Effects of filler geometry on internal structure and physical properties of polycarbonate composites prepared with various carbon fillers

Background: The effects of filler geometry are important for understanding the internal structure and physical properties of polymer composites. To investigate the effects of filler geometry on electrical conductivity as well as morphological and rheological properties, three types of polycarbonate (PC) composites were prepared by melt compounding with a twin-screw extruder. Results: The electrical conductivity of PC/carbon black (CB) and PC/ graphite (carbon) nanofibre (CNF) composites did not show a percolation threshold through the entire filler loading ranges. However, PC-blend-carbon nanotube (CNT) composites showed a percolation electrical threshold for a filler loading of 1.0 to 3.0 wt% and their maximum electrical conductivity approached 10^-3 S m^-1. PC-blend-CB and PC-blend-CNF composites showed Newtonian behaviour like pure PC matrix, but PC-blend-CNT composites showed yield stress as well as increased storage modulus and strong shear thinning behaviour at low angular frequency and shear rate due to strong interactions generated between CNT-CNT particles as well as PC molecules and CNT particles on the nanometre scale. Conclusions: The electrical conductivity of the PC composites with different carbon constituents was well explained by the continuous network structure formed between filler particles. The network structure was confirmed by the good dispersion of fillers as well as by the yield stress and solid-like behaviour observed in steady and dynamic shear flows.