乙二醛-尿素树脂改性花生蛋白胶黏剂的制备Preparation of glyoxal-urea modified peanut protein adhesive

采用氢氧化钠作为变性剂，乙二醛(G)和尿素(U)作为原料合成的乙二醛-尿素(GU)树脂作为改性剂，制备改性花生蛋白胶黏剂，以提高花生蛋白胶黏剂的耐水性。在单因素实验确定GU树脂改性剂合成的最佳条件的基础上，采用正交实验对改性花生蛋白胶黏剂制备工艺条件进行优化，并通过胶合性能测试、傅里叶变换红外光谱和差示扫描量热仪，对胶黏剂的结构和胶合性能进行分析。结果显示：GU树脂改性剂合成的优化条件为乙二醛与尿素摩尔比1.4∶ 1，反应温度80 ℃，总反应时间3.5 h；最优的改性花生蛋白胶黏剂制备工艺条件为碱处理pH 10.4、花生蛋白粉质量70 g（200 mL蒸馏水）、改性剂与碱处理花生蛋白质量比16∶ 84、反应时间3 h，在此条件下制备的改性花生蛋白胶黏剂的胶合强度大于GB/T 9846—2004中对Ⅱ类胶合板的要求（≥0.7 MPa），固体含量较碱处理花生蛋白胶黏剂降低，储存期延长。傅里叶变换红外光谱结果表明，氢氧化钠可使花生蛋白变性并暴露出更多的反应基团，GU树脂与碱处理花生蛋白形成了酯键，亲水基团减少，从而增加了耐水性；差示扫描量热仪结果表明，改性后的花生蛋白胶黏剂吸热起始峰温度和峰值温度均升高，热稳定性提高。 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.