Sustainable polyurethanes: toward new cutting-edge opportunities

Polyurethanes (PU) are ranked amongst the 6^th most manufactured worldwide polymers and are widely used in a variety of applications due to the diversity of properties they offer. Nevertheless, PUs are raising questions around environmental, legislative, health, and recycling concerns. In this context, due to the high isocyanate toxicity, blocked isocyanates, waterborne PU systems, and non-isocyanate polyurethane (NIPU) were introduced to prevent isocyanate handling risks. Moreover, sustainable feedstocks stood out to synthetize greener PU. In particular, bio-based polyfunctional short alcohol and isocyanate compounds have emerged to design fully bio-based PU materials with targeted chemical and mechanical properties. Finally, the large amounts of PU that have been placed on the market are now leading to environmental issues regarding its accumulation in the environment. Several methods have thus been recently developed to facilitate their end-of-life management and recyclability.

This review provides a complete overview on the most recent advances on PUs synthesis with focus on the replacement of toxic isocyanates and petroleum-based resources, the use of greener processes, and their recycling methods. After a quick summary on PUs history and worldwide situation, different bio-based alcohols and isocyanates introduced on academic and industrial sides, and the corresponding PU are outlined. Furthermore, different synthesis pathways to produce NIPUs are discussed. Finally, the enzymatic and chemical recycling of PUs are outlined.