温度和固含量对脲醛树脂预固化行为的影响

【目的】考察温度、固体含量对预固化脲醛树脂分子质量和化学结构的影响,为预固化行为的调控提供理论参考。【方法】采用凝胶色谱(GPC)和~(13)C-NMR分析了脲醛树脂在相同预固化处理时间,不同温度、固体含量条件下的分子质量分布及主要官能团的变化,对比了温度、固体含量对树脂羟甲基、亚甲基和醚键的贡献率。【结果】在相同预固化处理时间下,随着固化温度的升高,树脂的数均和重均分子质量均显著增大,伴随二亚甲基醚键总量先增大再减小趋势,端基羟甲基以及链状羟甲基结构含量下降,链状和网状亚甲基基团含量增大。在相同预固化处理时间下,高固体含量树脂的相对分子质量比低固体含量树脂的低,但高固体含量树脂间分子质量相差不大,尽管固体含量的增大使链状羟甲基结构、二亚甲基键和二亚甲基醚键含量略有上升,但对端基羟甲基结构和总量影响不大。【结论】通过对比温度和固体含量对羟甲基、亚甲基和醚键的贡献率可知,与固体含量相比,温度对树脂预固化行为的影响更显著。

Effects of temperature and solid content on the pre-curing behavior of urea-formaldehyde resin

Objective] Temperature and solid content significantly influence the molecular weight and chemical structure of pre-curing urea formaldehyde resins,playing an important role in regulating pre-curing behavior.Method] Gel chromatography(GPC) and 13C-NMR were used to investigate the effects of temperature and solid content on the molecular weight distribution and main functional groups of pre-curing urea-formaldehyde resins,as well as the relative amounts of methylol,dimethylene and dimethylene ether groups.Result] At constant pre-curing time,Mn and Mw increased with increasing curing temperature,with the content of dimethylene ethers initially increasing and then decreasing,whereas the content of terminal and linear methylol groups decreased and that of linear and network dimethylene groups increased.The molecular weight of higher-solid-content resins was higher than that of lower-solid-content ones,with insignificant differences observed between the former resins.Although the content of linear methylol,dimethylene and dimethylene ether groups slightly increased with increasing solid content,the total number of terminal methylol groups was unchanged.Conclusion] Temperature had a much more significant effect on the pre-curing of urea-formaldehyde resins than their solid content,as determined by comparing the contents of methylol,dimethylene,and ether functional groups.