Chemical recycling ofa 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.

Automated summary

The plastic waste crisis requires new polymers designed for recycling. Lignin, found in woody biomass, is a promising biobased source due to its aromatic nature. However, the reactivity and heterogeneous structure of lignin pose challenges for its use in polymers and designing recycling solutions. A chemical recycling technique is demonstrated here to depolymerize lignin and produce a recycled precursor that can be reused in non-isocyanate polyurethane foams. The closed-loop recycling process of lignin-derived foam shows a pathway towards a circular economy.