High-strength, self-reinforcing and recyclable multifunctional lignin-based polyurethanes based on multi-level dynamic cross-linking

The preparation of lignin-based polyurethanes with excellent mechanical properties and recyclability remains extremely challenging because of the poor compatibility of lignin and matrix. Inspired by the multiple structures of spider silk and pearl layers, high-strength, heat-resistant and recyclable lignin-based polyurethanes (LPUs) were prepared by introducing weak hydrogen bonds, strong hydrogen bonds and dynamic silyl ether covalent bonds. Multiple hydrogen bonds provided a large energy dissipation mechanism. The covalent linkage between lignin and matrix promoted their compatibility and formed a robust cross-linking network. Depending on the multi-level dynamic interactions, the prepared elastomer exhibited a mechanical strength of 73 MPa, which was 1.9 times higher than that of the blank sample, with an initial thermal decomposition temperature of 310.5 °C and a good recyclability. Especially, the mechanical strength of LPUs was up to 99 MPa after mechanical training. In addition, the abundant conjugated structure of lignin endowed LPUs with an excellent photothermal conversion ability. Under the irradiation of NIR light with 4000 w m−2, the surface temperature increased to 95 °C within two minutes, exhibiting a stable photothermal performance even after 6 cycles. This work showed the application prospects of LPUs in the fields of high strength engineering materials and photo-induced actuators.