Upcycling soy-based polyurethane foam waste into high-performance polypropylene blends through reactive compatibilization

Polyurethane foams (PUFs) are widely used across various applications due to their tunable density, porosity, and effective cushioning, thermal, and acoustic insulation properties. However, this growing demand raises concerns regarding petrochemical consumption and end-of-life waste. To address this issue, various recycling methods have been employed, with mechanical recycling being the most used approach for PUF waste. However, this often results in products with low mechanical performance and limited added value. This work proposes a viable alternative for upcycling PUF waste by incorporating it into a polyolefin matrix. Specifically, a soybean oil polyol-based polyurethane foam (SO-PUF) was ground and blended with polypropylene (PP) and maleic anhydride-grafted polypropylene (PPgMA). Reactive blending of PP, PPgMA, and SO-PUF (up to 60 wt%) resulted in a material with impact strength ten times higher than that of PPgMA and five times higher than that of PP. Furthermore, the blends prepared with SO-PUF showed a pronounced increase in tensile strength and elongation at break compared to those formulated with PUF based on petrochemical polyols. The interaction between the maleic anhydride groups and the functional groups of SO-PUF promoted strong interfacial adhesion, while PP played a critical role in enhancing the mechanical performance. This study presents an environmentally friendly and scalable strategy for upcycling PUF waste by formulating SO-PUF and reactively blending it with widely available commercial polyolefins, thereby reducing reliance on petrochemical polyols and adding value to materials that would otherwise be discarded. Ester–anhydride interfacial reactions enable high-loading upcycling of crosslinked soy-based polyurethane foam into impact-resistant polypropylene blends. • Upcycling of polyurethane foam waste into polypropylene blends. • Soy-based polyurethane foam enables improved interfacial compatibilization. • Up to 60 wt% foam waste incorporated into polypropylene matrix. • Impact strength up to 10× higher than PPgMA and 5× higher than PP. • Ester–anhydride reactions promote reactive compatibilization in blends.