脲醛树脂胶粘剂生产中凝胶的产生条件及其再利用研究

在脲醛树脂(UF)胶粘剂生产过程中会经常产生由各种原因导致的凝胶现象,轻者物料作废,重者造成"固罐",致使企业长时间停产。采用先弱碱后弱酸的合成工艺,通过对凝胶的产生条件和凝胶再利用的工艺过程进行考察后得知:凝胶产生时的黏度随n(甲醛)∶n(尿素)比值的增加而增大;当n(甲醛)∶n(尿素)从1.2∶1增至2.2∶1时,体系黏度从37s增至98s;缩聚阶段的pH值对凝胶的出现时间影响显著,当pH值为2.0(或5.5)时,凝胶出现时间为7min(或100min);反应温度对凝胶的出现时间有一定影响。凝胶再利用的工艺过程是:将甲醛加入到反应器中,调节体系的pH值为8.5、温度为50℃;边搅拌边将凝胶加入到甲醛溶液中,凝胶的加入量以满足体系中n(甲醛)∶n(尿素)≥5.5∶1为宜;待凝胶完全溶解后,再按正常的合成工艺进行操作。

Study on occurring conditions and reuse of gel in production of urea-formaldehyde resin adhesive

The gel could be often produced from various reasons in production process of urea-formaldehyde resin(UF) adhesive,and gel could induce reactants waste or stop production for long due to reaction equipment curdled by reactants. So occurring conditions and reuse of gel were reviewed by synthesis technics of weak basicity- weak acidity. The results showed that the viscosity of occurring gel was increased with increase of molar ratio of formaldehyde to urea. The system viscosity was increased from 37 s to 98 s...