Soy-Based Adhesives with 1, 3-Dichloro-2-Propanol as a Curing Agent

Increasing concern over the impact of formaldehyde on human health has prompted a need for a formaldehyde-free wood adhesive. In this study, we investigated a new formaldehyde-free wood adhesive system consisting of soy protein (SP) and 1, 3-dichloro-2-propanol (DCP). DCP served as a crosslinking agent for SP. The shear strength of wood composites bonded with a SP-DCP adhesive depended on the SP/DCP weight ratio and the reaction conditions such as reaction time and reaction temperature under which the SP-DCP adhesive was prepared. For a given SP/DCP weight ratio, the higher the reaction temperature, the higher the shear strength. Under the same reaction conditions, increasing the SP/DCP weight ratio, i.e., decreasing the relative amount of DCP in the adhesive, resulted in a decrease in the shear strength and water resistance of the resulting wood composites. Of all the SP/DCP weight ratios studied. 6:1 SP/DCP weight ratio at 85°C for 1.0 h gave the highest shear strength in the resulting wood composites. In terms of the shear strength, the 8:1 and 10:1 SP/DCP weight ratios were comparable to each other and were only slightly lower than with the 6:1 SP/DCP ratio. Further increasing the SP/DCP ratio to 12:1 or 15:1 greatly decreased the shear strength. The shear strength slightly increased with pressing temperature in the range of 100°C to 160°C at a press time of 5 min. Press times in the range of 1 min to 9 min had insignificant effects on the shear strength at a press temperature of 140°C. Storage of SP-DCP adhesive at room temperature for one or two days did not significantly affect the shear strength. However, a significant reduction of the shear strength was observed after the adhesive was stored at room temperature for 5 days. Wood composites bonded with a SP-DCP adhesive did not delaminate after they underwent a water-soaking-and-drying test and a boiling-water test. The crosslinking reactions between SP and DCP are discussed in detail