Water-resistant and anti-mildew soy protein adhesive with network structures based on reversible boron-oxygen bonds and multiple hydrogen bonds

Soy protein adhesives have great potential for development and have gradually become one of the research hot spots in recent years. However, the unmodified soy protein adhesives have many problems such as poor bonding performance and water resistance, high viscosity and easy to mildew, which affect their wide industrial application. In this study, soy protein adhesives were modified with borax and tannic acid to investigate the structural characteristics, physicochemical properties and mildew resistance of soy protein adhesives and to explore the strength mechanism of the modifier. Results showed that boron-oxygen reversible dynamic covalent, multiple hydrogen bonds and electrostatic interactions are formed between borax-tannic acid and soy protein isolate, and the synergistic effect of these multiple network structures improves the properties of soy protein adhesive. Therefore the dry and wet shear strength of the modified soy protein adhesive increased by 54 % and 45.8 % to 2.37 MPa and 1.115 MPa compared with unmodified soy protein adhesives. In addition, the anti-mildew performance of the liquid adhesives was extended from 2 d to more than 96 h. This research provides a simple and green method to improve the comprehensive properties of soy protein adhesive, and promotes the application of soy protein adhesive in wood industry.