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


  • Ilkka Rytöluoto Tampere University
  • Minna Niittymäki Tampere University
  • Kari Lahti Tampere University
  • Eetta Saarimäki VTT Technical Research Centre of Finland Ltd
  • Timo Flyktman VTT Technical Research Centre of Finland Ltd
  • Mika Paajanen VTT Technical Research Centre of Finland Ltd
  • Mikko Karttunen VTT Technical Research Centre of Finland Ltd



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.


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