Electrical properties and percolation phenomena in carbon black filled polymer composites

The electrical conductivity and related percolation phenomena in polypropylene/carbon black (PP/CB) composite systems have been studied. The carbon black concentration was systematically varied in a wide range. The electrical and dielectric properties of these materials were investigated by means of broadband AC (10^-1-10⁶ Hz) dielectric relaxation spectroscopy techniques. By complex dielectric permittivity measurements, the dependence of AC conductivity, σ _AC, and DC conductivity, σ_DC, on the frequency and on the concentration of the conductive filler was investigated. The dielectric behaviour of this system can be satisfactorily described in terms of percolation theory. According to our results, the percolation threshold was calculated to be 6.2 wt.% CB. The concentration and frequency dependence of the conductivity was studied in detail. Both, dielectric constant and dc conductivity, follow power-law behaviour yielding values for the critical exponents which are in good agreement with the theoretical ones