High Temperature Dielectric Properties of Polyimide/Boron Nitride Nanocomposites: Nanoparticle Size and Filler Content Effects

An interesting way to improve high temperature polyimides (PI) electrical properties by filling it with boron nitride nanoparticles (BN) is proposed in this study. The filler content (from 0 to 60 vol.%) and the average diameter size (35 nm and 120 nm) of these nanoparticles have been varied. The preparation of the patented PI/BN nanocomposite films was performed following an optimized process in order to obtain a good dispersion of the nanoparticles in the films. The nanocomposite films were electrically characterized in the range 200–350 °C. In the case where the nanoparticles had the smallest size, the DC conductivity and leakage currents decreased from 4 to 6 orders of magnitude when the PI/BN films were compared to the neat PI films. The improvement of this property was obtained by a small amount of nanoparticles (1.6 vol.%). Results also show an increase in the dielectric strength of 1 MV/cm for a filler content of 42 vol.%. In the case where the nanoparticles had a larger size, a small improvement was seen on the DC conductivity and leakage currents. In contrast, the breakdown field was lower than the one of the neat PI, due to aggregate formation within the films.