Chonung Kim

Influence of aluminum nanoparticle surface treatment on the electrical properties of polyethylene composites

In this study, we investigated the influence of the surface treatment of Al nanoparticles on the electrical properties of linear low density polyethylene composites. Octyl-trimethoxysilane was used as a nonpolar silane coupling agent for the surface treatment of Al nanoparticles. It was found that the incorporation of nonpolar octyl groups onto the surface of Al nanoparticles not only increased the percolation threshold and the resistivity but also improved the dielectric properties as compared to the composites filled with unsurface-treated nanoparticles. The surface treatment makes it possible to easily control the frequency and concentration dependences of dielectric constant and provided an excellent approach able to considerably reduce the dielectric loss of the nanocomposites, which is of great significance from the viewpoint of practical application of the polymer/metal nanocomposites in the electrical and electronic industries. It is concluded that the improved electrical properties could be direc...

Influence of silica nanoparticle surface treatments on the water treeing characteristics of low density polyethylene

Premature failure of XLPE cables can occur due to water trees increased the susceptibility of polyethylene insulation to breakdown, and extensive studies have been made to improve the resistance of polyethylene to water treeing in the past. In this study, we investigated the influence of the incorporation of silica nanoparticles and the surface modification of silica nanoparticles on the water treeing characteristics of low density polyethylene (LDPE). It was found that the water tree retardation of LDPE was improved with the incorporation of the silica nanoparticles and that the water tree retardation of non-surface treated silica was superior to that of surface treated silica nanoparticles.

Electrical conductivity of polyethylene aluminum nanocomposites with different particle surface chemistry characteristics

We investigated the influence of the surface modification of Al nanoparticles on the electrical conduction of polyethylene composites. Octyl-trimethoxysilane was used as a coupling agent for the treatment of Al nanoparticle. It was found that the incorporation of octyl groups onto the surface of Al nanoparticle altered the time dependence behaviors of polarization and depolarization current and increased the percolation threshold and the resistivity of the polyethylene composites. It is concluded that, based on our morphology observation of the nanocomposites, the improved electrical properties could be directly ascribed to the good dispersion and special electrical feature of the surface-treated nanoparticles in the polymer matrix.

Effects of high-dose gamma ray irradiation on the physicochemical properties and water-treeing deterioration of cross-linked polyethylene cable insulation

The article aims to explain how gamma ray irradiation influences the physicochemical properties and morphological characteristics of cross-linked polyethylene cable insulation and to show experimentally the influence of the radiation dosage on water-treeing behavior in cross-linked polyethylene cable insulation.

Effect of SEBS on water treeing behaviors of cross-linked polyethylene

We investigated the effect of an aromatic polymer, styrene-(co-ethylene-butadiene)-styrene (SEBS), on water tree resistance of cross-linked polyethylene (XLPE). The XLPE/SEBS samples were characterized by means of gel content determination, different scanning calorimetry (DSC), scanning electron microscopy (SEM) and the accelerated water treeing experiment. Our results clearly indicated that the samples with SEBS showed improved water tree resistance in comparison to blank samples. It was also found that the blends had excellent dielectric property form the viewpoint of practical application.

STUDIES ON APPARENT KINETICS AND RHEOLOGICAL BEHAVIOR OF EPOXY/ACRYLATE IPNS AS VACUUM PRESSURE IMPREGNATION RESINS

The apparent kinetics and cure behavior of novel interpenetrating polymer networks (IPNs) based on cycloaliphatic epoxy resin (CER) and tri-functional acrylate have been investigated by means of differential scanning calorimetry (DSC) and Fourier transform infrared spectroscopy (FT-IR). The results of DSC measurements show that the curing reaction of the TMPTMA component is much earlier than that of the CER component, which can lead to the formation of the IPNs. In contrast to neat anhydride-CER system, the anhydride-CER/TMPTMA systems exhibit relatively lower curing temperatures. The activation energy for initiating the reaction of the anhydride-CER system slightly increases, whereas the activation energy for propagating the reaction markedly reduces during the full IPNs formation. The FT-IR spectroscopic changes are interpreted in terms of curing mechanism of CER and TMPTMA components. The extent of reaction is calculated from FT-IR absorption bands, which depends on the reactive group concentration. The experimental results of FT-IR measurements are in good agreements with those of DSC measurements. The rheological behavior of anhydride-CER/TMPTMA systems during IPNs formation is studied in this paper. It is confirmed that the introduction of TMPTMA monomer into anhydride-epoxy resin has significant effects on the rheological behavior of the system.

Effect of modifier TMPTMA on electrical properties of cured epoxy system for V.P.I. resin

V.P.I. is the most advanced impregnation technology for the electrical machines that have been developed. With the rapid development of the electrical industry, demands of improving the properties of V.P.I. resins become higher and higher. It is of practical significance to investigate the effect of the modification of the epoxy resin TMPTMA on the cross-linking structure, the dc electrical resistivity and dielectric breakdown characteristics of the cured epoxide for V.P.I. insulation. This paper aims to explore the effect of TMPTMA concentration on the temperature dependence of the dc resistivity of the cured system and to study the dielectric breakdown behaviors of the cured systems with different TMPTMA concentrations. The modification of the epoxy resin by TMPTMA has been found to surely provide the possibility for improving the density of the cross-linking structures, electrical properties and thermal stability for V.P.I. resin based on the epoxy resin.

Study on structures and properties of carbon nanotubes/thermosets nanocomposites subjected to external electric field during cure stage

MWCNTs were dispersed in IPNs based on acrylate and epoxy. The influences of external electric field on the MWCNTs dispersion had been evaluated by optical microscopy and SEM. The microscopy measurements showed that the distribution of the MWCNTs depended strongly on the properties of the applied electric field. Applying ac electric field to the liquid MWCNTs/thermosets nanocomposites during curing stage could redistribute the MWCNTs, arranges them in chain-like structures and orients fibrous inclusions parallel to the applied electric field. However, dc electric field could not do so. We also presented the relationships between the microstructures and various physical properties of nanocomposites. The resulting nanocomposites displayed the interesting dielectric properties, which were significantly dependence on their special microstructures of inclusions and host matrix.

The influence of dielectric permittivity and its distribution on water tree initiation and growth in XLPE cables

During the growth of water trees in the XLPE cable insulation, the distribution of the electric field is modified because of the local change of the dielectric properties of the material. A better knowledge of the comparative danger for the different kinds of water trees could lead to a way of improving the quality of cable insulation. Numerical analysis results show that the dielectric permittivity of a water tree itself and its distribution inside it are so influential to the electric field intensity both in the tip and on the surface of the water tree that they may play important roles both in water tree inception and growth and in the morphology of water treeing.