聚乙烯交联过程结构演化的流变学研究

采用耐压等级分别为35kV及110kV的两种不同商业化可交联聚乙烯(XLPE)电缆料为研究模型,考察其化学交联过程中结构演化与线性黏弹响应的关系.研究结果表明,流变学方法可敏感表征较低温度、较长时间下XLPE交联过程的结构演化.随着交联温度的升高,体系预交联时间缩短,而黏弹特性的变化速率不变;交联导致体系弹性和黏性均增加,但弹性增加幅度远大于黏性增加幅度.比较两种样品交联过程的流变行为,发现随着交联反应的进行,两者的黏性增长速率基本一致,但35kV电缆料样品的弹性增长略大.采用低频率区域(频率末端区)的动态储能模量(G′),计算体系交联点之间的平均分子量(Mc),以表征样品的交联密度.同时用常规的溶胀平衡法研究了两种电缆料Mc与交联时间的依赖关系.

STUDIES ON STRUCTURE EVOLUTION OF LDPE DURING CROSSLINKING PROCESS BY RHEOLOGICAL TESTS

Two commercial crosslinkable polyethylene insulation cable granules,used for 35 kV and 110 kV voltage insulation respectively,with the similar melting point and crosslinking temperature,were chosen as experimental samples for examining their linear dynamic responses during cross-linking.In order to detect the structure evolution of the two samples during crosslinking,dynamic time sweep test was carried out at 140℃,145℃ and 150℃ using parallel plates model with an Advanced Rheometric Expansion System.It can be found that the pre-crosslinking time decreased with the increase of crosslinking temperature for both samples during the dynamic time sweep test,but the rising rates of the dynamic viscosity (η') and dynamic rigidity (η″) for both samples were independent of temperature.Compared with 110 kV insulation cable granules,35 kV insulation cable granules showed higher rising rate of η″,similar rising rate of η' and longer pre-crosslinking time at the same temperature during crosslinking.As a criteria of crosslinking density,the number-average molecular weight between the junction of the networks for crosslinked samples,Mc,was calculated on the basis of the rubber elasticity theory,using the data of dynamic modulus G' obtained from plotting dynamic storage modulus (G') versus frequency (ω) at terminal zone where ω approaches 0.The value of Mc of 35 kV insulation cable granules calculated through rheological method was lower than that of 110 kV insulation cable granules.Moreover,the Mc dependence on crosslinking time was probed through the equilibrium swelling method.The values of Mc of totally crosslinked insulation cable getting from rheological method were similar to those from equilibrium swelling method although they crosslinked at different conditions.