Effect of Graphite and Carbon Black Fillers on the Processability, Electrical Conductivity and Mechanical Properties of Polypropylene-Based Bipolar Plates

This study investigates the hybrid effect between graphite and carbon black in a polypropylene (PP) matrix, based on optical microscopy. PP sheets filled with various types of carbon black and graphite were prepared, and the effects of fillers on the flowability, electrical conductivity and mechanical properties were investigated. The effects of three kinds of carbon black with different specific surface areas (65, 770, 1400 m ² /g) on the increase of conductivity in the polypropylene (PP) matrix were compared. The best performance was observed when the carbon black with the highest specific surface was used; therefore it was used for preparing the hybrid-filled (graphite – carbon black) materials by melt blending. Optical microscopic studies proved that the carbon black exerted not only a direct but also an indirect influence on the conductivity and on the mechanical properties of the hybrid composites, as it influenced the distribution of graphite significantly. At lower graphite contents the material became more flexible because of the better dispersion of graphite, but at higher carbon black contents the stiffness increased significantly.