibility of Poly-(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) and Poly-(lactic acid) for Potential Food Packaging Applications. THESIS Presented in Partial Fulfillment of the Requirements for the Degree Master of Science in the Graduate School of The Ohio State University By Sunny Jitendra Modi Graduate Program in Food Science and Nutrition The Ohio State University 2010 Master's Examination Committee: Dr. Yael Vodovotz, Advisor Dr. Kurt Koelling Dr. Sudhir Sastry Copyright by Sunny Jitendra Modi 2010 Abstract Poly (hydroxybutyrate) (PHB) is biodegradable aliphatic polyester that is produced by a wide range of microorganisms. Basic PHB has relatively high glass transition and melting temperatures. To improve flexibility for potential food packaging applications, syntheses of PHB with various co-polymers such as Poly-(3- hydroxyvalerate) (HV) decreases the glass and melting temperatures as well as broadens the processing window since there is improved melt stability at lower processing temperatures. In this study, PHB was synthesized with different valerate contents (5, 12, and 20%) and molecular weights ranging from 150 to 600 kDa. Several objectives of this study were to first characterize the thermal, mechanical, rheological, and barrier properties of PHB synthesized with different valerate contents, and second to compare these properties in PHBV with similar hydroxyvalerate content but different molecular weight. Finally, the properties obtained were compared against commonly used thermoplastic packaging materials. All PHBV materials displayed a glass transition between -10 to 20ºC. The two melting transitions found for Aldrich 5%, 12%, and Tianan 20%, resulted from crystals formed during cooling of the samples. The melt rheology suggested thermal instability of samples as the complex viscosity decreased with increasing temperature due to a decrease in molecular weights of the materials. These results suggest that processing the copolymer below 160ºC would be beneficial with low screw speed. The mechanical results indicate all PHBV materials had high ii elastic modulus and flexural strength with low tensile strength and elongation at break. The WVTR results indicated the polymer to be very hydrophilic, which resulted in higher transmission rates. Individually PHBV and PLA polymers have serious disadvantages when compared to thermoplastics that are currently used. To address high costs and thermal instability, blends of PHBV with PLA were explored as an alternative way of acquiring novel materials with desired properties. At the start of this work, three grades of PLAs were commercially available for purchase with different D- and L- lactide ratios and molecular weights used in extruding to injection molding. Miscibility of PHBV with PLA was studied using Differential Scanning Calorimetry (DSC) and Thermogravimetric Analysis (TGA). Three different blends of commercially available PLAs and one grade of PHBV were blended using a micro-compounder at 175ºC. The composition of PHBV in blends ranged from 50 to 80%. Therefore, the aim of this study was to characterize thermal properties of three PLA resins blended with PHBV, and to assess the effect of varying PHBV concentrations on these properties in the blends. DSC analysis indicated the blends were immiscible due to separate melting temperatures representing individual polymers. However, minimal changes in the glass transitions were witnessed for both PHBV and PLA materials. These changes in temperature were due to weak hydrogen bonding and spherulites overlapping. The TGA analysis showed two degradation peaks for individual PHBV and PLA polymers, thus supplementing the results observed for DSC analysis. The mechanical properties of the blends were also investigated using an Instron and Rheological Solids Analyzer units. The results showed significant iii improvements in the elastic modulus, flexural strength, and elongation at break. In general, the viscosity decreased with increasing rotational frequency due to break-up of entanglements between polymers. At various concentrations, the melt viscosity of PHBV was improved with the addition of PLAs at 160 and 170ºC. At melting temperatures, the addition of PLA caused no significant improvements in the complex viscosity. iv Dedication To my parents, my little sister, and good friend Heather Ann Stewart. v Acknowledgments This thesis would not have been possible without the combined effort of my graduate committee members Dr. Yael Vodovotz, Dr. Kurt Koelling, and Dr. Sudhir Sastry. They provided counsel and feedback on coursework and thesis. I would like to express my sincerest gratitude to Dr. Yael Vodovotz for being more than an advisor but also being a wonderful friend. In addition, I would like to thank the Center for Advanced Processing and Packaging Studies (CAPPS), the Institute for Materials Research (IMR), for funding this research project. Furthermore, I would like to thank Stephen Myers of The Ohio BioProducts Innovation Center (OBIC) for supplying the lab with TA Instruments used for this study. Finally, the materials used for study were obtained from Tianan Biologic Material Company and Jamplast Inc., and I would like to thank representatives from both companies for countless technical assistants. Finally, I would like to thank my “joint” lab mates in Food Science for their help. Thanks to Rachel Crockett, Ruth Lucius, and Alex Siegwein for passing their valuable knowledge on thermal and rheology analysis. In addition, I would like to thank Luca Serventi for keeping the lab joyful and stress free, “you wanna eat.” I would also like to thank Alex Suter and Amber Simmons for talking many classes together, so we could understand the material better. In addition, I am deeply in debt to Amber for her help vi proofreading and editing the thesis. I would like to thank Merliana Winardi Leim “Lia” for her help during lab experiments and extrusions. Furthermore, I would like to acknowledge Jennifer Ahn-Jarvis for having our “5-minutes power conversation” and sharing her hints/experiences. Finally, I would like to thank Michael Boehm, Lu Feng, Christopher Kagarise, Koki Miyazono, and Bin Zhu for sharing their extrusion, rheology, and general chemical engineering knowledge. vii Vita August 2003 ...................................................Collins Hill High School Suwannee, Georgia May 2007 .......................................................B.A. Food Science and Technology, The University of Georgia May 2007 .......................................................Minor in Chemistry, The University of Georgia 2007-2010 ......................................................Graduate Research Assistant at The Ohio State University. Master of Science in Food Science and Technology emphasizing potential applications of bio-based polymer in food packaging. Publications S. Modi, K. Koelling, Y. Vodovotz, “Thermal and Rheological Properties of PHB Synthesized with Various Hydroxyvalerate Content for Potential Use in Food Packaging”, Proceedings of SPE – ANTEC, (2009) viii S. Modi, K. Koelling, Y. Vodovotz, “Thermal and Rheological Properties of Poly-(3- hydroxybutyrate-co-3-hydroxyvalerate) and Poly (Lactic Acid) blends for Food Packaging Applications”, Proceedings of SPE – ANTEC, (2010) Fields of Study Major Field: Food Science and Nutrition ix Table of Contents Abstract ………………………………………………………………………………… ii Dedication ……………………………………………………………….……………… v Acknowledgments ………………………………………...…………………………… vii Vita …….…………………………………………………………………..………….. viii List of Tables ………………………………………………………………………..… xiv List of Figures ……………………………………………………...……………..…… xvi Chapter 1: Introduction……………………………………………...…………………… 1 Chapter 2: Statement of the Problem ……………………………………………………. 4 Chapter 3: Literature Review …………………………………………………………… 6 3.1: Introduction to thermoplastic polymer ……………………………………... 6 3.1.1: Problems with thermoplastics ……………………………………. 8 3.2: Introduction to biodegradable polymer ……………………………………... 9 3.3 Polyhydroxyalkanoates (PHA) …………………………………………….. 10 3.3.1 Polyhydroxyalkanoates (PHA) synthesis …………………….…... 12 3.3.2: Physicochemical properties of PHA, specifically PHB ……….… 15 3.3.3: PHB plasticized with Poly-(3-hydroxyvalerate) (HV) ………... 17 3.4: Introduction to Poly(lactic acid) (PLA) ....................................................... 19 3.4.1: Poly(lactic acid) (PLA) production ............................................... 20 x 3.4.2: Poly(lactic acid) (PLA) structure .................................................. 23 3.4.3: Poly(lactic acid) (PLA) physical properties .................................. 23 3.4.4: Poly(lactic acid) (PLA) rheological behavior ................................ 25 3.4.5: Poly(lactic acid) (PLA) mechanical properties .............................. 25 3.5: Importance of Food Packaging ..................................................................... 27 3.6: Importance of Thermal Analysis .................................................................. 27 3.7: Importance of Mechanical Analyses ............................................................. 29 3.8: Importance of Rheological and Barrier Analysis ......................................... 30 Chapter 4: Assessment of PHB with Varying Hydroxyvalerate content for Potential Packaging Applications ................................................................ 32 4.1: Introduction .................................................................................................. 33 4.2: Materials ......................................................................................................
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