Silica-Polypropylene Nanocomposites for Film Capacitors: Structure–Property Studies and the Role of Biaxial Stretching Conditions

Biaxial-stretching-induced morphology development and dielectric properties of hydrophobic fumed silica-BOPP nanocomposite films were investigated. The precursor (cast) film morphology, pre-heating as well as biaxial stretching
temperature and stretch ratio were found to profoundly affect the silica-BOPP film bulk morphology, surface texture and the formation of particle/agglomerate-induced cavitation upon biaxial stretching. Isothermal high-field conductivity and thermally stimulated depolarization current measurements indicated decreasing high-field/high-temperature conductivity
and modification of trap density of states upon incorporation of nanosilica in comparison to neat BOPP. Large-area DC dielectric strength is, however, sensitive to thermal/mechanical stresses upon biaxial stretching, hence necessitating careful optimization of the nanocomposite formulation and processing.