Clemson University TigerPrints All Theses Theses 12-2014 Microanalysis of Polymer Chain Diffusion in Heat Seals Russell Cooper Clemson University, [email protected] Follow this and additional works at: https://tigerprints.clemson.edu/all_theses Part of the Engineering Science and Materials Commons, Materials Science and Engineering Commons, and the Polymer Science Commons Recommended Citation Cooper, Russell, "Microanalysis of Polymer Chain Diffusion in Heat Seals" (2014). All Theses. 2039. https://tigerprints.clemson.edu/all_theses/2039 This Thesis is brought to you for free and open access by the Theses at TigerPrints. It has been accepted for inclusion in All Theses by an authorized administrator of TigerPrints. For more information, please contact [email protected]. MICROANALYSIS OF POLYMER CHAIN DIFFUSION IN HEAT SEALS A Thesis Presented to the Graduate School of Clemson University In Partial Fulfillment of the Requirements for the Degree Master of Science Packaging Science by Russell Timms Cooper December 2014 Accepted by: Dr. Duncan Darby, Committee Chair Dr. Robert Kimmel Dr. Patrick Gerard ABSTRACT Heat sealing is an integral method for the closure and protection of packaging. Previous work has shown that seal strength is developed by the interdiffusion of polymer chains within heat seals. Heat seals were made between two dissimilar materials. Poly(ethylene-co-acrylic acid) (EAA) was heat sealed to ionomer. Diffusion within the EAA-ionomer heat seals was estimated. The diffusion estimates were then related to resulting seal strength in the EAA-ionomer sealant system. Heated tooling sealing was utilized to make heat seals at 40 psi (275.79 kPa), 0.5 seconds, and a range of temperatures between 180˚F (82.22˚C) and 300˚F (148.89˚C). Scanning electron microscopy and energy dispersive x-ray spectroscopy was employed to measure the diffusion of polymer chains within the heat seals. Two estimators for polymer chain diffusion were made for each heat seal. The results of this study agree with previous theories and computations on heat sealing. Polymer chain diffusion was measured in two ways. It was found that heat energy drives polymer chain diffusion. Diffusion consistently increased as the heat seal temperature was increased. Greater polymer chain diffusion distances resulted in heat seals with greater seal strength. ii DEDICATION I dedicate this body of work to my friends and family. Pursuing my M.S. in Packaging Science was the greatest decision that I have made in my life so far. However, it was not an easy decision. Packaging was an uncharted territory for me before I started my master’s work. I thank my best friend, Jennifer Johnson, for encouraging me to break out and pursue this endeavor. Today, it is hard to imagine a better career fit for myself than packaging. I would not have made it through my daily struggles without the help of my friends and family. My parents molded me into the person that I am today and I’m forever grateful. iii ACKNOWLEDGMENTS I would like to thank my graduate advisor, Dr. Duncan Darby, for guidance throughout this research. Dr. Darby is not your typical advisor, teacher, or scientist. He cares about the unmeasureable traits within people and works to bring the best out of the people that he works with. He doesn’t see situations and problems in black and white. He sees the grays. I was smart enough to listen to Dr. Darby and try to absorb his way of thinking. There is no doubt that I am a better scientist and a better person after working under him. Dr. Robert Kimmel and Dr. Patrick Gerard were also great influences in my research. It was clear from the beginning that the cared about my work as much as I did. This level of support is something special and something that I am thankful for. Pat Marcondes and Jerry Stoner were like second parents to me throughout my work. They imparted their experiences and wisdom in the lab to help me with important decisions in my research. Finally, I would like to thank the Packaging and Specialty Plastics TS&D department at The Dow Chemical Company for material donations and guidance throughout my research. This research would not have happened without the materials that were donated. Thank you for taking the time to advise me on my research. iv TABLE OF CONTENTS Page TITLE PAGE .................................................................................................................... i ABSTRACT ..................................................................................................................... ii DEDICATION ................................................................................................................ iii ACKNOWLEDGMENTS .............................................................................................. iv LIST OF TABLES ......................................................................................................... vii LIST OF FIGURES ...................................................................................................... viii CHAPTER I. INTRODUCTION ......................................................................................... 1 II. REVIEW OF LITERATURE ........................................................................ 4 Packaging ................................................................................................. 4 Packaging Materials ................................................................................. 5 Plastics for Packaging Applications....................................................... 19 Flexible Packaging ................................................................................. 28 Heat Sealing ........................................................................................... 31 Heat Sealing Methods and Applications ................................................ 38 Seal Strength Testing and Seal Failure Modes ...................................... 41 Previous Work ....................................................................................... 48 The Need for Polymer Chain Diffusion Measurement .......................... 52 Measuring Polymer Chain Diffusion ..................................................... 54 Scope of This Research Study ............................................................... 64 III. MATERIALS AND METHODS ................................................................. 65 Materials, Equipment, and Software ...................................................... 65 Selection of Materials ............................................................................ 67 Cast Film Extrusion ............................................................................... 69 Sample Preparation ................................................................................ 70 Heat Sealing ........................................................................................... 72 Seal Strength Testing ............................................................................. 76 Diffusion Measurement ......................................................................... 79 v Table of Contents (Continued) Page Diffusion Quantification ........................................................................ 87 IV. RESULTS AND DISCUSSION .................................................................. 91 Heat Seal Strength.................................................................................. 91 Polymer Chain Diffusion ..................................................................... 103 Relating Heat Seal Strength to Polymer Chain Diffusion ................... 112 V. CONCLUSIONS AND RECOMMENDATIONS .................................... 122 Conclusions .......................................................................................... 122 Recommendations for Future Work..................................................... 124 APPENDICES: SAS® Code Used for Diffusion Curve Quantification ..................... 127 REFERENCES ............................................................................................................ 128 vi LIST OF TABLES Table Page 1 Orbital and Subshell Capacities ..................................................................... 8 2 Bond Energy Examples for Various Types of Bonding .............................. 16 3 List of Materials ........................................................................................... 65 4 List of Equipment ........................................................................................ 66 5 List of Software............................................................................................ 67 6 Extruder Conditions for EAA Film Extrusion ............................................. 70 7 Electron Beam Settings ................................................................................ 83 8 EDS Linescan Settings ................................................................................. 86 9 Seal Strength Measurements for All Heat Seals ........................................ 101 10 SAS® Output for Change Point, Diffusion Slope, and Diffusion Distance Estimates for Specimen 3 of the 220˚F (104.44˚C) Heat Seal Batch ................................................. 107 11 Diffusion Slope Measurements for All Heat Seals .................................... 108 12 Diffusion Distance Measurements for All Heat Seals ............................... 110 vii LIST OF FIGURES Figure Page 1 Atomic Structure of Carbon ..........................................................................