Effect of Acetophenone on Dielectric Properties of Low-density Polyethylene

The development of Extra/Ultra high voltage (EHV/UHV) transmission requires high-performance insulating dielectrics. Dielectric properties of cross-linked polyethylene (XLPE) used in high-voltage insulated cables are key to ensuring the stability of EHV/UHV transmission line. Acetophenone is one of the main byproducts produced in XLPE after crosslinking with dicumyl peroxide (DCP). This paper intends to quantitatively investigate the effect of acetophenone on the dielectric properties of polyethylene. The low-density polyethylene (LDPE)/acetophenone composites with different contents of acetophenone are prepared by soaking pure LDPE samples in acetophenone for various times. Gas chromatography (GC) is employed to test the contents of acetophenone. The dielectric constant, dielectric loss and AC breakdown strength at the power frequency (50 Hz) of LDPE and LDPE/Acetophenone composites are tested. To explore the underlying mechanism, first principles method and molecular dynamics (MD) simulation are employed to calculate the dipole moment, electron level and electrostatic potential (ESP) distribution of materials in this paper. The experimental and calculation results show that the dielectric constant of the LDPE/Acetophenone composites increases with the increase of acetophenone content because of the newly established dipolar polarization, which originates from the introduction of polar acetophenone. While the AC breakdown strength of the composites decreases obviously as the acetophenone content increases, which is attributed to the low band gap and uneven ESP distribution in them. Our results demonstrate that the existence of acetophenone can lead to the severe degradation of dielectric properties. It provides insight into the quantitative effect of the acetophenone on dielectric properties of LDPE and provides guidance for improving the dielectric properties of XLPE.