Abstract: Soy protein adhesive (SPA) was prepared by using soy protein as raw material and its thermodynamic behavior was also studied. The synthesis conditions were optimized by orthogonal balanced block designs analysis method GL₉(3⁴). The results showed that the optimal conditions of synthesis process were as follows: thiourea 1.5 mol, silica 0.5 g, sodium tripolyphosphate 3 g. The wet-like bonding strength of wood materials of SPA synthsized under the optimal conditions (OSPA) reached 1.01 MPa, and the bonding strength reduced by 10 %, but the compression rate of plywood reduced by 29.35 % compared with those of orthogonal balanced block designs experiment 7 (SPA7). The variable coefficient of wet-like bonding strength was 1.7 %, which indicated a high stability and practicability. Crystallization endothermic peak appeared on the DSC curve, and initial temperature of OSPA reduced. The peak temperature increased slightly, while the heat enthalpy (ΔH) increased from 83.89 J/g to 99.61 J/g. TG analysis showed that the decomposition temperature of OSPA swayed to high and the carbon yield was 25.20 % at 800 ℃. This suggested a high thermal stability. SEM images showed that crazing was induced in the interface of OSPA, and morphology of section layer combined closely, which improved bonding strength and water resistance of the soy protein based biomass adhesives.

Key words: soy protein, biomass resin, bonding strength, water resistance, thermodynamic property