Low-temperature chemical upcycling of poly(ethylene terephthalate) waste to recyclable polyurethane thermosets using biomass-derived materials

Abstract

Addressing the global challenge of plastic waste, particularly poly(ethylene terephthalate) (PET), requires innovative chemical upcycling strategies. In this study, we report a sustainable approach for transforming PET waste into chemically recyclable polyurethane (PU) thermosets. Using a low-temperature glycolysis process with potassium carbonate, 1,4-butanediol and chlorobenzene, bis(4-hydroxybutyl) terephthalate (BHBT) was obtained with a conversion rate exceeding 99 % and an isolated yield of 55.4 %. The BHBT was subsequently used to synthesize PU thermosets with bio-based pentamethylene diisocyanate trimer and 2-methyltetrahydrofuran as a solvent. The resulting thermosets demonstrated excellent mechanical properties, including a tensile strength of 21.8 MPa, elongation at break of 151 %, and a Young’s modulus of 279 MPa. The PU thermosets were chemically recyclable, enabling a closed-loop process where BHBT was recovered with 84.5 % yield via glycolysis. Furthermore, the BHBT-based PU thermosets were successfully applied to carbon fiber-reinforced polymer composites, maintaining their mechanical integrity after recycling. This work highlights a promising route for the upcycling of PET waste, contributing to the development of sustainable polymer materials and supporting the principles of a circular economy.