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

摘要

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 (S 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 x 10~(-6), 5.0 x 10~(-5), 2.5 x 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.