[目的]当尿素/甲醛物质的量比降低时,合成的脲醛树脂甲醛释放量大幅度减少,但同时板材强度也大幅度下降;加入三聚氰胺改性后可克服低摩尔比树脂胶结性能较差的劣势,但是制备过程中尿素/甲醛摩尔比的降低以及三聚氰胺的加入都会导致树脂固化时间延长,添加固化剂的改善效果不明显.本研究探讨加入催化剂对树脂胶接固化性能的影响,以期为后续研究提供理论依据.[方法]在脲醛树脂合成过程中加入不同种类的催化剂,比较添加催化剂前后树脂的物化性能,包括固含量、固化时间、游离甲醛含量和羟甲基含量,并对树脂进行 DSC 固化动力学分析计算树脂的固化反应活化能,DEA树脂固化特性分析研究树脂固化过程,以及对树脂 FTIR 红外谱图进行分析比较添加不同添加剂后树脂官能团的变化,来选择适当的催化剂,以期缩短树脂固化时间,提高固化速度,解决低甲醛释放脲醛树脂固化速度慢、影响生产效率的问题.[结果]在加成阶段加入氯化铵、硼酸铵、磷酸铵和硫酸铵后,低摩尔比脲醛树脂的固化速度都明显提高,固化时间为80 ~92 s,均少于添加催化剂之前树脂的固化时间96 s;4 种催化剂均起到了降低固化反应活化能的作用,其中硼酸铵、硫酸铵降低固化反应活化能的作用最显著,固化反应活化能分别为62. 31 和62. 02 kJ·mol -1 ,明显低于未添加催化剂的脲醛树脂固化反应活化能( 68. 25 kJ·mol -1 ); 根据DEA分析结果,4 种催化剂均有明显加速树脂固化的作用,其中硼酸铵、硫酸铵对树脂固化速率的提高最大; 加入4 种催化剂后,热压制备的胶合板板材强度基本不变,甲醛释放量低于未添加固化剂脲醛树脂胶合板的甲醛释放量0. 37 mg·L -1.[结论]以硫酸铵为催化剂的脲醛树脂制备的胶合板,树脂的固化反应活化能降低幅度较大,固化时间明显缩短,可有效提高低摩尔比脲醛树脂的固化速度,并可降低其胶接制品的游离甲醛释放量,用其制备的胶合板甲醛释放量达到日本 JIS标准的 F四星级,为改性效果最佳的催化剂.%[Objective]Urea-formaldehyde resin adhesive was the most widely used adhesive in the world. When the molar ratio of urea/formaldehyde reduced,the corresponding formaldehyde-emission decreased greatly,but at the same time the strength of plywood also declined dramatically. Therefore,many researches showed that the adhesives modified by melamine can effectively reduce formaldehyde-emission,and the wet strength of adhesives with low molar ratio was improved. However,low-formaldehyde-emission urea-formaldehyde resin modified by melamine resulted in extending the gel time,which cannot be solved by adding curing agent. [Method]Aiming at shortening the curing time and enhance production efficiency,different activators in urea-formaldehyde were studied by analyzing solid content,curing time,free formaldehyde content and hydroxymethyl content. DSC was applied on the dynamic analysis of curing reaction. DEA was used to investigate the resin curing process. moreover,FTIR analysis was also carried out to compare functional groups after adding different additives to select an appropriate catalyst for shorting the resin curing time and reducing formaldehyde-emission.[Result]Adding the ammonium chloride, ammonium boric acid, ammonium phosphate and ammonium sulfate respectively during addition polymerization,the curing rate of low molar ratio urea-formaldehyde resin was all improved significantly. Four kinds of activators had played an significant role in reducing the curing reaction activation energy,especially for the ammonium boric acid and ammonium sulfate. According to the results of DEA,four kinds of activators obviously accelerated resin curing,particularly for the ammonium boric acid and ammonium sulfate. After adding four kinds of activators,the strength of hot-pressing plywood almost remain unchanged and formaldehyde-emission reduced.[Conclusion]when the amount of (NH4)2SO4 was 0. 3% of the total weight during addition stage,the activation energy of the cure reaction was greatly decreased,and the curing time was also considerably reduced. Moreover, the formaldehyde emission of the plywood can meet the requirement of F****for JIS.
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