Abstract
Five types of nanofillers, namely, silica, surface-silylated silica, alumina, surface-silylated alumina, and boron nitride, were tested in this study. Nanocomposites composed of an epoxy/amine resin and one of the five types of nanoparticles were tested as dielectrics with a focus on (i) the surface functionalization of the nanoparticles and (ii) the water absorption by the materials. The dispersability of the nanoparticles in the resin correlated with the composition (OH content) of their surfaces. The interfacial polarization of the thoroughly dried samples was found to increase at lowered frequencies and increased temperatures. The β relaxation, unlike the interfacial polarization, was not significantly increased at elevated temperatures (below the glass-transition temperature). Upon the absorption of water under ambient conditions, the interfacial polarization increased significantly, and the insulating properties decreased or even deteriorated. This effect was most pronounced in the nanocomposite containing silica, and occurred as well in the nanocomposites containing silylated silica or non-functionalized alumina. The alternating current (AC) breakdown strength of all specimens was in the range of 30 to 35 kV·mm−1. In direct current (DC) breakdown tests, the epoxy resin exhibited the lowest strength of 110 kV·mm−1; the nanocomposite containing surface-silylated alumina had a strength of 170 kV·mm−1. In summary, water absorption had the most relevant impact on the dielectric properties of nanocomposites containing nanoparticles, the surfaces of which interacted with the water molecules. Nanocomposites containing silylated alumina particles or boron nitride showed the best dielectric properties in this study.
Highlights
Epoxide resins are among the most commonly used polymer-based insulating adhesives in high-voltage insulations [1,2]
The epoxy/amine resin composed of DGEBA and AEAP was used as the polymer matrix in this study, in which the effect of nanoparticles on the water uptake and the dielectric properties of the nanocomposites were investigated
In this highly reproducible process, HMDS alters the hydrophilic properties of the prisitne nanoparticles into hydrophobic ones, yielding trimethyl silyl-functionalized alumina (Al2 O3 -TMS) and silica particles (SiO2 -TMS)
Summary
Epoxide resins are among the most commonly used polymer-based insulating adhesives in high-voltage insulations [1,2]. Epoxy-based composites with inorganic fillers have been found to meet these demands [3,4,5,6,7], and, in the last two decades, the design of composite materials comprised of either micro-scaled or nano-scaled inorganic particles has gained increased attention. Inorganic fillers such as AlN, BN, SiO2 , Al2 O3 , TiO2 , SiC, ZnO, etc. Inorganic fillers such as AlN, BN, SiO2 , Al2 O3 , TiO2 , SiC, ZnO, etc. [8,9,10] have been used for the fabrication of electrically insulating polymers, aiming to deliver the targeted electrical, mechanical, and thermal properties.
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