Multifunctional composites are in high demand where a material needs to simultaneously satisfy several functional requirements. Bipolar plates of polymer electrolyte membrane fuel cells are great examples of this kind, requiring very high electrical and thermal conductivities together with good mechanical properties and environmental durability. Conductive filler/polymer composites (CPCs) have shown some promise towards this application. However, achieving high levels of through-plane and in-plane electrical conductivities in CPCs while maintaining scalable processability and satisfactory level of mechanical performance is challenging. In this work, a polymeric blend system together with hybrid conductive fillers was designed, manufactured, and characterized in an attempt to obtain melt-processable, highly conductive composites. Polycarbonate (PC) and high-density polyethylene (HDPE) were employed as the blend matrix with polyethylene glycol (PEG) as the compatibilizer. Carbon nanotubes (CNT), carbon fibers (CF), and graphite (G) were utilized as the conductive fillers. The HDPE was used as the minor component of blend matrix at 30 wt.% of the major matrix PC, with PC having the better affinity to the fillers. This was done to localize the conductive fillers in the major PC component of the blend. CF and G were used in ranges of 10–30 wt. % and 30–50 wt. % of the composites, respectively. CNT and PEG were fixed at 3 wt. % and 1.5 wt. %, respectively. The composites were first compounded using a twin-screw extrusion system and the test specimens were then made using compression molding process. The results showed that due to the preferential localization of the fillers in PC component of the PC/HDPE blend, the electrical conductivities were increased by about three times, compared to that of CPCs made with PC-only matrix. Consequently, high through-plane and in-plane conductivities of 10.0 and 61.1 S/cm, respectively, were achieved, which are superior to most of the previously reported results. The findings suggest that integrating blending and hybrid filler strategies could be a promising approach towards scalable manufacturing of highly conductive CPCs for applications such as bipolar plates.

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