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Title:Advanced manufacturing of sustainable materials
Author(s):Lloyd, Evan Michael
Director of Research:Moore, Jeffrey S; Sottos, Nancy R
Doctoral Committee Chair(s):Schroeder, Charles M
Doctoral Committee Member(s):Guironnet, Damien S
Department / Program:Chemical & Biomolecular Engr
Discipline:Chemical Engineering
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):frontal polymerization
transient materials
metastable polymers
Abstract:Since Bakelite and Rayon were first introduced in the early twentieth century, global plastic production has grown to over 300 million metric tons per annum and is expected to double in the next twenty years. Unfortunately, plastics were integrated into our daily lives and virtually every industrial sector without first considering the lifecycle of these materials. Despite their ease of processing, polymeric materials require significant external energy inputs during manufacturing, and subsequently, plastics have an embodied energy that greatly exceeds most material classes. Further, the covalent chemical networks to which plastic materials owe their exceptional performance also prevents their degradation. Polymeric materials are, therefore, accumulating in our landfills and oceans at alarming rates. To prevent further damage to our ecosystem, both the initial manufacture and the end of life of plastic materials must be engineered for sustainability. We first created a model system capable of cycled polymerization and depolymerization utilizing an engineering thermoplastic with a low ceiling temperature, cyclic poly(phthalaldehyde) (cPPA). cPPA depolymerization proceeded under mild thermal conditions, and quantitative recovery of the monomer was possible. Direct repolymerization of the recovered monomer yielded high-quality materials with chemical and mechanical properties equivalent to or greater than the original material. Closed-loop recycling of cPPA was also extended to fiber-reinforced polymer composites. cPPA depolymerization proceeded without damage to the fibers, and both the fiber reinforcements and the composite materials retained 100 % of their mechanical performance through multiple generations. To improve the performance of cPPA-based materials, we explored the thermal depolymerization mechanism and discovered that single electron transfer (SET) and cleavage of the resulting radical cation served as the primary thermal trigger for cPPA depolymerization. These findings were extended to other modes of SET triggering, including photoredox catalysis. Incorporation of acridinium salts into cPPA blends yielded photodegradable monolithic solids that rapidly deteriorated in the presence of UV-light. The discovery of a SET triggering mechanism provides a route towards novel environmental triggers including electrochemical oxidation and enzymatic catalysis. We next sought to address the initial manufacture of polymeric materials, specifically patterned materials. In synthetic systems, patterns are often generated through lengthy multistep processes and access to spatially varying properties is limited. Patterns in natural systems, however, arise through non-deterministic symmetry-breaking events. Impressively, natural patterns are replicated throughout species with high fidelity of both function and form. Inspired by natural phenomena, we leveraged the competition between reaction and thermal transport processes of frontal polymerization to create tunable thermal instabilities and spontaneous breaks from symmetry. The undulations in reaction temperature were harnessed to drive orthogonal chemistries and pattern the morphological, optical, chemical, and mechanical properties of engineering polymers. The complex dynamics of frontal polymerization represent a path towards the non-deterministic, developmental manufacturing of synthetic materials. Finally, the concepts of frontal polymerization and degradable materials were combined by copolymerizing cleavable cyclic olefins during the frontal ring-opening metathesis polymerization (FROMP) of dicyclopentadiene (DCPD). FROMP copolymers possessed material properties that were comparable with native pDCPD, but they were easily degraded into high-value fragments by hydrolysis. The degradation fragments, which were rich in hydroxyl functionality, were recycled into polyurethane networks by reaction with commercially available diisocyanates. The recycled materials displayed thermomechanical properties that greatly exceeded those of the original copolymer, a true embodiment of upcycling. We foresee many opportunities for the energy-efficient manufacture of multifunctional materials by frontal copolymerization.
Issue Date:2021-01-26
Rights Information:Copyright 2021 Evan Michael Lloyd
Date Available in IDEALS:2021-09-17
Date Deposited:2021-05

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