Surface degradation and dielectric response of inorganic fillers in the polyethylene matrix

The dielectric properties of PE composite materials with various inorganic fillers (aluminum oxide, Al₂O₃; aluminum nitride, AlN, zirconium dioxide, ZrO₂, titanium dioxide, TiO₂, silicon dioxide, SiO₂ boron nitride, BN) were characterized at room temperature using dielectric spectroscopy in a wide range of frequencies (10^-2 Hz - 10 kHz). In few cases, we found a slight change of real permittivity (ε_r) after addition of 20%vol of fillers. The permittivity values found for the different composite films investigated ranged from 2.4 to 22.5 (ε_r) at 0.1 Hz, depending on the additive. The composites with TiO₂ and ZrO₂ additives were found to have the highest values of permittivity. Furthermore, at high frequencies, almost all composite films were found to reach a low dielectric constant (i.e. comparable to that of neat PE) whatever the permittivity value of the fillers. Surface erosion tests showed a good surface resistance to partial discharges when the filler permittivity was low.