Chemomechanics in the Solvent-Assisted Recycling of Engineering Composites

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Many engineering composites are troublesome to recycle because the polymers used in these materials are bonded together permanently. Currently, the disposal of composite wastes mainly relies on the landfills or incineration, which lead to significant environmental and health burdens. A new green, sustainable recycling method was recently developed to address this problem. It uses a bond-exchange reaction between a solvent and the composite to decompose the polymer material at a mild temperature and reclaim clean fibers. The decomposed products can be used to fabricate new composites with near identical material and mechanical properties for the same applications. However, due to the nascent development of this recycling technique, existing studies are limited to the proof of concept demonstrations. This award supports fundamental studies to uncover the relationships between waste material properties, processing conditions, recycling speed, and final mechanical properties of recycled thermosets and composites. The provided scientific knowledge will pave the road for the immediate applications of this innovative recycling method and significantly ease the environmental and health concerns associated with the traditional waste disposal methods. This research will also impact large-scale applications in other industries involving polymer decomposition and recycling, such as removable encapsulation of electronics, non-destructive surface coatings, controlled drug delivery, membrane science, and microlithography. Additionally, the project will provide opportunities to educate and train graduate and undergraduate students with a focus on underrepresented students in science, technology, engineering, and math.The research objectives will be realized using an integrated experimental - theoretical - computational approach at multiple length scales: In the microscale, constitutive chemomechanics relations will be defined to link the molecular-level bond-exchange reactions to the evolution of stress field, network structure, and mechanical properties of thermosets during the recycling. In the mesoscale, the constitutive relations will be incorporated into a computational model to study the influences of the fiber-polymer interface on the recycling performance of a composite lamina. In the macroscale, an efficient reduced-order computational model will be developed to guide the selection of solvent and processing conditions to recycle composite structures with the well-controlled geometry and mechanical properties. The chemomechanics theory defined in this award will be used to address three fundamental questions that are mostly concerned in the composite recycling industry: (i) how fast can the composites be recycled, (ii) what is the lowest recycling cost, and (iii) how to improve the mechanical properties of recycled products?This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.