Preparation of Water-Resistant Gelatin-Based Wood Adhesive via Synergistic Supramolecular Preassembly and Covalent Cross-Linking

Gelatin, a partially hydrolyzed derivative of collagen, is recognized for its low cost, abundant availability, and eco-friendly profile. Nevertheless, its application as a wood adhesive is constrained by the need for higher curing temperatures and its inherently low water resistance. To overcome these limitations, this study proposes an approach that integrates noncovalent synergistic covalent interactions to reinforce the cross-linked network. The developed adhesive system comprises gelatin (Gel), polyamide-epichlorohydrin (PAE), and sodium alginate (SA). In this system, PAE serves as a reactive cross-linking agent, forming a covalent network with Gel. Concurrently, electrostatic interactions between SA and PAE contribute to partial pre-cross-linking, reducing the dependency on high-temperature-induced covalent bonding to establish a robust network structure. Plywood bonded with this adhesive achieves a wet shear strength of up to 1.32 MPa, which exceeds that of commercial aldehyde-based adhesives. Moreover, owing to the formation of a dense network driven by moisture evaporation, the adhesive exhibits excellent room-temperature bonding performance on both bamboo and beech. This work presents a promising strategy for developing biobased adhesives with reduced curing temperatures and enhanced bonding properties.