Chemical recycling of a lignin-based non-isocyanate polyurethane foam

The crisis of plastic waste in the environment calls for new polymers that are designed specifically for recycling at the end of their life. Lignin, which is present in approximately 15–40% of woody biomass, is an attractive biobased source for polymers given its aromatic nature. However, the use of lignin in polymers is complicated by its own reactivity and heterogeneous structure, factors that also create difficulties for designing end-of-life solutions for lignin-based polymers. Here we demonstrate a chemical recycling technique that prevents the loss of functionality to lignin and produces a recycled precursor capable of entering back into the synthetic sequence for non-isocyanate polyurethane foams. This technique enables the depolymerization of the polymer and isolation of lignin with enhanced solubility and hydroxyl content so that it can be reused in second-generation polymers. Detailed structural analysis of lignin after chemical recycling reveals the insertion of ethylene glycol in the side-chain region during a high-pressure hydrolysis recycling procedure. The closed-loop recycling process for the lignin-derived non-isocyanate polyurethane foam demonstrates a pathway towards a circular economy.