Miyuki Harada

Enhanced partial discharge resistance of epoxy/clay nanocomposite prepared by newly developed organic modification and solubilization methods

Frequency accelerated partial discharge (PD) aging of epoxy nanocomposite with 5 wt % additions of clay was investigated in comparison with that of epoxy without clay in terms of PD erosion depth. It was found that the change in the erosion depth is far smaller in specimens with clay than those without clay. The newly developed organic modification and solubilization methods give comparable PD resistance characteristics. The latter would be more resistant to PDs than the former, if specimens were prepared properly. It was clarified that nano-micro mixed composites were superior to the single nanocomposite. Nano segmentation with some interaction zone effect is proposed as a mechanism of improvement in PD resistance.

Dielectric properties of epoxy/clay nanocomposites - effects of curing agent and clay dispersion method

Effects of the differences in the curing agent and filler dispersion method on the dielectric properties were examined for epoxy/clay nanocomposites. Irrespective of the clay dispersion method, relative permittivity and electrical conductivity are higher in the samples cured with the amine. Moreover, negative heterocharge accumulates in the vicinity of the anode in the amine-cured samples, whereas positive homocharge accumulates in the acid anhydride-cured samples. From the results of UV photon absorption and PL measurement, the bandgap or the energy at which the photon absorption increases drastically is smaller in the amine-cured samples than in the acid anhydride-cured samples. Ion migration can occur easily in the amine-cured samples whose electrical conductivity and relative permittivity are higher than the acid anhydride-cured samples. The curing agent gives the strongest effect, while the existence of clay affects secondly and the filler dispersion method has the weakest effect.

Improving Epoxy-based Insulating Materials with Nano-fillers toward Practical Application

A primary concern in recent nanocomposite research is practical application. In this study, various kinds of epoxy-based nanocomposites were made and their properties evaluated to determine their applicability as insulating materials for heavy electric apparatuses. Experimental results demonstrated that nano-fillers enhance insulation breakdown properties in nanocomposites. Moreover, nano- and micro-filler combinations were adopted as an approach toward practical application of nanocomposite insulating materials. These nano- and micro- filler mixed composites had the same low thermal expansion as aluminum, and insulation breakdown properties superior to those of conventional insulating materials. Consequently, an aluminum conductor and a vacuum interrupter were molded by the nano- and micro-filler mixed composites for the first time in nanocomposite research.

Comparison of dielectric properties between epoxy composites with nanosized clay fillers modified by primary amine and tertiary amine

Epoxy-based nanocomposites (NCs) were prepared using clay modified by either primary amine or tertiary amine, and the effect of the difference in modifier on the thermal and dielectric properties of the NCs were discussed. The NC with clay fillers modified by the primary amine, 1C, shows a glass transition end temperature (Teg) at a temperature 20°C lower than the neat epoxy (N). This indicates that the resin of 1C is less crosslinked than that of N. On the other hand, the sample 3C, in which the clay was modified by the tertiary amine, shows a DSC spectrum close to that of N. Namely, 3C has a high crosslinking density similar to N. While the three samples show a relaxation peak in their dielectric loss spectra, the peak appears at high frequencies in 1C compared to N and 3C. Moreover, ionic conduction current flows more at high temperatures in 1C than in N or 3C. These facts are ascribable to the difference in their crosslinking densities.

Frequency Accelerated Partial Discharge Resistance of Epoxy/Clay Nanocomposite Prepared by Newly Developed Organic Modification and Solubilization Methods

Frequency accelerated partial discharge degradation of epoxy nanocomposite with 5 wt % additions of clay (layered silicate) was evaluated by a rod-to-plane electrode system, and investigated in comparison with that of epoxy without clay. Comparisons were made as to erosion depth using a laser surface profilometer. It was found that the change in the erosion depth is far smaller in specimens with clay than those without clay. It was also found that the solubilization method using acid anhydride curing agent seems to give PD resistance characteristics superior to the organic modification method using amine and acid anhydride curing agents and even to the solubilization method using amine curing agent.

Network chain orientation in the toughening process of the elastomer modified mesogenic epoxy resin

A biphenol-type epoxy resin, which has a mesogenic group in the backbone moiety, was modified with a reactive elastomer (CTBN). Toughness of the epoxy resin was significantly increased with the addition of the CTBN elastomer compared with that of the bisphenol-A type epoxy resin. It was clearly observed by SEM that a large plastic deformation occurred near the crack-tip in the biphenol-type epoxy resin modified with CTBN. The arrangement of the network chains in the plastic deformation region was quantitatively studied by polarized microscopic FT-IR technique, which was related to the toughening mechanism of the elastomer modified epoxy resin.

Nano- and micro-filler combination enabling practical use of nanocomposite insulating materials

Recent interests concerning nanocomposites are shifting emphasis from fundamental research to application-oriented research. In this study, nano- and micro-filler mixed composites were made and evaluated toward practical use of nanocomposite insulating materials. Some kinds of the nano-filler/micro-filler combinations such as nano-layered silicate/micro-silica, nano-silica/micro-silica and nano-titania/micro-silica were compared from viewpoints of volume resistivitiy, relative permittivity, thermal expansion and insulation breakdown properties. Comprehensive consideration based on experimental results determined a candidate nano- and micro-filler mixed composites to make trial models. An aluminum conductor and a vacuum interrupter were molded from the nano- and micro-filler mixed composites for the first time in nanocomposite research.

Effects of curing and filler dispersion methods on dielectric properties of epoxy nanocomposites

Effects of the differences in the curing agent and filler dispersion method on the dielectric properties were examined for epoxy/clay nanocomposites. Measurements of permittivity, conductivity, and space charge distribution suggest that the curing agent gives a strong effect and the presence of nanofillers affects secondly, while the filler dispersion method gives a weak effect.

Nano-clay and micro-silica mixed composites for insulating materials for environmentally-conscious switchgear

Nano-clay and micro-silica mixed composites were made for use as insulating materials for switchgear. Observation of nano-clay dispersion and measurements of insulation breakdown properties under a homogeneous electric field were conducted of these composites. Moreover, simulations were carried out to estimate the curing reaction and rheological behavior of the composite in an automatic pressure gelation system. Experimental results demonstrated that these composites have suitable material characteristics for practical use in switchgear.

Bonding Properties of Liquid Crystalline Epoxy Resins Having Different Phase Structures

ABSTRACT Liquid-crystalline epoxy resin systems, which have different phase structures (isotropic and nematic polydomain), were prepared. The bonding properties of their systems were investigated and related to their phase structure. As a result, the lap shear strength of the nematic system was lower than that of the isotropic system, although the nematic adhesive layer showed larger deformability than the isotropic one. The interfacial bonding properties of both the isotropic and nematic systems were investigated, and, thus, it was clarified that the low bonding strength of the nematic system was due to the low concentration of hydroxyl groups at the adhesive interface. The decrease in the concentration of hydroxyl groups was due to the restriction of the molecular motion derived from the ordered structure of the nematic system.