Polypropylene (PP) is regarded as an environmentally friendly cable insulation material to replace cross-linked polyethylene owing to its thermoplastic nature, high-temperature resistance, and outstanding dielectric characteristics. Grafting modification was applied to satisfy the demand for a higher-voltage power grid, and it was proved to be effective in enhancing the insulating performance of PP. The electrical tree is a common cause of cable insulation failure. This study examines the electrical tree initiation and growth characteristics of methyl methacrylate (MMA) grafted PP under different temperatures. Our results indicate that high temperature can promote the electrical treeing process, while grafting modification can hinder the process. The trap characteristics show that more deep traps are introduced in the grafted materials that can limit the motion of electrons and, thus, restrict the electrical tree initiation process. The crystallization morphology shows that the size of spherulites increases and the boundaries of the spherulites become blurry with higher MMA content. The compressed amorphous region and the tortuous boundaries of the crystalline can hinder the electrical treeing process. High temperature may improve charge carrier mobility and enhance the molecular chain relaxation, thus enlarging the free volume and finally accelerating the treeing process. The findings of this study would serve as a reference for designing grafted pP insulation for power cables.

The electrical properties of polypropylene (PP) insulation material decrease dramatically at high temperature, which limits its application in harsh environments. This study investigates how grafting styrene (St) improves the high‐temperature electrical properties of PP. Compared with pure PP, the space charge of the St‐grafted PP (PP‐g‐St) samples is suppressed, the volume resistivity is significantly improved, and the breakdown strength at room temperature (30°C) and high temperature (90 and 110°C) is increased by 35.04%, 36.98% and 34.86%, respectively. The results show that the side chains generated by grafted St can increase the number of spherulites and improve the crystallinity, making the boundaries of the spherulites tortuous and narrow, which is not conducive to the formation of low‐density regions. At the same time, because of the entanglement of grafted side chains and the presence of deep traps inside the PP‐g‐St samples, which inhibit the injection and migration of carriers, the effect of high temperature on the free volume is weakened. Consequently, the ability to capture charges at high temperature is enhanced, leading to an improvement in the high‐temperature electrical properties of PP. This research can provide a reference for the development of high‐performance grafted PP insulation materials.

La₂O₃-B₂O₃-CaO glasses with different B₂O₃ content were synthesized by melting method to produce glass/ceramic composites in this work. XRD and DSC results revealed that the diminution of B₂O₃ content was beneficial to increase the crystallization tendency of glass and improve the quality of crystalline phase, while decreasing the effect of glass during sintering process as sintering aids. The choice of glass/ceramic mass ratio was also influenced by the B₂O₃ content of glass. Dense samples sintered at 875 ºC showed good dielectric properties which meet the requirement of LTCC applications: moderate dielectric constant (7.8-9.4) and low dielectric loss (2.0×10^-3).

Polyimide is one of the key insulation materials for electrical and electronic components, including solar arrays and their drive assembly, which is subjected to long-term exposure to low-energy electron irradiation of electronvolt to kiloelectronvolt in low-earth orbit. The charge accumulation in dielectric materials due to electron radiation is the significant cause of discharges and anomalies in aerospace systems, and trap distribution characteristic plays an important role in revealing the charge accumulation mechanism. Therefore, in this article, the thermally stimulated depolarization current (TSDC) experiment is carried out to investigate the trap distribution characteristics of polyimide after long-term exposure to 20-keV, 8-nA/cm $^{\mathbf{2}}$ electron irradiation. The results indicate that with increasing electron irradiation time, the trap levels gradually increase. The $\alpha$ trap density increases with time and reaches a maximum increase of 1032.1% at 432 h compared to the original sample. The growth rate of the $\alpha$ trap density is small during 0–48 h, increases during 48–192 h, and decreases during 192–432 h. The $\gamma$ and $\beta$ traps decrease during 0–48 h and then increase by 210.7% and 174.4% during 48–432 h. The effects of structural changes on trap distribution characteristics are investigated through electron paramagnetic resonance (EPR), X-ray photoelectron spectroscopy (XPS), and X-ray diffraction (XRD) experiments. It is found that the presence of free radicals during electron irradiation increases the $\alpha$ trap density. The growth rate of free radical relaxation time is positively correlated with the growth rate of $\alpha$ trap density. During 0–48 h, a small amount of free radicals in the sample mainly induce imidization reactions and C–C cross-linking. This leads to a decrease in end groups and the formation of cross-linking networks, resulting in a decrease in $\gamma$ and $\beta$ trap density separately. From 48 to 432 h, a large number of free radicals induce C–C bond breakage, C–O, and C $=$ O bond recombination, resulting in molecular chain fragmentation and an increase in $\gamma$ and $\beta$ trap density. The findings of this study can provide a reference for the failure mechanisms of polyimide applied on spacecraft and the design of radiation-resistant materials.

The electrical tree in grafted polypropylene (PP) is inhibited compared with that of pure PP. To understand the free radicals that are generated during the treeing process, we study the electron paramagnetic resonance (EPR) spectra. Additionally, to provide a clearer explanation of the suppression of electrical trees, this research uses electroluminescence (EL) and excitation computation. These methods help us to observe the movement of electrons and to understand the geometric and electronic structures involved. In pure PP, the energy required to excite the electrons is approximately the same as the band gap of PP while electrons are easier to be excited in grafted PP than in pure PP, because the band gap is narrower. As a result, though the electrical tree length is shorter in PP-g-MMA, the EPR signal is more intense because of the uneven distribution of electrons.

Grafted polypropylene (PPG) has demonstrated significant potential as a recyclable insulation material for high-voltage cables. While its fundamental electrical, mechanical and thermal properties have been widely studied, research on its long-term performance remains insufficient. This study comparatively investigates the thermo-oxidative ageing performance of PPG and traditional cross-linked polyethylene (XLPE) to evaluate the expected lifespan of cable insulation. The evolution of mechanical and electrical properties of PPG and XLPE was monitored during accelerated thermo-oxidative ageing experiments conducted at their respective maximum allowable operating temperatures, and the most sensitive ageing parameter was identified. Furthermore, the influence of thickness on the insulation ageing process was examined through experiments on samples of different thicknesses. Results indicate that the estimated thermo-oxidative ageing lifespan of XLPE at its maximum operating temperatures of 90 °C is 37.75 years, while that of PPG at 110 °C is 45.65 years. This work offers a practical methodology for polymer ageing lifespan analysis and provides valuable insights for assessing the long-term performance of PPG cables in high-voltage applications.