Electrical properties of carbon black/ copolymer composites above and below the melting temperature

The electrical properties of a composite, consisting in a matrix of ethylene butylacrylate (EAB) reinforced with carbon black particles (CB) are studied in the temperature range from 27 to 127 °C. The DC conductivity measurements show an insulator/conductor transition at a volume concentration of about ®*~11%. The electrical resistivity is constant with temperature, at concentrations below the conduction threshold ®*. For concentrations above ®*, the resistivity presents a significant increase for temperatures above the melting point, Tm ~ 91 °C, which corresponds to the phenomenon known as positive temperature coefficient in resistivity (PTCR effect). Besides, the AC conductivity of these composites was analysed in the frequency range from 40 Hz to 0.1 MHz. The frequency dependence of the AC conductivity is characterized by a low frequency region of constant conductivity followed by a gradual transition at higher frequencies to a frequency dependent conductivity. This behavior can be approximated by the empirical power law of Jonscher. We found that the activation energy is insensitive to the presence of the carbon particles, it means that the carbon particles do not interact or only weakly with the chain segments of the macromolecules in the copolymer.