Mechanical flexible PI/MWCNTs nanocomposites with high dielectric permittivity by electrospinning

•PI/MWCNTs nanocomposites were fabricated by electrospinning.•Homogeneous distribution of MWCNTs in nanofibers and nanocomposite films.•Highly enhanced dielectric permittivity, low dielectric loss, and high energy storage density.•Mechanical flexible nanocomposites.•Excellent thermal stabilities. High permittivity polyimide/carbon nanotubes (PI/MWCNTs) nanocomposites with good mechanical flexibility were prepared by electrospinning and hot-pressing. The homogeneity of MWCNTs in PI nanofibers and matrix were confirmed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The PI/MWCNTs nanocomposites showed high dielectric permittivity of 147–161 (at 1kHz) at percolation threshold of 12–14vol% concentration of MWCNTs and low dielectric loss below the percolation threshold. The PI/MWCNTs nanocomposites with 20vol% concentration of MWCNTs had the highest dielectric permittivity of 217 (at 1kHz), which was 57.5 times higher than the pure PI had. Compared to the maximum energy storage density of pure PI (0.404J/cm3), the best maximum energy storage density of 1.957J/cm3 was achieved by incorporating 12vol% of MWCNTs into PI. The PI/MWCNTs nanocomposites (14vol%) showed good mechanical flexibility with tensile strength, elongation at break and toughness more than 90MPa, 12.8% and 5.0J/g respectively and excellent thermal stability with 5% weight loss temperature of more than 560°C. Therefore, this high performance PI/CNTs nanocomposites would be good candidates for modern microelectronics in high temperature areas.