脲醛树脂室温下的固化机制

以脲醛树脂为试验材料,通过测定凝胶时间和凝胶色谱(GPC),分析了添加固化剂氯化铵的脲醛树脂在室温环境下,固化过程中的黏度、凝胶时间和分子质量分布变化规律。结果表明:添加2.0%氯化铵的树脂前8 h黏度增长缓慢,而8 h到10 h黏度从99 mPa？s升到10 020 mPa？s。从外观上看,添加固化剂8 h脲醛树脂已黏稠结团; 到10 h时,已成型并具有一定硬度。凝胶时间经过10 h预固化后由137 s减少到40 s,树脂的数均分子质量和重均分子质量明显增大。从分子质量分布来看,小分子逐渐消失,中等分子和大分子比例增大,同时树脂分散度由1.11减小到1.08,分子均一性有所提高。随着适用期内时间的延长,脲醛树脂凝胶程度增大,活性降低。
This article investigates the change of viscosity, gel time and molecular weight distribution of urea-formaldehyde(UF)resin with curing agent ammonium chloride(NH4Cl)under ambient temperature by measuring gel time and gel permeation chromatography(GPC)analysis. It was found that the viscosity of UF resin with 2.0% NH4Cl changed slightly at the beginning, but sharply increased from 99 mPa？s to 10 020 mPa？s after 8 hours. The resin thickened and clustered at this stage. After 10 hours, UF resin took shape and became hard and its gel time decreased to 40 s from 137 s for the un-cured resin. Number average molecular weight and weight average molecular weight increased significantly, and small molecular disappeared gradually while molecular of medium and high weight accounted for higher proportion. The molecular uniformity of UF was improved degree of dispersion dropped from 1.11 to 1.08. The degree of gelation increases and the activity of applicable UF resin decreases with longer elapsed time