Development of soybean meal based adhesives with excellent wet-resistance and prepressing bonding strength via disulfide bond reshuffling strategy

Abstract

The superabundant disulfide bonds (S-S) between high-temperature soybean meal (HSM) protein molecules lead to agglomeration and inferior dispersion, resulting in low cohesion strength and poor initial viscidity of current HSM-based wood adhesives. This work prepares HSM-based adhesives with high wet-resistance and prepressing adhesion via a novel strategy that breaks inherent intramolecular disulfide bonds and induces a disulfide network reestablishment between the protein and crosslinking agents. The “S-S” strategy is introduced into polyamidoamine prepolymer to synthesize sulfide polyamide-epichlorohydrin (PAE-DS). Driven by reducing agents (free -SH) and heating, protein molecules and PAE-DS molecules interact to open the inherent “S-S” and the promote new “S-S” intersect rebuilt with PAE-DS. The new disulfide bonds provide strong cohesion to the resultant adhesives and enables the plywood adhered by these bonds to meet the standards for indoor-use plywood (Chinese National Standards, GB/T 9846-2015). When the added PAE-DS amounts is 25% of the HSM protein, the resultant adhesives exhibit an excellent wet bonding strength (1.69 MPa), which is 382.85% higher than that of the neat HSM adhesives. This ratio also enhances the prepressing bonding performance in plywood (483 kPa) by 96.34% compared to that of the neat sample. Furthermore, the incorporation of PAE-DS makes the adhesives to exhibit desirable dry bonding strength and other physical properties. This study has certainly enabled the use of HSM for adhesives and can potentially enhance various physical and mechanical properties of other plant-protein-based composites.