PERCOLATION CONCEPT AND THE ELECTRICAL-CONDUCTIVITY OF CARBON BLACK-POLYMER COMPOSITES .2. NON-CRYSTALLISABLE CHLOROPRENE RUBBER MIXED WITHHAF CARBON-BLACK

The concentration and temperature dependence of the electrical conduct ivity (a) of the non-crystallisable chloroprene rubber CR(WRT) mixed w ith high abrasion furnace (HAF) carbon black was investigated. It was found that the concentration dependence of a satisfied the scaling law of percolation clusters [sigma = sigma(0)(P - P-c)(beta)] through the range of P-c less than or equal to P less than or equal to 0.43, wher e P-c is the percolation threshold, P is the carbon concentration and P is the exponent (accounts for the cluster size). The difference betw een the obtained value of P and that of the scaling law was attributed to the occluded rubber which acts as a part of carbon rather than as a part of the matrix. The occupation number (Z) was found to be 8.2 as calculated from the percolation threshold. The correlation between be ta and Z was found to be beta approximate to Z + 1. It was also found that the filling factor of HAF carbon is 0.70 which is the mean value of the filling factors of spheres, random close packing and rods and u niaxial simple cubic. The temperature dependence of a was thermally ac tivated below the percolation threshold, while, above the percolation threshold, the variation of a with temperature was attributed to the b reakdown and re-formation of carbon clusters with temperature. (C) 199 7 Elsevier Science S.A.