This study aims to improve the electrical-mechanical performance of traditional epoxy/graphite composites for engineering applications. The improvement in the properties of these composites depended on the incorporation of different sizes of graphite particles of the same type and controlling their curing process conditions. The thermal properties and microstructural changes were also characterized. A maximum in-plane electrical conductivity value of approximately 23 S/cm was reported for composites containing 80 wt.% G with a particle size of 150 µm. The effect of combining large and small G particles increased this value to approximately 32 S/cm by replacing the large particle size with 10 wt.% smaller particles (75 µm). A further increase in the electrical conductivity to approximately 50 S/cm was achieved due to the increase in curing temperature and time. Increasing the curing temperature or time also had a crucial role in improving the tensile strength of the composites and a tensile strength of ~19 MPa was reported using a system of multiple filler particle sizes processed at the highest curing temperature and time compared to ~9 MPa for epoxy/G150 at 80 wt.%. TGA analysis showed that the composites are thermally stable, and stability was improved by the addition of filler to the resin. A slight difference in the degraded weights and the glass transition temperatures between composites of different multiple filler particle sizes was also observed from the TGA and DSC results.
The investigations in this study focused on the characteristic of feedstock in an effort to understand the mechanism of injection molded in composite material. A composite, which has 75% wt. filler, consist of graphite (G), carbon black (CB) and polypropylene copolymer (PP). Twinscrew co-rotating extruder used for mixing materials. The conductivity of the molded parts measured using a four-point probe test procedure. The results showed that the injection molding conducting composites, which aggregated into larger clusters, tended to disperse unevenly into the PP, resulting in fewer particle-particle contacts and, consequently, a lowerconductivity composite in some part of the molded.
This study is to investigate the flowability of the injection molded conductive composite material containing filler content from 70 up to 80 wt% by using spiral mold. Several moulding compounds, containing polypropylene (PP) as a matrix and graphite (G) and carbon black (CB) as conductive fillers prepared by melt compounding using twin-screw extruder. Carbon black is added as much as 10% and 20% respectively, in order to improve the electrical conductivity of composite material. Results show that the flowability of injection molded conductive composite material decreases with decreasing graphite size and with increasing filler (graphite and carbon black) content. It was found that composites containing G with particle size distribution (≤100 μm) entirely exhibits a relatively higher flowability, in the range of 10.67–6.21 cm, compared to the small size (25-60 μm), in which flowability is in the range of 5.23–3.37 cm. An attempt to combine carbon black as second filler with the PP and G found that composites containing CB showed decreased flowability of the injection molded conductive composite material, especially when the electrical conductivity formed through the resin. Results indicate that the flowability of the injection molded conductive composite material is an important design parameter to fabricate cost-effective, large, or thin composite bipolar plates.
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