Dielectric Breakdown Properties of Mechanically Recycled SiO₂–BOPP Nanocomposites

This paper reports on the effects of multiple compounding cycles on the structural, chemical, rheological and DC dielectric breakdown properties of bi-axially oriented silica–polypropylene nanocomposite films. While the effect of multiple compounding cycles on the silica particle agglomeration remains seemingly modest according to the quantitative structural analysis, the recompounding is found to markedly affect the steady shear viscosity and film processability. Fourier transform infrared spectroscopy is utilized to ascertain that no thermo-oxidative degradation is occurring during the processing. The large-area multi-breakdown measurements indicate a ~13 % shift towards higher DC dielectric strength after the second recompounding cycle, an effect which is believed to be attributable mainly to the changes in film processability. Surprisingly, a 75:25 mixture of the virgin and three-times-reprocessed nanocompounds exhibits a similar increase in dielectric strength. Particularly from the processing perspective, the results emphasize the necessity of careful consideration of property modifications upon incorporation of nanofillers.