极性分子的结构异同性对接枝改性交联聚乙烯材料直流电性能的影响

doi:10.19595/j.cnki.1000-6753.tces.231423

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摘要为改善高压直流电缆运行过程中绝缘层材料的电导率对温度与电场强度敏感性所导致的电场反转问题,以及直流高压长时间作用下的空间电荷积聚现象,该文采用极性基团接枝改性的方式提升交联聚乙烯（XLPE）材料的直流电性能。由于接枝单体一般为沸点较低的极性小分子化合物,为避免材料在接枝过程中单体的气化损失,首先通过平行双螺杆挤出机配合低温高压计量泵装置实现熔融接枝反应。将丙烯酸酯类小分子化合物（丙烯酸甲酯（MA）、丙烯酸丁酯（BA）、甲基丙烯酸甲酯（MMA））分别预先接枝到低密度聚乙烯（LDPE）大分子链上制备接枝材料,通过红外光谱测试分析得出接枝单体皆成功接枝到LDPE大分子链上,熔融指数与凝胶含量测定表明材料的流变性能并未发生显著改变,X射线衍射测试与扫描电子显微镜观测发现接枝改性材料的结晶特性保持与基础树脂相似。进一步对三种接枝母料按一定比例稀释并完成交联过程,通过变温直流电导测试发现三种接枝改性材料的电导率-温度敏感性均出现不同程度的下降,综合高温空间电荷测试可以得出,接枝MA的XLPE材料电导率-温度敏感性下降幅度最大、空间电荷分布特性优异;结合第一性原理仿真计算可以进一步得到,三种接枝单体改性XLPE模型的陷阱能级较为一致,其直流电性能的改善效果与接枝单体的静电势分布存在显著关联。

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	王凯
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	王暄

关键词 ：交联聚乙烯, 接枝改性, 丙烯酸酯, 电导率-温度敏感性, 静电势分布

Abstract：Cross-linked polyethylene (XLPE) materials are limited in their application as insulation materials for high-voltage direct current cables, due to issues of the temperature and field-dependent conductivity, as well as problems with space charge injection and accumulation. Generally, graft-modified XLPE can significantly improve the space charge distribution characteristics and reduce the DC conductivity. However, the difficulty lies in the micro-doping and low-gasification temperature of small molecule grafting monomers, which affects the difficulty of the melting grafting process. Additionally, the pre-grafted low-density polyethylene (LDPE) materials is severely affected by the initiation of free radicals during the preparation process, which affects the grafting rate and rheological properties of the materials. At the same time, the improvement of the DC electrical performance of pre-grafted and cross-linked XLPE materials still needs further exploration. Therefore, this paper proposes the preparation of graft-modified materials using a low-temperature high-pressure metering pump in conjunction with a parallel co-rotating twin-screw extruder, then evaluates the grafting rate, rheological properties, and crystallization characteristics of the materials. The pre-grafting materials is then diluted to the same grafting content to prepare graft-modified XLPE materials. Through tests on DC conductivity and space charge distribution, combined with first-principles calculations, the effect of pre-grafted XLPE materials on DC improvement is explored, as well as the influence of grafting monomer structural differences on the materials.
First, acrylate small molecule compounds (methyl acrylate (MA), butyl acrylate (BA), methyl methacrylate (MMA)) were prepared to graft LDPE materials. Based on the analysis of infrared spectroscopy and melt flow rate test, the characteristic absorption peak of carbonyl group (C=O) appeared at wave number 1 740 cm^-1, indicating the successful grafting of small molecules onto the LDPE macromolecular chains. The grafting masterbatch prepared with 0.2 phr peroxide initiator, dicumyl peroxide (DCP), showed a high grafting rate and acceptable melt flow rate. Compared to MMA monomer containing easily breakable bonds and methyl groups with steric hindrance, MA and BA grafting modified XLPE materials exhibited a higher grafting rate. The grafting masterbatch and LDPE material had similar crystallinity, with spherulite size of about 3.8~3.9 µm.
Further, the three different grafted materials were diluted in specific proportions and subjected to the cross-linking process. It was found in the temperature-dependent DC conductivity test that XLPE-g-MA exhibited the largest decrease in conductivity-temperature sensitivity. Under polarization voltage of 40 kV/mm at 80℃, XLPE-g-MA demonstrated excellent characteristics in the spatial charge distribution. Combined with the first-principles simulation calculation, it can be further obtained that the trap energy levels of the three grafted modified XLPE models are relatively consistent, and the improvement effect of the DC performance is significantly related to the electrostatic potential distribution of the grafted monomer. In summary, XLPE-g-MA exhibited excellent DC electrical performance and is highly promising as an insulation material for HVDC cables.

Key words： Cross-linked polyethylene grafting modification acrylate conductivity-temperature sensitivity electrostatic potential distribution

收稿日期: 2023-08-31

PACS:

TM215.1

基金资助:国家自然科学基金资助项目（U20A20307）

通讯作者: 赵洪男,1955年生,教授,博士生导师,研究方向为极性化合物接枝改善聚烯烃直流电性和新型接枝方法。E-mail：hongzhao@hrbust.edu.cn

作者简介: 王凯男,1998年生,博士研究生,研究方向为接枝改性XLPE绝缘材料的直流电性能。E-mail：kaiwang7827@163.com

引用本文:

王凯, 赵新东, 郑海峰, 杨旭, 邵满志, 赵洪, 王暄. 极性分子的结构异同性对接枝改性交联聚乙烯材料直流电性能的影响[J]. 电工技术学报, 2024, 39(1): 34-44. Wang Kai, Zhao Xindong, Zheng Haifeng, Yang Xu, Shao Manzhi, Zhao Hong, Wang Xuan. Influence of the Structural Similarities of Polar Molecules on DC Properties of Grafted Modified Cross-Linked Polyethylene Materials. Transactions of China Electrotechnical Society, 2024, 39(1): 34-44.

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