This paper reports the dielectric relaxation studies of carbon nanotubes loaded in polyester polymer matrix. The study was carried out in the frequency range between 100 Hz and 1 MHz at constant temperature, T = 300 K. The frequency dependence of the electrical data was treated in the frameworks of the impedance Havriliak-Negami formalism and by using the universal Jonscher power law. The imaginary and real parts of the dielectric permittivity change with concentration of the carbon nanotubes. This work consists in studying the influence of these nanoparticles on the dielectric properties, describing the electrical relaxation and the conduction mechanisms.

Binary and ternary composites were synthesized using a polyester matrix reinforced by two types of carbon inclusions, namely, carbon nanotubes (CNT) and graphite (Gt) (CNT/Gt/Polyester). Thermal analyses were performed, using thermogravimetry and differential scanning calorimetry, which allowed us to observe significant changes in glass transition temperatures and degradation temperatures of the composites. Dielectric measurements were performed in a frequency range from 100 Hz to 1 MHz and temperature from –33 to 107°C. The dielectric permittivity values of the CNT/Gt/Polyester ternary composites, compared to the Gt/Polyester binary composites, indicate that the addition of CNT particles to the Gt/Polyester binary system significantly improved the dielectric permittivity, due to the enhanced interfacial polarization of the host matrix, while the frequency dependence of the electrical modulus spectra revealed a Maxwell–Wagner–Sillars dielectric relaxation process that was found to follow the Cole–Davidson approach.

The electrical properties of carbon nanotubes loaded in polyester polymer matrix were studied by using the impedance spectroscopy technique. The study was carried out in the frequency range between 100 Hz and 1 MHz and temperature between 170 and 400 K. Cole–Cole representation was used to interpret the impedance spectra of all the samples. The variation of the electrical conductivity, as a function of temperature, for concentrations higher than the conduction threshold was analyzed. This variation undergoes a significant decrease from a critical temperature that corresponds to the phenomenon known as positive temperature coefficient in resistivity. Tunneling effect is responsible for the change of the conductivity. The carbon particles are not in physical contact and the electrons tunnel through the insulating polymer gap between particles. With the rise of temperature, the gap between particles increases and tunneling becomes less probable. Consequently, above this temperature, the electrical conductivity begins to increase, due to the fact that the temperature dependence of conductivity is mainly related with different thermal expansion of polymer matrix and carbon nanotubes. POLYM. COMPOS., 39:1297–1302, 2018. © 2016 Society of Plastics Engineers

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