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Barrier Properties of Ethylene Vinyl Alcohol Films

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Barrier Properties of Ethylene Vinyl Alcohol Films BARRIER PROPERTIES OF ETHYLENE VINYL ALCOHOL FILMS IN THERMAL PROCESSING By KEREILEMANG KHANAH MOKWENA A dissertation submitted in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY WASHINGTON STATE UNIVERSITY Department of Biological Systems Engineering MAY 2010 To the Faculty of Washington State University: The members of the Committee appointed to examine the dissertation of KEREILEMANG KHANAH MOKWENA find it satisfactory and recommend that it be accepted. _______________________________ Juming Tang, PhD., Chair _______________________________ Marvin Pitts, PhD. _______________________________ Carolyn F. Ross, PhD. _______________________________ Marie-Pierre Laborie, PhD. ii ACKNOWLEDGEMENT I would like to thank my advisor, Dr. Juming Tang, for his great support throughout the years I spent here at Washington State University. I acknowledge his tireless efforts in providing technical and scientific direction for me to carry out my research. The financial support afforded for both research and personal living cannot be overemphasized. Through him I was able to stay and work with EVAL Company of America where I learned a great deal about the materials used in this study, and gained appreciation of industry work. I also thank my committee members Dr. Marvin Pitts, Dr. Carolyn Ross and Dr. Marie-Pierre Laborie for all their constructive critique which helped to shape my research work and contributed positively to my research experience. My colleagues and fellow students are not to be forgotten for their everyday assistance. Galina Mikhaylenko has all the patience and determination to attend to each and every small and big issue around the laboratory. Gopal Tiwari helped a lot with some of the issues I went through in executing experiments and analyzing my data. Dr. Frank Liu assisted with the initial pilot plant experiments that shaped up the whole research. Wayne Dewitt often helped me with fixing my test cell whenever something went wrong. I thank them and other unnamed colleagues for their often overlooked support. I owe much to EVAL Company of America for giving me an opportunity to do a major part of my experimental work in their facilities with their technical support. Their financial support allowed me to stay two summers in Houston, TX, to carry out this work. The staff at Kuraray Research and Technical Center in Pasadena, TX, were all great to iii work with: Edgard, Robert, Al, Julie, Tammie and others. I also thank Dr Nindo and Binying Ye of the University of Idaho in Moscow, ID, for letting me use their equipment for some of my experiments. I thank Dr Shyam Sablani and the students in his laboratory, particularly Roopesh Syamaladevi, for assistance in some of my work. My heartfelt appreciation goes to my family who provided the much needed moral support. My husband Patrick was a great inspiration and his daily encouragement kept me motivated everyday even though we were miles apart. My little Lara-Mmei had to live with the daily paperwork from the day she was born. I thank all the friends I made in Pullman since I came here. Finally, I acknowledge the financial support and the opportunity I was given by my employer, Botswana College of Agriculture, to come and have the experience here at Washington State University. iv BARRIER PROPERTIES OF ETHYLENE VINYL ALCOHOL FILMS IN THERMAL PROCESSING ABSTRACT by Kereilemang Khanah Mokwena, PhD Washington State University May 2010 Chair: Juming Tang Ethylene vinyl alcohol (EVOH) copolymers are widely used in food packaging for shelf stable foods because of their good oxygen barrier. However, EVOH is very sensitive to moisture which adversely affects its oxygen barrier. The overall objective of this research was to understand the influences of thermal processing on oxygen barrier properties of multilayer EVOH films, with emphasis on influence of water absorption by packaging films when exposed to conditions of high moisture and high temperature during processing. The research focused on two multilayer films containing EVOH as the oxygen barrier which were used as lidstock for rigid trays. Film A was a laminated structure of oriented polyethylene terephthalate (PET), EVOH and polypropylene (PP). Film B consisted of PET laminated to a co-extruded structure of PP/tie/Nylon 6/EVOH/Nylon 6/tie/PP. Oxygen transmission rates were measured on films after retort v and combined microwave-hot water heating under conditions necessary to produce shelf- stable low acid foods. For both films, the retort treatments resulted in more deterioration of the oxygen barrier than microwave treatments. This was attributed to the amount of moisture absorbed during retort treatment, which was thought to be directly related to duration of direct exposure of films to high temperature humid environment during processing. Storage of packages for 2 months under ambient conditions resulted in recovery of more than 50% of the oxygen barrier. Further studies were carried out to investigate the relationship between the amount of water absorbed during retort processing and oxygen transmission through the films. Results confirmed dramatic increases in oxygen transmission at high film water contents which was attributed to plasticization and stresses created by high moisture and temperature conditions. Water absorption behavior of multilayer films was also studied at different temperatures and compared to monolayer films representing the individual components of the multilayer films. A preliminary study on use of split post dielectric resonator (SPDR) technique as a method for measuring amount of water in polymers was carried out. The measured dielectric property data correlated well with water absorption data, indicating that the method can be used to rapidly and non-destructively measure water absorption in these films. vi Table of Contents ACKNOWLEDGEMENT ................................................................................................. iii ABSTRACT ........................................................................................................................ v LIST OF TABLES ............................................................................................................ xii LIST OF FIGURES ......................................................................................................... xiii CHAPTER 1 INTRODUCTION ........................................................................................ 1 1.1 Background .......................................................................................................... 1 1.2 Rationale ............................................................................................................... 3 1.3 Research Hypothesis and Objectives ................................................................... 4 1.4 Research Layout ................................................................................................... 8 References ....................................................................................................................... 9 CHAPTER 2 REVIEW OF ETHYLENE VINYL ALCOHOL ....................................... 11 2.1 Introduction ........................................................................................................ 11 2.2 Overview of Oxygen Barrier Properties of EVOH ............................................ 13 2.3 EVOH Synthesis ................................................................................................ 15 2.4 Degree of Crystallinity ....................................................................................... 17 2.4.1 Molecular and Crystal Structure of EVOH ................................................. 19 2.4.2 Orientation .................................................................................................. 24 2.5 Free Volume ....................................................................................................... 25 vii 2.6 Glass Transition .................................................................................................. 26 2.7 Sensitivity of EVOH to Moisture ....................................................................... 28 2.7.1 Effect on Oxygen Permeability ................................................................... 30 2.7.2 Effect on Glass Transition Temperature ..................................................... 31 2.8 EVOH Use in Food Packaging ........................................................................... 33 2.9 Conclusions ........................................................................................................ 36 References ..................................................................................................................... 37 CHAPTER 3 THERMAL PROCESSING EFFECTS ON OXYGEN TRANSMISSION RATES OF MULTILAYER EVOH FILMS .................................................................... 46 3.1 Introduction ........................................................................................................ 46 3.2 Overview of Thermal Processing Methods ........................................................ 48 3.3 Materials and Methods ....................................................................................... 51 3.3.1 Experimental Design ................................................................................... 51 3.3.2 Description of Multilayer EVOH Films and Rigid Trays ........................... 52 3.3.3 Preparation of Mashed Potato ....................................................................
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