Highly water-resistant soy protein adhesives based on thermochemical activation and multiple cross-linking design

High-temperature soybean meal (HSM) has emerged as an attractive raw material for the producing of wood adhesives, but its lack of reactivity along with poor water solubility hinder its water resistance and adhesion strength due to severe denaturation during high-temperature desolvation. In this paper, a moderate-temperature chemical modification process was employed to reorganize the structure of HSM, thereby fully activating its functional groups to interact with the polyamide-epichlorohydrin (PAE) and form a robust covalent cross-linking network structure, significantly enhancing the bonding properties of HSM-based adhesives. Structural analysis of the modified HSM revealed that moderate-temperature chemical modification could fully swell HSM, disrupting its highly aggregated protein structure and releasing active groups that enhanced subsequent Maillard reactions with carbohydrates and facilitated covalent cross-linking with the crosslinking agent. The optimized adhesive formulation, HSM-NS-2-based adhesive, was successfully developed using HSM modified with a combination of 1.5 % sodium dodecyl sulfate and 1 % sodium hydroxide at 55 °C, Notably, this adhesive demonstrated a remarkable cycle wet bond strength of 1.29 MPa, surpassing the minimum requirement of 0.98 MPa for structural applications. Furthermore, moderate-temperature chemical modification could impart excellent viscosity, wettability, and coating performance to the adhesive without compromising its moisture retention, making it beneficial for industrial-scale promotion and application. • Preparation of HSM-based adhesive by thermochemical activation and multiple cross-linking design. • The adhesive exhibits excellent bonding performance, with a 92.53 % increase in aged wet strength. • The resultant adhesive has good viscosity, wettability, and coating performance. • Low-cost HSM and simple steps achieved cost effectiveness of adhesives.