PERCOLATION CONCEPT AND THE ELECTRICAL-CONDUCTIVITY OF CARBON BLACK-POLYMER COMPOSITES - BUTYL RUBBER MIXED WITH SRF CARBON-BLACK

The concentration and temperature dependence of the electrical conduct ivity (sigma) of butyl rubber (IIR) mixed with semi-reinforcing furnac e (SFR) carbon black have been investigated. It was found that the con centration dependence of sigma satisfied the scaling law of percolatio n clusters (sigma = sigma0 (p - p(c))beta) through the range of p(c) l ess-than-or-equal-to p less-than-or-equal-to 0.46 where p(c) is the pe rcolation threshold and p is the carbon concentration. The great diffe rence between the obtained value of beta and that of the scaling law w as attributed to the occluded rubber which acts as part of carbon rath er than as part of the matrix. The occupation number (Z) was found to be 6 as calculated from the percolation threshold. The variation of si gma with temperature below the percolation threshold was characterized by thermally activated behavior above a certain temperature. The temp erature dependence of sigma above the percolation threshold was attrib uted to both breakdown and re-formation of carbon clusters with temper ature. It was also found that, above the percolation threshold, the te mperature cycling changed the behavior of sigma with temperature and l ed to good reproducibility.