Water-Resistant Soybean Adhesive for Wood Binder Employing Combinations of Caustic Degradation, Nano-Modification, and Chemical Crosslinking

In an attempt to develop a soybean-protein wood adhesive with improved water resistance and good technical applicability, soybean protein was first degraded under strong alkali conditions and then subjected to chemical crosslinking combined with nano-modification. Results of plywood evaluation, GPC analysis, and XRD determination indicated that a soybean-protein adhesive that could bear 28 h boilingdry cycled treatment according to standard JIS K6806-2003. The waterresistance improvement was attributed to both the chemical crosslinking of the degraded soybean protein (DSP) by MDI and the nanomodification of DSP by intercalated or exfoliated montmorillonite (MMT). Caustic degradation improved the technical applicability of the DSP adhesive by sharply reducing the viscosity of high-content protein solution. MMT nano-modification can obviously prolong the pot lives of MDI-modified DSP adhesives but slightly decrease their dry bond strength.