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

Abstract

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.

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Fig. 1: Chemical recycling scheme.
Fig. 2: Recycled lignin yield and solubility.
Fig. 3: 31P NMR spectroscopy of raw Kraft lignin and recycled lignin.
Fig. 4: 2D HSQC NMR of control reactions and recycled lignin.
Fig. 5: Comparison of first- and second-generation CC lignin and NIPU foams.

Data availability

Additional data that support the findings of this study are available from the corresponding author upon request.

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Acknowledgements

We thank O. Sequerth, L. Slann and A. Devol of Clemson University for their support during this project. Research was supported by the Department of Energy, Basic Energy Sciences, award no. DE-SC0021367 (chemical recycling and characterization), by Sonoco FRESH initiative at Clemson University (NIPU synthesis) and as part of the AIM for Composites, an Energy Frontier Research Center funded by the US Department of Energy (DOE), Office of Science, Basic Energy Sciences (BES), under award no. DE-SC0023389 (NMR studies). In addition, S.P. acknowledges the Robert Patrick Jenkins Professorship. J.S. acknowledges graduate fellowship support through Cooper-Standard, Draexlmaier and Sonoco foundations.

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J.S. and S.P. contributed jointly to this paper. S.P. conceptualized the scope of the study and guided the research progress and manuscript editing. J.S. completed the experimental design, characterization of materials and manuscript writing.

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Correspondence to Srikanth Pilla.

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Nature Sustainability thanks Maurice Collins and the other, anonymous, reviewers for their contribution to the peer review of this work.

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Supplementary Figs. 1–7, Tables 1–5 and Notes 1–3.

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Sternberg, J., Pilla, S. Chemical recycling of a lignin-based non-isocyanate polyurethane foam. Nat Sustain (2023). https://doi.org/10.1038/s41893-022-01022-3

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