Percolation concept and the electrical conductivity of carbon black-polymer composites .3. Crystallisable chloroprene rubber mixed with FEF carbon black

The filler concentration and temperature dependence of the electrical conductivity (sigma) of the crystallisable chloroprene rubber CR(Butaclor 41H) mixed with fast extrusion furnace (FEF) carbon black was investigated. It was found that the percolation concept holds true for these composites where sigma shows a nearly sharp increase when the mass fraction of FEF carbon black in the mixture exceeds 20%. The estimated values of the filling factor (f) and the occupation number (Z) were found to be 0.82 and 8.2 respectively. The scaling law of the percolation clusters [sigma = sigma(0)(P - P-c)(beta)] was valid within the range P-c less than or equal to P less than or equal to 0.34 and the estimated value of beta is 6.8. The temperature dependence of a is thermally activated below and at the percolation threshold with the same activation energy. The decrease in sigma with temperature followed by a subsequent increase above certain temperature was attributed to the phase transition of CR(41H) and the change in the size of carbon black clusters from infinite to finite with temperature. In the highly loaded compounds the temperature dependence of a is controlled by the break-down and re-formation of carbon clusters with temperature. (C) 1997 Elsevier Science S.A.