Influence of addition of hydroxyl-terminated liquid nitrile rubber on dielectric properties and relaxation behavior of epoxy resin

Epoxy resin is one of the most popular insulation materials used in power equipment, whereas it is easy to crack when used in some large equipment due to its poor toughness. In order to increase the toughness of epoxy resin, adding liquid rubber into epoxy resin is a common way employed in industrial production. However, the dielectric properties of epoxy resin changes while the toughness increases. In this paper, hydroxyl-terminated liquid nitrile rubber (HTBN) was used as the filler to toughen the epoxy resin. Through comparing and analyzing the glass transition temperature and permittivity of composites with different filler contents, the influence of rubber particles on the mechanical and dielectric properties of epoxy resin was studied. The results indicate that the glass transition temperature decreases with the increase of filler content. When HTBN content is more than 15%, the toughness of composites is enhanced. With the increasing content of HTBN, the volume resistivity decreases, while the relative permittivity and dielectric loss tangent increase. The breakdown strength reveals little change. The addition of HTBN has a certain effect on the dielectric relaxation behaviors of epoxy resin, and the dielectric relaxation which caused by the interfacial polarization between rubber particles and epoxy matrix appears at the temperature above 5 °. Therefore, the influences of fillers on the dielectric properties should be considered while toughening the epoxy through adding liquid rubber during the formula design.