Tailoring the electrically conductive network of injection-molded polymer-carbon nanotube composite at low filler content

Abstract Electrically conductive nano-fillers, such as carbon nanotubes (CNT), carbon black (CB) and carbon fibers (CF), have been of great interest to polymer scientists because their reinforcement into polymer matrices gives rise to conductive thermoplastics. However, it is found that their orientation distributions after the injection molding process reduce the interparticle contacts between particles and thus decreases the electrical conductivity. In this study, it is shown that electrically conductive networks can be re-tailored through post-processing annealing at a temperature higher than the glass-rubber transition temperature of the polymer. We demonstrate these results for polycarbonate (PC) composites produced by injection molding using different fillers including single-walled CNT (SWCNT), multi-walled CNT (MWCNT), CB and CF. The annealing-induced increase in the electrical network path is proved by electrical conductivity improvement. It can be explained by a transition from aligned, unconnected particles before annealing to an interconnected network after annealing through the viscoelastic relaxation of the polymer. Compared with CB- and CF-based PC composites, CNT-based PC composites at low contents exhibited outstanding conductivity improvement after isothermal annealing for several minutes. Moreover, the CNT network helps to keep the composite shape and strength after annealing. Especially, SWCNT nanocomposites have potential to rapid the tailoring process of the electrical network without significant size extension and strength reduction. The post-processing annealing may exploit the future applications of injection-molded CNT polymer composites.