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OA

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.