Reverse Regulation of Order and Autocatalysis Reactions During the Cross-Linking Process of Low-Density Polyethylene Used in High-Voltage Cable Insulation
Li Jiacai, Shang Kai, Si Zhicheng, Wang Shihang, Li Shengtao
State Key Laboratory of Electrical Insulation and Power Equipment Xi’an Jiaotong University Xi’an 710049 China
Abstract：Extruded cross-linked polyethylene (XLPE) insulating materials with excellent thermal, mechanical and electrical properties have been widely used in high-voltage cable insulation. The insulating materials are composed of low-density polyethylene (LDPE) by introducing cross-linking agent (dicumyl peroxide, DCP) and antioxidants. During the continuous extrusion process, the increase of local temperature causes the decomposition of DCP in advance, which results in the phenomenon of pre-cross-linking and even scorch in the melt. However, scorch will not only reduce the extrusion quality of insulating materials, but also threaten the electrical performance of XLPE. Scorch and cross-linking degree are essentially the reflection of the cross-linking reaction and its results. Under the premise of ensuring the cross-linking degree, improving the anti-scorch performance is one of the most important factors to promote the further development of domestic LDPE insulating materials used in high-voltage cables. Herein, the correlation mechanism between cross-linking reactions with anti-scorch properties and cross-linking degree of insulating materials used for high-voltage cables was discussed. Firstly, a quantitative characterization method for the anti-scorch properties of insulating materials was proposed based on macromolecular chemorheology and gel theory. Moreover, insulating materials adding with different antioxidants were prepared. The correlation mechanism between cross-linking reactions with anti-scorch properties and cross-linking degree of insulating materials was established by experimental analysis and reaction kinetic method. Finally, the regulation strategies of order and autocatalysis reactions to improve the anti-scorch performance under the premise of ensuring the cross-linking degree were discussed by employing the compound antioxidants. The following conclusions can be drawn. Firstly, a quantitative characterization method for the anti-scorch performance of insulating materials is proposed, and this method can accurately obtain the characterization parameters of anti-scorch performance, which is scientific and universal. Moreover, the cross-linking reaction process of LDPE insulating materials involves the order and autocatalysis reactions. Meanwhile, the lower the order of order reaction at low temperature, the more beneficial it is to delay the pre-cross-linking reaction to form gel, whereas the higher the order of autocatalysis reaction at high temperature, the more beneficial it is to enhance the gel content after complete cross-linking. Besides, the single additive has the same effect on the order and autocatalysis reactions, while the appropriate compound additives can reversely regulate the order and autocatalysis reactions of insulating materials, which is ascribed to the fact that the compound additives have different degrees of interaction at different temperatures. Therefore, reverse regulation of the order and autocatalysis reactions can be realized by the appropriate additives, which contributes to improving the anti-scorch performance under the premise of ensuring the cross-linking degree of the insulating materials. This study provides the important theoretical guidance for the actual formulation design of insulating materials used for high-voltage cables, which can promote the development of domestic insulating materials. Based on this research, the improvement strategy of high purity in high-voltage cable insulating materials will be explored in the future from the perspective of regulating cross-linking reactions.
李加才, 尚恺, 司志成, 王诗航, 李盛涛. 高压电缆绝缘低密度聚乙烯交联过程中级数和自催化反应的逆向调控[J]. 电工技术学报, 2024, 39(1): 13-22.
Li Jiacai, Shang Kai, Si Zhicheng, Wang Shihang, Li Shengtao. Reverse Regulation of Order and Autocatalysis Reactions During the Cross-Linking Process of Low-Density Polyethylene Used in High-Voltage Cable Insulation. Transactions of China Electrotechnical Society, 2024, 39(1): 13-22.
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