Dielectric properties of polypropylene loaded with synthetic organoclay

The incorporation of synthetic silica nanoparticles into polypropylene is shown to increase the ac breakdown strength compared to unfilled material. This breakdown strength stays unchanged during application of a 40 kV/mm dc field for up to 500 h at both, room temperature and 90°C. Dielectric spectroscopy shows an increase of dielectric loss factor, tan¿, with nanoflller concentration and a distinct relaxation around 60°C. The increase of tan¿ caused by nanoparticles is moderate and thus manageable in practical applications. Subjecting specimens to a dc field did not significantly change the dielectric loss spectra. The dc conductivity of the materials with nano-filler was found to be higher than for unfilled materials. This is believed to be caused by the overlapping of the diffuse double layers surrounding nanoparticles, which provide a path for the migration of electric charge. Aging nanocomposites in a dc field resulted in the increase of conductivity but the increments were significantly smaller than those observed in the material without organoclay.