Circular Reprocessing of Thermoset Polyurethane Foams.

Thermoset polyurethane (PU) foams are widely used in industrial applications, but they cannot be recycled by conventional melt reprocessing because of their cross-linked structures. The introduction of carbamate exchange catalysts converts thermoset PU into covalent adaptable networks (CANs), which are amenable to reprocessing at elevated temperatures. However, this approach has produced solid PU films, which have fewer uses and lower commercial demand. Here, we demonstrate simultaneous reprocessing and refoaming of thermoset PU foams by leveraging the melt-processability of PU CANs and allowing cell growth by gas generation in a twin-screw extruder. The optimal operating temperature of the refoaming process was determined through chemical, thermal, and structural analysis of PU foam extrudates. The foam-to-foam extrusion process produced controllable, continuous, and uniform foam structures, as characterized by cell diameter and cell number density. Low-density PU foams were obtained through a process simulating injection molding. The compression properties of reprocessed PU foam were compared with as-synthesized PU foam to demonstrate efficacy of the refoaming processes. These results demonstrate that PU foams can be prepared through recycling while maintaining microstructural and chemical integrity. In the future, this strategy might be applied to thermoset PU foams of various chemical compositions and shows promise for scalability. This article is protected by copyright. All rights reserved.