低甲醛释放脲醛树脂固化反应历程的研究

STUDY ON CURING MECHANISM OF LOW-FORMALDEHYDE-EMISSION UREA-FORMALDEHYDE RESINS

在采用13CNMR对3种典型脲醛(UF)树脂化学构造进行分析的基础上,分别利用扭辫分析法(TBA)和差示扫描量热法(DSC)对不同固化体系、不同种类UF树脂固化反应过程中的动态粘弹性和固化特性进行了研究。结果表明,树脂合成配方不同,其化学结构明显不同。不添加固化剂时,树脂相对刚性率在升温过程中几乎不增长,当温度达到128℃时其相对刚性率急剧下降,几乎不发生缩聚交联反应,表现出热塑性树脂的特性,在温度超过135℃时才开始固化交联反应。树脂相同而固化体系不同时,UF树脂的固化反应历程不同。相同升温速率下,不加任何改性剂的UF树脂固化起始温度稍低一些,固化反应比较剧烈,放出热量最多。加入三聚氰胺和改性剂M的2种树脂固化反应进行得比较平稳,放出的热量较少。

Based on evaluation of chemical structures of three typical urea-formaldehyde（UF） resins by ^13C NMR, the techniques of torsion braid analysis （TBA） and differential scanning calorimetry （DSC） were applied, respectively, in order to analyze dynamic viscoelasticity and curing characteristics of these UF resins in different curing systems. UF resins from different formulations have quite different chemical structures, in which the modifier, melamine, was well copolymerized with urea. The relative rigidity of UF resins without curing agent was kept almost consistent during heating-up, then decreased quickly when temperature reached 128℃, which indicated that no crosslinking reaction occurred, and exhibited only the thermoptasticity of the resin. When temperature was higher than 135 ℃, crosslinking started. The curing mechanisms of UF resins in different curing systems were different from each other. UF resin without modifier started its curing reaction at lower temperature and gave off more heat during the more violent reaction. Curing of both UF resins modified by melamine or modifier M gave off less heat and proceeded more stably.