Influence of process parameters on the bonding performance of wood adhesive based on thermally modified soy proteins

Abstract

The adhesive bonding strength and water resistance of wood adhesive based on thermally modified soy protein isolate (SPI) were optimized by varying the SPI concentration, pressing temperature and pressing time. Commercial SPI was thermally modified in a vacuum chamber at 50 °C, and dispersions were prepared with SPI mass fractions of 9.09, 9.91, 10.71, 11.50, and 12.28 % in distilled water. The pH of the dispersions was adjusted to 10.0, then afterwards stirred at 50 °C for 2 h. The adhesive viscosity was measured. Effective penetration (EP) and tensile shear strength of beech wood specimens bonded under the same bonding conditions were determined (according to the European Standards EN 204 and EN 205). Adhesive with optimal SPI concentration was used for bonding at different pressing temperatures (100, 110, 120, 130, and 140 °C), whilst other bonding conditions were the same as by optimising SPI concentration. The optimal pressing temperature was determined based on tensile shear strength results. It was then used for bonding at different pressing times (6, 7, 8, 9, 10, 12, and 15 min). Optimal pressing time was determined based on tensile shear strength results. The viscosity of the adhesive increased with increased SPI concentration. The EP increased with increased viscosity and SPI mass fraction up to 11.50 % and then decreased. The adhesive with SPI mass fraction of 11.50 % showed the best water resistance. For this adhesive the optimal pressing temperature was 110 °C and optimal pressing time 10 min. The adhesive passed the durability class D3.