Conductive polymer composites with high electrical and mechanical properties are in demand for bipolar plates of phosphoric acid fuel cells (PAFC). In this study, composites based on natural graphite/fluorinated ethylene propylene (FEP) and different ratios of carbon black are mixed and hot formed into bars. The overall content of natural graphite is replaced by carbon black (0.2 wt% to 3.0 wt%). It is found that the addition of carbon black reduces electrical resistivity and density. The density of composite materials added with carbon black 3.0 wt% is 2.168 g/cm3, which is 0.017 g/cm3 less than that of non-additive composites. In-plane electrical resistivity is 7.68 μΩm and through-plane electrical resistivity is 27.66 μΩm. Compared with non-additive composites, in-plane electrical resistivity decreases by 95.7 % and through-plane decreases by 95.9 %. Also, the bending strength is about 30 % improved when carbon black is added at 2.0 wt% compared to non-additive cases. The decrease of electrical resistivity of composites is estimated to stem from the carbon black, which is a conductive material located between melted FEP and acts a path for electrons; the increasing mechanical properties are estimated to result from carbon black filling up pores in the composites.

A composite material was prepared for the bipolar plates of phosphoric acid fuel cells(PAFC) by hot pressing a flake type natural graphite powder as a filler material and a fluorine resin as a binder. Average particle sizes of the powders were 610.3, 401.6, 99.5, and 37.7 μm. The density of the composite increased from 2.25 to 2.72 g/cm3 as the graphite size increased from 37.7 to 610.3 μm. The anisotropy ratio of the composite increased from 1.8 to 490.9 as the graphite size increased. The flexural strength of the composite decreased from 15.60 to 8.94MPa as the graphite size increased. The porosity and the resistivity of the composite showed the same tendencies, and decreased as the graphite size increased. The lowest resistivity and porosity of the composite were 1.99 × 10−3 Ωcm and 2.02 %, respectively, when the graphite size was 401.6 μm. The flexural strength of the composite was 10.3MPa when the graphite size was 401.6 μm. The lowest resistance to electron mobility was well correlated with the composite with lowest porosity. It was possible the flaky large graphite particles survive after the hot pressing process.

This paper shows the feasibility on the application of E-glass fiber/epoxy(GFRP) composite materials to an automotive leaf spring. In order to keep much lighter weight by replacing the steel with the composite material, it is important to optimize the material parameters and design variables consisting of the structure. This paper focused on the effects of material compositions and its fiber orientations for estimating the static behaviors of leaf spring. First of all, basic material properties of GFRP composite were measured by five types of coupon specimens from ASTM standard test. The reverse implementation was also done to obtain the complete set of in-situ fiber and matrix properties from ply test results. Finally, the static spring rates was examined for the variation of thickness and material parameters such as fiber angles and resin contents of composite leaf spring.