Strong and Tough Lignin-Containing Waterborne Polyurethane Nanocomposites with Multiple Hydrogen Bonds as Photothermal Power Generation Coatings

The use of lignin as feedstock to prepare lignin-containing waterborne polyurethane (LWPU) is of great significance for the sustainable development of low carbon materials. However, the utilization method and function of lignin in LWPU need to be further explored and developed. In this study, homogeneous and stable LWPU emulsions were prepared with low-molecular-weight lignin. Then, strong and tough LWPU/lignin nanocomposites were prepared by blending dialyzed alkali lignin (DAL) nanomicelles with LWPU emulsions. The well-dispersed DAL nanoparticles formed multiple hydrogen bonds with the LWPU matrix attributed to the existence of lignin in the polyurethane chain segments, which endowed the nanocomposites with excellent mechanical properties. When the total lignin content was 23.8 wt %, the tensile strength and toughness of LWPU/lignin nanocomposites reached 38.3 MPa and 173.9 MJ/m³, respectively. Benefiting from the photothermal function of lignin, the LWPU/lignin nanocomposites showed outstanding photothermal conversion ability, which was demonstrated as an excellent photothermal coating for photothermo-electric power generation. In addition, DAL nanoparticles enhanced the aging-induced self-reinforcing properties of the LWPU/lignin nanocomposites. This work represents a simple route for the preparation of high-performance waterborne polyurethane materials with high lignin content and opens up a novel value-added application of lignin in photothermal-electricity conversion coatings.