Adhesive strength of guanidine hydrochloride—modified soy protein for fiberboard application

Adhesive properties of guanidine hydrochloride (GuHCl)-modified soy protein isolate (SPI) for uses in fiberboard were investigated. In addition, effects of GuHCl concentration, SPI concentration, press conditions, and assembly time on gluing strength were studied. Shear strength changed with variation of GuHCl concentration and had a maximum value at 1.0 M GuHCl. Increasing the SPI content improved shear strength greatly at a low concentration, and increasing SPI to high concentrations had little additional effect. Overall shear strength decreased after water soaking, but showed same trends with GuHCl concentration and with SPI content as unsoaked samples. Shear strength increased as press temperature increased but leveled off at high temperature. Press temperature had a greater effect on the soaked samples. Both press time and assembly time had significant effects on shear strength. The maximum shear strength was obtained with a press time of 5 min and assembly times of 10–15 min, respectively. All samples prepared at 75°C or above exhibited cohesive failure within fiberboard. However, samples prepared at 25°C and 50°C showed both cohesive failures within fiberboard and locus of failure following the interface between the adhesive and adherend. Furthermore, some glued specimens fell apart after soaking.