The effect of nano size fillers on electrical performance of epoxy resin

Abstract

Epoxy resin is widely used in high voltage apparatus as insulation due to its excellent mechanical, electrical and chemical properties. Fillers are often added to epoxy resin to enhance its mechanical, thermal and chemical properties. With the new development in nanotechnology, it has been widely anticipated that the combination of nanoparticles with traditional resin systems may create nanocomposite materials with enhanced electrical, thermal and mechanical properties. The project aims to improve the overall electrical performance by adding nanoparticles into epoxy resin. In the present thesis a detailed study on dielectric permittivity, AC breakdown strength and space charge behaviour of epoxy resin/nanocomposites with nano-fillers of SiO₂ and Al₂O₃ has been carried out. The epoxy resin/nanocomposite thin film samples were prepared and tests were carried out to measure their dielectric permittivity and tan delta value in frequency range of 1Hz- 1MHz. The space charge behaviours were also observed by using the pulse electroacoustic (PEA) technique. The influence of filler type, filler size and filler concentration on nanocomposites ac breakdown strength were also examined. In addition, traditional epoxy resin microcomposites were also prepared and tested and the results were compared with those obtained from epoxy resin/nanocomposites. The present results indicate that the presence of nano-sized fillers enhances the insulation properties of the epoxy resin and the dielectric properties are strongly influenced by the interfacial region between epoxy and nano particles. It is the key factor that affects the electrical performance of epoxy nanocomposites. The multi core model has been applied to explain the effects of such interfacial region on the electrical performance epoxy nanocomposites. A new phenomenon of space charge accumulation at higher nano size filler loading concentration has been observed at a filler loading concentration above 3wt%. This phenomenon is a result of the formation of electrical double layer surrounding the nano particles. A comparison study between epoxy nanocomposites loaded with both surface treated and non-surface treated nano particles has also been carried out. The results indicate that nano particle dispersion rate is an important factor in determine the electrical performance epoxy nanocomposites. Surface functionalisation on nano size fillers by using silane as a coupling agent could help avoiding the formation of large agglomerations resulting in better insulating performance. In addition, it has also been found that the presence of water inside epoxy nanocomposites also leads to the reduction in dielectric properties due to the formation of water layers surrounding the nano particles. Those water layers could act as a conductive path to help charge carriers travelling through the bulk of the materials.

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