Sustainable foamed polyurethane composites with recycled content: Thermal decomposition and fire performance toward a circular material cycle

In this work, both chemical and mechanical recycling of rigid polyurethane foams (RPUFs) containing fly ash (FA) filler has been performed, and the flammability and thermal decomposition behaviour of the recycled products investigated to check their performance in a closed-loop material cycle. The glycolysis of FA-modified RPUF waste, using diethylene glycol and ethanolamine, yielded a reactive glycolysate that was then reused as a polyol component in new foam formulations. Subsequent steps involved the preparation of sustainable RPUFs through the partial replacement of virgin polyol with 5–10 wt% glycolysate and 5 wt% ground RPUF_FA waste. The morphological analysis revealed that the incorporation of glycolysate resulted in the formation of a uniform cellular structure. By contrast, the presence of ground foam led to an increase in macroscopic cell irregularity. The flammability parameters were comparable across all sustainable RPUFs. However, smoke and CO/CO 2 emissions increased when both types of recyclates were used. Thermal analysis confirmed that degradation proceeded via typical two-step mechanisms. The study demonstrates that chemically recovered polyols can be successfully reused in RPUF/fly ash compositions without substantial loss of performance, thus contributing to the development of circular and sustainable polyurethane materials. Nevertheless, the application of recyclates on an industrial scale would need further optimization to minimise smoke and toxic gas emissions during decomposition.