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Strategies to Manufacture Poly(Lactic Acid) Blown Films Without Melt Strength Enhancers

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Strategies to Manufacture Poly(Lactic Acid) Blown Films Without Melt Strength Enhancers STRATEGIES TO MANUFACTURE POLY(LACTIC ACID) BLOWN FILMS WITHOUT MELT STRENGTH ENHANCERS By Sonal Sanjay Karkhanis A THESIS Submitted to Michigan State University in partial fulfillment of the requirements for the degree of Packaging - Master of Science 2016 ABSTRACT STRATEGIES TO MANUFACTURE POLY(LACTIC ACID) BLOWN FILMS WITHOUT MELT STRENGTH ENHANCERS By Sonal Sanjay Karkhanis Poly (lactic acid) (PLA), a bio-based polymer derived from renewable resources, is an alternative to petroleum-based polymers because it reduces general dependency on oil availability and environmental concerns of common petroleum-based plastics, among others. Despite these attributes, PLA has relatively few commercial applications, concentrating mainly in the biocompatible biomedical device markets and as a commodity polymer for rigid containers and bottles used for packaging. However, its widespread applicability in flexible sheets/films is limited because of several drawbacks, among which its insufficient melt strength and low thermal stability, leading to narrow processing windows. Melt strength enhancers (MSEs) are often blended with PLA matrix to increase its melt strength, allowing the extrusion blowing and casting of the films. However, these additives are costly and not approved for food applications. Hence, there is a need to manufacture PLA films without any MSEs. Processing strategies were developed in this study to produce PLA blown films without any MSEs. Using a thermodynamic approach, the effects of various processing conditions and material characteristics on PLA’s melt rheology (zero shear, shear and elongational viscosities) and film’s blow-up ratio (BUR) were examined. Experimental results indicate that extrusion- blown PLA films could be successfully manufactured without MSEs, irrespective of PLA’s degree of crystallinity, by tailoring the melt rheology through processing temperature and controlling other processing conditions such as the film’s take-up ratio, as well as internal and external air pressures. Copyright by SONAL SANJAY KARKHANIS 2016 Dedicated to my parents Sanjay and Mohana Karkhanis iv ACKNOWLEDGEMENTS I am extremely thankful to my advisor Dr. Laurent Matuana (School of Packaging, Michigan State University) for his never ending support and guidance. I never found the door closed to Dr. Matuana’s office when I ran into a roadblock or had a question about my research. He has been an excellent teacher and mentor to me. He has constantly helped me improve myself in all aspects of my career including scientific writing and communication skills. Moreover, I am extremely thankful to my committee members, Dr. Eva Almenar (School of Packaging, Michigan State University) and Dr. Yan Liu (Biosystems and Agricultural Engineering, Michigan State University) for their invaluable time commitment, expertise and suggestions. I would also like to acknowledge Mr. Aaron Walworth (School of Packaging, Michigan State University) and Mr. Mike Rich (Composite Materials and Structures Center, Michigan State University) for helping me learn and set up equipment used as a part of this study. Additionally, I am grateful to my colleague Dr. Cheng Xing and undergraduate students, Anna Marra, Lauren Chard and Cameron Freisen for their help with this research. We gratefully acknowledge the USDA Forest Service and The U.S. Endowment for Forestry and Communities-P3Nano (Grant No. P3-8b) for financial support of this research work. Also, I extend my heartfelt gratitude to the School of Packaging, its faculty and staff. Finally, I must express my very profound gratitude to my parents for providing me with unfailing support and continuous encouragement. They have always been there for me whenever I needed them. This thesis would not have been possible without them. I am also very grateful to my friends, Gauri and Shivam, for constantly cheering me up. Thank you. v TABLE OF CONTENTS LIST OF TABLES ....................................................................................................................... viii LIST OF FIGURES ........................................................................................................................ x Chapter 1 ......................................................................................................................................... 1 INTRODUCTION .......................................................................................................................... 1 1.1 Introduction ............................................................................................................................... 1 1.2 Objectives ................................................................................................................................. 7 1.3 Hypothesis................................................................................................................................. 8 1.4 Structure of thesis ..................................................................................................................... 8 REFERENCES ............................................................................................................................... 9 Chapter 2 ....................................................................................................................................... 13 BACKGROUND AND LITERATURE REVIEW ...................................................................... 13 2.1 Introduction ............................................................................................................................. 13 2.2 Poly (lactic acid) ..................................................................................................................... 13 2.2.1 Synthesis of PLA ..................................................................................................... 13 2.2.2 Properties of PLA .................................................................................................... 15 2.2.2.1 Thermal properties .................................................................................... 16 2.2.2.2 Mechanical properties ............................................................................... 16 2.2.2.3 Barrier properties ...................................................................................... 16 2.2.2.4 Rheological properties .............................................................................. 18 2.3 Processing technologies of PLA ............................................................................................. 20 2.3.1 Drying ...................................................................................................................... 20 2.3.2 Extrusion .................................................................................................................. 21 2.3.2.1 Blown film extrusion ................................................................................ 21 2.3.2.1.1 Rheological requirements of material ........................................ 22 2.3.2.1.2 Processing parameters affecting film quality ............................. 23 2.3.2.1.2.1 Temperature profile .................................................... 24 2.3.2.1.2.2 Take-up ratio (TUR) ................................................... 24 2.3.2.1.2.3 Internal air pressure..................................................... 25 2.3.2.1.2.4 External air pressure ................................................... 25 2.3.2.1.3 Defects ....................................................................................... 25 2.3.2.2 Cast film extrusion .................................................................................... 27 2.3.2.3 Extrusion blow molding ............................................................................ 28 2.3.3 Injection ................................................................................................................... 28 2.3.3 1 Injection blow molding ............................................................................. 29 2.3.3 2 Injection stretch blow molding ................................................................. 29 2.3.4 Thermoforming ........................................................................................................ 30 2.3.5 Foaming ................................................................................................................... 30 REFERENCES ............................................................................................................................. 32 vi Chapter 3 ....................................................................................................................................... 37 EXPERIMENTAL ........................................................................................................................ 37 3.1 Materials ................................................................................................................................. 37 3.1.1 Melt flow index (MFI) ............................................................................................. 38 3.1.2 Thermal properties ................................................................................................... 39 3.2 Sample manufacturing ............................................................................................................ 40 3.2.1 Rheological measurements ...................................................................................... 40 3.2.1.1 Shear viscosity .........................................................................................
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