脱气时间对交联聚乙烯电缆绝缘材料聚集态结构与链结构的影响

摘要

The crosslinked polyethylene (XLPE) is degassed in laboratory,and the crosslinking by-products content,the aggregation structure and the chain structure are investigated by tensile test,degree of crosslinking measurement,infrared spectroscopy,differential scanning calorimetry (DSC) and scanning electron microscopy (SEM) at different degassing time.The results show that the crosslinking by-products are effectively eliminated during the degassing process,and the acetophenone content is significantly reduced after 168 h degassing,then the reduction rate slows down and remains unchanged until 336 h.However,the reduction rate of cumyl alcohol content is small,the degassing trend slows down after 336 h.Experimental results show that the optimum degassing time of XLPE cable is limited within 168-336 h.In the beginning of degassing,the free radicals inside XLPE insulation are cross-linked again and the chain structure changes,which increases elongation at break.And there are two kinds of aggregation structure changes in crystal nucleus formation and crystalline grain growth.The newly developed small crystals facilitate further promoting elongation at break,the spherocrystal growth becomes perfect,and the crystallinity increases.Moreover,the duration of chain structure changes for a shorter period while the duration of aggregation structure changes for a longer period,and those changes remain stable in the late degassing.According to the above experimental results,a change model of aggregation and chain structure of XLPE cable insulation in the degassing process is constructed,and the changes of microstructure and macroscopic elongation at break are explained.%通过对完整切段交联聚乙烯(XLPE)电缆进行实验室脱气处理,在不同脱气处理时间下对其绝缘层材料XLPE进行了红外光谱测试、差示扫描量热分析(DSC)、扫描电镜分析(SEM)、交联度测量及拉伸测试,研究XLPE中交联副产物含量、聚集态结构与链结构的变化.结果表明:XLPE中的交联副产物在脱气处理过程中得到了有效消除,其中苯乙酮含量随脱气处理进行至168 h大幅减少,而后趋势变缓至336 h后不再显著变化;枯基醇减少速度缓慢,随脱气处理进行至336 h后减少趋势才变缓,说明XLPE电缆合理脱气时间应在168～336 h内.脱气处理前期,XLPE电缆绝缘材料内部自由基再交联,链结构发生变化,导致断裂伸长率增大,同时还产生晶核生成和晶粒生长两种聚集态结构变化的现象,新的小晶体出现,进一步促进断裂伸长率增大,且球晶生长完善,结晶度增大.其中链结构变化持续时间较短,聚集态结构变化持续时间较长,随着脱气处理的进行,这些变化在后期均趋于稳定.根据上述实验结果,提出了XLPE材料内部在脱气处理过程中的聚集态结构和链结构变化模型,对脱气处理过程中微观结构和宏观断裂伸长率变化进行了解释.