Thermoset polyurethane (PU) is a ubiquitous commodity plastic, and it is produced on the order of 10 million tons annually. Despite extensive use of PU thermosets, this plastic has well-recognized end-of-life challenges. Previous studies showed that Lewis acid catalysts such as dibutyltin dilaurate (DBTDL) can facilitate dynamic exchange between carbamate linkages. Consequently, addition of DBTDL to PU networks transforms them to covalent adaptable networks (CANs), and they are processable at elevated temperatures through twin-screw extrusion. While this method represents a significant breakthrough for PU recycling via carbamate exchange, organotins are immunotoxic, teratogenic, and environmentally toxic. Therefore, two green zirconium-based catalysts have been identified to improve viability and sustainability of this reprocessing method. Catalyst-containing foams were microcompounded, yielding PU films. Thermoset PU foams containing zirconium catalysts exhibit characteristic stress relaxation times from a range of 1-100 s, on par with or outperforming DBTDL. These catalysts are also capable of reprocessing PU foam up to four cycles, and dynamic mechanical thermal analysis indicates zirconium-based catalysts can preserve glass transition temperature and crosslink density between cycles. Therefore, these zirconium catalysts are appropriate green catalysts for bulk reprocessing of thermoset PU plastics. Further work on determining appropriate catalysts for different commercial PU waste streams and developing a solvent-free process will expand the viability of this bulk reprocessing method and thermoset PU circularity.

Reprocessing thermoset polyurethane through twin-screw extrusion and green catalysis

Fall 2022 abstracts, posters, and presentations will launch in mid-September.

ACS Fall 2022

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.