Properties of a soybean meal-based plywood adhesive modified by a commercial epoxy resin

In this study, soybean meal flour, polyacrylamide (PAM), sodium dodecyl sulfate (SDS), and a commercial epoxy resin (EP) was used to develop different adhesive formulations. The solid content and viscosity of the adhesives were measured. Three-ply plywood was fabricated to measure the water resistance of the different adhesives. The crystallinity and infrared spectra of the cured adhesives were investigated. The results indicated that PAM and SDS acted as denature and retention agents, respectively, to improve the water resistance of the resulting adhesive by 38.7%. EP reacted with active groups on protein molecules to form a cross-linking network to decrease the crystallinity of the cured adhesive and improve its water resistance. Incorporating 5 wt% EP improved the water resistance of the adhesive by 236.7% and the wet shear strength of the resulting plywood to 1.12 MPa, which met interior use requirement. Adding EP also increased the adhesive solid content to 32.85 wt% and decreased the adhesive viscosity to 20,415 mPa s, which would be beneficial to soybean meal-based adhesive industrial applications.