| To improve the water resistance of peanut protein adhesive, the modified peanut protein adhesive was prepared using NaOH as denaturant and glyoxal-urea (GU) resin synthesized from glyoxal (G) and urea (U) as modifier. On the basis of single factor experiment to determine the optimal GU resin synthesis conditions, the preparation conditions of modified peanut protein adhesive were optimized using orthogonal experiment, and the structure and adhesive properties of the adhesive were analyzed by bonding performance tests, Fourier transform infrared spectroscopy and differential scanning calorimetry. The results showed that the optimal GU resin synthesis conditions were obtained as follows: molar ratio of glyoxal to urea 1.4∶ 1,reaction temperature 80 ℃,and total reaction time 3.5 h.The optimal preparation conditions of modified peanut protein adhesive were obtained as follows: peanut protein powder 70 g (dissolved in 200 mL distilled water),NaOH treatment pH 10.4, mass ratio of GU to NaOH treated peanut protein 16∶ 84, and reaction time 3 h.Under the optimal conditions, the adhesive strength of the modified peanut protein adhesive was greater than required the for Class II plywood (≥ 0.7 MPa) in GB/T 9846-2004,and had lower solid content and longer storage life compared with NaOH treated peanut protein adhesive. Fourier transform infrared spectroscopy results showed that NaOH could denature peanut protein and expose more reactive groups, resulting in the formation of ester bond between GU resin and NaOH treated peanut protein and fewer hydrophilic groups,so the water resistance increased.Differential scanning calorimetry results showed that the heat absorption onset peak temperature and peak temperature of modified peanut protein adhesive were higher, so the thermal stability increased. |
