Environmental benefits of valorising food waste into bio-based polyols for the production of polyurethane rigid foams

Abstract

Under the global pursuit of sustainable development, waste streams are being recognised as renewable feedstocks to produce value-added products. Given this, food waste (FW) was explored to synthesise bio-based polyols to further develop polyurethane rigid foams (PURF). However, relevant environmental aspects are yet to be examined to support this biorefinery scheme as a green and sustainable solution. In this work, we examined the environmental performance associated with the production of PURF using polyols derived from a FW biorefinery scheme by life cycle assessment (LCA). Analysis was first conducted at the polyol level. Different allocation and offset options were examined to configure the LCA model. Based on mass allocation, compared with fossil-based production, the production of FW-derived polyols achieved reductions of 24.30 % and 34.19 % in global warming potential (GWP) and cumulative energy demand (CED), respectively. At the midpoint level, FW-derived polyols had reduced impacts on human carcinogenic toxicity, freshwater eutrophication, and fossil resource scarcity but caused additional burdens on freshwater and marine ecotoxicity. Key environmental hotspots at this level included diethylene glycol, ion exchange resin (epoxidation catalyst), and hydrogen peroxide. The lipid content in FW also played a significant role. It was demonstrated that reducing the use of enzymes for FW hydrolysis to a cost-effective level remarkably mitigated the overall impacts of FW-derived polyol production. At the next level, we examined the production of FW-derived PURF using the obtained polyols. When 70 % of the polyols were replaced with bio-based products, the resultant PURF production achieved a GWP and CED of 5.67 kg CO_2eq and 110.66 MJ/kg, respectively. In general, FW-derived PURF leads to environmental benefits compared to fossil-based ones. However, isocyanate used for foam formulation was the dominant contributor, causing almost two-thirds of the total impacts. The flame retardant also caused considerable impacts. Through the systematic examination of FW-derived polyols and PURF, this study demonstrated that FW-derived PURF could benefit the sustainable development of FW biorefineries and bio-based plastic industries, while the identified environmental hotspots need to be further studied and replaced with greener substitutes.