High-temperature soybean meal adhesive based on disulfide bond rearrangement and multiple crosslinking: Water resistance and prepressing adhesion

The main aim of this work is to prepare a high-temperature soybean meal (HSM) wood adhesive with excellent water resistance and prepressing adhesion to satisfy the requirements of green wood-based composites. Different from traditional complex modification methods, a lignosulfonate (LS)-assisted thiol-grafted polyamide-epichlorohydrin (PAE-SH) reinforced HSM wood adhesive was developed via a simple and novel design. The reduced –SH groups were grafted onto polyamide-epichlorohydrin (PAE) to break the S–S in HSM proteins and prompt a disulfide bonds rearrangement between PAE-SH and protein. LS was then introduced into PAE-SH to induce multiple crosslinking interactions, including cation-π interactions and electrostatic interactions. The generation of the LS-assisted PAE-SH not only contributed to the formation of a stable multiple cross-linked adhesive system for strong cohesion, but also provided a suitable solid content of adhesives for the formation of mechanical nail in plywood veneers. The plywood bonded using the PAE-SH/LS-modified adhesive displayed a wet bonding strength of 1.41 MPa, which is 402.9% higher than that of the neat soybean meal adhesive. It was also showed a prepressing bonding strength of 548 kPa, which is more than twice of the pure HSM-based adhesive (245 kPa), greatly reducing the transportation difficulty of veneers before being hot-pressed. This study provides a novel strategy for preparing a water-resistant protein-based adhesives with great potential for industrial application.