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The morphology, crystallinity, and electrical conductivity (σ′ and σ″) as a function of frequency of polypropylene (PP) melt-extruded with different amounts of as-grown carbon nanofibers (CNFs) from 0 to 1.4 vol. % are examined. The PP/CNF composites present CNF aggregates randomly distributed within the PP and an insulator–conductor transition at CNF contents near 0.9 vol. %. The degree of crystallinity of PP/CNF composites with loadings of 1.4 vol. % increases ∼15% with respect to the neat PP (∼34%), with σ´ ∼ 8.6 × 10−5 S m−1 (σ″ ∼ 8.3 × 10−4 S m−1) at 2 MHz. In addition, the values of the electrical conductivity σint´ ∼2.9 × 10−6 S m−1 (σint″∼3.7 × 10−4 S m−1) at 2 MHz, as a result of the interphase (ϕint ∼0.05 vol. %) of the 1.4 vol. % PP/CNF composites, are estimated by the use of a modified generalized effective medium model (GEM). The analysis gathered in here indicates that the interphase between the polymer and the conducting particle may have a quantifiable effect on the electrical properties of carbon-based polymer composites, and this fact should not be neglected in the production of conducting polymer composites (CPCs) with enhanced electrical properties.

This study predicts the effect of the conducting filler/ insulating matrix interphase on the electrical properties of two series of percolated systems, differing from the type of carbon black particles mixed in an aminecured epoxy matrix, diglycidylic ether of bisphenol F. To take into account the interactions between the conducting filler and the matrix, as well as filler-filler overlapping, we introduce three parameters, characteristic of the interphase zone, such as concentration, conductivity and volume, on the generalized effective medium (GEM) model for DC and AC electrical conductivities. These interphase parameters, characterizing the boundary of the shaded zone between the macromolecular chain and the conducting particles, depend on the filler type and concentration. One output of GEM-modified model is that it provides a mean to estimate the volume, concentration and intrinsic conductivity of the interphase in a composite by fitting the experimental data over a broad range of frequency.

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