Abstract:

Soy protein-based adhesive(SUG) was prepared using urea-glyoxal(UG) resin and soy protein isolate(SPI) as the main raw materials, and the solid content, viscosity, surface tension coefficient, contact angle, and bonding performance of the soy protein-based adhesive were tested. Then, the structure of the synthesized soy protein-based adhesive was characterized by XPS, FT-IR and ¹³C NMR. The curing performance of the adhesive was determined by DSC and DMA. The results showed that the solid content, viscosity, surface tension coefficient, and contact angle of the modified soy protein adhesive increased with the increase of SPI content, where the viscosity exhibited the most significant change. The synthesized soy protein adhesive mainly contained functional groups such as C—C, C—O—C, C＝O, C—N and C—O. Combined with the results of ¹³C NMR and FT-IR analysis, it could conclud that cross-linking occurred between UG resin and SPI. When the amount of SPI was 30 g and the amount of UG resin was 50 g, the prepared soy protein adhesive exhibited better performance, and the cured adhesive had a high storage modulus, which was 4 082 MPa. The wet strength values of the plywood prepared at 160 ℃ and 180 ℃ hot pressing temperatures in cold water for 24 h were 1.23 and 1.48 MPa, respectively. The hot water wet strength values after 3 h were 1.05 and 1.22 MPa, which were significantly higher than the requirements for Class II plywood according to the national standard GB/T 9846—2015, and the prepared plywood adhesive exhibited a certain level of water resistance.

Key words: urea-glyoxal resin, soy protein adhesive, characterization, bond strength