Vitrimerization of rigid thermoset polyurethane foams: A mechanochemical method to recycle and reprocess thermosets

Polyurethane (PU) thermosets are extensively used in different applications and recycling the large amount of PU thermoset waste remains a universal challenge. Recycling the thermoset waste through vitrimerization is a feasible, cost-effective, and environmental-friendly approach. In this work, triazabicyclodecene (TBD) is used as organocatalyst in the vitrimerization process to recycle and reprocess thermoset rigid polyurethane foams. The results show that the permanent crosslinked structure of the PU thermoset foam is converted to a dynamic network upon vitrimerization. The vitrimerized network can rapidly relax the stress in 10 s at temperatures as low as 120 degrees C. The topology rearrangement happens through the carbamate exchange reaction, mainly via a dissociative mechanism. The vitrimerized network retains high mechanical strength with Young's Modulus of 2.7 GPa and tensile strength of 76.4 MPa and can be reprocessed for a second time without addition of extra catalyst and without loss in mechanical properties. The vitrimerized network can also be foamed by applying small pressure at high temperatures.