Dielectric breakdown strength and electrical conductivity of low density polyethylene octylnanosilica composite

Abstract

Abstract-One challenge in studying nanodielectric composites is to produce reliable, reproducible samples. A common strategy to suppress aggregation and make the particles more compatible with the polymer matrix is to modify the nanoparticle surface chemistry but, often, evaluation of the effectiveness of the chosen surface functionalization process can prove difficult. In this paper the emphasis is on feasible ways to monitor the production of silane coupled nanosilica low density polyethylene (LDPE) composites, using Fourier transform infrared spectroscopy (FTIR) and thermal gravimetric analysis (TGA). The AC-breakdown properties of the resulting composites is studied and the field dependency of the DCconductivity is measured and also calculated using a space charge limited conduction (SCLC) model together with densities of states obtained from ab initio calculations. For composites containing 13 wt% of nanosilica, breakdown strengths some 18 % higher than that of the unfilled LDPE were obtained. However, the results are not stable over time. This appears to be related to how extensively the composite is dried at elevated temperatures under vacuum.

Electrical conductivity of waxes as model systems for polyethylene: Role of water

“…Considering, now, Figure (c) and the Arrhenius plot shown in Figure (d), it is evident that the values obtained for LDPE are consistent with the available literature . We have taken steps to minimize the effects of the electrodes on the measured data by using a low enough applied field and, as a result, we observe that the conductivity of the LDPE is independent of the electrode material.…”

“…A number of preliminary tests were performed to ascertain the effects of applied field and, for as supplied C12 and PW, over the voltage range of 0.5–4 kV (maximum voltage due to the ratings of the high vacuum connectors) the measured conductivity was not observed to vary significantly with applied field (0.5–4 kV mm −1 ), in line with published reports . Application of the same field range to LDPE necessitated applied voltages between 100 and 800 V, which were too low to ensure measurable currents.…”

“…Accordingly, the same range of voltages was applied to these samples (equating to fields of 2.5–20 kV mm −1 ) and no significant variation of conductivity with applied field was noted. For consistency and to ensure the field applied to LDPE was not excessive, all tests were performed at 2 kV, resulting in applied fields of 2 kV mm −1 on C12‐x and PW and 10 kV mm −1 on LDPE. The final testing protocol was to test at a fixed field for 30 min (one measurement every 10 s) using a series of increasing temperatures between 25 and 65 °C in steps of 5 °C.…”

“…Theoretical models predict that above ~10 kV mm −1 the measured conductivity is strongly influenced by the applied field and this is borne out by experiment . For instance, electrical conductivity is reported to be independent of applied field in the range 2–15 kV/mm while, elsewhere, it was reported that the electrical conductivity is strongly dependent on applied field above 20 kV mm −1 . In the work reported here, we sought to work in a regime where the measurements are not unduly influenced by the applied electric field, which suggests that: (1), a constant applied field is used and (2) all work is performed with fields <20 kV mm −1 .…”

Electrical Conductivity and Moisture Uptake Studies of Low Density Polyethylene Octylnanosilica Composite

“…Silica nanopowder (Sigma-Aldrich) with a quoted particle size range from 10 to 20 nm was used as the nanofiller. Materials were prepared as outlined previously [13]. Composites were formulated by solvent blending: one set using the nanosilica as-supplied, while the other set containing octyl-silane functionalised nanosilica.…”