A facile method to increase the charge storage capability of polymer nanocomposites

A class of microcellular polymer nanocomposites of multi-walled carbon nanotubes (MWCNT) is reported that exhibits a stable and significantly high dielectric permittivity coupled with a stable and low dielectric loss in a wide range of frequency. Polypropylene (PP)-MWCNT nanocomposites with a cellular structure were prepared by melt mixing followed by physical foaming in an injection molding process. The generation of a cellular structure inside the nanocomposites provides a unique planar-like arrangement of the MWCNTs around the cells. This enhances the dielectric permittivity of nanocomposites up to an order of magnitude. Therefore, microcellular PP-1.25 vol% MWCNT presents a dielectric permittivity of epsilon' = 57.2 and a dielectric loss of tan delta=0.05 at 0.1 MHz, highly superior to the best values of the solid nanocomposites prepared by regular compression molding (epsilon' =14.1 and tan delta=0.39) and by injection molding (epsilon' =17.8 and tan delta=0.04). Also, microcellular PP-1.66 vol% MWCNT exhibits epsilon'=95.6 and tan delta=0.14, which surpasses the dielectric performances reported in the literature. Hence, these nanocomposites with a cellular structure provide a novel and general approach to develop microscopically tailored structures for dielectric applications using facile methods. Such dielectrics can be used for energy storage in modern electronics and electrical power systems. (C) 2015 Elsevier Ltd. All rights reserved.