Dielectric Properties of Biaxially Oriented Polypropylene Nanocomposites Prepared Based on Reactor Granule Technology

The addition of inorganic nanoparticles is one of the most widely studied strategies to improve dielectric properties of thin film capacitors, but its application to biaxially oriented polypropylene (BOPP) has rarely been reported due to the difficulty of stretching without break. Here, we have investigated dielectric properties of BOPP/TiO2 nanocomposites prepared by a reactor granule technology, in which precursors impregnated in the pores of PP reactor granule are converted into highly dispersed oxide nanoparticles during melt mixing. The permittivity of the nanocomposites was greatly enhanced beyond classical mixing rules by the addition of a small amount of TiO2 nanoparticles (1–5 wt %), and the enhancement was very sensitive to the stretching ratio. A critical role of the interphase region was suggested. The AC breakdown voltage (BDV) of the BOPP/TiO2 nanocomposites decreased sharply with respect to the amount of TiO2 added. The detailed analysis suggested the roughening of the film surface around the nanoparticles due to stretching as the main cause of the BDV reduction.