Optimization of preparation conditions of soy flour adhesive for plywood by response surface methodology

Response surface methodology was applied to optimize the preparation conditions of soy flour adhesive (SFA). A boiling water test was used to assess the wet strength of plywood bound with this adhesive. The effects and interactions of treatment time (X1), treatment temperature (X2) and additive amount of acid-salt solution (X3) on wet strength were investigated. The regression model for the SFA preparation was significant (p < 0.0001). X2 and X3 had a significant effect on wet strength, whereas the effect of X1 was insignificant. X2 and X3 showed interactions with wet strength. The optimal preparation conditions were: acid-salt solution 3.0 g, treatment time 33 min and treatment temperature 29 °C. Under these conditions, the wet strength was 1.18 ± 0.08 MPa, which is in agreement with the predicted value (1.11 MPa). An analysis of the Fourier transform infra-red spectroscopy spectra of the SFAs further confirmed the validity of the optimal preparation conditions.