A high wet strength and toughness soy-based adhesive prepared by single cross-linking

Soy-based adhesives are considered to be a substitute for toxic petroleum-based adhesives in wood industry because of its environmentally-friendly property. However, their application range is limited by the lack of high wet bond strength and high toughness. While it is possible to impart these properties to soy-based adhesives by adding a variety of corresponding modifiers, it is difficult to do so by adding a single modifier. In this work, a multifunctional cross-linking agent dodecanedioic acid diglycidyl ester (DADE) with high reactivity, toughening, and hydrophobic effects was synthesized and incorporated into soy-based adhesive to ameliorate the bonding performance of the adhesives. The reaction process between DADE and protein was confirmed by instrumental analyses. Results revealed that the introduction of 4% DADE increased the wet bond strength of the soy protein adhesive by 140% to 1.57 MPa, whereas the wet bond strength (1.11 MPa) of soybean meal adhesive containing 4% DADE was comparable to that of MUF resin. The micrographs of the fracture surface and the force-distance curves of the shear strength test showed that the toughness of the adhesives was significantly improved by DADE. These improvements were attributed to the long hydrophobic aliphatic chains and highly reactive groups from DADE. This modification method avoided using large amounts of chemical additives. This work may provide an efficient and low-consumption method for producing bio-based adhesives with excellent bonding properties.