The influence of biowaste-based fillers on the mechanical and fire properties of rigid polyurethane foams

Increasing emphasis on the circular economy is driving the development of environmentally friendly rigid polyurethane foams (RPUFs). In this work, polyurethane foams were altered with an addition of fillers, i.e. sunflower husks, rice husks and buckwheat hulls at various weight ratios (5 wt%, 10 wt%, 15 wt%). The aim of the study was to investigate the influence of bio-fillers on the structure, mechanical properties, and thermal properties as well as dimensional stability, water absorption and apparent density of RPUFs. The obtained results indicated that foam modified with these types of fillers, compared to the reference foam, which did not contain fillers, has a higher apparent density (38–51 kg⋅m−3), lower water absorption (18–32%) and higher compressive strength (50–90 kPa). Moreover, the fire behaviour of the produced composites was investigated with the use of a cone calorimeter. The foam containing 5 wt% of rice hulls showed the highest resistance to fire. The obtained results show the possibility of introducing bio-fillers to polyurethane materials as ingredients which can enhance the properties of these materials.