298 / 2018-09-25 21:45:50

Effects of HBP-modified Nanosilica on Electrical Tree Propagation of Epoxy Resin Composites

hyperbranched polyester, nanocomposite, interface property, trap, electrical tree

Hyperbranched polyester is an effective modifier for improving mechanical and dielectric properties of polymer composites. In this study, a hyperbranched polyester with terminal carboxyl groups was used to treat nanosilica surface. During the grafting process, the molecular weight and terminal radical number of hyperbranched polyester were adjusted to obtain various thickness and chemical activity of functional layer on nanosilica surfaces. Then, the physical and chemical change on nanofiller surface were observed or analyzed by TEM, XPS and FT-IR spectrum. Based on these experimental results, the effects of hyperbranched polyester on nanofiller surface activity and interface bond strength with epoxy resin matrix were discussed. As a next step, polyester-treated nanosilica were used to prepare epoxy resin nanocomposites with 1 to 10% filling content. Temperature dependent of complex permittivity was measured under 20 to 200℃. Dielectric loss factor and trap activation energy were calculated based on the experimental results of complex permittivity. Next, under ac high voltage filed, the field strength of initial partial discharge and the process of electrical tree development were investigated by a needle-plate electrode system. These insulating experiments of nanocomposite were conducted under room temperature and under high temperature around its glass transmission temperature, respectively. The field strength of tree initiation, tree growing speed and tree shapes were detailedly studied. The relationship between electrical tree propagation and the interfacial properties of nanocomposite was also discussed by summarizing experimental results. Finally, based on trap theory and multi-region structure model of nanocomposites, the effects of nanosilica surface modification on partial discharge and electrical tree development were discussed. Implanted deep traps in interface areas of nanocomposite contribute to the inhibition of seed electrons. The enhanced interfacial bond strength is considered to result in big barrier for carrier transport. The increased crosslink degree of polymer matrix is deemed as a dominant reason for improved insulating property of resisting electric tree under high temperature. This study indicates that inorganic nanofiller surface modification realized by hyperbranched polyester is beneficial for electrical tree retardant and is an effective way for improving ageing behavior of polymer dielectrics.