Electrical conductivity of carbon black-polyethylene composites - Experimental evidence of the change of cluster connectivity in the PTC effect

The electrical resistivity of carbon black filled high density polyethylene increases significantly when the composite is heated to the melting temper ature of the matrix. The paper aims to provide new insights on this feature , known as the Positive Temperature Coefficient (PTC) effect for resistivit y. The influence of the volume fraction cb of carbon black and of the tempe rature on the DC conductivity is analyzed and compared to their influence o n matrix expansion. Measurements of the dependence on frequency of the AC c onductivity of carbon black-polyethylene composites, at different loadings and at different temperatures, are performed. They yield experimental evide nce of a change of connectivity of the conducting network during heating ne ar the melting temperature of polyethylene. It is shown that the initial vo lume fraction of carbon black strongly affects the PTC mechanism. (C) 2001 Elsevier Science Ltd. All rights reserved.