ASSESSMENT OF THE PROPERTIES OF POLY (LACTIC ACID) SHEETS WITH DIFFERENT AMOUNTS OF POST-CONSUMER RECYCLED POLY (LACTIC ACID) By Chaiyatas Chariyachotilert A THESIS Submitted to Michigan State University in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE Packaging 2011 ABSTRACT ASSESSMENT OF THE PROPERTIES OF POLY (LACTIC ACID) SHEETS WITH DIFFERENT AMOUNTS OF POST-CONSUMER RECYCLED POLY (LACTIC ACID) By Chaiyatas Chariyachotilert The main objective of this research was to evaluate the properties of sheet containing mechanically recycled post-consumer polylactic acid (PLA) bottle flakes blended with virgin PLA resin. PLA bottles were flaked, cleaned, blended with virgin resin and then extruded and thermoformed into trays. The molecular weight, physical, optical, thermal and mechanical properties of sheet containing 0, 20, 40, 60, 80 and 100 wt.-% recycled content were evaluated. Cleaning conditions were evaluated using response surface methodology, and conditions of 15 min, 85 °C, 1 wt.-% NaOH, and 0.3 wt.-% surfactant were adopted for cleaning the PLA flake. Virgin PLA sheet possessed superior properties to recycled sheet with statistically significant differences at α=0.05. PLA sheets were darker and absorbed more UV light in the 260 to 285 nm range when 20% or more recycled content was added. At 40% recycled content, the sheet had increased blue and red tones and the mechanical properties in the cross-machine direction decreased. At 60% recycled content or above, reduction of weight average molecular weight (Mw), tensile strength and tensile strength at yield in the machine direction (MD) were found. At 80% recycled content, the melting temperature and modulus of elasticity in the MD decreased. All of the sheet samples were successfully thermoformed into trays. Dedicated to my father and mother iii ACKNOWLEDGMENTS I would like to acknowledge the individuals who have supported me to complete this thesis. First, I would like to thank Dr. Rafael A. Auras for being an exceptional advisor. His academic guidance, patient and encouragement helped me through my research. As well, I would like to thank my co-advisor, Dr. Susan E. M. Selke. Her expertise in plastics packaging and packaging waste methods helps me finish the thesis. I admire Dr. Auras and Dr. Selke’s professionalism and work ethic. They have demonstrated me of how to achieve in academic career. I would like to thank Dr. Satish Joshi, my committee member. His professional advices and recommendations helped me improving the quality of the thesis. I would like to acknowledge Primo Water Corporation for the poly(lactic acid) bottles. They are one of the most essential materials for my research. I would also like to thank NatureWorks LLC for providing the PLA resin. I would like to thank Dharmendra Mishara from the Statistical Consultant Center at MSU for his support in helping me in design and run the analysis of the response surface methodology of the cleaning processes. I would like to recognize the support from my research group members, seniors and friends at the School of Packaging for their advices, friendship and encouragement. I am extremely lucky to have received the love and support from my family; especially my mother, Sineenart Chariyachotilert, and my girlfriend, Pansa Ratanajan, for their encouragement during my most difficult times during the research. I am also deeply grateful to iv my uncle Lerwut Wongsarnpigoon and his family, and my cousins: Yodsanan and Jaturapon Sanpavat for their care and support during my stay in the USA. v TABLE OF CONTENTS LIST OF TABLES .............................................................................................................................. viii LIST OF FIGURES ............................................................................................................................... x LIST OF ABBREVIATIONS OR SYMBOLS .......................................................................................... xii CHAPTER 1 INTRODUCTION ............................................................................................................................... 1 Background ......................................................................................................................... 1 Objective ............................................................................................................................. 4 CHAPTER2 LITERATURE REVIEW ....................................................................................................................... 5 Poly (lactic acid), PLA .......................................................................................................... 5 PLA synthesis ....................................................................................................................... 6 Morphology and Properties .............................................................................................. 10 Industrial applications ....................................................................................................... 15 Polymer sheet extrusion ................................................................................................... 18 Polymer thermoforming ................................................................................................... 19 Degradation ...................................................................................................................... 20 Hydrolytic degradation ......................................................................................... 20 Thermal degradation ............................................................................................ 21 End of life of PLA ............................................................................................................... 22 Recycling ........................................................................................................................... 24 Raw material sources and management .............................................................. 25 Manufacturing ...................................................................................................... 28 Chemical recycling ................................................................................................ 29 Mechanical recycling ............................................................................................. 29 Markets and economics ........................................................................................ 30 Response surface methodology ........................................................................................ 30 CHAPTER 3 MATERIALS AND METHODS .......................................................................................................... 32 Introduction ...................................................................................................................... 32 Materials ........................................................................................................................... 34 Methods ............................................................................................................................ 34 Sample preparation - Flake preparation process ............................................................. 34 Experimental design for the cleaning process of the PLA flake........................................ 34 PLA sheet extrusion process ............................................................................................. 37 Sample analysis ................................................................................................................. 39 vi Molecular weight properties ............................................................................................ 39 Physical properties ............................................................................................................ 39 Optical properties ............................................................................................................. 40 UV light .............................................................................................................................. 40 Color .................................................................................................................................. 40 Infrared ............................................................................................................................. 40 Thermal properties ........................................................................................................... 41 Heat deflection temperature ................................................................................ 41 Mechanical properties ...................................................................................................... 42 Thermoforming ................................................................................................................. 42 Statistical analysis ............................................................................................................. 42 CHAPTER 4 RESULTS AND DISCUSSION ........................................................................................................... 43 Properties of virgin resin and flake before cleaning process ........................................... 43 Thermal and molecular weight properties ........................................................... 43 Experimental design of the cleaning process for the PLA flake