Coordination-reinforced lignin/polyvinyl alcohol composites for indoor UV protection and temperature management

Polyvinyl alcohol (PVA) is a promising biodegradable and biocompatible polymer material. However, the large number of hydrogen bonds in PVA leads to a contradiction between strengthening and plasticization, which limits its widespread application. To address this challenge, the most abundant aromatic biopolymer, lignin, was adopted as a biobased reinforcing agent for PVA. The simultaneous reinforcement and toughening of PVA by lignin were achieved through the construction of interfacial coordination bonds and hydrogen bonds. The tensile strength and Young's modulus of coordination-reinforced lignin/vanillin-modified PVA (VPVA) composites reached 101 MPa and 1694 MPa, respectively. The thermal processing window of the composites increased from 25.5 °C to 100.5 °C, which provided a potential in thermal processing. Besides, dense hydrogen bonds and coordination bonds conferred good self-healing and water recovery properties onto the composites. Interestingly, the incorporation of lignin also endowed the composites with good photothermal conversion capabilities, making the composites suitable for indoor thermal management. Under simulated solar irradiation of 200 mW/cm², the composites could reduce the indoor temperature rise by 8 °C. This work presents a novel approach for effectively enhancing the comprehensive performance of lignin/PVA composites by coordination bonds, and also presents a pioneering investigation for the high-value utilization of lignin.