Preparation of Wood Adhesives Based on Soybean Meal Modified with PEGDA as a Crosslinker and Viscosity Reducer

Abstract

To increase the water resistance and reduce the viscosity of soybean meal (SM)-based non-formaldehyde wood adhesives, polyethyleneglycol diacrylate (PEGDA) used as crosslinker and viscosity reducer was introduced into the SM adhesive system. The apparent viscosity was evaluated by rheological measurements; gel content and water absorption of adhesives, the wet shear strength of plywood bonded with these modified adhesives were tested to evaluate their water resistance. In addition, the crosslink structures of modified adhesives were characterized by Fourier transform infrared (FTIR) spectroscopy and solid-state 13C NMR analysis. The results indicated that all of the SM adhesives were pseudoplastic fluids with the property of shear-thinning. The viscosity of modified SM adhesives effectively decreased by 35% compared with the addition of PEGDA, and the wet shear strength of their bonded plywood increased; the wet shear strength of plywood bonded with 4% PEGDA-modified SM adhesive increased 114.2% compared to SM adhesive. FTIR spectroscopy and solid-state 13C NMR analysis demonstrated that the crosslinking reaction of the PEGDA occurred successfully during the curing process of PEGDA modified SM adhesive, and no crosslinking reaction between the PEGDA and soy meal adhesive appeared to have occurred. Interpenetrating networks (IPNs) might be formed between the cured PEGDA and SM adhesive system.