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Isotropic conductivities in chopped carbon fiber composites using expanded polypropylene

The aims of this study were to fabricate lightweight composites having isotropic electrical and thermal conductivities. The composites consist of expanded polypropylene (EPP) and chopped carbon fibers. They were randomly mixed together and fusion-bonded using steam at a high temperature with a high saturation vapor pressure. The quasi-isotropic electrical conductivities and isotropic thermal conductivities of the composites were achieved by the secondary expansion of the EPP. The densities, electrical and thermal conductivities of the composites with volume fractions of carbon fibers ranging from 4.2 to 8.5% were in the ranges of 0.2–0.3 g/cm3, 1.1–105.8 × 10−4 S/cm, and 0.51–0.86 W/mK, respectively. The thermal conductivities of the composites were shown to increase monotonically with increasing volume fractions of carbon fibers, which is in agreement with the theoretical values using the series model.