Dielectric properties of epoxy/clay nanocomposites : effects of curing agent and clay dispersion method (Final draft (Post-print) version)

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

Effects of Resin/Filler Adhesion on the Thermal and Electrical Conductivity of Polyimide Nanocomposites

With an aim to develop a good coil winding insulation film, fillers of boehmite alumina in the shape of a roughly rectangular plate were added with ratios of 10 and 20 wt% to polyimide. The filler surface was untreated or treated with a methacrylic or an epoxy silane coupling agent. Such prepared polyimide nanocomposites were subjected to various tests to measure the tensile strength, elastic modulus, complex permittivity, and thermal conductivity. It was found that samples with fillers treated using the methacrylic silane coupling agent have the strongest adhesion at the filler/polyimide interfaces and the lowest dielectric loss factor at high temperatures. A positive relationship between the filler/polyimide adhesion and the thermal conductivity is also indicated. These findings are significant since they indicate that the adhesion status at the filler/polymer interface exerts a strong influence on the thermal and electrical conduction processes in the polymer

Penetration Routes of Oxygen and Moisture into the Insulation of FR-EPDM Cables for Nuclear Power Plants

The polymeric insulation used in nuclear power plants (NPPs) carries the risk of molecular breakage due to oxidation and hydrolysis in the event of an accident. With this in mind, tubular specimens of flame-retardant ethylene-propylene-diene rubber (FR-EPDM) insulation were obtained by taking conductors out of a cable harvested from an NPP. Similar tubular specimens were made from a newly manufactured cable and those aged artificially using a method called the “superposition of time-dependent data.” The inner and outer surfaces of each tubular specimen were subjected to various instrumental analyses to examine their oxidation, moisture uptake, and cross-linking. As a result, it has become clear that oxygen penetrates the cable through gaps between the twisted conductor strands. Meanwhile, water vapor diffuses more often through the sheath than through gaps between the conductor strands. Of the two methods used to simulate design-based accidents in NPPs, the one used to simulate the designed loss-of-coolant accident is more severe to FR-EPDM than the one used to simulate the designed severe accident. In addition, the validity of the method called the “superposition of time-dependent data,” which is used to give artificial aging treatments to cable samples, was confirmed. Measurements of spin-spin relaxation time and residual dipolar coupling using time-domain nuclear magnetic resonance were found suitable to use to obtain information on the cross-linking of FR-EPDM insulation