Effect of inhomogeneous size and shape of graphite particles on the in-plane electrical conductivity of PP/G/CB composites

In-plane electrical conductivity higher than 100 S cm(-1) for composite bipolar plates is required in fuel cells. The effect of the conductive filler size and shape, as one important factor, on the conductivity of polypropylene/graphite/carbon black (PP/G/CB) composites is investigated in this study. The "as-received" G particles were sieved to different sizes; melt compounded with PP and CB, then compression moulded to plates for conductivity measurements. G particles have different size distributions and their morphology appear with irregular shapes. The intermediate G size and relatively narrow distribution (40-150 mu m) shows the highest conductivity at 80 wt.% filler loading of about 88.6 S cm(-1). The presence of small G particles between larger ones and the particle's point-to-point and surface-to-surface contacts are found to be important factors in determining the conductivity values. The flexural properties are still below the target and need to be improved.