Low-Temperature Phase-Separating Hydro-alcoholytic Depolymerization of Polyurethanes

Abstract

Polyurethane (PU) is a non-biodegradable thermoset plastic and a persistent waste burden with an annual production of around 26 million tonnes. Conventional disposal routes squander valuable resources and generate greenhouse gas emissions. Though chemical recycling offers a sustainable reuse route by depolymerizing PU into monomers, existing methods remain energy-intensive and require burdensome purification, highlighting the need for improved strategies. Here, we present a low-temperature, base-mediated hydrolysis that efficiently depolymerizes PU into high-purity polyols and oligoureas. Applied to flexible foam, the process is completed within an hour at 100 °C, producing distinct phase separation that enables easy recovery of the individual components. Other PU materials, including end-of-life mixed foam waste, are also effectively depolymerized, underscoring the potential as a practical recycling strategy. Finally, the process was scaled up to a 100 g reaction, with a polyol recovery of >85%, demonstrating its feasibility for large-scale implementation. The recycled polyol matched the virgin polyol in hydroxyl number, and the oligourea fraction was hydrolyzed into the corresponding anilines displaying the potential for full monomer recovery. This low-temperature hydrolysis approach not only enables efficient release of monomers under mild conditions but also simplifies downstream separation, positioning it as an attractive alternative to existing chemical recycling methods.