Dielectric breakdown strength of poly (ethylene-co-butyl acrylate) (EBA)nanocomposites filled with spherical alumina particles was studied as a function of particle coating, moisture content and the effective specific surface area. Two kinds of alumina nanoparticles were used: NA (25 nm in diameter) or ND (45 nm in diameter). The particles were either unmodified or surface-treated with aminopropyltriethoxy silane or octyltriethoxy silane. Two different relative humidities of air were used for conditioning the samples prior to testing: 0 % RH (dry case) and 86 % RH (samples were saturated with moisture). The dielectric breakdown strength measurements were performed with a DC ramp of 1.2 kV/s. Twenty samples were tested for each material formulation -ten of which were tested in dry conditions and ten were tested after conditioning in humid environment. Results were compared to the reference unfilled EBA samples. Applying Weibull analysis to the measured breakdown voltages indicated that the material filled with amino-coated ND particles exhibited the highest breakdown strength under dry conditions. As expected, conditioning materials in a humid environment had a negative impact on breakdown strength. This effect was more pronounced for nanocomposite materials, compared to the unfilled reference material.

Pre-breakdown currents through the poly (ethylene-co-butyl acrylate) (EBA) nanocomposites filled with spherical alumina particles were studied as a function of particle coating and moisture content. The nanocomposites were prepared from a mixture of EBA formulations (13 wt% butyl acrylate groups content) and alumina powder. Two kinds of alumina nanoparticles were used: NA (25 nm in diameter) and ND (45 nm in diameter). The particles were either unmodified or surface-treated with aminopropyltriethoxy silane or octyltriethoxy silane. Two different relative humidities of air were used for conditioning the samples prior to testing: 0 % RH (dry case) and 86 % RH (samples were saturated with moisture). The pre-breakdown current measurements were performed with a DC ramp of 1.2 kV/s. Twenty samples were tested for each material formulation -ten of which were tested in dry conditions and ten were tested after conditioning in humid environment. Results were compared to the reference unfilled EBA samples. The measured currents were analyzed under the assumption of space charge limited conduction. As expected, conditioning materials in humid environment caused an increase in pre-breakdown currents. This effect was more pronounced for nanocomposite materials, while the reference unfilled material was least affected.

Abstract-Dielectric breakdown strength of poly (ethylene-cobutyl acrylate) (EBA) nanocomposites filled with spherical alumina particles was studied as a function of particle coating and relative air humidity. The nanocomposites were prepared from a mixture of EBA formulations (13 wt% butyl acrylate groups content) and alumina powder. The particles were either unmodified or surface-treated with aminopropyltriethoxy silane or octyltriethoxy silane. The filler content studied was 6 wt%. Every material formulation was thoroughly examined under SEM in order to verify homogeneous particle dispersion. Two different relative humidities of air were used for conditioning the samples prior to testing: 0 and 86 % RH.The dielectric breakdown strength measurements were performed with a DC ramp of 1.2 kV/s. Ten samples were tested for each material formulation. Results were compared to the pristine EBA samples. Applying Weibull analysis to the measured data indicated a slight increase in breakdown strength for the dry nanocomposites filled with amino-treated particles as compared to the reference material in dry conditions. As expected, conditioning materials in humid environment had a negative impact on breakdown strength. This effect was more pronounced for nanocomposite materials, while the reference unfilled material was affected the least.

The purpose of this investigation was to interpret the bitumen-aggregate adhesion based on the dielectric spectroscopic response of individual material components utilizing their dielectric constants, refractive indices and average tangent of the dielectric loss angle (average loss tangent). Dielectric spectroscopy of bitumen binders at room temperature was performed in the frequency range of 0.01 to 1000 Hz. Dielectric spectroscopy is an experimental method for characterizing the dielectric permittivity of a material as a function of frequency. Adhesion data has been determined using the Rolling bottle method.The results show that the magnitude of the average tangent of the dielectric loss angle (average loss tangent) depends on bitumen type. The average loss tangent in the frequency range 0.01 to 1 Hz is introduced as a potential indicator for predicting polarizability and, thereby, adhesion potential of bitumen binders to quartz aggregates when using Portland cement. In order to obtain acceptable adhesion of 70/100 penetration grade bitumen binders and quartz aggregates when using Portland cement, it is suggested that the binder have an average tan  > 0.035 in the frequency range 0.01 to 1 Hz.

<p>The current through the poly(ethylene-co-butyl acrylate) with 13 wt% of butyl acrylate (EBA) filled with 6 wt% of alumina nanoparticles with an approximate diameter of 45 nm was studied under constant stress application. The particles were either unmodified or surface-treated with aminopropyltriethoxy silane. The current was measured either until breakdown or for maximum stress duration of 10 minutes. Two voltage levels were chosen: 15 and 22.5 kV, which were low enough not to cause a breakdown during the ramping of the voltage at the rate of 490 V/s to the constant voltage level at room temperature. Several ramping rates {100, 260, 500, 1007} V/s were also tested for the reference unfilled material to evaluate its influence on the time to breakdown. Several temperature levels were tried: 20 (room temperature), 40 and 50 ºC.<br />As expected, higher applied voltage caused higher current through the materials, while higher temperature caused earlier breakdown as well as higher current. At the lower voltage level most of the materials survived the testing. At the higher voltage level most of the samples of the unfilled reference material failed at the temperatures above room temperature while most of the nanocomposite samples survived the testing even at higher temperatures.</p>