PERCOLATION CONCEPT AND THE ELECTRICAL-CONDUCTIVITY OF CARBON BLACK-POLYMER COMPOSITES .3. CRYSTALLISABLE CHLOROPRENE RUBBER MIXED WITH FEFCARBON-BLACK

The filler concentration and temperature dependence of the electrical conductivity (sigma) of the crystallisable chloroprene rubber CR(Butac lor 41H) mixed with fast extrusion furnace (FEF) carbon black was inve stigated. It was found that the percolation concept holds true for the se 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 f ound to be 0.82 and 8.2 respectively. The scaling law of the percolati on clusters [sigma = sigma(0)(P - P-c)(beta)] was valid within the ran ge P-c less than or equal to P less than or equal to 0.34 and the esti mated value of beta is 6.8. The temperature dependence of a is thermal ly activated below and at the percolation threshold with the same acti vation energy. The decrease in sigma with temperature followed by a su bsequent increase above certain temperature was attributed to the phas e transition of CR(41H) and the change in the size of carbon black clu sters from infinite to finite with temperature. In the highly loaded c ompounds the temperature dependence of a is controlled by the break-do wn and re-formation of carbon clusters with temperature. (C) 1997 Else vier Science S.A.