温度对聚乙烯水树枝老化特性的影响

为研究温度对PE水树枝老化特性的影响,选用低密度聚乙烯(LDPE)、过氧化物(DCP)交联聚乙烯(XLPE)作为试验材料。在室温(20°C)、40°C、60°C、80°C 4个温度下,采用水针电极法培养水树枝,用金相显微镜观测水树枝形态,并统计水树枝尺寸和引发率。研究发现,在60°C以上,温度对PE水树枝老化特性影响显著;水树枝的引发率随温度的升高先减小后增大;水树枝的尺寸随温度的升高总体呈现增大的趋势;LDPE和XLPE的试验得到类似的结果,但XLPE的抗水树枝老化性能优于LDPE。同时研究发现,随温度的升高,材料的力学性能大幅下降。经分析认为,交联限制大晶块的形成,使材料的力学性能增强,是XLPE抗水树枝化性能优于LDPE的两个主要原因;高温下两种材料力学性能下降、微孔膨胀、水分和盐离子的加速扩散是高温下水树枝劣化加速的主要原因。

Influence of Temperature on Water Treeing in Polyethylene

In order to study water treeing in polyethylene at different temperatures,low density polythene and peroxide cross-linked polyethylene were chosen as the testing materials.At room temperature(20°C),40°C,60°C and 80°C,liquid needle electrodes method was used for water tree development,and metallographic microscope was used for observation of water tree morphology.Meanwhile,sizes and initiation rates of water trees were counted.Experimental results show that water treeing characteristics are significantly influenced by temperature when temperature exceeds 60°C.Water tree initiation rates first decrease and then increase with increasing temperature,and water tree sizes show an increasing trend with increasing temperature.The experimental results on LDPE are similar to those on XLPE,but XLPE has better anti-water-treeing performances than LDPE.Meanwhile,experimental results show that mechanical properties of materials dropped significantly as temperature increases.After analyses,it is believed that,cross-linking limits the formation of large crystal block and strengthens the mechanical properties of materials,thus,the anti-water-treeing performance of XLPE is superior to that of LDPE.Meanwhile,the decrease in mechanical prosperities of materials,pore expansion,the accelerated movement of water molecules,and ions are the reasons of acceleration of water treeing at high temperatures.