ISOTROPIC FUSED FILAMENT FABRICATION ADDITIVE MANUFACTURING by Kejia Yang APPROVED BY SUPERVISORY COMMITTEE: ___________________________________________ Walter E. Voit, Chair ___________________________________________ Ronald A. Smaldone ___________________________________________ Mihaela C. Stefan ___________________________________________ Duck Joo Yang Copyright 2017 Kejia Yang All Rights Reserved For my mother None of it would have happened, if it weren’t for her. ISOTROPIC FUSED FILAMENT FABRICATION ADDITIVE MANUFACTURING by KEJIA YANG, BS, MS DISSERTATION Presented to the Faculty of The University of Texas at Dallas in Partial Fulfillment of the Requirements for the Degree of DOCTOR OF PHILOSOPHY IN CHEMISTRY THE UNIVERSITY OF TEXAS AT DALLAS December 2017 ACKNOWLEDGMENTS First I would like to thank my advisor, Dr. Walter Voit, for giving me the opportunity to join the Advanced Polymer Research Laboratory (APRL) to be part of numerous inspiring research projects. His support, guidance and willingness to provide me with freedom to operate both enabled this dissertation and allowed me to grow tremendously as a scientist. I have been fortunate to work with very talented colleagues in APRL and at UT Dallas. I would like to express my gratitude to my fellow lab mates Dr. Radu Reit, Dr. Jonathan Reeder, Tony Kang, Josh Salazar, Romil Modi, Dr. Greg Ellson, Lucy Ramirez, Aldo Garcia-Sandoval, Dr. Cary Baur, Mahmoud Hosseini, Yuta Suzuki, Zhuo Chen, Jing Xu, Chao Long, and post-doctoral researchers/research professors/APRL alumni Dr. Faisal Mahmood, Dr. Alexandra Joshi-Imre, Dr. Ben Batchelor, Dr. Taylor Ware, Dr. Benjamin Lund, Dr. Melanie Ecker, Keri Denson, Xavier Carrier, and Jesus Espinoza. Additionally, I appreciate the suggestions, insights, and collaborative efforts from my committee members, Prof. Ronald A. Smaldone, Prof. Mihaela Stefan, and Prof. DJ Yang. I am also very thankful for all the great efforts from all of the undergraduate students who have worked with me over the past four years; particularly I would like to recognize Francesca Daigle, Jesse Grant, Jacob Houser, Frankie Imperial, and Patrice Lamey, for their amazing work ethic and excellent leadership. It has been an honor to work with them. I would also like to thank Dr. Emily Jackson, Mark Douthey, David Stimson, and Kevin Masten for their invaluable support and patience to help me ensure the lab safety, diagnose and repair lab instruments, and even machine critical parts for lab instruments. Furthermore, I would like to express my appreciation to Renata Freindorf, for her excellent work on all the administrative work in APRL, and her indispensable help in my life outside of the lab. Finally, I would like to thank my family. We live an ocean apart, but the Pacific never gets in the way of their unconditional love and ever-lasting support. I am grateful to have a father who knows exactly when to stop holding my hand and begin watching my back. And I dedicate this dissertation to my mother, who was my confidant and my cheerleader in my life. Missing her dearly, I am trying to live my life to the fullest every day to carry on her legacy and make her proud. Most importantly, I want to thank my fiancé, Lunci, for his incredible patience and support, for his standing by me during the darkest days in my life, for powering me through the shenanigans in my graduate school life, and for his cheering on every little achievement I have obtained no matter how trivial it was. October 2017 ISOTROPIC FUSED FILAMENT FABRICATION ADDITIVE MANUFACTURING Kejia Yang, PhD The University of Texas at Dallas, 2017 ABSTRACT Supervising Professor: Dr. Walter E. Voit Additive manufacturing, also widely known as 3D printing, has attracted tremendous attention in almost every industry, from aerospace and defense, to automotive, electronics, dental and medical fields. It holds the promise to revolutionize the manufacturing. To date, however, parts printed from existing commercial materials for Fused Filament Fabrication (FFF) 3D printing, such as polylactic acid (PLA), acrylonitrile-butadiene-styrene (ABS), and NinjaFlex®, exhibit greater than 50% reductions in toughness when deformed perpendicular to the printed layers. The high anisotropy presented in the printed parts is the leading factor in the uncertain quality of final parts, and has obstructed FFF’s implementation in the additive manufacturing of functional engineering parts. In this work, two mechanisms are explored to enhance the interlayer adhesion, mitigate the anisotropy in printed parts and boost their reliability. One is the use of ionizing radiation to induce crosslinks between the printed layers after the part is printed. The γ ray radiation improves the interlayer adhesion by 60% in the case of parts printed from sensitized PLA. The other is applying dynamic furan-maleimide Diels-Alder chemistry in 3D printing materials, which has been validated as the second mechanism to introduce crosslinks into the vii printed part for anisotropy reduction. Parts printed from the Diels–Alder Reversible Thermoset (DART) polymers not only maintain greater than 95% toughness when deformed perpendicular to the printed layers, but exhibit smooth surface finish and reasonable bulk properties as well. Both mechanisms have enabled isotropic FFF 3D printing, and expanded the range of polymer choices for additive manufacturing applications that have more advanced requirements in materials and printed parts. viii TABLE OF CONTENTS ACKNOWLEDGEMENTS.............................................................................................................v ABSTRACT..................................................................................................................................vii LIST OF FIGURES........................................................................................................................xi LIST OF TABLES........................................................................................................................xvi CHAPTER 1 INTRODUCTION ...................................................................................................1 1.1 Motivation ................................................................................................................1 1.2 3D Printing and Additive Manufacturing ................................................................2 1.3 Ionizing Radiation Effects on Polymers ..................................................................5 1.4 Diels–Alder Chemistry ............................................................................................6 1.5 Objectives ................................................................................................................7 CHAPTER 2 MATERIALS AND METHODS .............................................................................9 2.1 Materials ..................................................................................................................9 2.2 Characterizations....................................................................................................11 2.3 Polymer processing ................................................................................................15 CHAPTER 3 ON REDUCING ANISOTROPY IN 3D PRINTED POLYMERS VIA IONIZING RADIATION ..............................................................................................................17 3.1 Introduction ............................................................................................................18 3.2 Experimental Methods ...........................................................................................23 3.3 Results ....................................................................................................................30 3.4 Discussion ..............................................................................................................43 3.5 Conclusion .............................................................................................................47 3.6 Perspective .............................................................................................................48 3.7 Acknowledgements ................................................................................................49 CHAPTER 4 HIGH GLASS TRANSITION REVERSIBLE THERMOSETS FOR ISOTROPIC FUSE FILAMENT FABRICATION 3D PRINTING ...................................................................50 4.1 Introduction ............................................................................................................50 4.2 Experimental ..........................................................................................................51 ix 4.3 Results ....................................................................................................................56 4.4 Discussion ..............................................................................................................58 4.5 Conclusion .............................................................................................................61 CHAPTER 5 DIELS–ALDER REVERSIBLE THERMOSET 3D PRINTING: ISOTROPIC THERMOSET POLYMERS VIA FUSED FILAMENT FABRICATION ..................................62 5.1 Introduction ............................................................................................................63 5.2 Results ....................................................................................................................68 5.3 Discussion ..............................................................................................................77