热处理对聚乙烯水树枝老化特性的影响

Influence of Heat Treatment on Water Treeing in Polyethylene

为研究热处理对聚乙烯(PE)中水树枝老化特性的影响,选用低密度聚乙烯(LDPE)、过氧化物交联聚乙烯(XLPE)作为试验材料,采用热循环和热冲击两种方法对试样进行处理。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;同时测试试样的力学性能,观测结晶形态,测定XLPE的交联度。结果表明:热处理后,LDPE的力学性能变化不大,XLPE的力学性能明显下降;LDPE的晶块尺寸变小且趋于均匀化,XLPE的晶块尺寸变大且趋于不均匀化;LDPE和XLPE中水树枝都容易发展,XLPE水树枝的老化特性受热处理影响更大。热处理导致材料中微孔聚集、力学性能下降,是造成热处理后材料抗水树枝化性能下降的主要原因。

In order to study the influence of heat treatment on the water treeing in polyethylene, low den-sity polythene and peroxide cross-linked polyethylene were chosen as testing materials, and they were treated by thermal cycle and thermal shock. The water trees were obtained by water-needle electrode method. The morphology of water trees and crystalline morphology was observed by metallographic micro-scope, and the size and initiation rate of water trees were counted. Meanwhile, the mechanical properties of samples and cross-linking degree of XLPE were measured. The results show that the mechanical prop-erties of LDPE change little and the mechanical properties of XLPE decrease obviously after heat treat-ment. The crystal block dimension of LDPE tends to be smaller and even, and the crystal block dimen-sion of XLPE tends to be larger and uneven. The water trees in LDPE and XLPE are both easy to develop, and the ageing characreristics of water trees in XLPE are impacted by heat treatment more obvi-ously. The heat treatment leads to micropore aggregate and mechanical properties decrease, which are the two main reasons of resistance to water trees decreasing for materials after heat treatment.