Dielectric spectroscopy analysis of EVA-silicate nanocomposite insulating materials

Nanocomposite materials show promising results for applications as electrical insulation. Among several materials presently under investigation, previous works indicate that polypropylene and ethylene-vinilacetate filled by nanosilicates present lower content of space charge and higher electric strength. However, efforts are needed to explain nanocomposite behaviour and characterize their electrical, thermal and mechanical properties. In this paper, the results of broad-band dielectric spectroscopy performed on ethylene-vinylacetate copolymer filled by layered micro and nanosized silicates are reported. The nanofillers consist of montmorillonite and fluorohectorite, that is, natural and synthetic clays. Isochronal and isothermal curves of complex permittivity, as well as activation energies of the relaxation processes are presented and discussed. It is shown that nanostructuration (verified by XRD and TEM analysis) gives rise to substantial changes in the polarisation and dielectric loss behaviour. While the relaxation process of EVA, associated to glass transition of the material amorphous phase, results unchanged, it has been observed the rise of a new process at higher temperatures, having different activation energy in intercalated and exfoliated samples, as well as a change of the distribution of relaxation times.