Recycling and Upcycling of Polyurethane Thermosets: The Second Life of Polymers

Polyurethanes (PU) have been widely utilized in various advanced sectors, from insulation, elastomers, adhesives, and coatings to civil engineering materials. However, within the framework of the circular economy and in light of the urgent need to reduce the environmental impact of plastics, technologies have been designed, assessed, and exploited for the recycling and upcycling of discarded PU thermosets, which are chemically crosslinked and difficult to reprocess. This review comprehensively examines the current state of PU thermosets, discusses various recycling technologies, and highlights emerging upcycling strategies that promise to transform low-value waste into high-performance products. By also addressing the design of smart PU derivatives featuring reversible covalent and non-covalent bonds, this paper provides a detailed analysis of how innovative material design can promote a more sustainable and circular life cycle for PU thermosets. Finally, the review offers perspectives on future research directions and industrial implementation of recycled/upcycled PU thermosets, providing readers with some perspectives about the possible future developments.