Improved Wide-Temperature-Range Insulation Properties of Block Polypropylene by UV-Irradiated Cografting of Maleic Anhydride and 4-tert-Butylstyrene

Abstract

Polypropylene (PP), as a recyclable thermoplastic polymer, is a promising insulating material for application as an environmentally friendly insulation layer in high-voltage-directcurrent (HVDC) cables. However, the lack of toughness and the poor wide-temperature-range electrical properties under a DC electric field seriously restrict its development and application. Herein, a block polypropylene with a low elastic modulus is selected and grafted with organic molecules of maleic anhydride (MAH) and 4-tert-butylstyrene (St*) as a masterbatch (PP-g-(St*co-MAH)) by an ultraviolet-irradiated radical reaction. The modified b-PP with different grafting contents was prepared by diluting the masterbatch through melt blending, and their DC electrical properties at a wide temperature range of 40−100 °C were tested. The results indicate that the introduction of a comonomer St* significantly improves the grafting rate of MAH and suppresses the degradation of PP chains during the grafting reaction; thus, the PP-g-(St*-co-MAH) possesses improved thermogravimetric performance and maintains the original mechanical properties and workability. The grafted functional groups introduce deep charge traps into the matrix and thus effectively suppress the space charge injection and accumulation, significantly reduce the conductivity, and enhance the breakdown strength of PP at wide temperature ranges. Among the tested materials, the PP grafted with 0.57 wt % St*-co-MAH exhibits the best electrical properties, while inadequate or excessive grafting content of St*-co-MAH relatively weakens the positive effects of grafting modification. The mechanism is analyzed based on calculation of the trap level and the three-dimensional (3D) electric potential.

Improved direct current electrical properties of XLPE modified by graftable antioxidant and crosslinking coagent at a wide temperature range

“…Before 90°C, a large area of negative electrostatic potential was formed due to the polarity of C=O group on the TMPTMA molecule, which can act as electron trapping centres and become electron traps, to capture the carriers in the material under electric field to hinder the charge transport, thereby reducing the electrical conductivity. Meanwhile, the deep traps at the interface between the material and the electrode can capture the charges injected by the Schottky emissions to constitute the Coulomb lattice and form the charge shielding layer, which can raise the charge injection barrier, and restrain the proliferation of the carriers injected by the electrode [30][31][32]. As a result, XLPE-g-TMPTMA showed suppressed conductance current and enhanced electrical breakdown strength.…”

Enhanced Dielectric Breakdown Property of Polypropylene Based on Mesoscopic Structure Modulation by Crystal Phase Transformation for High Voltage Power Cable Insulation

“…Polymers are used in various fields such as materials science, medicine, and environmental engineering due to their diversified features . Polypropylene (pp), in particular, has excellent thermal stability and insulation reliability even under high temperature and voltage conditions. , Moreover, its thermoplastic properties allow it to be degraded and recycled while avoiding the environmental pollution caused by incineration, which is compatible with the current environmentally friendly and sustainable development concepts, and therefore it has been widely used in power transmission equipment as the key basic material …”

“…3 Polypropylene (pp), in particular, has excellent thermal stability and insulation reliability even under high temperature and voltage conditions. 4,5 Moreover, its thermoplastic properties allow it to be degraded and recycled while avoiding the environmental pollution caused by incineration, which is compatible with the current environmentally friendly and sustainable development concepts, and therefore it has been widely used in power transmission equipment as the key basic material. 6 As a semicrystalline polymer, pp has both crystal and amorphous regions, which can be observed at the mesoscopic scale.…”

Revealing the pyrolysis mechanism of polypropylene cable insulation: A combined study of TG‐GC experiments and RMD/DFT simulations

“…5 However, the high bending modulus of pure PP makes it challenging to directly use it as the primary insulation material for cables. 6,7 To address this issue, styrene grafted polypropylene (PP-g-St) has been widely adopted in practical engineering applications. This material allows for microscopic regulation of the molecular chain, enabling control over macroscopic properties such as mechanical and electrical characteristics.…”

“…These properties are particularly important for improving the current‐carrying capacity and voltage level of cables 5 . However, the high bending modulus of pure PP makes it challenging to directly use it as the primary insulation material for cables 6,7 . To address this issue, styrene grafted polypropylene (PP‐g‐St) has been widely adopted in practical engineering applications.…”