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Influence of Moisture on Dielectric Properties of Alumina-filled poly(ethylene-co-butyl acrylate) Nanocomposites
KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
2011 (English)Conference paper, Presentation (Refereed)
Abstract [en]

The dielectric properties of poly(ethylene-co-butyl acrylate) with 13 wt% of butyl acrylate (EBA) filled with alumina nanoparticles (average diameter of 25 nm) were studied as a function of particle coating, filler content (2, 6 and 12 wt %) and relative humidity of the environment used for sample conditioning. The particles were either unmodified or surface treated either with aminopropyltriethoxy silane or octyltriethoxy silane. The samples were conditioned at 24, 56 and 86 % RH in desiccators in room temperature using salt solutions until saturation was reached.

The complex permittivity was measured with an IDA200 dielectric spectroscopy analyzer at applied voltage of 200 Vpeak with frequencies varying between 1 mHz and up to 1 kHz at room temperature.

Dielectric losses measured for pure EBA in both dry and humid conditions show very small variations, while measurements performed on the nanocomposites exhibit distinct loss peaks that depend on the filler content, particle coating and humidity of the environment used for conditioning. The loss peak amplitude depends on the filler content, the shape is determined by the type of coating used and the loss peak frequency is defined by both humidity level and type of coating used.

Place, publisher, year, edition, pages
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
URN: urn:nbn:se:kth:diva-104478OAI: diva2:564912
NORD-IS 2011: Nordic Insulation Symposium

QC 20121116

Available from: 2012-11-16 Created: 2012-11-05 Last updated: 2013-02-07Bibliographically approved
In thesis
1. Electrical Insulating Properties of Poly(Ethylene-co-Butyl Acrylate) Filled with Alumina Nanoparticles
Open this publication in new window or tab >>Electrical Insulating Properties of Poly(Ethylene-co-Butyl Acrylate) Filled with Alumina Nanoparticles
2013 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

In this work the electrical insulating properties of the nanocomposite materials based on poly(ethylene-co-butyl acrylate) filled with alumina nanoparticles are studied. The dielectric properties chosen for the evaluation are the dielectric permittivity and loss as well as the breakdown strength and the pre-breakdown currents. The reason for choosing these particular properties is partly due to the importance of these for the general electrical applications and partly due to the uncertainties involved for these particular properties of the nanocomposite materials.

The importance of moisture absorption for the dielectric properties is outlined in this work. All measurements were performed in both dry conditions and after conditioning of the materials in humid environment until saturation. The data for moisture absorption was taken from the water absorption study performed at the Department of Fibre and Polymer Technology, KTH.

The dielectric spectroscopy in frequency domain was employed for measuring dielectric permittivity and loss. Havriliak-Negami approximation was used for characterization of the measurement data and at the same time ensuring the fulfillment of the Kramers-Kronig relations. Results from the dielectric spectroscopy study in dry conditions suggest that dielectric spectroscopy can be used for evaluating nanoparticle dispersion in the host matrix, based on correlation between the morphology data obtained from SEM investigation and the scatter in the dielectric loss. The dielectric spectroscopy study performed on the nanocomposites after conditioning in humid environment showed that absorbed moisture has a distinct impact on the dielectric loss. Especially pronounced is its’ influence on the frequency behavior, when the dielectric loss peaks are shifted towards higher frequencies with increased moisture content. The nanocomposite materials characterized by higher specific surface area generally exhibit higher dielectric losses. Surface functionalization of the nanoparticles does not seem to have much influence on the dielectric loss in dry conditions. After conditioning in humid environment, however, the surface modification was shown to have a significant impact. Temperature is another significant factor for the frequency behavior of the dielectric loss: it was found that the studied nanocomposites can be characterized by Arrhenius activation.

The breakdown strength and pre-breakdown currents study outlined the influence of moisture as well. The study indicated that surface treatment of the nanoparticles can enhance properties of the nanocomposite materials, namely aminopropyltriethoxy silane was an especially successful choice:

• The highest breakdown strength was determined by the study for NDA6 material formulation in dry conditions.

• After conditioning in humid environment the NDA6 material continued showing the best breakdown strength among the nanocomposite mate rials, as well as this value was close to the breakdown strength of the reference unfilled material.

This study confirms the existence of the optimal nanofiller content or rather optimal specific surface area of the dispersed nanoparticles in the host matrix. The latter is supported by the comparison between the nanocomposites based on nanoparticles with two different specific surface areas, which shows that the dielectric properties worsen, i.e. the dielectric losses increase and the influence of absorbed moisture on the breakdown strength becomes more pronounced, for nanomaterials with larger specific surface area. The pre-breakdown currents were found to follow space-charge limited conduction mechanism reasonably well. The following conduction regimes were identified: constant region (likely due to measurement difficulties at low field strengths), Ohm’s regime, trap-filled-limit regime and trapfree dielectric regime. The breakdown usually occurred either during the trap-filled-limit regime, when the current increased dramatically for the small change in electric field, or during the trapfree dielectric regime. The threshold values between different conduction regimes seem to correlate well with the oxidation induction times (OIT), which in turn depend on the total specific surface area. The pre-breakdown currents tend to be highest for the materials filled with the untreated nanoparticles. Increased absorbed moisture content causes higher pre-breakdown currents for the nanocomposite materials, while for the reference unfilled material the pre-breakdown currents do not show such tendency. Generally it can be said that the repeatability in the measured data is higher for the nanocomposite materials in comparison to the unfilled host material, as was demonstrated by both dielectric spectroscopy and breakdown studies.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2013. xii, 70 p.
TRITA-EE, ISSN 1653-5146 ; 2013:005
nanocomposites, poly(ethylene-co-butyl acrylate), EBA, alumina, dielectric permittivity, absorbed water, humidity, temperature, dielectric spectroscopy, breakdown strength, pre-breakdown current
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
urn:nbn:se:kth:diva-116862 (URN)978-91-7501-647-4 (ISBN)
Public defence
2013-02-27, F3, Lindstetsvägen 26, KTH, Stockholm, 10:00 (English)

QC 20130207

Available from: 2013-02-07 Created: 2013-01-28 Last updated: 2014-02-11Bibliographically approved

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