A bio-based soy protein adhesive with high strength, toughness, and mildew resistance

Soy protein adhesives as a viable alternative eco-friendly biomass material, hold immense potential in replacing traditional formaldehyde-based adhesives. However, soy protein adhesives suffer from issues such as high bonding brittleness and susceptibility to mold. In this study, a modified agent (CS@PEI) was synthesized by grafting chitosan (CS) onto polyethyleneimine (PEI), and a tightly cross-linked network structure was created triglycidylamine (TGA) to modify the soy protein adhesive, improving its bonding toughness and anti-mildew properties. In comparison to the soy protein (SPI) adhesive, the wet shear strength of SPI/TGA/CS@PEI-4 adhesive was improved by 106.78 % (1.22 MPa), the dry/wet tensile strain increased by 13.1 % and 45.0 %, the residual ratio was augmented by 24.9 % (63.1 %), while the storage time was increased from 2 d to over 30 d. The presence of the modifier (CS@PEI) destroyed the bacterial habitat, while the cross-linking modification strategy facilitated the formation of a robust reticulated network structure within the adhesive, significantly enhancing its water resistance and mildew resistance capabilities. This modification strategy opens an innovative way for exploring the new anti-mildew protein-based adhesives.