A high bonding performance and antibacterial soybean meal adhesive with Maillard reaction based cross-linked structure

Environmentally friendly soybean meal-based (SM) adhesive has been developed to replace harmful formaldehyde-based adhesives in the wood-based panel industry. But, the extensive application of SM adhesives is limited by several deficiencies, including high brittleness, poor coating ability, and poor antibacterial/mildew resistance, etc. In this study, a new SM adhesive has been designed by constructing a hyperbranched cross-linked structure via the Maillard reaction instead of traditional epoxide-based crosslinking structure. Specifically, the hyperbranched poly(ethylenimine)-functionalized carboxymethyl chitosan was synthesized via a one-step procedure using carboxymethyl chitosan and polyethyleneimine, and then mixed with soybean meal and a crosslinker (2,3-butanedione) to develop a wood adhesive. The dry and wet shear strength of plywood bonded by the obtained adhesive was 55% and 357% higher than those of the original SM adhesive, respectively, which were attributed to the formation of Maillard reaction-based crosslinked structure and improvement of adhesive toughness. The corresponding wood failure percentage was increased to 70% compared to pure SM adhesive. Notably, the prepared adhesive exhibited mildew resistance for 240 h and had a uniform coating ability on the wood surface. Construction Maillard reaction based crosslinking structure has potential application in the enhancement of other bio-adhesives and protein-based hydrogels.