Controlled Fragmentation of Polyolefinic Materials triggered by Microwave Irradiation

Clemson University, Clemson SC

Investigators

Abstract

This project seeks to develop a novel strategy to convert a large class of conventional thermoplastics into materials suitable for further reuse, recycling, and upcycling. The design of materials that retain properties of conventional thermoplastics but are capable of end-of-life controlled deconstruction into reusable polymer chain fragments will be targeted. The polymer chain fragments produced by this thermal decomposition process will be used to synthesize recyclable polyesters, which in turn are expected to contribute to a circular economy, an economic system that reduces waste and avoids excessive use of resources. Polymer synthesis, materials fabrication, and multiscale modeling will be integrated in this project. The project is expected to establish guidelines for efficient design of thermoplastic materials; the ability to manufacture these materials could potentially open a novel direction in large-scale applications of recyclable components employed in the household, construction, automotive, and other sectors of the U.S. economy. The project will offer ample research and educational opportunities for graduate, undergraduate, and local high school students. Students working on this project will gain knowledge of fundamental concepts and an understanding of current challenges in materials science and sustainability. This multidisciplinary project is expected to stimulate the undergraduate and K-12 students’ interest and increase public awareness in STEM fields via gaining knowledge of the state-of-the-art polymer recycling/upcycling technologies. A strong emphasis will be placed on actively recruiting students with underrepresented backgrounds. Some of the outcomes of the research and relevant educational materials will be made available to the broad scientific community via a science and engineering gateway, nanoHUB, which is a part of the Network for Computational Nanotechnology. The objective of this research program is to develop a manufacturing strategy that enables microwave-triggered chemical upcycling of polyolefinic materials after their end-of-life. The design of polyolefinic materials (POMs) with properties of conventional polyolefins but capable of controlled deconstruction into macromolecular chain fragments with well-defined molecular weight distribution will be targeted. Functionalized nanosheets dispersed within the POMs will localize heating and trigger fragmentation upon application of short microwave pulses. Macromolecular chain fragments will be further used to synthesize recyclable semicrystalline polyesters (RPEs). Furthermore, cyclic depolymerization and repolymerization of these semicrystalline polyesters will be demonstrated. Experimental studies and computational modeling will be iteratively integrated. A multiscale model integrating coarse-grained (energy-conserving dissipative particle dynamics) and continuum approaches will be developed. Model parameters will be based on the experimental data, and model predictions will be validated with experiments. Modeling predictions will be used to understand and optimize the fragmentation process and RPE synthesis and depolymerization to achieve a targeted molecular weight distribution of chain fragments and to optimize depolymerization and repolymerization yield for the recyclable semicrystalline polyesters. The designed polyolefinic microwave-triggered fragmentation functionality will be built-in during fabrication without compromising the mechanical properties of the materials. The proposed research directly addresses current challenges by focusing on developing efficient chemical processes, improving environmental sustainability, designing tailor-made materials, and developing computer simulation approaches aiding composite material synthesis and processing. The multiscale modeling framework developed herein will account for the reactions, heat transfer, and diffusion of all the species including chain fragments, macroradicals, and low molecular weight reagents. This model, in conjunction with experimental validation, will allow one to gain a fundamental understanding of the dynamic processes taking place during controlled fragmentation and subsequent depolymerization/repolymerization cycles. The realization of the proposed program is anticipated to have a transformative impact on development of deconstructable-on-demand thermoplastics, with properties and processability of currently employed materials. Polyolefinic materials produced from plastic waste are envisioned to become an essential part of the circular economy. Undergraduate and graduate students will be trained in model and code development and in materials synthesis, fabrication, and characterization. Importantly, the students focusing on materials modeling and the students conducting experiments will interact closely within this project, so that all the students involved will gain a valuable collaborative experience and a broader perspective on their projects. A strong emphasis will be placed on supporting student diversity. Further, this project is expected to stimulate undergraduate and K-12 students’ interest in STEM fields. Selected research outcomes will be incorporated into courses taught by both PIs; related educational materials will be made available via the nanoHUB portal. This project is jointly funded by the Process Systems, Reaction Engineering, and Molecular Thermodynamics Program of ENG/CBET and the Established Program to Stimulate Competitive Research (EPSCoR), 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.