The effect of different carbon fillers on the electrical conductivity of ethylene vinyl acetate copolymer-based composites and the applicability of different conductivity models

Conducting carbon black (CCB), short carbon fiber (SCF), and multi-walled carbon nanotube (MWCNT)-filled conductive composites were prepared from ethylene vinyl acetate copolymer (EVA). Percolation thresholds of electrical conductivity in volume fraction (and in phr) for different carbon fillers were for CCB ∼0.14 (30 phr), for SCF ∼0.07 (15 phr) and for MWCNT mixed with solution process ∼0.03 (5 phr). No percolation threshold was observed for EVA–MWCNT composites mixed with dry process. Electrical conductivities at the percolation threshold for EVA–CCB, EVA–SCF and EVA–MWCNT (solution mix) composites were 2.5 × 10−6, 5.0 × 10−5, 2.5 × 10−4 S/cm, respectively. The applicability of different theoretical models to predict the conductivity of these composites was verified. The Scarisbrick model exhibited better agreement between theoretically calculated and experimentally determined conductivities for EVA–CCB and EVA–SCF composites at higher concentrations of filler but not at lower concentrations of filler. None of the models was found suitable for EVA–MWCNT composites. Deviations between the theoretical and experimental conductivities were substantially high for McCullough and Bueche models. Possible limitations in framing of different models were discussed. We have proposed a modified model, which exhibited better agreement between theoretical and experimental conductivities over wide range of concentrations for all three fillers.