Abstract:

This paper used non-volatile glyoxal(G) to replace formaldehyde to react with melamine(M) and urea(U) to prepare melamine-urea-glyoxal(MUG) co-condensed resins, at room temperature with the molar ratio of the raw material of U and G was 0.30:1.0, and with the dosage of M was 13.86, 17.64, 21.42 and 25.20 g, respectively. The basic properties, curing properties and bonding properties of the MUG resins were determined and analyzed. The structure of the resin was characterized by Fourier transform infrared spectroscopy(FT-IR), mass spectrometry(MS) and nuclear magnetic resonance carbon spectroscopy(¹³C NMR). The results showed that the solid content and viscosity of MUG resins were greatly affected by the molar ratio of raw materials, which increased with the increase of M content. The MUG resin mainly contained N—H, O—H, C═O, C—O, C═N and other functional groups, and the main infrared absorption peaks of MUG resin with different molar ratios of raw materials did not change significantly. The possible reaction mechanism was deduced according to the molecular fragments, proving the co-polycondensation reaction M, U and G in the system. When the amount of melamine added was 21.42 g, the curing temperature of the resin was lower and the storage modulus was higher. For the plywood fabricated by the as prepared resin, the dry bonding strength, wet strength cold water for 24 h and with hot water for 3 h were 2.51, 1.29 and 0.85 MPa, respectively.

Key words: melamine-urea-glyoxalco-condensed resins, molar ratio, reaction mechanism, bonding strength