Improved High-Temperature Electrical Properties of Polymeric Material by Grafting Modification

Abstract

Grafting modification is an effective method to enhance the electrical characteristics of polymeric materials by establishing deep traps that prevent carriers from being injected and transmitted. However, grafted polymers for electrical insulation suffer from large leakage current at elevated temperatures, limiting their application in harsh environments. We report that an itaconic anhydride grafted polypropylene synthesized by the solution grafting method preserves excellent insulating properties up to 120 °C. It is demonstrated that the grafted itaconic anhydride restrains free electrons employing strong electrostatic attraction and obstructs charge injection and transport. Furthermore, we reveal that strong intramolecular forces, deep energy traps, and fragmentized spherulites are essential factors contributing to grafted polymers' superior high-temperature electrical properties. This work provides insights into the sophisticated charge transport mechanisms in grafted polymers and their effects on the insulation characteristics, which is critical for the suitable design of polymeric materials with exceptional electrical properties.

Deep Trap Origins, Characteristics, and Related Mechanisms in Chemically Grafted Polypropylene with Enhanced Direct Current Volume Resistivity

“…PP is a semicrystalline polymer. Many investigations indicate that the charge traps in PP originate from the amorphous areas and crystalline–amorphous boundaries, especially the defects or impurities. − , Physical defects such as cavities and pores would introduce shallow traps, whereas chemical defects such as broken chemical bonds and polar groups would generate deep traps. − Therefore, only peak ρ1 in pure PP can be ascribed to the traps generated by the molecular interactions in the disordered areas (i.e., amorphous areas and boundaries). Concerning MMA-grafted PP, the grafted groups/chains would act as impurities and thus would be extruded along the boundaries or into the amorphous phases during the crystallization process .…”

“…1−3 Grafting modification by functional chemical groups has been proved to be a fairly effective method to further enhance the dielectric properties, especially for direct current (DC) insulation under high temperature. 4,5 It can achieve the same enhancement level as for the PP-based nanocomposite, but it is free of the agglomeration problem as exists in the latter. 6,7 Therefore, grafting-modified PP is very suitable for large-scale industrial production for the insulation of practical high-voltage apparatuses, such as high voltage direct current (HVDC) extruded cables 7 and metallized film capacitors.…”

“…Regarded as a promising insulation material for the next generation power system, polypropylene (PP) has been extensively studied and investigated in recent years, because of its high thermo-stability, excellent dielectric performances, and thermoplastic nature, which means it is recyclable and eco-friendly. − Grafting modification by functional chemical groups has been proved to be a fairly effective method to further enhance the dielectric properties, especially for direct current (DC) insulation under high temperature. , It can achieve the same enhancement level as for the PP-based nanocomposite, but it is free of the agglomeration problem as exists in the latter. , Therefore, grafting-modified PP is very suitable for large-scale industrial production for the insulation of practical high-voltage apparatuses, such as high voltage direct current (HVDC) extruded cables and metallized film capacitors …”

“…Dang et al and He et al attempted to grafting-modify PP by maleic anhydride (MAH), which is a polar group with two carbonyls in the chemical structure, and realized a significant enhancement on DC dielectric properties, including enhanced DC volume resistivity and DC breakdown strength, suppressed space charge accumulation, which is very beneficial to the application in DC cables. Related experimental characterizations indicate that grafting modification can affect the crystallization morphology of PP, − thus further affecting the macroscopic properties. Furthermore, what is more arrestive, the thermally stimulated depolarization current (TSDC) results implicate large quantities of deep traps are introduced in the PP matrix after grafting modification. − Considering this phenomenon is similar to that in PP-based nanocomposites, , one can speculate the trap theory of nanodielectrics may also be available in grafting-modified PP, and the key point might be the grafted polar group.…”

Progress of application of functional atomic force microscopy in study of nanodielectric material properties

“…有研究表明 绝缘的无机纳米结构可用于阻止电荷载流子在介 电聚合物中的传输 [117] , 所得聚合物纳米复合材料 在高温下同时实现了高能量密度和放电效率, 但随 着温度的进一步升高, 纳米复合材料的能量密度和 效率都急剧下降. Yuan等 [118] 提出使用介电聚合 物与低浓度的高电子亲和力分子半导体混合制备 柔性全有机复合材料, 在200 ℃下表现出高能量…”