In order to increase the thermal conductivity of neat epoxy resin and broaden its practical application in high-voltage insulation systems, we have constructed four kinds of epoxy resin nanocomposite models (a neat epoxy resin (EP), a graphene-doped epoxy resin nanocomposite (EP/GR) and hydroxyl- or carboxyl-functionalized graphene-doped epoxy resin nanocomposites (EP/GR-OH or EP/GR-COOH)) to systematically investigate their thermodynamic and electrical properties using molecular dynamics (MD) simulations. Compared with the EP model, carboxyl-functionalized graphene particles enhanced the thermal conductivity of the EP/GR-COOH model by 66.5% and increased its T_g by 26.6 K. Furthermore, the dielectric constant of the EP/GR-COOH model was significantly reduced. To investigate the intrinsic mechanism, the lowest fraction of free volume (13.22%) and the largest number of hydrogen bonds (102.2) in the EP/GR-COOH model were identified as playing essential roles for its excellent thermodynamic properties and favorable electrical performance. The present study provides a molecular-level understanding of the satisfactory thermodynamic and electrical properties of the EP/GR-COOH nanocomposite, which will aid in designing novel epoxy resin nanocomposite materials with high thermal conductivity.

The impregnation and curing process of dry bushing requires the epoxy material for bushing to have a good process performance. In addition, the actual operating conditions of dry bushing put forward high requirements on the dielectric properties of the epoxy material. Amine accelerators can not only improve the technological properties of epoxy materials such as gel time and curing exothermic temperature rise by regulating the reaction rate of epoxy resin and anhydride curing agent, but also optimize the dielectric properties of epoxy materials by regulating the crosslinking density of epoxy materials. However, there are many types of amine accelerators, and the effects of amine accelerators with different nucleophilicity on epoxy materials vary greatly. In this paper, four kinds of amine accelerators with different nucleophilic ability were selected to study the influence of the nucleophilic ability of amine accelerators on the process and dielectric properties of epoxy materials. The results show that the stronger the nucleophilicity of the amine accelerator, the shorter the gel time of the epoxy mixture and the higher the exothermic temperature rise during curing, indicating a poorer processing performance. However, stronger nucleophilicity also endows the epoxy material with superior dielectric properties. Among them, the strong nucleophilic ability of TEA shortens the gel time of the material by 50% and increases the curing exothermic temperature rise by 55.3% compared with the weak nucleophilic ability of the DET epoxy system; the dielectric constant and dielectric loss of the material are reduced by 8.3% and 39.5%, respectively, and the breakdown strength is improved by 11.4%. This paper reveals the contradictory relationship between the process and dielectric performance of epoxy materials triggered by the difference in the nucleophilic ability of amine accelerators, and it also provides a new research idea for the improvement of the process and in the dielectric performance of epoxy materials for dry bushing.