The effect of material composition and temperature on electrical tree growth in epoxy resins

The epoxy resin prepolymers used in producing the blend materials were CY1301 and CY1311 and both use the hardener HY1300 with the same weight ratio. Although both prepolymers have the same cure chemistry, they contain different levels of additives such as flexibilisers and tougheners. The change over in the tree growth behaviour could therefore be due to a critical change in the composition of the blend samples. The changeover in the tree growth behaviour at the glass transition could therefore be coincidence or due to an increased mobility of unreacted additives as the resin changes from a glassy state over to a flexible state. In order to separate these two factors, structural or compositional, tree growth experiments were taken on fully cured pure CY1301 epoxy resin as a function of temperature. In this paper we describe the results of these measurements and compare the results obtained with the tree growth behaviour ofthe blend materials