Preparation of a High-Temperature Soybean Meal-Based Adhesive with Desired Properties via Recombination of Protein Molecules

A soybean protein-based adhesive with desired adhesion properties and low processing cost is prepared by a simple and practical method, which is of great significance to the sustainable utilization of resources and human health. Nevertheless, the protein of high-temperature soybean meal (HSM) has a high degree of denaturation and low solubility, endowing the resultant soybean-based adhesive with a high viscosity and unstable bonding performance. Herein, we propose the strategy of protein molecular recombination to improve the bonding properties of the adhesive. First, chemical denaturation was carried out under the combined action of sodium sulfite, sodium dodecyl sulfate, sodium hydroxide, urea, or sodium dodecyl sulfate/sodium hydroxide to reshape the structure of the protein to release active groups. Then, thermal treatment was employed to facilitate the protein repolymerization and protein-carbohydrate Maillard reaction. Meanwhile, the epichlorohydrin-modified polyamide (PAE) as a crosslinking agent was introduced to recombine unfolded protein and the products from Maillard reaction to develop an eco-friendly soy protein-based adhesive with an excellent and stable bonding performance. As expected, the highest cycle wet bond strength of the adhesive sample of 1.20 MPa was attained by adding a combination of 2% SDS and 0.5% sodium hydroxide, exceeding the value required for structural use (0.98 MPa) of 22.44% according to the JIS K6806-2003 commercial standard. Moreover, the adhesive possessed the preferable viscosity and viscosity stability accompanied by good wettability. Noteworthily, the adhesive had a short time of dry glue, which could be solved by combining it with soybean meal (SM) at the ratio of 30:10.