Glycidyl Methacrylate Grafted onto Enzyme-Treated Soybean Meal Adhesive with Improved Wet Shear Strength

Abstract

In order to decrease the viscosity and improve the wet shear strength of soybean meal (SM) adhesive, in this study, SM adhesive, enzyme-treated SM adhesive(ESM), and the ESM grafted GMA (ESM-g-GMA) adhesive were prepared. The properties of these adhesives were characterized by rheological measurement, mechanical performance testing, Fourier transform infrared spectroscopy (FTIR), and thermogravimetric analysis (TGA). The results indicated that the apparent viscosity of the adhesives decreased due to the enzymatic treatment and the presence of GMA. The wet shear strength of the plywood panels bonded with ESM-g-GMA adhesive was significantly improved from 0.45 MPa to 1.05 MPa, which met the interior plywood requirement (≥0.7 MPa) of the China National Standard. This study also investigated the pot life of the ESM-g-GMA adhesive and the impact of hot pressing. The change in wet shear strength was not obvious within 24 h. The optimum hot press temperature and time were 150 °C and 6 min, respectively. FTIR showed that GMA was successfully grafted onto the ESM adhesive. TGA indicated that the peak degradation temperature of the ESM-g-GMA adhesive was higher than that of the SM adhesive due to the cross-linking reaction that created the macromolecular dense structure between the ESM adhesive and the GMA monomer.