University of Tennessee, Knoxville TRACE: Tennessee Research and Creative Exchange Doctoral Dissertations Graduate School 5-2021 Stretching the applications of biomass: Development of lignin based thermoplastic elastomers and composite materials Anthony Stephen Bova [email protected] Follow this and additional works at: https://trace.tennessee.edu/utk_graddiss Part of the Polymer and Organic Materials Commons, Polymer Chemistry Commons, and the Polymer Science Commons Recommended Citation Bova, Anthony Stephen, "Stretching the applications of biomass: Development of lignin based thermoplastic elastomers and composite materials. " PhD diss., University of Tennessee, 2021. https://trace.tennessee.edu/utk_graddiss/6634 This Dissertation is brought to you for free and open access by the Graduate School at TRACE: Tennessee Research and Creative Exchange. It has been accepted for inclusion in Doctoral Dissertations by an authorized administrator of TRACE: Tennessee Research and Creative Exchange. For more information, please contact [email protected]. To the Graduate Council: I am submitting herewith a dissertation written by Anthony Stephen Bova entitled "Stretching the applications of biomass: Development of lignin based thermoplastic elastomers and composite materials." I have examined the final electronic copy of this dissertation for form and content and recommend that it be accepted in partial fulfillment of the equirr ements for the degree of Doctor of Philosophy, with a major in Energy Science and Engineering. Amit K. Naskar, Major Professor We have read this dissertation and recommend its acceptance: David Harper, Nicole Labbe, Sudarsanam Babu Accepted for the Council: Dixie L. Thompson Vice Provost and Dean of the Graduate School (Original signatures are on file with official studentecor r ds.) Stretching the applications of biomass: Development of lignin based thermoplastic elastomers and composite materials A Dissertation Presented for the Doctor of Philosophy Degree The University of Tennessee, Knoxville Anthony Stephen Bova May 2021 Copyright © 2021 by Anthony Stephen Bova All rights reserved. ii DEDICATION I dedicate this work to my mom, Genevieve. Every day, you encouraged me to reach for the future and spend time doing what makes me happy, because that was the true definition of success. I know you would be here to celebrate with me, if you could. iii ACKNOWLEDGEMENTS My time as a graduate student, and completing this dissertation has been one of the most enlightening, educational, and challenging things I’ve ever set out to do. As an undergraduate student finishing a degree in chemistry, I only had a small insight into what it would take to complete a PhD. I’m happy to extend my most heartfelt thanks to everyone who has supported me along this journey. To my advisor, Dr. Amit Naskar. Thank you for extending the offer to join your research group, and making me feel like a colleague from day one. Being your first graduate student was a learning process for both of us, and I am grateful to have had the exposure to not only your experience and insights, but the broader implications of what it meant to be a successful, interdisciplinary researcher. You helped me think both about science and engineering, fundamental and application, and laboratory to industry. To my committee. Drs. Niki Labbé, David Harper, and Suresh Babu for the time and energy they have taken to mentor me, provide insight and guidance into an entirely new field of materials science that I had little background in coming into my graduate career as a chemistry undergraduate, and for the continued feedback on this dissertation. To my labmates, Kokouvi Akato, Daniel Webb, Jimmy Kron, Chau Tran, Ramiz Boy, Kelly Meek, Ngoc Nguyen, Chris Bowland, Logan Kearney, and Nihal Kanbargi. Each of you taught me something new, provided great conversation and distraction on those languishing long laboratory days, and continue to inspire me with everything you do today. Whether it was an official lab meeting or a beer after work, your input was valuable in so many ways. I am incredibly honored to have met and been supported by Dr. Lee Riedinger, Dr. Mike Simpson, Wanda Davis, Dr. Suresh Babu, and the entire staff of The Bredesen Center. When I was an undergraduate student looking for interdisciplinary graduate programs, I never imagined I could find such a perfect fit of deep science academics, knowledge breadth flexibility for my interests in entrepreneurship and technology commercialization, and camaraderie with such a phenomenal group of peers across disciplines. The environment fostered in our program has been beyond supportive in every way – even during some of the most challenging times during this journey for me as a person. iv To the Haslam College of Business, where I became an unofficial student devouring every course on entrepreneurship I was allowed to take. I am eternally grateful for the openness in which you embraced students from outside the business world into your circle. To Lynn Youngs, Shawn Carson, and Tom Graves – thank you so much for including me in so much. I really felt like a member of the community that could offer my insight in a unique way that addressed the intersection of science, engineering, and entrepreneurship. To all of my friends that I had the pleasure of meeting during this journey, who were there with me to celebrate the high points and drink beer and complain about the low points. You know who you are. Spending our weekends closing down the pool table at the bar, trips to waffle house, and weekends brewing beer while we talked about how to approach the next conference presentations we had and classes we really loved (or hated). In particular, I have to thank Jeff Beegle, my close friend from undergrad, fellow graduate student, business partner and Lieutenant Beard. Who knew that a group of students with two beards and a pitch deck could take our science dreams and turn them into an actual business, write grants to collaborate with professors and businesses internationally, and have a heck of a good time doing it. For all of my education up to this, point, I cannot begin to thank all of those teachers and professors. In particular, so many of the amazing science teachers I’ve had. Mrs Amy Roediger, my high school chemistry teacher, for showing me how exciting this field of science really is. Dr. Mark Mason, my undergraduate research advisor and mentor, for teaching me the fundamentals of Green Chemistry and really encouraging me to think of ways where waste materials were feedstocks for a sustainable future. Lastly, I could not have done any of this, been where I am, and been who I am, without my family. Thank you to my dad, who was certainly one of the most patient parents in the world as I slowly rose from an unmotivated high schooler to CEO with a PhD. To my mom, whom I miss so much, for all of the little things she sacrificed so I could get not only the things I needed, but that I wanted. To my cat Dexter, who almost made it the entire way through it all. My dogs Pepperoni and Rogue, who are always in good spirits no matter the day. And last, but not least by any stretch of the imagination, my partner, my other half, my rock, Dr. Mallory Ladd. I am incredibly lucky to have found you in that nerdy chemistry club 10 years ago, and am proud to be your husband. You’ve supported me in more ways than you know. I love you – forever my Dr. Girlfriend. v ABSTRACT Bio-based plastics and composites have seen increased industry adoption in recent years due to growing demand for materials with a low carbon footprint. The use of lignin as a feedstock for polymers has seen growing interest as the concept of an integrated cellulosic biorefinery gains traction and advances the need to use all components of separated biomass for value-added applications. Historically, use of lignin in thermoplastic and elastomeric copolymers and blends has been bottlenecked by the inability to introduce lignin content above 30 weight percent due to difficulties with interfacial adhesion of lignin with other soft segments. Efforts to overcome this have typically involved solvent-based chemical modification of lignin, requiring energy intensive solvent separation, and generating waste. In this document, we demonstrate a solvent-free, reactive compounding method to produce lignin-based thermoplastic elastomers with lignin contents as high as 70 weight percent. Our ability to control the dispersion of nano-sized domains of lignin in synthetic elastomers with enhanced interfacial adhesion has resulted in thermoplastic elastomers with tunable mechanical properties, with tensile strengths as high as 45 MPa [megapascals] in some variations, rivaling some engineering thermoplastics like nylon and ABS [acrylonitrile butadiene styrene]. We found that by varying lignin content, type, and additives, the ultimate tensile strength and toughness of the materials could be controlled. Lignins displayed the ability to participate in free-radical based crosslinking, both in the presence of an initiator and spontaneously. Additionally we demonstrated that lignin-based elastomers could be used to create fiber reinforced composites using bio-based fibers such as kenaf and hemp that demonstrate flexibility while maintaining significant tensile strengths. The demonstration of bio-based, flexible thermoplastic elastomers and elastomeric composites that make use of lignin, without the need for solvent-based chemical modification, presents significant promise for the future of renewable