Effect of sPP Content on Dielectric Relaxation and Trap Level Characteristics of PP blend insulation

Abstract

Polypropylene (PP) is regarded as a recyclable alternative to XLPE for cable insulation on account of its higher heat resistance and higher electrical resistivity. The dielectric relaxation and trap level characteristics of isotactic PP (iPP), syndiotactic PP (sPP) as well as atactic PP (aPP) blends are investigated. The associations between polymer polarization response and traps level characteristics of PP blends are discussed. Frequency-domain dielectric spectroscopy (FDS) methods are used to analyze the polarization response of five PP blends at 50, 70 and 90 0C. Isothermal surface potential decay (ISPD) tests are performed to acquire the traps level distribution and the influences of traps level characteristics on the dielectric response are discussed. The polymer polarization behaviours a and $\delta$ of five samples is closely related to segmental movements and carriers hopping behaviours, separately. The intensity of a relaxation strength ($\Delta\varepsilon_{a}$) declines with the increase of sPP content, because the related coefficient (g) between PP molecular chains is reduced. The calculated energy $E_{\tau}$ for $\delta$ process is in proportion to the shallow traps level, because the shallow traps with a higher level increase the potential barriers of carriers hopping behaviors. The increase in temperature causes the dipole to undergo intense Brownian motion in the electric field, resulting in a decrease in $\Delta\varepsilon_{a}$ with increasing temperature. The thermal motion of the charge increases the mobility of carriers in the PP and causes $\Delta\varepsilon_{\delta}$ to increasewith increasingtemperature.