On the design of the structure of epoxy resin networks

The molecular structure of epoxy resin plays a vital role in defining the properties of epoxy-based insulation. The reactions between the epoxy terminated resin and the hardener, result in the formation of the cured system. In the case of amine hardeners, a node is generated due to relatively simple reactions between the primary and secondary amine of the hardener and the epoxide groups of the resin. On the other hand, in the case of anhydride based hardeners, both etherification and esterification reactions take place to form the cured material. Our previous work has revealed that the modification of an amine cured system using an epoxy-based diluent can result in the formation of a branched molecular network, which can lead to increased breakdown strength of the system. In this study, the design of a molecular structure for both amine and anhydride cured systems with increased electrical strength is suggested by adopting the hypothesis of the branched molecular structure. Two epoxy resin based systems (amine and anhydride cured) were modified using a reactive diluent featuring at least one epoxide group within its chemical structure. Dielectric spectroscopy and breakdown strength measurements were used to study the behavior of the manufactured systems. The dielectric data obtained from the samples indicate that the permittivity is strongly affected by the functional group of the reactive diluent, while the breakdown strength depended on both the percent of added diluent and the functional group consequently introduced. By using a precisely designed three-component epoxy system, it has been possible to control the properties of the resulting system; materials with increased breakdown strength have been produced. This approach is of high potential importance because it may allow materials to be designed with controlled properties to suit particular applications.