Preparation and properties of soybean protein adhesive modified by chitosan/tannic-silver nanocomposite

Despite the recent advances in protein-based adhesives, the poor water resistance and unsatisfactory mechanical property limit the industrial application of soybean protein adhesive. It is challenging to achieve strong adhesion and high water resistance. In this work, chitosan, tannic acid and silver ion were used to modify soybean protein adhesive. Through chelation, redox reaction and hydrogen bonding, a dynamic crosslinking network structure was constructed, so as to prepare a bio-based adhesive with high water resistance and high bonding strength. It was revealed that when the tannic acid and silver nitrate were mixed at the same concentration of 10 mg/mL and the volume ratio of 1:1, silver nanoparticles with the highest content were produced. When the mass of soybean protein, chitosan, tannic-silver solution and distilled water was 15, 0.3, 30 and 55 g, respectively, the enhancement effect was the best. The dry shear strength increased by 171% to 3.03 MPa, and the wet shear strength increased by 93% to 1.29 MPa. The water resistance, thermal stability, hydrolysis stability, and the toughness and viscosity of the soybean protein adhesive were greatly improved. This study developed a new bio-based adhesive and expanded its potential application in wood products manufacturing.