Dielectric properties of aged polymers and nanocomposites

The research presented in this thesis is motivated by two current concerns for electrical wiring insulation materials: i) the aging of polymeric insulation that has been widely used for decades and ii) the development of new dielectric materials with advanced insulating properties, such as polymer-clay nanocomposites. The first part of this thesis investigated the deterioration of insulating function of three insulation polymers, PI (polyimide), PTFE (poly tetra fluoro ethylene) and ETFE (ethylene tetra fluoro ethylene), during various environmental aging processes. The permittivity and electrical breakdown strength of the polymers were measured after their exposure to heat, saline and/or tensile strain. The way in which the dielectric properties changed was determined to be associated with structural, chemical or physical changes in the material during aging processes, by using material characterization methods, such as X-ray Diffraction, Infrared Spectroscopy, Thermogravimetric Analysis, Differential Scanning Calorimeter and Dynamic Mechanical Analysis. In the second part, dielectric properties of PMMA-MMT nanocomposites was studied to analyzed effect of nanofiller on dielectric relaxation dynamics and conduction mechanism. A parametric approach was used to model frequency dependence of MWS, α- and β-relaxations and low-frequency conductivity effect of the nanocomposite materials. As MMT quantity increases, it is observed that the characteristic frequency and intensity of the dielectric relaxations varied significantly. The conduction mechanism, however, is independent of content of MMT, while the strength of conduction increases tremendously with MMT quality and temperature. This thesis has explored the influence of aging processes on dielectric parameters of three polymers that have been widely used as electrical insulation materials for several decades, and the dielectric properties of PMMA-MMT nanocomposites that are considered promising as next-generation insulation materials