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研究了脲醛树脂合成反应在不同时间的甲醛与尿素物质的量比、pH值和温度对反应速率的影响,在加成反应阶段测定了甲醛含量,并在缩聚反应阶段测定了树脂的粘度。实验发现,甲醛与尿素在初始碱性阶段10 min内反应速率最快,随后呈逐渐降低的规律。通过正交实验,回归得到了脲醛树脂在缩聚反应阶段的反应时间与粘度变化的万程式,通过比较理论值(由方程式计算而得)与实验值(相同试验条件下测得)可知,当温度为60-80℃、pH值为4.0～5.5以及在反应时间间隔内进行拟合时,两者粘度的绝对误差在2 s以内。
The effects of the molar ratio of formaldehyde to urea, the pH value and the temperature on the reaction rate were investigated. The formaldehyde content was determined during the addition reaction and the viscosity of the resin was measured during the polycondensation reaction. It was found that the reaction rate of formaldehyde and urea was the fastest in the initial alkaline stage within 10 min, then decreased gradually. Through orthogonal experiment, regression equation of reaction time and viscosity of urea-formaldehyde resin in the polycondensation reaction stage was obtained. By comparing the theoretical value (calculated from the equation) and the experimental value (measured under the same test conditions), when the temperature 60-80 ℃, pH value of 4.0 ~ 5.5 and the reaction time interval fitting, the absolute error of the two viscosities within 2 s.