Preparation of a moderate viscosity, high performance and adequately-stabilized soy protein-based adhesive via recombination of protein molecules

Abstract Developing a clean and environmentally-friendly soy protein adhesive to replace formaldehyde-based adhesive is of great significance for sustainable development of resources and human health. Due to the high molecular weight of protein, the resultant soy protein adhesive has a high viscosity and unstable bonding performance, which limit their application on plywood fabrication. Inspiring by theory of molecular recombination enhancing material properties, in this study, bromelain was used to degraded soy protein molecules into small polypeptide chains; a bio-derived cross-linker, triglycidylamine (TGA), was employed to recombine these polypeptide chains to develop a new cleaner soy protein-based adhesive with an excellent and stable bonding performance. The results showed that the molecular weight of soy protein decreased from 10 to 170 KDa to below 25 KDa by adding 0.4% bromelain. Using 3% TGA and 0.1% bromelain, the resultant adhesive viscosity decreased 95% and the wet shear strength increased 76.2% to 1.11 MPa compared with that of the unmodified adhesive. At the same time, the adhesive distribution, bonding stability have been improved significantly. More important, this molecular recombination soy protein adhesive reduced the amount of crosslinker more than 50% compared to other cross-linked modified soy protein adhesives.