乙酸基和羟基对固化的环氧树脂吸水性能的影响

应用称重法、差示扫描量热法和腐蚀测试法研究固化的环氧树脂的吸水行为。实验结果表明,该树脂中的羟基改为乙酸基后可降低树脂的饱和吸水率,并增大水在树脂中的扩散能力。邻甲酚环氧树脂用乙酸线型酚醛酯树脂固化后所得的树脂(EPA)在30℃时饱和吸水率为0.84%(质量分数),而用线型酚醛树脂固化所得的树脂(EP)的则为1.97%;水在EPA和EP中的扩散活化能分别为40和48kJ.mol^-1.这可归因于乙酸基中的甲基的憎水性,降低了吸水率,却因乙酸基的弱相互作用增强了链的柔顺性,而有利于水在链空间中的扩散。EPA涂层/金属铝界面的特殊结构降低了该界面的吸水率,从而提高了该涂层的防护性能。

Comparison of the Effects of Acetoxy and Hydroxy Groups on the Water Uptake into the Cured Epoxy Resin

Acomparison of the effects of acetoxy and hydroxy groups on the water uptake into the cured epoxy resin was made using the gravimetric method, DSCand corrosion test. The experimental results show that the replacing of the hydroxy groups with acetoxy groups in the resin causes less water uptake, but increases the diffusibility of water in the resin. For example, at 30℃, the equilibrium water sorption of the o-cresol novolac epoxy resin cured with phenol novolac acetate resin (EPA ) is 0.84% (mass fraction), while the epoxy resin cured with phenol novolac resin(EP) is 1. 97 %; the activation energies for diffusion of water in EPAand EPare 40 and 48 kJ. mol^-1 respectively. The effects may be mainly due to the hydrophobic methyl group of the acetoxy groups. The methyl group prevents the uptake of water, but makes the acetoxy group more flexible, which causes water diffusion less difficult. Moreover, the results show that the unique structure of the interphase of the EPAcoating/Al substrate even causes further less water uptake, and improves the effectiveness of corrosion protection for the coating accordingly.