Morphology and Electrical Properties of AC Electric-Field-Assisted Low-Density Polyethylene

The direct current (DC) electrical properties of insulating polymers (e.g., low-density polyethylene, LDPE) are very important for the development of high-voltage direct current (HVDC) cables. The electric field assist can improve the DC electrical properties of the electrical insulating polymers. However, there are rarely reports about the effect of the alternating current (AC) electric field on the electrical properties of insulating polymers. In this article, the effects of the AC-assisted electric field on the DC electrical properties and the morphology of LDPE are studied. LDPE is prepared under the AC-assisted electric field of 0, 0.3, 0.5, 1.0, and 2.0 kV/mm, respectively. The DC conductivity, space charge distribution, breakdown strength, surface potential decay, and morphology of LDPE are characterized. Experimental results show that the AC-assisted electric field not only reduces the DC conductivity and space charge accumulation but also increases the breakdown strength of LDPE. The AC-assisted electric field increases the nucleation rate of LDPE and contributes to forming more spherulites, which introduces more deep traps to improve the DC electrical properties of LDPE. Notably, compared with the untreated LDPE, the LDPE prepared with the AC-assisted electric field of 1.0 kV/mm decreases by 96% in conductivity and reduces by 52.6% in average space charge density, whereas its DC breakdown strength is enhanced by 35%. This work provides a foundation for the improvement of the electrical properties of the insulating polymers.