Electrical percolation behavior of carbon fiber and carbon nanotube polymer composite foams: Experimental and computational investigations

The effect of foaming on the electrical percolation of polymer composites was simulated by a random sequential additional (RSA) process. Polystyrene composites containing various amounts of carbon fiber (CF) and carbon nanotubes (CNTs) were prepared through melt blending in an internal mixer and subsequently compression-molded to solid and foam sheets. The electrical conductivity (EC) and percolation threshold (Pc) of both the solid and foam composites were determined to evaluate the simulation results. The experimental results show that the EC of the CF composites decreased with foaming, whereas for the CNT composites, no significant change was observed. The RSA process was used to construct the microstructure of the solid and foam composites and predict their Pcs. Several parameters, including the fiber aspect ratio, bubble volume fraction, and bubble size, were studied by the simulation approach. The Pcs obtained by simulation showed good agreement with the experimental values. When bubbles were excluded to define the volume fraction of the filler, the foam composites with bubbles, close to the fibers in size, had approximately the same Pcs as the solid composites. Better agreement between the experimental and simulation results was found for the foam composites with 30 vol % bubbles rather than those with 15 vol %. (C) 2015 Wiley Periodicals, Inc.