Investigation of a new formaldehyde-free adhesive consisting of soybean flour and Kymene® 736 for interior plywood

Abstract

Abstract A combination of Kymene® 736 (K736) resin [a paper wet strength agent from reactions of hexamethylenediamine (HMDA) and epichlorohydrin (ECH)] and defatted soy flour (DSF) was investigated as a formaldehyde-free wood adhesive. In focus was the pH influence on the pot life of the adhesive and the water resistance of the plywood prepared with the new adhesive. It was found that the pH of the DSF-K736 adhesive had to be ≥11 before the resulting plywood panels could meet industrial water resistance requirements for interior plywood. The DSF/K736 weight ratio significantly affected the water resistance of the resulting 5-ply plywood. The 11/1 was the highest ratio that still enabled the plywood to meet the water resistance requirements. The hot-pressing temperature of ≥110°C and the hot-pressing time of ≥4 min resulted in 5-ply plywood panels with water resistance properties. The probable mechanism is that K736 reacts with nucleophilic groups in DSF and highly crosslinked adhesive networks are formed. This supposition is supported by the presence of an ester band in the Fourier-transform infrared (FTIR) spectrum of the cured DSF-K736 adhesive.