Preparation and characterization of a novel environment-friendly urea-glyoxal resin of improved bonding performance

By using only glyoxal instead of formaldehyde to prepare environment-friendly amino resin for wood adhesives is a hot topic in the wood industry. However, the existing reports on UG resin present a poor bonding performance, and especially an almost complete absence of water resistance. Thus, to explore new synthetic processes to prepare UG resins with good water resistance is a work of considerable interest. In this work a novel formulation is developed by reacting hexamethylene diamine (H) and urea (U) via first deamination and then polymerization with glyoxal (G) to obtain HUGs green resins. These resins were used to prepare well bonded wood panels. The effect of different H/U ratios on resin performance was also investigated. At a H/U molar ratio of 1, the HUG resin presents the best performance, dry strength, 24 h wet strength, and 63 °C hot water soaking wet strength of the plywood bonded with it, these being respectively 1.18 MPa, 1.70 MPa, 0.92 MPa respectively. This means that the HUG resin has potential as an industrial adhesive to replace urea–formaldehyde or melamine-urea- formaldehyde resins in the production of wood composites.