Bio‐Inspired Sclerotization of Lignin: A Robust Adhesive for Photothermal Wood‐Based Panels

Developing formaldehyde‐free adhesives from biomass is critical for the wood‐based panel industry, yet progress is constrained by the poor bonding strength and water resistance of existing adhesives. Inspired by the sclerotization mechanism of insect exoskeletons, a high‐performance lignin adhesive is engineered using industrial alkali lignin, hyperbranched polyamide (HBPA), and a synthesized epoxide crosslinker. First, lignin is activated via ultrasonication to cleave β‐O‐4 aryl ether bonds, exposing free phenolic hydroxyl groups, which are then selectively oxidized into quinone structures. The treated lignin is subsequently grafted with HBPA to introduce a high density of amine functionalities, which ultimately form a robust network via epoxide crosslinking. The plywood bonded with this adhesive exhibits a wet shear strength of 1.02–1.21 MPa, comparable to that of conventional urea‐formaldehyde and phenolic resins. The adhesive imparts photothermal properties to the wood‐based panels: under natural outdoor sunlight, the panel surface sustained a temperature of approximately 52 °C, about 23 °C above ambient. This demonstrates a cost‐effective strategy for integrating solar‐harvesting functionality directly into structural building materials. Combined with a low material cost (~$2/kg), building energy simulations indicate a total HVAC‐load saving of 1.6%–6.5% in most heating‐dominated locations, rising to approximately 9%–10% in high‐irradiance plateau regions, supporting the panel's economic potential for energy‐saving building applications. This work presents a practical approach to developing high‐performance lignin adhesives and functional wood‐based panels and provides new insights into the efficient valorization of biomass resources.