A water-resistant and mildewproof soy protein adhesive enhanced by epoxidized xylitol

Soy protein-based adhesives show great prospects in replacing aldehydes resin adhesives to fabricate wood-based panels, however, high doses of synthetic resins as crosslinkers must be used to obtain good bonding performance. To reduce overreliance upon crosslinkers derived from fossil resources, a 100% bio-derived crosslinker-xylitol epoxide (EX) was synthesized from epichlorohydrin and xylitol, followed by blending with soy protein isolate (SPI) to create a functional biological adhesive. After using EX, the wet and dry shear strengths of plywood prepared by the SPI/4%EX adhesive increased by 138.6% and 55.6%, respectively, compared with the pure soy protein adhesive. This was attributable to the crosslinked network formed in adhesive and the enhanced adhesive toughness. The optimized process parameters of plywood prepared with EX-modified soy protein adhesive were 110 ℃, 1.3 min/mm and 0.8 MPa. The addition of EX also improved the mildew-resist property of the adhesive to 10 days, which prolonged the adhesive storage life and the service life of the resultant plywood. Therefore, EX could be utilized to enhance the mechanical and mildew-resist properties of protein-based materials, and shows great potential applications in adhesive, film, and hydrogel.