Dielectric properties of nylon 6,6/aramid fibre microcomposites in the presence of transcrystallinity

Dielectric spectroscopy was applied in the present work for the first time to polymeric composite materials containing transcrystallinity, wherein the dielectric properties of pure nylon 6,6 and of aramid fibre-reinforced nylon 6,6 microcomposites were examined over wide frequency and temperature ranges. The temperature behaviour of the dielectric losses of the materials indicated three polarization processes, related to either local or collective molecular mechanisms of motion. In addition, interfacial polarization of the Maxwell-Wagner-Sillars type was observed. The dielectric response was found to be sensitive to the presence of transcrystallinity in the microcomposites. It was found that the activation energy of the α, β and γ relaxations exhibits typical variations in the presence of reinforcement and transcrystallinity. The dielectric strength, calculated from fitting of the relaxation spectra to the Havriljak-Negami empirical term for all the relaxation processes, was found to be very sensitive to the morphology of the systems. The specific values at 1 MHz of the dielectric constant, dielectric loss and dielectric loss tangent as a function of temperature for the transcrystalline layer were retrieved from the composites data using the rule-of-mixtures. A comparison was conducted between the values of the transcrystalline layer and those of the bulk matrix to determine the effect of the transcrystalline layer on the dielectric properties.