Reprocessable non-isocyanate polyurethane foams from lignin: A sustainable route to high-performance thermal insulation materials

Developing sustainable, non-toxic and high-performance polyurethane foams from renewable feedstocks remains a critical challenge in green materials chemistry. In this work, lignin-derived epoxy resins (LEPs) were efficiently converted into lignin-based cyclic carbonates (LCCs) via catalytic CO 2 cycloaddition. Subsequent water-assisted curing of LCCs with Jeffamine T-403 yielded self-blown LNIPU foams, eliminating the need for toxic isocyanates or auxiliary blowing agents. To address the intrinsic hydrophilicity and enhance the overall performance, mercaptopropyl-functionalized polyhedral oligomeric silsesquioxane (POSS–SH) was incorporated via thiol–cyclic carbonate S-alkylation to construct LNIPU/POSS hybrid networks. Comprehensive structural and property analyses revealed that POSS incorporation significantly improved water resistance, thermal insulation and mechanical performance. At an optimal POSS loading of 5.40 wt%, the LNIPU/POSS foams exhibited a compressive strength of 4.21 MPa (340 % enhancement), a specific compressive strength of 13.12 kN·m/kg and a low thermal conductivity of 0.0406 W·m −1 ·K −1 . Moreover, the dynamic covalent structure endowed the foams with excellent recyclability and robust dual-/triple-shape memory behavior, with reprocessed samples retaining over 87.5 % of their original tensile strength after two hot-pressing cycles. This work presents a green, efficient and scalable strategy for valorizing lignin and CO 2 into high-value foam materials, offering a promising route toward the sustainable production of advanced bio-based polyurethane materials.