Buds for Treeing in Epoxy Nanocomposites and their Possible Interaction with Nano Fillers

Breakdown lifetime for treeing is enormously extended for polymers when they are doped with nano fillers. It includes a budding process and a growing process. The latter process is mainly determined by erosion due to partial discharge attack, and thus suppressed by existing nano fillers. The former process is not so clear, but it must be a dielectric breakdown that takes place due to electron injection and transport at high electric field. How would nano fillers react to the budding? SEM observation indicates for epoxy/silica nanocomposites that treeing buds of several tens nm in diameter are closely linked with nano fillers. Such tree buds are analyzed from the basic process of electron injection and transport in polymers at high electric field with the aid of a Schubweg concept and a multi-core model. As a result, it is concluded that buds for treeing is possibly affected by trapping by localized states and local electric field induced by nano fillers.