Study on the Bonding Properties of Phenol-urea-glyoxal Copolycondensation Resin Reinforced by Epoxy Resin

In order to improve the bonding properties and water resistance of glyoxal-based resin adhesive, a new EPR−PUG multi-component cocondensation resin adhesive was synthesized using epoxy resin(EPR), phenol(P), urea(U) and glyoxal(G) as raw materials. The basic properties, curing properties, and bonding properties of the resins were investigated to determine the effect of P/U/G molar ratio on the properties of the resin adhesive and the optimum synthetic formula. The structure and synthesis mechanism of the EPR−PUG resin adhesive were analyzed by contact angle, fourier infrared spectroscopy(FT−IR), nuclear magnetic resonance carbon spectroscopy(¹³C NMR) and X-ray photoelectron spectroscopy(XPS). The results showed that the functional groups of the raw materials were crosslinked effectively, and a dense network structure was formed among the molecules, which improved the overall performance of the resin adhesive system. Under the conditions of P/U/G molar ratio of 0.1∶1.0∶1.5, reaction pH of 4–5, reaction temperature of 70–80 ℃, reaction time of 3 h, and EPR mass fraction of 13%, the adhesive has the best performance. The dry/wet strength was 2.48 MPa, 1.33 MPa(cold water), 0.72 MPa(63 ℃ hot water), respectively, which meets the requirements of the national standard for class II plywood and does not release formaldehyde.