Fully bio-based wood adhesives from lignin and zein protein.

Manufacturing of wood-based panels predominantly relies on formaldehyde-containing adhesives, whose volatile organic compound emissions raise serious concerns about indoor air quality and human health. Although bio-based adhesives derived from proteins, polysaccharides, or lignin have been explored, achieving strong bonding performance while maintaining green, scalable, and practical processability remains challenging. In this study, we present a waterborne wood adhesive in which zein protein is dispersed within a viscous micellar lignin gel. Drawing inspiration from the interactions between proteins and polyphenols, we designed this system to be fully bio-based and free of cross-linkers. When birch veneers were hot-pressed with this adhesive, the resulting three- to five-layer plywood materials showed competitive performance compared with existing bio-based adhesive formulations. Meanwhile, this approach also delivers favorable green metrics, including an Eco-scale score of 94, supported by the absence of organic solvents, a minimal number of steps, and the waterborne nature of the formulation. Notably, the adhesive can be debonded in a 70% ethanol-water solution, allowing its recovery and reuse. The combined results indicate the potential of the lignin-protein system as a sustainable alternative to conventional petroleum-based commercial adhesives for indoor use.