Upcycling of thermoplastic polyurethane into covalent adaptable networks via chain breaking-crosslinking strategy

Thermoplastic polyurethane (TPU), as one of the most widely used elastomers, has received rapid development, and its recycling becomes increasingly urgent. In this work, a TPU is upcycled to PU covalent adaptable networks (CANs) via chain breaking-crosslinking strategy of being extruded with polyol and isophorone diisocyanate (IPDI) on a micro twin-screw extruder. The carbamate exchange between the polyol and TPU breaks the chain of TPU and introduces plenty of reactive hydroxyl groups, which activates the TPU chain. Long-chain-branched TPU with hydroxyl groups is obtained during the chain-breaking step and then crosslinked with IPDI to obtain highly crosslinked networks. PU-CANs exhibit improved mechanical properties and elastic recovery rate, which is propitious to elastomers. Moreover, the crosslinked network greatly enhances the creep resistance and solvent resistance of the material. PU-CANs maintain favorable reprocessability, suitable for screw extrusion and hot-press processing. This work provides a simple and efficient method to upcycle TPU into reprocessable highly-crosslinked polymers and improve the properties of polymers. Graphical