Abstract：To address the dual requirements of low-temperature toughness and high-voltage direct current (HVDC) insulating performance of polypropylene, impact copolymer polypropylene (IPC) was used as the matrix, and 30% of polyolefin plastomer (POP), polyolefin elastomer (POE), and styrene-ethylene/butylene- styrene block copolymer (SEBS) were separately incorporated. A systematic comparison of their effects on microstructure, crystallization behavior, mechanical properties, and DC electrical characteristics was conducted, aiming to elucidate the electrical-mechanical coupling mechanism mediated by interfacial traps. The results show that POP and POE exhibit poor compatibility with IPC, presenting a coarse phase-separated morphology with sharp and distinct interfaces that act as stress concentration sites, leading to significant decreases in elongation at break and tensile strength. Quantitative X-ray diffraction analysis reveals that both POP and POE promote the transformation from β-crystals to α-crystals: the crystallinity of the β(300) crystal plane decreases from 4.51% for pure IPC to 1.01% and 2.22%, respectively; correspondingly, the crystallinity determined by differential scanning calorimetry (DSC) drops from 40.97% to 32.40% (POP) and 23.49% (POE). The DSC curves further indicate that POP exhibits a viscous flow transition peak at 102.3℃, and POE at 35.3℃, implying insufficient thermodynamic stability. Thermally stimulated depolarization current (TSDC) measurements reveal that both blend systems introduce a large number of shallow traps with an energy level of approximately 0.95 eV at the interfaces. In particular, the IPC/POE system, owing to the highest interfacial defect concentration, exhibits a shallow trap density as high as 20.88×1021 eV-1·m-3. These shallow traps intensify carrier detrapping and charge injection, resulting in severe space charge accumulation and local electric field distortion, which ultimately cause a reduction of approximately 21% in the DC breakdown strength of both blends at 80℃ compared with pure IPC. In striking contrast, SEBS demonstrates the best compatibility with IPC, featuring a dense and blurred interface, the smallest and most uniform dispersed phase domains. The polystyrene hard segments of SEBS act as heterogeneous nucleation agents, effectively inducing β-crystal formation and raising the β(300) crystallinity to 6.19%, while the DSC crystallinity remains at a relatively high level of 33.94%. No viscous flow transition is detected in this system. Dynamic mechanical analysis (DMA) confirms that the storage modulus decreases in the order of IPC>POP>POE>SEBS, and no abnormal increase in the loss factor is observed in the high- temperature region. Mechanical tests show that the IPC/SEBS blend exhibits the lowest flexural modulus, an elongation at break comparable to that of pure IPC, and nearly complete elastic recovery with minimal residual deformation in creep-recovery tests at 90℃. With regard to electrical performance, the phenyl groups in the SEBS segments introduce deep electron traps with an energy level of approximately 1.06 eV, while simultaneously forming a polar shielding layer at the electrode-dielectric interface, which effectively suppresses carrier injection and bulk transport. This dual mechanism endows the IPC/SEBS system with the lowest conduction current density over the entire electric field range of 5~40 kV/mm at both 30℃ and 80℃, after polarization at 80℃, the residual space charge density is only 0.63 C/m3. the DC breakdown strength at 30℃ is 2.2% higher than that of pure IPC, and although a slight decrease occurs at 80℃, it still significantly outperforms the POP and POE systems. The above results delineate an interfacial compatibility-mediated electrical-mechanical coupling mechanism: poor interfaces simultaneously act as mechanical stress concentrators and electrical shallow trap sources, synergistically degrading the toughness and insulating properties of the material; conversely, excellent interfacial bonding combined with intrinsic deep trap functionality can simultaneously achieve toughening and charge suppression. Therefore, SEBS can be considered a preferential toughening modifier for recyclable polypropylene-based insulating materials for HVDC cable applications.
赵新东, 罗东旭, 王凯, 杨佳明, 杨旭, 赵洪. 弹性体增韧聚丙烯高压直流绝缘材料的电-力耦合机制与界面陷阱特性[J]. 电工技术学报, 2026, 41(19): 6476-6490.
Zhao Xindong, Luo Dongxu, Wang Kai, Yang Jiaming, Yang Xu, Zhao Hong. Electrokinetic Coupling Mechanism and Interface Trap Characterization of Elastomer-Toughened Polypropylene for HVDC Insulation Materials. Transactions of China Electrotechnical Society, 2026, 41(19): 6476-6490.
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2026, Vol. 41 
