Electrical and thermal properties of polypropylene filled with steel fibers

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Abstract
Polypropylene (PP) compositions containing 0–20 vol % of steel fibers (SF) [neat or with 5 wt % of maleated propylene wax (MPP)] were prepared and tested for electrical and thermal conductivities. It was found that, at room temperature, the volume resistivity Ωv fell below 10 ohm cm at SF loading of about 10 vol %. However, as the test temperature increased to 120°C, higher loadings were required to secure the same resistivity, i.e., 12 and 14 vol % of SF for composites without and with MPP, respectively. By contrast with a sharp decrease of Ωv (by 16 orders of magnitude upon addition of a few percent of SF), the increase of thermal conductivity was much less dramatic. The thermal conductivity k of the composites was found to be proportional to volume loading, increasing by a factor of 1.8 on addition of 20 vol % of SF, independently of temperature and MPP presence. Annealing had a small positive effect on k.