Effects of polyisocyanate on properties and pot life of epoxy resin cross‐linked soybean meal‐based bioadhesive

ABSTRACT In this study, polyisocyanate (pMDI) was introduced into epoxy resin modified soybean meal‐based bioadhesive to address the issue of low dry bond strength. Specifically, we investigated the effects of adding pMDI in terms of amount and storage time on dry bond strength, water resistance, and pot life of adhesive. Factors examined included shear strength, apparent viscosity, chemical reaction, crystallinity, and morphology of modified adhesives. Results indicated that the dry bond strength and water resistance of the resultant plywood was respectively improved 29.5% and 39.7% by adding 2% pMDI. In addition, the pot life of modified adhesive reached in 4 h. Results also shown that the cross‐linking reactions between epoxy group and carbonyl as well as isocyano and amino increased the cross‐linking density and formed a denser cross‐linking network structure of cured adhesive. The composite cross‐linked soybean meal‐based adhesive is environmental‐friendly and high‐performance, which will promote the industrial application of the soy protein‐based adhesives. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133 , 43362.