In order to meet the needs of mechanical properties of cable insulation, polypropylene (PP) needs to be blended with low modulus materials to achieve toughening and softening. However, the compatibility between two or more resins can significantly affect the electrical properties of the composites. To solve this problem, the styrene-ethylene/butylene-styrene block copolymer (SEBS) with high heat resistance is selected as the blending elastomer, and grafted polypropylene (GPP) is prepared to be as basic resin. The morphological structure, thermal properties, mechanical properties and high temperature DC electrical properties of PP, GPP, PP/SEBS and GPP/SEBS are studied. The results demonstrate that compared with PP/SEBS, GPP/SEBS has significantly refined 'island phase' structure, further reduced storage modulus and slightly increased tensile strength and elongation at break and higher viscosity at low shear frequency. Electrical properties test results show that the grafted composite exhibits obvious suppression effect on space charge and conductance current, and enhances the DC breakdown strength. The introduction of the grafted material not only effectively improves the compatibility of the composites but also significantly improves the electrical properties of the material. This result can provide a reference for the development of eco-friendly high voltage cable materials.

High-voltage direct-current (HVDC) cable insulation requires balancing high-temperature reliability and sustainability. Conventional crosslinked polyethylene faces severe recycling challenges, while thermoplastic blends often suffer from dielectric degradation due to interfacial defects. Herein, an in-situ dynamic interfacial topological reconstruction strategy based on Diels-Alder (D-A) chemistry is proposed to fabricate high-performance PP-v-PE containing a thermoreversible covalent adaptable network. By macromolecule modification, thermo-responsive covalent network is constructed between incompatible isotactic polypropylene and low-density polyethylene, refining the phase morphology and establishing strong covalent coupling across the phase interfaces, while imparting excellent mechanical flexibility (550.8% elongation at break). In addition, deep charge traps introduced by d-A adducts significantly suppress space charge accumulation and reduce leakage current density of PP-v-PE by one to two orders of magnitude. Consequently, the DC breakdown strength at 90 °C reaches 279.0 kV mm–1, a 41.2% improvement over physical blends. Furthermore, the thermo-reversibility of d-A bonds ensures efficient closed-loop recycling, maintaining high dielectric performance after repeated processing. This catalyst-free strategy is compatible with industrial cable extrusion, providing a versatile design paradigm for a thermoreversible interfacial stabilization strategy for recyclable polyolefin materials under thermomechanical and electrical service conditions.

Compared to cross-linked polyethylene (XLPE), the use of thermoplastic polypropylene (PP) in cable insulation can effectively reduce carbon emissions, making it a more environmentally friendly choice. Among various PP materials, impact copolymer polypropylene (IPC) offers a unique combination of flexibility and heat resistance, making it the preferred material for developing PP insulated power cables. However, for large cross section high-voltage cables, the long straight-chain structure of IPC results in low zero-shear viscosity, which makes it difficult to meet the roundness requirement after insulation extrusion. To regulate the viscosity characteristics and dc performance of IPC, we synthesized modified IPC with a high branching structure through maleimide functionalization of maleic anhydride (MAH) grafted PP, thereby increasing the complexity of the IPC chain structure. Due to enhanced interchain forces and branching, the ethylene propylene rubber (EPR) phase disperses more uniformly. Additionally, the crystallization and melting temperatures slightly increase, while the material's viscosity at a shear rate of 0.05 rad/s rises substantially by 238%. The dc performance results indicate that the functionalized modified PP with maleimide exhibits superior high-temperature space charge properties and a higher dc breakdown strength. Enhanced the EPR phase dispersibility, and the introduction of polar groups (carbonyl and amino) has significantly improved the viscosity characteristics, stress-strain characteristics, space charge behavior, resistivity, and electrical strength, resulting in a 33.2% increase in dc breakdown strength. This work provides a novel technological route to synergistically improve the viscosity properties and dc electrical performance of IPC, which is essential for the development of long-length, HVdc PP power cable insulation materials.

ABSTRACT Crosslinked polyethylene (XLPE) is the benchmark insulation for high‐voltage direct‐current (HVDC) cables, yet its amorphous phase remains the Achilles' heel—vulnerable to space charge accumulation, oxygen permeation, and thermo‐oxidative degradation that synergistically trigger premature failure. Here, we report a multiscale molecular design strategy that covalently grafts a tailored voltage stabilizer, 3‐amino‐5‐chloro‐3′‐fluorobenzophenone (ACFM), onto XLPE chains to concurrently engineer deep charge traps, dense amorphous‐phase packing, and oxidative resistance. First‐principles calculations and atomistic simulations reveal that the grafted ACFM introduces localized π‐conjugated states within the XLPE band gap, forming deep electron traps (0.9–2.2 eV) and hole traps (0.5–1.7 eV) that suppress carrier transport and dissipate hot‐electron kinetic energy via phonon coupling. Simultaneously, multi‐dipolar ACFM side chains enhance cohesive energy density, reduce fractional free volume, and diminish thermodynamic compatibility with O 2 , thereby lowering oxygen solubility and self‐diffusion coefficients across the 300–400 K operational window. Oxidation pathway calculations further demonstrate that the grafted ACFM moiety reduces reaction exothermicity by ~50% and elevates activation energy relative to pristine XLPE segments, conferring sacrificial antioxidant protection. Experimentally, 1.0 wt% ACFM grafting increases DC dielectric breakdown strength by 13.6% (from 368.5 to 418.7 kV/mm) and achieves an unprecedented 88.0% retention after 504 h of thermo‐oxidative aging at 135°C, substantially outperforming conventional stabilizers and representing the first demonstration of a grafted voltage stabilizer maintaining effectiveness under standardized severe aging conditions. These findings establish a “charge trap–dense aggregation–anti‐oxidation” synergistic paradigm and offer a transferable molecular blueprint for fortifying polyolefin dielectrics against multi‐stress degradation in advanced HVDC systems.

To address the limitation of traditional elastomer blending methods that often reduce the dielectric strength in toughening polypropylene (PP) cable insulation materials, this study proposes a separately grafted and blended method by grafting maleic anhydride (MAH) onto impact polypropylene compound (IPC) and metallocene polyethylene (mPE). Unlike conventional elastomer-modified systems or single-phase MAH grafting approaches reported previously, the independent grafting of MAH onto each phase significantly enhances the non-bonding energy and interfacial interaction, promoting deep interpenetration of molecular chains. This effectively addresses the problem of poor mechanical properties in the blend system while maintaining low hardness and storage modulus. Simultaneously, MAH optimizes the two-phase distribution and introduces uniformly dense deep traps that act as charge capture sites. The isothermal surface potential decay (ISPD) and simulation results indicate that grafting MAH introduces deeper trap energy levels into the material. The mPE-M/IPC-M exhibits superior DC electrical performance compared, achieving a synergistic improvement in the mechanical and DC electrical properties of IPC. This study breaks through the bottleneck of mutual constraint between mechanical and electrical properties in traditional blending modification, providing important theoretical and technical support for the development of recyclable insulation materials for HVDC cables.

A multiscale molecular simulation framework that integrates density functional theory(DFT),molecular dynamics(MD),and Monte Carlo(MC)methods is employed to elucidate the molecular mechanisms underlying the synergistic enhancement of electrical insulation,oxidative resistance,and thermal stability in polypropylene/styrene-ethylene-butylene-styrene(PP/SEBS)composite via covalent grafting of a tailored voltage stabilizer(3-amino-5-chlorophenyl 3-fluorophenyl methanone,ACFM).First-principles calculations demonstrate that ACFM grafts efficiently introduce multiple charge traps—specifically,electron traps(0.4-2.2 eV)and hole traps(0.5-1.6 eV)—within the electronic bandgaps of both the PP macromolecule and PP/SEBS interfacial region,effectively suppressing charge carrier migration.The delocalized p-conjugated system of ACFM phenylene moieties promotes hot-electron kinetic energy dissipation via carrier-phonon coupling,thereby inhibiting impact ionization and enhancing the intrinsic dielectric breakdown strength.MD and MC simulations further reveal that the grafted multi-dipolar ACFM side chains enhance the thermodynamic compatibility between PP and SEBS segments,promote densification of the amorphous region,and significantly reduce fractional free volume and oxygen permeability.Consequently,oxygen absorption capacity and self-diffusion coefficients decrease markedly across the operational temperature range(300-600 K),effectively suppressing oxidative penetration and free-volume-mediated electrical breakdown.Reaction pathway calculations indicate that ACFM-grafted PP exhibits an approximately 50%reduction in the oxidative exothermic heat compared to pristine PP and SEBS,accompanied by a slight increase in activation energy,thereby corroborating the enhanced antioxidative stability.The covalent immobilization of ACFM thus collectively enhances charge trapping capability,thermal endurance,oxygen barrier performance,and oxidative resistance,thereby establishing a comprehensive molecular design paradigm for advanced polymer dielectrics operating under harsh environmental conditions.

Polypropylene (PP) resin is a promising thermoplastic high-voltage direct current (HVDC) cable material by virtue of its excellent heat resistance, mechanical and physical properties, insulation properties, and environmental protection and energy saving advantages. However, the current research focuses on polypropylene insulating materials, and less research on semi-conductive shielding materials for high-voltage direct current. In this paper, PP is the basic skeleton of semiconducting shielding materials, styrene-ethylene-butylene-styrene block copolymer (SEBS) as a toughening and dispersion of carbon black main body to join the processing aids to make their own semiconducting shielding materials, through the selection of different content of ethylene propylene rubber phase of PP, to study the impact of its shielding material carbon black dispersion, and further study of the semiconducting shielding layer on the insulating layer at high temperatures and high fields under the charge transport behavior. The experimental results show that PP with high rubber phase content as the skeleton carbon black dispersion and various properties are superior to the composite system with low rubber phase content. The composite system with high rubber phase content has good matching characteristics with the space charge of the insulation layer under high temperature and high field, proving that the semiconductor material developed in this paper can reduce the injection behavior of charges under high temperature and high field.

Traditional blending methods often lead to a deterioration in the mechanical and electrical properties of polypropylene (PP) cable insulation materials while improving their toughness. To overcome this bottleneck, polyethylene (PE) and impact polypropylene copolymer (IPC) were grafted with maleic anhydride (MAH), respectively. The strong polarity of MAH promotes mutual penetration between IPC and PE, thereby improving the mechanical properties of PE/IPC. Additionally, the deep traps introduced by MAH optimize the material's DC electrical performance. A comparison was made between metallocene polyethylene (mPE), linear low-density polyethylene (LLDPE), and low-density polyethylene (LDPE) in terms of their effects on PE/IPC performance before and after MAH grafting. Due to its extremely high regularity, mPE can form effective penetration with IPC, and the performance improvement after grafting modification is the most significant. This effectively addresses the poor mechanical properties of mPE/IPC while maintaining low hardness. The deep traps introduced by MAH result in excellent DC electrical performance of mPE/IPC. In contrast, the branched chain structures of LLDPE and LDPE tend to encapsulate the grafted MAH within the PE phase, weakening the effect of interfacial polar molecular interactions and leading to limited improvements in mechanical and electrical properties.

Traditional crosslinked-polyethylene (XLPE) insulation suffers from high recycling costs and low efficiency due to its thermosetting properties. In contrast, thermoplastic polypropylene (PP), with advantages of melt recyclability, low energy consumption, and excellent comprehensive performance, has emerged as an ideal alternative to XLPE. This study conducts a comparative analysis of low-voltage cables insulated with PP, silane-crosslinked XLPE (XLPE-S), and UV-crosslinked XLPE (XLPE-U), focusing on production processes, mechanical properties, thermal stability, and electrical performance. Tensile test results show that PP exhibits the highest elongation at break (>600%) before aging, and its tensile strength (>20 MPa) after aging outperforms that of XLPE, indicating superior flexibility and anti-aging capability. PP exhibits a lower thermal elongation (<50%) at 140 °C compared to XLPE, and its high-crystallinity molecular structure endows better heat-resistant deformation performance. The volume resistivity of PP reaches 9.2 × 1015 Ω·m, comparable to that of XLPE-U (3.9 × 1015 Ω·m) and significantly higher than XLPE-S (3.0 × 1014 Ω·m). All three materials pass the 4-h voltage withstand test, confirming their satisfied insulation reliability. PP-insulated low-voltage cables demonstrate balanced performance in production efficiency, energy consumption cost, mechanical toughness, and electrical insulation. Notably, their recyclability significantly surpasses traditional XLPE, showing potential to promote green upgrading of the cable industry and providing a sustainable insulation solution for low-voltage power distribution systems.

To solve the space charge accumulation and electric field reversal in the insulation layer of cross-linked polyethylene (XLPE) high-voltage direct current (HVDC) cables. The small molecule compound 3,4-diacetyloxyethylene styrene (DAS) and the co-crosslinking agent trimethylolpropane trimethylallyl trimethacrylate (TMPTMA) were grafted onto XLPE. Thermal stimulation current and quantum chemical calculations indicated that DAS and TMPTMA introduced high-density deep traps in XLPE, which reduced mobility and suppressed charge injection by capturing carriers. The conductivity current and temperature sensitivity of modified XLPE were decreased significantly, the phenomenon of electric field reversal was suppressed considerably, the breakdown strength was increased substantially, and it exhibited reasonable space charge suppression characteristics. Among them, the conductive current of XLPE-g-(TMPTMA-co-DAS) is only 0.1% of that of unmodified XLPE, while the breakdown strength has increased by more than 34%. This provides theoretical support for the development of DC cable insulation materials with high voltage levels.

Overhead transmission lines have long relied on cross-linked polyethylene (XLPE) insulation. The production of XLPE insulation requires silane cross-linking, which generates by-products, consumes high energy, and results in poor recyclability-retired XLPE insulation can only be disposed of through incineration or landfilling. Additionally, its high density leads to increased cable weight and sag, reducing the service life of the cables. Therefore, there is an urgent need to develop recyclable and lightweight insulation materials. In this study, recyclable polypropylene (PP) was used as a substitute for XLPE. Hollow glass microspheres (HGM) were incorporated to reduce weight, and hydrogenated styrene-ethylene-butylene-styrene block copolymer (SEBS) was added for toughening, thereby constructing a PP/HGM/SEBS ternary composite system. The results show that the introduction of HGM into the PP matrix effectively reduces the material density, decreasing from 0.890 g/cm3 (pure PP) to 0.757 g/cm3—a reduction of 15%. With the addition of SEBS, the mechanical properties of the composite are significantly improved: the tensile strength increases from 14.94 MPa (PP/HGM) to 32.40 MPa, and the elongation at break jumps sharply from 72.02% to 671.22%, achieving the synergistic optimization of “weight reduction” and “strengthening-toughening”. Electrical performance tests indicate that the PP/HGM/SEBS composite exhibits a volume resistivity of 1.66 × 1012 Ω·m, a characteristic breakdown strength of 108.6 kV/mm, a low dielectric loss tangent of 2.76 × 10−4, and a dielectric constant of 2.24. It achieves density reduction while maintaining low dielectric loss and high insulation strength, verifying its feasibility for application in lightweight insulation scenarios of overhead transmission lines.

Grafting modification represents a critical method for augmenting the electrical properties of polypropylene (PP), as an insulating material in high-voltage direct current (HVDC) cables. Additionally, the aging performance requires further enhancement since cables are the power equipment that operates over the long term. Grafting antioxidants that contain charge trapping functional groups has the potential to enhance both the electrical and aging properties simultaneously. Nevertheless, direct grafting remains a formidable challenge due to the low grafting reactivity of antioxidants and the high susceptibility to degradation of PP. Drawing inspiration from click chemistry, this paper selects PP grafted with maleic anhydride (PP-g-MAH) as the reaction platform. Nphenyl-p-phenylenediamine (AD) is covalently attached to the MAH side groups through the maleimidefunctionalized reaction. This results in forming a functionalized material, PP-g-(MAH-co-AD). Compared with PP and PP-g-MAH blended with traditional antioxidants, PP-g-(MAH-co-AD)s demonstrate enhanced thermooxidative aging resistance and more remarkable improvement in DC electrical properties. Before and after aging, it sustains a robust suppression of space charge and conduction current. Moreover, it displays a lower decline rate in DC breakdown strength and reveals a substantial reduction in the sensitivity of conductivity to temperature. The observed improvement can be ascribed to the (MAH-co-AD) groups. These groups introduce not only electron deep traps but also hole deep traps and maintain localized deep traps even after aging. In summary, compared with cross-linked polyethylene (XLPE) and PP modified by molecular grafting with single functional properties, the functionalized PP demonstrates superior aging resistance and more pronounced enhancement of electrical properties.

Space charge injection in polypropylene (PP) significantly weakens the stability of HVDC cables. Impact polypropylene copolymer (IPC) is often used as insulation material for AC cables, but in the DC field, IPC has the problem of space charge accumulation. This is because there is a multi-phase structure inside the IPC to which ethylene monomer was added in the production process, and the difference in physicochemical properties of each phase is an important reason for the accumulation of space charge inside the material. In this work, the vinyl phases and propenyl phases of two types of IPC were separated. The film samples were prepared and tested at 30 °C and 50 °C for DC electrical conductivity, and at 30 °C, 50 °C, and 80 °C for space charge. The experimental results show that the DC conductivity of vinyl phases is significantly higher than that of propenyl phases in both types of IPC. The degrees of mismatch between the DC conductivity of vinyl phase and that of propenyl phase are different in the two types of IPC, and the mismatch degree of DC conductivity is from several times to hundreds of times. The conductivity of the two vinyl samples is ohmic. The conductivity of the two propenyl phases shows nonlinearity under different electric field intensity, and the mismatch degree of the two phases increases with temperature. Compared to untreated IPC, at all test temperatures, the maximum space charge density of the propenyl samples is much lower, which can be reduced by about 1/3 at 50 °C and by about 50% at 80 °C. The density of heteropolar charge produced by impurity ionization in the samples and the depth of electrode injection both decreased. At each temperature, the distortion rate of the electric field in propenyl samples is lower than that in IPC, the distortion rate can be reduced by more than 15%, and the distortion rate can be reduced by nearly half at 80 °C. The charge dissipation characteristic of propenyl samples during depolarization is also optimized compared with IPC samples, the time required for charge dissipation to reach stability is shortened, and the residual charge density in the sample is reduced at the end of depolarization. In addition, the relevance between the variation of DC conductivity of phases and space charge characteristics was discussed according to SCLC (space charge limited current) theory. This work provides a feasible reference for the manufacture of high-reliability polypropylene-based cable material with excellent insulation performance.

Different from cross-linked polyethylene (XLPE) insulated cables, short-circuit current thermal shock will permanently deform the thermoplastic insulated cable's insulation layer. To investigate the insulation eccentricity caused by short-circuit thermal shock, a numerical calculation method is established based on electromagnetic-thermal equations that simulate conductor heating, heat transfer equations that calculate the temperature distribution, and fluid control equations that simulate the melt flow. Based on the enthalpy-porosity model, the melt crystallization and rheological properties of screen and insulation materials are measured and introduced into heat transfer and fluid equations. Taking a high-voltage (HV) single-core polypropylene (PP)-based insulated cable as the object, the entire process of the cable undergoing short-circuit thermal shock under rated operating conditions is simulated. The simulation results indicate that the insulation structure continues to eccentrically deform within 4756 s after a single thermal shock, and the eccentricity ratio eventually reaches 3.28%, which remains far below the standard requirement of 10%. The insulation eccentricity ratio shows a linear accumulation relationship with the times of thermal shock. This simulation method provides a reference for the design and reliability assessment of thermoplastic insulation cables.

To achieve exceptional recyclable DC cable insulation material using thermoplastic polypropylene (PP), we have introduced the organic polar molecule styrene-maleic anhydride copolymer (SMA) into PP-based insulation materials following the principles of deep trap modification. PP, PP/SMA, PP/ethylene-octene copolymer (POE), and PP/POE/SMA insulating samples were prepared, and their meso-morphology, crystalline morphology, and molecular structure were comprehensively characterized. The results indicate that SMA can be uniformly dispersed in PP with minimal impact on the crystalline morphology of PP. The DC electrical properties of the materials were tested at temperatures of 30, 50, and 70 °C. The findings demonstrate that the introduction of SMA can improve the DC properties of the material in both PP and PP/POE. The thermal stimulated depolarization current results reveal that SMA can introduce deep traps into the material, thereby improving its DC properties, which is in agreement with the quantum chemical calculation results. Subsequently, a bipolar carrier transport model was employed for coaxial cables to simulate the space charge distribution in the insulation layer of the four sets of insulation samples as well as the actual cable in service. The results highlight that SMA can significantly suppress space charge in PP and PP/POE systems, and it exhibits excellent electric field distortion resistance. In summary, the results illustrate that SMA is expected to be used as an organic deep trap modifier in PP-based cable insulation materials.

Abstract To enhance the DC electrical performance of cross‐linked polyethylene (XLPE), the graftable antioxidant methacrylic acid 2‐hydroxy‐3‐(4‐anilinoanilino) propyl ester (GA), which contains carbonyl and amino groups, and the crosslinking coagent trimethylolpropane trimethacrylate (TMPTMA), which contains carbonyl groups, are individually or co‐grafted onto XLPE. The slightly higher deep trap density introduced by higher grafting concentration of TMPTMA results in more significant suppression effect of conductance current and enhanced breakdown strength at a lower temperature, while the suppression effect for the conductance current at 90°C becomes weakened due to limited trap energy. Meanwhile, the deeper energy level introduced by GA suppresses the conductance current and improves the electrical strength of XLPE at 90°C more significantly. By co‐grafting, the conductance current of XLPE in a wide range temperature can be significantly reduced, especially for the temperature dependence of conductance current, which is beneficial to suppress the field strength reversal. The results of thermally stimulated current and molecular simulation show that the polar groups of two monomers introduce deep charge traps in XLPE. The co‐grafting system ensures the rationality of the crosslinking reaction kinetics and does not affect the cable manufacturing.

In order to figure out the effects of charge-attracting molecules on the direct current electrical performance of crosslinked polyethylene (XLPE), the molecules with different structures and functional groups were grafted onto XLPE, and their space charge, volume resistivity and thermal stimulated depolarization current were investigated. Based on density function theory, the trap distribution and charge-attracting properties of the grafted XLPE were calculated. For the charge-attracting groups, the results indicate that with the grafted of trap molecules containing polar groups CO and N-H, the electron and hole traps are introduced and the ability of attracting negative charges and positive charges are extremely improved, respectively, resulting in the enhanced space charge hindering and suppressed resistivity. The benzene ring can form both electron and hole traps with relatively shallower energy level, and results in an improved space charge dissipation and decreased resistivity. For the combination of charge-attracting groups, the continuous arrangement of homogeneous charge-attracting groups can achieve an enhanced modification effect, and heterogeneous charge-attracting groups will attenuate the modification ability. For the molecule structure, the grafting of compact cyclic molecular can affect the electrostatic potential distribution on XLPE’s chain, and exhibits a stronger modification effect.

During the normal laying and operation of a three-core umbilical cable, AC current can easily lead to AC electrochemical corrosion on the outer surface of the steel tube. To explore the electrochemical corrosion mechanism and the factors affecting the three-core umbilical cable, this paper optimizes the internal induced potential calculation method for three-core umbilical cables. It analyzes the changes in the characteristics of the induced potential and explores the variations in the density of induced current under different conditions. The research results show that by optimizing the calculation method for the induction potential of the umbilical cable’s steel pipe, for the electromagnetic significance of the smallest repeating unit, the induction potential on the steel pipe’s surface exhibited a cyclic change. The peak part of the induction potential is most likely to experience electrochemical corrosion. Additionally, reducing the radius of the outer insulation aperture of the steel pipe and improving the conductivity of seawater will increase the density of the induced current in the insulation aperture, thereby increasing the risk of electrochemical corrosion. As the cable pitch and AC frequency increase, the current density in the steel pipe pores will also rise.