为研究聚合物聚集态变化与水树生长特性之间的关系,对不同温度下交联聚乙烯(XLPE)材料内的水树生长特性进行对比分析.采用水针电极老化法,分别在-15、0、20、40、60、80℃下对XLPE薄片进行加速水树老化,利用显微镜观察水树形态,并对水树尺寸进行了测量统计.同时利用动态力学分析(DMA)对XLPE分子链在不同温度下的松弛行为进行了测试分析.显微镜观测结果表明:低温下水树枝干清晰,沿着电场线方向排列.随着温度的升高,水树枝干逐渐变粗变密,并且在0℃和60℃下水树整体尺寸最大.DMA结果表明:XLPE新样本的玻璃化温度为-5℃左右,α松弛峰值温度为60℃左右,材料的这两个特征转变温度与最大水树尺寸对应的温度一致.在不同温度下,聚合物分子链的运动单元不同,由于在材料聚集态转变温度处发生了运动单元的突变,从而使得水树生长速率加快.
In order to study the relationship between polymer morphology change and water tree propaga-tion, the propagation characteristics of water trees in XLPE material at different temperatures were com-pared. The accelerated water tree ageing experiments were performed at -15, 0, 20, 40, 60, 80 ℃ for XLPE specimens through water-needle electrode method respectively. The morphologies of water trees were observed by optical microscope, and the sizes of water trees were measured and counted. The relax-ation behavior of XLPE molecular chains at different temperatures was tested by dynamic mechani-cal analysis (DMA). The optical microscope observation results show that the branches of water trees are clear at low temperature and arrange along the electric field lines. With the rise of temperature, the branches tend to be wider and denser, and the sizes of water trees are the biggest at 0℃ and 60℃. The DMA results show that the glass transition temperature of new XLPE specimen is about -5℃, and the α-relaxation temperature is about 60 ℃. The two temperatures are consistent with the temperatures where the size of water tree is the biggest. The motion units of polymer chains are different at differ-ent temperatures, and the motion units change suddenly at the transition temperature of aggregation state, so the propagation rate of water trees accelerates.
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