Modification mechanism of low-density polyethylene insulation by hydrophilic and hydrophobic porous SiO2 nanoparticles

Abstract

To study the modification effect and mechanism of porous nanoparticles on electrical insulation performance, SiO2/low-density polyethylene (LDPE) nanocomposites with different filler concentrations are prepared by filling two kinds of porous SiO2 nanoparticles. The microstructure and dispersion of SiO2 in LDPE are characterized by scanning electron microscope [ the effect of nanofilling on the crystallinity of LDPE is analyzed by Differential Scanning Calorimetry (DSC)]. The mechanism of insulation modification of nanocomposites is studied by space charge and direct current conductance analysis of charge transport and Weibull distribution of breakdown field strength. By filling nanoscale SiO2 particles, the crystallinity of the LDPE matrix can be changed effectively. It is indicated that the hydrophobic SiO2 nanofillers with higher dispersity in LDPE matrix are more effective than hydrophilic SiO2 nanofillers to improve the crystallinity of LDPE matrix. The LDPE crystallinity of hydrophobic 1 wt% SiO2/LDPE nanocomposite approaches the highest value through heterogeneous nucleation. Compared with pure polyethylene, the conductivity of nanoporous SiO2 filled polyethylene composites is reduced obviously and the lowest conductivity is obtained for the nanocomposites filled with hydrophobic SiO2 nanoparticles in 1 wt% filling rate. The space-charge distribution and electric breakdown field strength further demonstrate that the filling of 1 wt% hydrophobic SiO2 nanoparticles can efficiently inhibit carrier injection and increase the breakdown field strength. The heterogeneous nucleation of porous SiO2 nanofillers increases the crystallinity of LDPE, and thus decreases the carrier mobility and increases the probability of charge charge trapping. The dispersion of nanofillers in composite is improved significantly by the symmetrical group –CH3 on the surface of hydrophobic SiO2 nanoparticles, which effectively suppresses the space-charge accumulation and evidently increases the electric breakdown field strength. It is proved that the special nanoscale interface in nanodielectrics can substantially improve the dielectric properties of polyethylene.