Further investigation of poly(glycidyl methacrylate- co -styrene) as a curing agent for soy-based wood adhesives

In this study, poly(glycidyl methacrylate-co-styrene) (PGS) was investigated as a curing agent for soybean flour (SF)-based wood adhesives in the presence of polyethyleneimine (PEI). The seven-ply plywood panels made with the SF-PGS-PEI adhesives passed a three-cycle soak test that is the industrial standard test for evaluation of the water resistance of decorative plywood panels in the USA. SF, PGS, and PEI were found to be all essential components for the adhesives. The mixing of SF and PGS first, followed by addition of PEI, was found to be the only mixing order that was able to result in superior properties of the adhesives. The viscosity of SF-PGS-PEI adhesives remained relatively low for at least 60 min of the storage, which made the adhesives easy to use. Effects of weight ratios among SF, PGS, and PEI in the adhesives, the molar ratio between glycidyl methacrylate and styrene in the PGS, and hot-press conditions of making the plywood panels on the water resistance of the resulting plywood panels were extensively investigated. The adhesion mechanisms are discussed in detail.