Effect of microwave—Chemical modification on properties of soybean meal‐based wood adhesive

Abstract To enlarge the industrial application of plywood made from soybean meal‐based adhesive (SMA), the properties improvement, especially wet shear strength of SMA which was modified by microwave‐chemical treatment was studied. The purpose of this research was to optimize microwave conditions combined with polyethylene glycol (PEG) and polyethyleneimine (PEI) treatment, to maximize the water resistance of SMA. The viscosity, shear strength and solids content of modified SMA were determined. In addition, the modified mechanism was characterized by using Fourier transform infrared spectroscopy, Scanning electron microscope, X‐ray diffraction and thermogravimetric analysis. Results indicated that the wet shear strength of SMA reached at 0.93 MPa when the microwave power was 350 W, microwave time was 3 min, and concentration of soybean meal was 28%. The result was 32.86% higher than China National Standard for interior use of plywood (≥0.70 MPa). From the results of mechanism, the bonding performance of the prepared plywood was improved after PEG‐PEI and microwave modification, which improved the water resistance of SMA. The improvement due to the formation of crosslinking in curing process by the reaction between active groups of soybean protein molecules and crosslinking agent under microwave modification, which provided favorable conditions for further application of SMA.