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Melt-Electrospinning of Thermoplastic Polymers Melt-electrospinning of Thermoplastic Polymers: An Experimental and Theoretical Analysis A Thesis Submitted to the Faculty of Drexel University by Jason Michael Lyons in partial fulfillment of the requirements for the degree of Doctor of Philosophy October 2004 ii DEDICATIONS I would like to dedicate this work to my entire family and my godfather without whom I would not be where I am today. They offered help both motivationally and financially whenever I was in need and were so unselfish in their desire to make all of my dreams come true. Whenever I had doubt of the final outcome, a solution or a smile was just a phone call away. To you all I am forever grateful and you will never understand the dept of thanks that I owe to you. Thank you for everything. iii ACKNOWLEDGEMENTS I would like to start by thanking my advisor, Dr. Frank Ko for taking me under his wing as a graduate student and not only sharing his knowledge with me throughout my four and a half years at Drexel, but by being a leader in the field of textile engineering to whom I aspire. Without your constant encouragement, advice, demands, and financially support, this work would not be possible. I would also like to thank Dr. Christopher Pastore who has been the driving force towards my graduate degree since 1997. Without his advice, and constant demands of me to perform better without even saying it, I am forever thankful. If you did not care what happened to your students, I may still be a fashion merchandising major. You pushed me to want to get a graduate degree, and you pushed me to want to exceed in my field of choice. You were always there whenever I needed anything at all and for that, I am still in debt. I must also extend thanks to my other committee members Dr. Christopher Li, Dr. Roger Doherty, and Dr. Yury Gogotsi. Your wisdom and ideas on how to deepen my understanding of my work were invaluable. Whether it be advice about modeling, polymers, or characterization, your ideas and suggestions always lead to a better understanding of my thesis topic. You would not accept mediocrity and you all pushed until the problem was solved on all levels of understanding. You have all been inspirations of what it is to be a teacher, researcher and friend. I thank you all. Special thanks must also be extended to Mr. David Von Rohr, Mr. Timothy Kelly, Ms. Hoa Lam, Ms. Gwénaëlle, Mr. Josh Houskamp, Mr. Kishore Kumar Tenneti, Mr. Heejae Yang, Dr. Miland Gandhi, Mr. Nick Titchenal, and Mr. Sean Fader who have all iv helped me to use some piece of machinery or software that was crucial to the completion of this thesis. Without you, I may still be reading the manual with 3 years left to finish my work. I thank you all very much. I would also like to thank the rest of the student body and faculty in the Department of Materials Science and Engineering. The friendships that were made will extend well beyond the duration of our graduate careers. The faculty that are not on my committee have taught me well and I have learned something from all of you, whether that be in a class room, a discussion about my thesis topic or over a drink at the Christmas parties. Thank you all so very much. Finally I would like to thank my mom and dad. They are the ones that pushed me to be the best that I can be and they never settled for anything less. Without them, I would not be where I am today…literally. v TABLE OF CONTENTS LIST OF TABLES...........................................................................................................viii LIST OF FIGURES ........................................................................................................... ix ABSTRACT..................................................................................................................... xiv CHAPTER 1: INTRODUCTION....................................................................................... 1 CHAPTER 2: LITERATURE REVIEW............................................................................ 4 2.1. Electrohydrodynamic Atomization.......................................................................... 4 2.2. Electrospinning ...................................................................................................... 10 2.3. Characterization ..................................................................................................... 19 2.3.1. Physical............................................................................................................20 2.3.2. Mechanical.......................................................................................................21 2.3.3. Chemical ..........................................................................................................23 2.4. Theoretical Modeling............................................................................................. 24 2.5. Trends in Electrospinning...................................................................................... 25 2.6. Statement of Problem............................................................................................. 26 CHAPTER 3: MATERIALS AND METHODS .............................................................. 31 3.1. Introduction............................................................................................................ 31 3.2. Materials ................................................................................................................ 31 3.3. Melt-electrospinning of Polypropylene and Poly(ethylene terephthalate) ............ 34 3.3.1. Melt-electrospinning Systems..........................................................................34 3.3.2. Experimental Parameters .................................................................................37 3.3.3. Collection Devices...........................................................................................39 vi 3.4. Melt-electrospinning Polypropylene with Vapor Grown Carbon Nanofibers....... 42 3.5. Annealing of Poly(ethylene terephthalate) and Polypropylene ............................. 45 3.6. Characterization Techniques.................................................................................. 46 3.6.1. Environmental Scanning Electron Microscope (ESEM) .................................46 3.6.2 Raman Micro-spectrometer ..............................................................................49 3.6.3 Differential Scanning Calorimetry (DSC) ........................................................50 3.6.4 Kawabata KES-G1E1 Single Fiber Tester........................................................52 3.6.5. Polarized Light Microscopy.............................................................................54 CHAPTER 4: RESULTS & DISCUSSION ..................................................................... 56 4.1. Polypropylene Diameter ........................................................................................ 56 4.1.1. Diameter Frequencies ......................................................................................56 4.1.2. Mean Fiber Diameter of Polypropylene ..........................................................58 4.1.3. Effect of Electric Field Strength on Fiber Diameter........................................61 4.1.4. Effect of Molecular Weight on Fiber Diameter...............................................65 4.1.5. Effect of Polymer Tacticity on Fiber Diameter ...............................................68 4.1.6. Effect of Flow Rate on Fiber Diameter............................................................71 4.1.7. Effect of Processing Temperature on Fiber Diameter .....................................74 4.2. Melt-electrospinning with Carbon Nanotubes................................................ 78 4.3. Degraded Poly(ethylene terephthalate) Diameter.................................................. 79 4.3.1. Diameter Frequencies ......................................................................................79 4.3.2. Mean Fiber Diameter of Degraded Poly(ethylene terephthalate)....................81 4.3.3. Effect of Electric Field Strength on Fiber Diameter........................................82 4.4. Crystallinity and Chain Orientation....................................................................... 84 vii 4.4.1. Polypropylene ..................................................................................................84 4.4.2. Degraded Poly(ethylene terephthalate)............................................................94 4.5. Structure............................................................................................................... 100 4.5.1. Polypropylene ................................................................................................100 4.5.2. Degraded Poly(ethylene terephthalate)..........................................................103 4.6. Mechanical Properties.......................................................................................... 105 4.6.1. Polypropylene ................................................................................................105 4.6.2. Degraded Poly(ethylene terephthalate)..........................................................117 4.7. Empirical Modeling Through Response Surface Methodology .......................... 119 4.7.1 Polypropylene .................................................................................................119 CHAPTER 5: THEORETICAL MODELING ............................................................... 125 5.1. Introduction.........................................................................................................
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