紫外光交联线性低密度聚乙烯水树老化特性研究

Research on Water Tree Aging of UV-photoinitiated Crosslinking of Linear Low Density Polyethylene

以线性低密度聚乙烯（linear low density polyethylene,LLDPE）为基础树脂,采用紫外光交联法制备了交联聚乙烯试样（记为XLPE1）,并利用水刀电极法比较了XLPE1与过氧化物交联低密度聚乙烯（记为XLPE2）在抗水树性能的差异。结果表明,未经过交联反应的LLDPE的水树枝尺寸明显低于低密度聚乙烯（linear low density polyethylene,LDPE）,即使两种材料在经过交联反应后抗水树能力均变强,但XLPE1的抗水树性能仍优于XLPE2。拉伸实验过程中出现的应变硬化现象表明,交联键以及LLDPE中密集的短支链均可以增加无定形相的连接分子链密度,延缓了水树的生长。另外,动态热机械分析（dynamic mechanical analysis,DMA）结果表明交联反应使材料无定形相韧性增加,有助于吸收微水珠的冲击力。XLPE1具有相对优异的抑制水树生长能力,这可能与LLDPE抗水树性能略好以及其交联度略高有关。

On the basis of linear low density polyethylene （LLDPE）, the crosslinked polyethylene specimens （denoted by XLPE1） were obtained through UV-photoinitiated crosslinking process. The water blade electrode method was applied to accelerate water-tree aging of specimens, and comparison of anti-water-treeing performance with peroxide crosslinked low density polyethylene （denoted by XLPE2） were made in this paper. Experimental results show that the size of water tree in LLDPE is much smaller than low density polyethylene （LDPE）. Even through crosslinking reaction greatly restrain the growth of water tree, the anti-water-treeing performance of XLPE2 is inferior to XLPE1. The strain hardening during the tensile test indicates that the densities of tie molecule chains could significantly increase due to the existence of both cross-linked bond and short-chain branch of LLDPE, stunting the invasion of water droplets in amorphous phase. In addition, the increasing amplitude of loss modulus E＂ and loss factor Tanθ in β relaxation measured by dynamic mechanical analysis （DMA） means that crosslinking reaction could enhance the toughness of amorphous phase, leading to the absorbing impact force produced by water droplets. The reason for XLPE1 has better anti-water-treeing performance than XLPEz may be due to both the better water tree-resistance of LLDPE and its higher crosslinking degree.