Polypropylene (PP) has become one promising material to potentially replace the cross-link polyethylene used for high voltage direct current cables. Besides the isotactic polypropylene, the block polypropylene (b-PP) and random polypropylene (r-PP) can be synthesized through the copolymerization of ethylene and propylene molecules. In this letter, the effect of morphology and crystalline phases on the insulating electrical properties of PP was investigated. It was found that the introduction of polyethylene monomer resulted in the formation of β and γ phases in b-PP and r-PP. The results from the characteristic trap energy levels indicated that the β and γ phases could induce deep electron traps which enable to capture the carriers. And the space charge accumulation was obviously suppressed. Besides, the decreased electrical conductivity was observed in b-PP and r-PP. It is attributed to the existence of deep traps which can effectively reduce the carrier mobility and density in materials.
Polypropylene is one kind of eco-friendly insulating material, which has attracted more attention for use in high voltage direct current (HVDC) insulation due to the long-distance transmission, low loss, and recyclability. In this work, the morphology and thermal and electrical properties of the block polypropylene with various β-nucleating agent (β-NA) contents were investigated. The relative fraction of the β-crystal can reach 64.7% after adding 0.05 wt. % β-NA. The β-NA also greatly reduced the melting point and improved the crystallization temperature. The electrical property results showed that the alternating and direct current breakdown strength and conduction current were obviously improved. In addition, space charge accumulation was significantly suppressed by introducing the β-NA. This work provides an attractive strategy of design and fabrication of polypropylene for HVDC application.
Polypropylene (PP) as an environmentally friendly insulation material has been paid more attention. It is considered as a potential insulating material to replace cross-linked polyethylene (XLPE) for high voltage direct current (HVDC) applications. In this work, PP and PP/low-density polyethylene (LDPE) composites with different LDPE loading were prepared by melt blending method and the corresponding electrical properties were investigated. Results showed that the addition of LDPE significantly changed the microstructure of PP and the trap density was increased in the composites compared with pure PP. The conduction current of PP/LDPE composites was greater than that of PP. The electrical breakdown strength decreased at low LDPE contents and increased at high contents. Space charge was remarkably suppressed in the blend with 40 wt% LDPE loading. This work indicates that the improvements in the electrical properties, especially the charge transport and space charge suppression in the composites are closely related to the trap level density.
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