固体核磁共振法对低甲醛释放脲醛树脂化学结构的研究

Study on Chemical Structure of Urea-formaldehyde Resin with Low Formaldehyde Emission by ^(13)C CP/MAS NMR

在采用液体核磁对3种低甲醛释放脲醛树脂化学构造进行分析的基础上,利用13C CP/MAS NMR对脲醛树脂固化产物的化学结构进行了研究。结果表明,不同固化体系下,3种低甲醛释放脲醛树脂胶黏剂的固化历程不同,固化后树脂的结构有所差别。不添加固化剂时,脲醛树脂的固化交联反应程度低,固化产物中羟甲基含量高,甲醛释放量也随之增加。加入固化剂后,促进了羟甲基的固化交联反应,脲醛树脂固化产物中羟甲基含量普遍降低。3种固化体系下,UF-3羟甲基含量最高;在氯化铵为固化剂的条件下,UF-2羟甲基含量最低,为0.058 2;不添加固化剂和复合固化体系条件下,UF-1羟甲基含量最低,分别为0.0784和0.0713。不同固化体系对不同种类脲醛树脂的固化效果不同,固化后树脂的结构不同,其力学性能和甲醛释放能力也不同。

Based on the evaluation of the chemical structures of three kinds of urea-formaldehyde（UF） resin with low formaldehyde emission by ^13C NMR, the technique of ^13C CP/MAS NMR was applied to study the chemical structure of UF resins. Results indicated that the curing procedure of three kinds of UF resin with low formaldehyde emission was diverse in different curing system, the structure of cured resin was different as well. Without hardener, the cross-linkage degree of UF resin was lower, the content of methylol of cured UF resin was the higher and formaldehyde emission was increased. The hardener accelerated the curing reaction, the content of methylol was decreased. In three kinds of curing system, the content of methylol was the highest for UF-3; it was the lowest of 0. 058 2 for UF-2 with ammonium chloride as curing agent; for UF-1, it was the lowest without hardener and composite curing system of 0. 078 4 and 0. 071 3 respectively. The curing reaction of different kinds of UF resin was different in different curing system, the structure of cured resin, mechanical properties and formaldehyde emission were different too.