Upcycling Biobased Polyurethane Foams into Thermosets: Toward the Closing of the Loop

Abstract

With the growing environmental concerns that society is nowadays facing, the development of biobased materials has intensified and biobased polyisocyanates have emerged in the market. Their commercialization enabled to synthesize the first four biobased polyurethanes foams (PUFs) from biobased isocyanates, containing up to 93% of renewable carbons. Their mechanical and thermomechanical properties were compared. In particular, one of the four PUF formulations was very promising: it foamed at room temperature and produced a low density foam 78 kg/m3, comparable to that of conventional fossil-based PUFs. To consider the full life cycle of such materials, these PUFs were upcycled and reshaped to bulk polyurethanes (PUs) by transcarbamoylation reaction up to 5 cycles. Moreover, a unique material (mixPU) composed of the four PUFs was prepared and reshaped, by compression molding at 160 °C for 30 min, thus demonstrating the potential of this recycling pathway for PUFs from different origins. Finally, stress-relaxation experiments were carried out to evaluate the dynamic properties of the mixPU material, which was shown to behave as a covalent adaptable network.