Preparation and performance of rapid water activation lignin-based wood adhesive films.

To advance lignin utilization in wood adhesives, this work presents the development of poly(vinyl alcohol)-lignin (PVAL) films by solution casting. Water spray activation rapidly switched the film from a dormant to an adhesive state, enabling immediate hot-pressing of plywood. Bonding performance was assessed by tensile strength testing. A systematic parametric study was conducted on the PVA concentration, lignin addition amount (relative to PVA), pH value, and film thickness to determine the optimal formulation. This was shown to be formed by a 12 wt% aqueous PVA solution, 50 wt% lignin relative to PVA, pH 4, and a film thickness of 0.14 mm. Under these conditions, plywood achieved a wet tensile strength of 2.13 MPa after 3 h immersion in water at 63 ± 3. This is three times higher than the GB/T 9846-2015 requirement (≥0.70 MPa). After 10 wet-dry cycles (3 h hot-water immersion +12 h oven drying), strength remained at 1.07 MPa. PVAL films showed good storage stability and easy handling, with better environmental compatibility than conventional liquid synthetic-resin adhesives. This study provides a scalable biomass-derived approach to high-performance lignin-based plywood adhesives and sustainable adhesive development from renewable feedstocks.