改性超支化聚合物对脲醛树脂性能的影响

采用“碱-酸-碱”合成工艺,在树脂合成反应末期加入不同比例的尿素及改性超支化聚合物,合成了2种脲醛树脂(UF0和UF1),测试了2种脲醛树脂的基本性能及其所制胶合板的力学性能,并借助差示扫描量热仪(DSC)和热重分析仪(TG)对树脂的固化性能及耐热性能进行了表征和分析。试验结果表明:加入改性超支化聚合物的UF1树脂具有较低的固化温度,有利于提升树脂的固化速度,且树脂具有较好的热稳定性; 胶合板的2 h耐冷水胶合强度可以提升近50%,树脂中游离甲醛含量明显下降,而对树脂的固体含量及黏度影响不大。13C NMR 结构分析表明,改性超支化聚合物的加入可以有效提升树脂中亚甲基桥键(―CH2―)和尤戎环(Uron)的比例,对树脂耐冷水性能的提升具有重要作用。
With the “alkali-acid-alkali” technology, two kinds of urea-formaldehyde resins(UF0 and UF1)were synthesized in laboratory by adjusting the mass ratio of urea and modified hyperbranched polymer at the end of resin synthesis, and the properties of the two urea-formaldehyde resins were tested according to the standard of GB/T 14074-2006. At the same time, the curing characteristics and thermal resistance performance of the two resins were analyzed by the differential scanning calorimeter(DSC)and thermogravimetric analysis(TG), respectively. The results showed that the resin with modified hyperbranched polymer(UF1)had lower curing peak temperature with or without curing agent, being beneficial to improve the resin curing rate, increase productive efficiency, and enhance the thermal resistance performance because of the higher carbon content and thermal decomposition temperature. It was found that the urea-formaldehyde resin with modified hyperbranched polymer had better performance compared with the unmodified urea-formaldehyde resin did under the same conditions. Moreover, the three-layer poplar plywood was made in the laboratory, and the bonding strength was evaluated after 24 h stress-release and equilibrium at room temperature. In this study, the wet bonding strength was determined after the specimens were immersed into cold water for 2 h at room temperature. The results showed that the wet bonding strength of modified urea-formaldehyde resin was improved by nearly 50%, and the free formaldehyde content in resin(UF1)decreased markedly. The structures of the two resins were analyzed by using the 13C nuclear magnetic resonance(13C NMR), and the results further indicated that the contents of the methylene(―CH2―)and uron in the modified resin with hyperbranched polymer was much higher than those in the unmodified resin. The methylene played an important role in bonding, while uron was beneficial to waterproof performance of urea-formaldehyde resin