Lightweight polypropylene-carbon nanotube foams with low filler content, high permittivity and low dielectric loss for charge storage applications

Microcellular polypropylene-multiwalled carbon nanotube (MWCNT) composites with low filler content exhibiting high dielectric permittivity, and low dielectric loss are reported. Nanocomposites were prepared by melt compounding and foamed using supercritical carbon dioxide in a batch process. The introduction of cellular structure decreased the dielectric loss of the nanocomposites up to five orders of magnitude, while the decrease in dielectric permittivity was only 2-4 times. Thus, microcellular composites containing only ∼ 0.34 vol.% MWCNT presented a frequency-independent high dielectric permittivity (∼ 30) and very low dielectric loss (∼ 0.06). The improvement in dielectric loss was explained in terms of the formation of effective nano-capacitors caused by foaming action (biaxial stretching and uniaxial compression) and volume exclusion. The results of this work reveal that high dielectric nanocomposites can be developed using foaming technologies for charge storage applications.