| 1. |
- Andersson, Johan, 1978, et al.
(författare)
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Deterioration of internal interfaces between silicone and epoxy resin
- 2006
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Ingår i: 2006 IEEE International Symposium on Electrical Insulation, ISEI 2006; Toronto; Canada; 11 June 2006 through 14 June 2006. - 0164-2006. - 9781424403332 ; 2007, s. 527-530
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Konferensbidrag (refereegranskat)abstract
- Interfacial defects, such as loss of adhesion together with environmental effects, such as moisture intrusion into the defect, can cause interfaces to become weak points in an insulation system. Silicone rubber moulded onto internal epoxy components is commonly used in high voltage outdoor composite insulation systems. For evaluating the interfacial properties of such a material combination, samples containing interfacial defects were prepared. In the samples a transparent silicone rubber was moulded onto a primer pre-treated epoxy substrate, while the spots to be characterized by a loss of adhesion were left unprimed. In this way air-filled defects between the two materials were created. The samples were thereafter exposed to an electric aging test with a needle-ring electrode arrangement attached to them. The electrode arrangement provided stress characterized by a high content of tangential field component along the interface and the field strength at the needle tip was kept at high enough level to maintain corona discharge activity. The ageing was performed under normal and humid conditions. The latter was performed to secure moisture ingress into the interface area through the silicone rubber. After the testing, the defect surfaces were analysed chemically to investigate reactions involved in the ageing processes. In addition, optical microscopy was used to evaluate a risk for void growth, which could potentially be caused by hydrolysis of the primer. The defect area was chemically evaluated by infrared spectroscopy.
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| 2. |
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| 3. |
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| 4. |
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| 5. |
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| 6. |
- Andersson, Johan, 1978, et al.
(författare)
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Properties of interfaces in silicone rubber
- 2007
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Ingår i: IEEE Transactions on Dielectrics and Electrical Insulation. - 1558-4135 .- 1070-9878. ; 14:1, s. 137 - 145
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Tidskriftsartikel (refereegranskat)
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| 7. |
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| 8. |
- Andersson, Johan, 1978, et al.
(författare)
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Tracking behaviour in the presence of conductive interfacial defects
- 2009
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Ingår i: Annual Report - Conference on Electrical Insulation and Dielectric Phenomena, CEIDP. - 0084-9162. - 9781424445592 ; , s. 230-233
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Konferensbidrag (refereegranskat)abstract
- The study presented in this paper aim at extending the knowledge on how interfacial defects in composite insulation systems may affect surface tracking under contaminated conditions. Model samples mimicking an interfacial conducting defect were made of high temperature vulcanised silicone rubber moulded on epoxy substrate with a circular metallic foil inserted at the interface. They were tested for the tracking resistance by means of the inclined plane test procedure. The samples with defects exhibited shorter time to track compared to reference samples without defects. In addition the tracking was more severe on the defected samples. Electric field simulation performed in parallel revealed that presence of surface contamination increases the distortion of electric field around the defect and thus explain both the effects of more severe damage of material surface and lower time to tracking experienced in this study.
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| 9. |
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| 10. |
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| 11. |
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| 12. |
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| 13. |
- Atari Jabarzadeh, Sevil, et al.
(författare)
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Image Analysis Determination of the Influence of Surface Structure of Silicone Rubbers on Biofouling
- 2015
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Ingår i: International Journal of Polymer Science. - : Hindawi Limited. - 1687-9422 .- 1687-9430.
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Tidskriftsartikel (refereegranskat)abstract
- This study focuses on how the texture of the silicone rubber material affects the distribution of microbial growth on the surface of materials used for high voltage insulation. The analysis of surface wetting properties showed that the textured surfaces provide higher receding contact angles and therefore lower contact angle hysteresis. The textured surfaces decrease the risk for dry band formation and thus preserve the electrical properties of the material due to a more homogeneous distribution of water on the surface, which, however, promotes the formation of more extensive biofilms. The samples were inoculated with fungal suspension and incubated in a microenvironment chamber simulating authentic conditions in the field. The extent and distribution of microbial growth on the textured and plane surface samples representing the different parts of the insulator housing that is shank and shed were determined by visual inspection and image analysis methods. The results showed that the microbial growth was evenly distributed on the surface of the textured samples but restricted to limited areas on the plane samples. More intensive microbial growth was determined on the textured samples representing sheds. It would therefore be preferable to use the textured surface silicone rubber for the shank of the insulator.
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| 14. |
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| 15. |
- Bjurstrom, Anton, et al.
(författare)
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A Review of Polyolefin-Insulation Materials in High Voltage Transmission; From Electronic Structures to Final Products
- 2024
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Ingår i: Advanced Materials. - : Wiley. - 0935-9648 .- 1521-4095.
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Forskningsöversikt (refereegranskat)abstract
- This review focuses on the use of polyolefins in high-voltage direct-current (HVDC) cables and capacitors. A short description of the latest evolution and current use of HVDC cables and capacitors is first provided, followed by the basics of electric insulation and capacitor functions. Methods to determine dielectric properties are described, including charge transport, space charges, resistivity, dielectric loss, and breakdown strength. The semicrystalline structure of polyethylene and isotactic polypropylene is described, and the way it relates to the dielectric properties is discussed. A significant part of the review is devoted to describing the state of art of the modeling and prediction of electric or dielectric properties of polyolefins with consideration of both atomistic and continuum approaches. Furthermore, the effects of the purity of the materials and the presence of nanoparticles are presented, and the review ends with the sustainability aspects of these materials. In summary, the effective use of modeling in combination with experimental work is described as an important route toward understanding and designing the next generations of materials for electrical insulation in high-voltage transmission.
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| 16. |
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| 17. |
- Cobo Sanchez, Carmen
(författare)
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Inorganic and organic polymer-grafted nanoparticles : their nanocomposites and characterization
- 2018
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Nanocomposites (NCs) have been widely studied in the past decades due to the promising properties that nanoparticles (NPs) offer to a polymer matrix, such as increased thermal stability and non-linear electrical resistivity. It has also been shown that the interphase between the two components is the key to achieving the desired improvements. In addition, polymer matrices are often hydrophobic while NPs are generally hydrophilic, leading to NP aggregation. To overcome these challenges, NPs can be surface-modified by adding specific molecules and polymers. In the present work, a range of organic and inorganic NPs have been surface-modified with polymers synthesized by atom transfer radical polymerization (ATRP) or surface-initiated ATRP (SI-ATRP).Cellulose nanofibrils (CNF) and cellulose nanocrystals (CNC) are highly crystalline NPs that can potentially increase the Young’s modulus of the NC. In this study, a matrix-free NC was prepared by physisorption of a block-copolymer containing a positively charged (quaternized poly(2-(dimethylamino)ethyl methacrylate), qPDMAEMA) and a thermo-responsive (poly di(ethylene glycol) methyl ether methacrylate, PDEGMA). The modified CNF exhibited a thermo-responsive, reversible behavior. CNCs were polymer-modified either via SI-ATRP or physisorbed with poly (butyl methacrylate) (PBMA) to improve the dispersion and interphase between them and a polycaprolactone (PCL) matrix during extrusion. The mechanical properties of the NCs containing CNC modified via SI-ATRP were superior to the reference and unmodified materials, even at a high relative humidity.Reduced graphene oxide (rGO) and aluminum oxide (Al2O3) are interesting for electrical and electronic applications. However, the matrices used for these applications, such as poly(ethylene-co-butyl acrylate) (EBA) and low density polyethylene (LDPE) are mainly hydrophobic, while the NPs are hydrophilic. rGO was modified via SI-ATRP using different chain lengths of PBMA and subsequently mixed with an EBA matrix. Al2O3 was modified with two lengths of poly(lauryl methacrylate) (PLMA), and added to LDPE prior to extrusion. Agglomeration and dispersion of the NCs were dependent on the lengths and miscibilities of the grafted polymers and the matrices. rGO-EBA NCs showed non-linear direct current (DC) resistivity upon modification, as the NP dispersion improved with increasing PBMA length. Al2O3-LDPE systems improved the mechanical properties of the NCs when low amounts of NPs (0.5 to 1 wt%) were added, while decreasing power dissipation on the material.Finally, PLMA-grafted NPs with high polymer quantities and two grafting densities in Al2O3 and silicon oxide (SiO2) nanoparticles were synthesized by de-attaching some of the silane groups from the surfaces, either by hydrolysis or by a mild tetrabutylammonium fluoride (TBAF) cleavage. These compounds were characterized and compared to the bulk PLMA, and were found to have very interesting thermal properties.
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| 18. |
- Greijer, Helena, et al.
(författare)
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Tuneable conductivity at extreme electric fields in ZnO tetrapod-silicone composites for high-voltage power cable insulation
- 2022
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Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322 .- 2045-2322. ; 12:1, s. 6035-
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Tidskriftsartikel (refereegranskat)abstract
- Resistive Field Grading Materials (RFGM) are used in critical regions in the electrical insulation system of high-voltage direct-current cable systems. Here, we describe a novel type of RFGM, based on a percolated network of zinc oxide (ZnO) tetrapods in a rubber matrix. The electrical conductivity of the composite increases by a factor of 108 for electric fields > 1 kV mm-1, as a result of the highly anisotropic shape of the tetrapods and their significant bandgap (3.37 eV). We demonstrate that charge transport at fields < 1 kV mm-1 is dominated by thermally activated hopping of charge carriers across spatially, as well as energetically, localized states at the ZnO-polymer interface. At higher electric fields (> 1 kV mm-1) band transport in the semiconductive tetrapods triggers a large increase in conductivity. These geometrically enhanced ZnO semiconductors outperform standard additives such as SiC particles and ZnO micro varistors, providing a new class of additives to achieve variable conductivity in high-voltage cable system applications.
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| 19. |
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| 20. |
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| 21. |
- Hillborg, Henrik
(författare)
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Loss and recovery of hydrophobicity of polydimethylsiloxane after exposure to electrical discharges
- 2001
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Silicone rubber based on polydimethylsiloxane is used ashigh voltage outdoor insulation, due to its ability to preservethe hydrophobic surface properties during service and evenregain hydrophobicity after exposure to electrical discharges.The underlying processes for the hydrophobic recovery arediffusion of low molar mass siloxanes from the bulk to thesurface and reorientation by conformational changes ofmolecules in the surface region. Only little is known of whichfactors are responsible for the long-term stability of thishydrophobic recovery. It is therefore important to increase theknowledge about the fundamental mechanisms for the loss andrecovery of hydrophobicity of silicone rubbers, exposed toelectrical discharges. Addition-cured polydimethylsiloxanenetworks, with known crosslink densities, were exposed tocorona discharges and air/oxygen-plasma and the loss andrecovery of hydrophobicity was characterised by contact anglemeasurements. The degree of surface oxidation increased withincreasing exposure time with a limiting depth of 100- 150 nm,as assessed by neutron reflectivity measurements. The oxidationrate increased with increasing crosslink density of the polymernetwork, according to X-ray photoelectron spectroscopy. Withinthe oxidised layer, a brittle, silica-like layer was graduallydeveloped with increasing exposure time. The hydrophobicrecovery following the corona or air/oxygen- plasma exposuresoccurred at a slow pace by diffusion of cyclic oligomericdimethylsiloxanes through the micro-porous but uncrackedsilica-like surface layer or at a much higher pace by transportof the oligomers through cracks in the silica-like layer. Theoligomers were present in the bulk, but additional amounts wereformed during exposure to corona discharges. High-temperaturevulcanised silicone rubber specimens were aged in a coastalenvironment under high electrical stress levels (100 V/mm). Thechanges in surface structure and properties were compared tothe data obtained from specimens exposed to coronadischarges/plasma. The dominating degradation mechanism wasthermal depolymerisation, initiated by hot discharges. Thisresulted in the formation of mobile siloxanes, of which the lowmolar mass fraction consisted of cyclic oligomericdimethylsiloxanes. Oxidative crosslinking resulting insilica-like surface layers was not observed during theseconditions.Keywords:silicone rubber, polydimethylsiloxane,hydrophobicity, corona, air-plasma, oxygen-plasma, surfacecharacterisation, degradation products, crosslink density.
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| 22. |
- Hjortstam, Olof, et al.
(författare)
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Humidity and Temperature Dependences of Resistivities of Various Formulations of Silicone Rubber for HVDC Applications
- 2023
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Ingår i: Annual Report - Conference on Electrical Insulation and Dielectric Phenomena, CEIDP. - 0084-9162.
-
Konferensbidrag (refereegranskat)abstract
- Silicone rubber (SiR) is extensively used as housing material for outdoor HV insulators thanks to its excellent long-term stability combined with high hydrophobicity. For HVDC applications, the resistivity of SiR is a key design parameter and knowledge about its changes under various conditions is crucial. In the present work, the influences of relative humidity in air and temperature on the resistivities of five different HTV SiR formulations are studied. The resistivity is calculated from the results of the leakage current measurements conducted on 1.3 mm thick SiR samples under DC voltage. It is found that both the relative humidity and temperature have a significant impact on the resistivity of the studied materials the magnitudes of which varied over several orders. Furthermore, it is observed that SiR formulations with similar composition may have significantly different resistivities under the same temperature and humidity. Accordingly, it is concluded that the resistive properties of each SiR formulation used for HVDC applications need to be carefully evaluated to secure a reliable design and operation.
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| 23. |
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| 24. |
- Jäverberg, Nadejda, 1977-, et al.
(författare)
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Dielectric Properties of Alumina-filled Poly (ethylene-co-butyl acrylate) Nanocomposites Part II - Wet Studies
- 2012
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Ingår i: IEEE transactions on dielectrics and electrical insulation. - 1070-9878 .- 1558-4135. ; 19:2, s. 391-399
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Tidskriftsartikel (refereegranskat)abstract
- The influence of moisture on the dielectric properties of different types of poly (ethylene-co-butyl acrylate) filled with alumina nanoparticles was systematically investigated by varying the type of aluminum oxide, particle surface treatment and filler content (2, 6 and 12 wt%). The nanoparticles were either unmodified or surface-treated with either aminopropyl triethoxysilane or octyltriethoxy silane. The complex permittivity was measured with an IDA200 dielectric spectroscopy analyzer at applied voltage of 200 V-peak with frequencies varying between 1 mHz and 1 kHz. The measurements were performed at 25 degrees C and relative air humidities of 24, 54 and 86 %. In order to expand the frequency range the HP 4284A precision LCR meter was used for measuring sample impedance at the frequency range of 100 Hz to 1 MHz. From the frequency dependence of dielectric losses it can be seen that absorbed water plays a significant role in determining the dielectric properties of the nanocomposites. The magnitude of tan delta seems to be determined primarily by the particle size and filler content, while the peak frequency is mostly influenced by the amount of absorbed water and the type of particle coating.
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| 25. |
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| 26. |
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| 27. |
- Karlsson, Mattias, 1988-, et al.
(författare)
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DC Conductivity Measurements of LDPE: Influence of Specimen Preparation Method and Polymer Morphology
- 2017
-
Ingår i: Proceedings of the biannual nordic symposium on materials, components and diagnostics. - : Norwegian University of Science and Technology (NTNU) Library.
-
Konferensbidrag (refereegranskat)abstract
- DC conductivity measurements are important for gaining fundamental understanding of conduction mechanisms of insulation materials, as well as in the development of HVDC power system components, such as extruded cable systems. In this study, the influence of sample processing on the morphology and DC conductivity of low-density polyethylene (LDPE) has been studied. Direct compression moulding of LDPE pellets is commonly used in research laboratories for obtaining plaque samples, whereas extrusion is an additional commonly used technique for dispersion of particles in nanocomposites prior to the compression moulding process. In this study LDPE plaques have been obtained by either compression moulding directly from pellets, or by extrusion followed by compression moulding. The morphology obtained in the first case consisted of banded spherulites, whereas the latter method yielded a morphology of small axialites. The difference in sample processing had also an impact on the DC conductivity. The DC conductivity at 22 °C and 3.3 kV mm-1 was of the order of 4x10–18 S m-1 for the plaques obtained by extrusion and compression moulding whereas the plaques obtained by direct compression moulding exhibited a conductivity of 1x10–16 S m-1 . In addition, the reproducibility of the performed DC conductivity measurements was also verified in a round robin test performed between the Royal Institute of Technology and Chalmers Technical University.
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| 28. |
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| 29. |
- Karlsson, Mattias E., et al.
(författare)
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Lamellae-controlled electrical properties of polyethylene - morphology, oxidation and effects of antioxidant on the DC conductivity
- 2020
-
Ingår i: RSC Advances. - : Royal Society of Chemistry. - 2046-2069. ; 10:8, s. 4698-4709
-
Tidskriftsartikel (refereegranskat)abstract
- Destruction of the spherulite structure in low-density polyethylene (LDPE) is shown to result in a more insulating material at low temperatures, while the reverse effect is observed at high temperatures. On average, the change in morphology reduced the conductivity by a factor of 4, but this morphology-related decrease in conductivity was relatively small compared with the conductivity drop of more than 2 decades that was observed after slight oxidation of the LDPE (at 25 degrees C and 30 kV mm(-1)). The conductivity of LDPE was measured at different temperatures (25-60 degrees C) and at different electrical field strengths (3.3-30 kV mm(-1)) for multiple samples with a total crystalline content of 51 wt%. The transformation from a 5 mu m coherent structure of spherulites in the LDPE to an evenly dispersed random lamellar phase (with retained crystallinity) was achieved by extrusion melt processing. The addition of 50 ppm commercial phenolic antioxidant to the LDPE matrix (e.g. for the long-term use of polyethylene in high voltage direct current (HVDC) cables) gave a conductivity ca. 3 times higher than that of the same material without antioxidants at 60 degrees C (the operating temperature for the cables). For larger amounts of antioxidant up to 1000 ppm, the DC conductivity remained stable at ca. 1 x 10(-14) S m(-1). Finite element modeling (FEM) simulations were carried out to model the phenomena observed, and the results suggested that the higher conductivity of the spherulite-containing LDPE stems from the displacement and increased presence of polymeric irregularities (formed during crystallization) in the border regions of the spherulite structures.
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| 30. |
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| 31. |
- Li, Wangshu, et al.
(författare)
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Influence of Process Conditions and Particle Dispersion on the AC Breakdown Strength of Polyethylene-aluminium Oxide Nanocomposites
- 2015
-
Ingår i: IEEE transactions on dielectrics and electrical insulation. - : IEEE. - 1070-9878 .- 1558-4135. ; 22:6, s. 3536-3542
-
Tidskriftsartikel (refereegranskat)abstract
- The voltage level in power transmission systems is increasing in order to transmit energy more efficiently and this requires efficient insulating materials. The dielectric breakdown strength of polymers used as electrical insulation can be increased by the addition of inorganic nanoparticles. A uniform particle dispersion is however important; large agglomerates may have a negative effect on the breakdown strength. The effects of temperature, screw rotation velocity and processing time in a micro-extruder on the dispersion of neat aluminium oxide nanoparticles in LDPE were studied, and it was possible to obtain an essentially agglomerate-free particle dispersion at optimum extrusion conditions. Smaller particle agglomerates (< 3 mu m) had no significantly negative impact on the AC dielectric breakdown strength. Composites with higher filler fractions (>= 3 wt.%) containing larger particle agglomerates (>15 mu m in diameter) showed a significant reduction in the breakdown strength compared to the neat polymer.
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| 32. |
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| 33. |
- Li, Wangshu, et al.
(författare)
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Structure and Electrical Properties of Silicone Rubber Filled with Thermally Reduced Graphene Oxide
- 2016
-
Ingår i: IEEE transactions on dielectrics and electrical insulation. - : IEEE. - 1070-9878 .- 1558-4135. ; 23:2, s. 1156-1163
-
Tidskriftsartikel (refereegranskat)abstract
- Graphene oxide (GO) was heat treated at different temperatures between 120 and 220 degrees C and the structural changes were assessed by thermogravimetry, infrared spectroscopy, X-ray photoelectron spectroscopy and scanning electron microscopy (SEM). The resulting reduced graphene oxide (rGO) fillers showed markedly lower oxygen contents (primarily by reduction of epoxide and hydroxyl groups) than GO. SEM of silicone rubber composites containing 3 wt.% rGO or GO filler showed that the nanoparticles were uniformly distributed in the polymer. The rGO-filled composites exhibited electric field-dependent resistivity; the resistivity decreased from 10(14) to 10(11) ohm m as the electric field was increased from 0.2 to 6 kV (mm)(-1). The composites exhibited an increased resistivity after being exposed to a combined thermal cycling and electrical field. An increase in the resistivity of samples aged at 120 degrees C for more than 17 h was observed; the resistivity-electric field behavior and the dielectric constant of the aged composite resembled that of GO-filled composite. The composites exhibited dielectric constant values between 4.0 and 5.2 and a low tan delta (<= 0.015) at frequencies between 10(-2) and 10(4) Hz. The results suggest that the resistivity of the composites can be tuned by adjusting the degree of reduction of GO. The low rGO-filler content that was required to achieve this adequate property profile is attractive, which makes these composites potentially useful as electric field-grading material in HVDC cable accessories. However, this requires that the long-term stability problem can be sensible addressed.
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| 34. |
- Ma, Bin, 1981, et al.
(författare)
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AC and DC Corona/Ozone-Induced Ageing of HTV Silicone Rubber
- 2011
-
Ingår i: IEEE Transactions on Dielectrics and Electrical Insulation. - 1558-4135 .- 1070-9878. ; 18:6, s. 1984-1994
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Tidskriftsartikel (refereegranskat)abstract
- On the way of making efforts to standardize the selection of polymeric materials for high voltage outdoor environments, the resistance to corona and ozone has been recognized as one among twelve parameters to be evaluated within the CIGRÉ Working Group D1.14 [1]. Our previous related work reported on the evaluation of the resistance of five commercially available polymeric materials to ac corona-ozone treatment, according to the test procedure recommended by this Working Group. With the same test arrangement in use, this report focuses on comparing the influences of ac and dc corona-ozone exposures on high temperature vulcanized (HTV) silicone rubbers. For this purpose, two types of HTV materials were used, each one characterized by different resistivity levels and tensile strength. For defining the treatment conditions, the ac and dc coronas were characterized by measuring the associated discharge current as well as the power released from the electrode. The intensity of ac corona discharge was found to be higher than that of dc corona, the latter being controlled by electrostatic charging of the treated polymeric surfaces, which also resulted in significant differences of the resulting ozone concentration. Experimental investigations after the treatments concentrated on evaluating dielectric properties (e.g. surface and volume resistivities, dielectric response (DR)), mechanical properties (e.g. tensile strength and elongation at break), as well as chemical and structural analyses (e.g. X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR)). Results obtained from the measurements of dielectric properties indicated a strong sensitivity of surface resistivity to the treatments, though the impact of the dc corona remained less pronounced. On the other hand, the dielectric response and volume resistivity did not exhibit a high susceptibility to the exposure. No substantial differences were also found among the ac and dc corona treated samples as regards the mechanical properties. The XPS and FTIR analyses revealed proofs of surface oxidation for the samples treated by ac corona, while the samples treated by dc corona showed much less tendency for oxidation.
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| 35. |
- Ma, Bin, 1981, et al.
(författare)
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AC or DC Corona Ageing of HTV Silicone Rubber
- 2011
-
Ingår i: 2011 Nordic Insulation Symposium. - 9789521525629 ; , s. 37-40
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Konferensbidrag (refereegranskat)abstract
- The test rig proposed by CIGRE WG D 1.14 [1] for evaluating the resistance to corona and ozone of polymeric materials for high voltage outdoor applications makes use of a multi-needle electrode as an artificial corona source for treatment of material samples. The electrode can be energized from either AC or DC high voltage sources. Two types of commercially available high temperature vulcanized silicone rubbers (HTV) were selected for the study described in this paper. Experimental investigations were carried out to evaluate dielectric properties (e.g. surface and bulk resistivities, dielectric response), mechanical properties (e.g. tensile strength, elongation at break), and chemical structural changes (analyzed by X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR)) of material samples after exposure to ac or dc corona discharges. In addition, the loss and recovery of hydrophobicity of the materials were characterized by contact angle measurements.
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| 36. |
- Ma, Bin, 1981, et al.
(författare)
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Performance of HTV Silicone Rubber under Artificial AC and DC Corona/Ozone Test
- 2011
-
Ingår i: the Proceedings of 17th International Symposium on High Voltage Engineering. - 9783800733644 ; , s. E-036
-
Konferensbidrag (refereegranskat)abstract
- This paper concentrates on presenting the changes of properties of high temperature vulcanized (HTV) silicone rubbers when exposed to 100 hours long corona/ozone treatment in a multi-needle electrode system, as suggested by CIGRE Working Group D1.14 and in detail reported in our former publication. The material samples were treated by either AC or DC corona sources. The HTV samples used in this test contained one type of a commercial HTV silicone rubber (including both post- and unpostcured specimens) based on polydimethylsiloxane (PDMS) as well as model HTV silicone rubbers containing increased amount of methylvinylsiloxane (MVS) and filled with aluminum-trihydrate (ATH) of different proportions. Material characterization methods involving volume and surface resistivity measurements, dielectric response (DR) measurement, as well as tensile tests were adopted to trace the performance changes of the samples induced by the AC or DC corona treatments.
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| 37. |
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| 38. |
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| 39. |
- Mendoza Alvarez, Ana Isabel, et al.
(författare)
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Super-hydrophobic zinc oxide/silicone rubber nanocomposite surfaces
- 2019
-
Ingår i: Surfaces and Interfaces. - : Elsevier. - 2468-0230. ; 14, s. 146-157
-
Tidskriftsartikel (refereegranskat)abstract
- This study presents comparative assessments on hydrophilic and hydrophobic ZnO nanoparticles and their deposition methods on the surface hydrophobicity of silicone rubber (PDMS) and glass substrates. The influence on the surface hydrophobicity and wettability of all the variables regarding the deposition methodologies and the interaction of the nanoparticles with the substrates were within the scope of this study. The different surfaces created by spraying, dipping and drop-pipetting deposition methods were assessed by static contact angle measurements and contact angle hysteresis from advancing and receding angles, as well as by the calculation of the sliding angle and the surface energy parameters. An accurate methodology to determine the contact angle hysteresis was proposed to obtain repetitive and comparative results on all surfaces. All the measurements have been correlated with the morphology and topography of the different surfaces analysed by FE-SE microscopy. The spray-deposition of hydrophobic ZnO nanoparticles on PDMS resulted in super-hydrophobic surfaces, exhibiting hierarchical structures with micro-and nanometer features which, together with the low surface energy, promotes the Cassie-Baxter wetting behavior. This study provides the fundamental approach to select critically the most promising combination in terms of materials and deposition techniques to create silicone-based super-hydrophobic surfaces with potential to be applied in high voltage outdoor insulation applications.
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| 40. |
- Nawaz, Sohail, et al.
(författare)
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Antioxidant activity in aluminium oxide - Poly(ethylene-co-butyl acrylate) nanocomposites
- 2012
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Ingår i: Polymer degradation and stability. - : Elsevier BV. - 0141-3910 .- 1873-2321. ; 97:6, s. 1017-1025
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Tidskriftsartikel (refereegranskat)abstract
- The antioxidant activity of Irganox 1010 (0.2 wt%) in aluminium oxide (2-12 wt%) - poly(ethylene-co-butyl acrylate) nanocomposites was studied. The aluminium oxide nanoparticles were in three different forms: uncoated and coated with either octyltriethoxysilane or aminopropyltriethoxysilane. The activity of the stabilizer in the nanocomposites was assessed by determining the oxidation induction time (OIT) using DSC. Composites with untreated aluminium oxide nanoparticles showed a much shorter OIT than the pristine polymer with the same overall antioxidant concentration indicating adsorption of the antioxidant onto the nanoparticle surfaces. The adsorption of antioxidant onto both uncoated and coated nanoparticles was confirmed by X-ray photoelectron spectroscopy. Composites containing coated nanoparticle fillers showed a significantly smaller depression of the OIT, indicating that the replacement of hydroxyl groups with organic silane tails decreased the concentration of available adsorption sites on the particle surfaces. Composites with a filler coated with a silane having terminal aliphatic amine groups showed an increased OIT with respect to that of the pristine polymer suggesting a synergistic on the stability effect between the antioxidant and the amine groups. The long-term activity of the stabilizer was assessed by measuring the OIT on samples after ageing in air at 90°C for 720 h. The decrease in OIT with increasing ageing time of the nanocomposites was slower than for the unfilled polymer. A possible interpretation of these data is that the antioxidant was slowly released from the adsorption sites on extended ageing.
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| 41. |
- Sanchez, Carmen, et al.
(författare)
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Characterization of Reduced and Surface-Modified Graphene Oxide in Poly(Ethylene-co-Butyl Acrylate) Composites for Electrical Applications
- 2019
-
Ingår i: Polymers. - : MDPI. - 2073-4360. ; 11:4
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Tidskriftsartikel (refereegranskat)abstract
- Promising electrical field grading materials (FGMs) for high-voltage direct-current (HVDC) applications have been designed by dispersing reduced graphene oxide (rGO) grafted with relatively short chains of poly (n-butyl methacrylate) (PBMA) in a poly(ethylene-co-butyl acrylate) (EBA) matrix. All rGO-PBMA composites with a filler fraction above 3 vol.% exhibited a distinct non-linear resistivity with increasing electric field; and it was confirmed that the resistivity could be tailored by changing the PBMA graft length or the rGO filler fraction. A combined image analysis- and Monte-Carlo simulation strategy revealed that the addition of PBMA grafts improved the enthalpic solubility of rGO in EBA; resulting in improved particle dispersion and more controlled flake-to-flake distances. The addition of rGO and rGO-PBMAs increased the modulus of the materials up to 200% and the strain did not vary significantly as compared to that of the reference matrix for the rGO-PBMA-2 vol.% composites; indicating that the interphase between the rGO and EBA was subsequently improved. The new composites have comparable electrical properties as today's commercial FGMs; but are lighter and less brittle due to a lower filler fraction of semi-conductive particles (3 vol.% instead of 30-40 vol.%).
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| 42. |
- Wåhlander, Martin, 1982-
(författare)
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Controlled Polymer Grafting from Nanoparticles for the Design of Dielectric Nanocomposites
- 2017
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The interest for polymeric nanocomposites has rapidly grown during the last decades, fuelled by the great potential and superior properties of nanoparticles (NPs). The production volumes of commercial NPs have increased exponentially during the last ten years, and the quality has been significantly improved. The aim of this study was to design polymer grafted commercially available metal-oxide NPs, and graphene oxide (GO), to develop isotropic (homogeneous) and anisotropic (heterogeneous) polymer nanocomposites for dielectric applications. The motivation was to formulate functional insulation materials for compact components in future power-grid systems using high-voltage direct-current (HVDC) or high-voltage alternating-current (HVAC), and to fabricate responsive sensor materials for monitoring e.g. temperature and voltage fluctuations in so called “Smart Grids”.Aluminium oxide (Al2O3), zinc oxide (ZnO) and reduced GO (rGO) NPs were modified with sparse polymer grafts via a controlled “covalent route” and were mixed with silicone (PDMS) or polyethylene matrices (EBA and LDPE) commonly used in HV-cable systems. The graft length and the graft-to-matrix compatibility were tailored to obtain nanocomposites with various self-assembled NP-morphologies, including well-dispersed, connected and phase-separated structures. The graft length was used to adjust the inter-particle distance of nanocomposites with continuous morphologies or connected (percolated) NPs. It was found that nanocomposites with percolated NPs and short inter-particle distances exhibited 10-100 times higher conductivity than the unfilled (neat) polymer, or displayed a rapid non-linear increase in conductivity (~1 million times) with increasingelectric field, while well-dispersed NPs with long inter-particle distances exhibited 10-100 times lower conductivity (i.e. higher resistivity) as an effect of their trapping of charge carriers. These tunable and functional properties are desirable for HV-insulation, field-grading applications, and flexible electronics.In addition it was shown that GO modified with dense polymer grafts via a “physisorption route” formed suspensions with liquid crystals, or matrix-free GO-composites with well-dispersed GO in isotropic or nematic states. These materials were reinforced by the GO, and exhibited elevated glass transition temperatures and a rapid thermo-responsive shape-memory effect, and are thus proposed to have a great potential as sensor materials and responsive separation membranes.
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| 43. |
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| 44. |
- Wåhlander, Martin, et al.
(författare)
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Polymer-grafted Al2O3-nanoparticles for controlled dispersion in poly(ethylene-co-butyl acrylate) nanocomposites
- 2014
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Ingår i: Polymer. - : Elsevier BV. - 0032-3861 .- 1873-2291. ; 55:9, s. 2125-2138
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Tidskriftsartikel (refereegranskat)abstract
- We report a model system to control the dispersion and inter-particle distance of polymer-grafted Al2O3-nanoparticles in high molecular weight poly(ethylene-co-butyl acrylate). The proposed methods make it possible to extend the use of surface initiated atom transfer radical polymerization (SI-ATRP) in combination with more commercial grades of silanes and particles, showing the versatility of this polymerization process. The nanoparticles were surface-modified by an amine-terminated silane, forming multilayered silane coatings to which moieties capable of initiating ATRP were attached. Subsequently, "short" (DP: 117) and "long" (DP: 265) chains of poly(n-butyl acrylate) were grafted from the particles via SI-ATRP. The graft density was found to be in accordance with the density of the accessible amine groups and could therefore be assessed directly after the initial silanization step using UV-Vis spectrometry. From AFM micrographs, the grafted nanoparticles were found to be well-dispersed in the matrix. This observation was corroborated by a novel simulation method capable of transforming the inter-particle distances from 2D to 3D, for the closest and more distant neighbors. Further, we calculated the deviation ratios and concluded that the dispersions were homogeneous and that the inter-particle distances were related to the graft length. The homogeneous dispersions were explained by dominating enthalpic contributions of the polymer grafts to the nanocomposites in combination with shielding of the nanoparticle core-core attraction by the silane multilayer (similar to bimodal systems).
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| 45. |
- Wåhlander, Martin, 1982-, et al.
(författare)
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Reduced and Surface-Modified Graphene Oxide with Nonlinear Resistivity
- 2017
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Ingår i: Macromolecular rapid communications. - : John Wiley & Sons. - 1022-1336 .- 1521-3927. ; 38:16
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Tidskriftsartikel (refereegranskat)abstract
- Field-grading materials (FGMs) are used to reduce the probability for electrical breakdowns in critical regions of electrical components and are therefore of great importance. Usually, FGMs are heavily filled (40 vol.%) with semi-conducting or conducting particles. Here, polymer-grafted reduced graphene oxide (rGO) is used as a filler to accomplish percolated networks at very low filling ratios (<2 vol.%) in a semi-crystalline polymer matrix: poly(ethylene-co-butyl acrylate) (EBA). Various simulation models are used to predict the percolation threshold and the flake-to-flake distances, to complement the experimental results. A substantial increase in thermal stability of rGO is observed after surface modification, either by silanization or subsequent polymerizations. The non-linear DC resistivity of neat and silanized rGO and its trapping of charge-carriers in semi-crystalline EBA are demonstrated for the first time. It is shown that the polymer-grafted rGO improve the dispersibility in the EBA-matrix and that the graft length controls the inter-flake distances (i.e. charge-carrier hopping distances). By the appropriate selection of graft lengths, both highly resistive materials at 10 kV mm-1 and FGMs with a large and distinct drop in resistivity (six decades) are obtained, followed by saturation. The nonlinear drop in resistivity is attributed to narrow inter-flake distance distributions of grafted rGO.
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| 46. |
- Wåhlander, Martin, 1982-, et al.
(författare)
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Tailoring Dielectric Properties using Designed Polymer-Grafted ZnO Nanoparticles in Silicone Rubber
- 2017
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Ingår i: Journal of Materials Chemistry A. - : RSC Publishing. - 2050-7488 .- 2050-7496. ; 5, s. 14241-14258
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Tidskriftsartikel (refereegranskat)abstract
- Polymer grafts were used to tailor the interphases between ZnO nanoparticles (NPs) and silicone matrices. The final electrical properties of the nanocomposites were tuned by the grafted interphases, by controlling the inter-particle distance and the NP-morphology. The nanocomposites can be used in electrical applications where control of the resistivity is desired. Hansen's solubility parameters were used to select a semi-compatible polymer for grafting to obtain anisotropic NP morphologies in silicone, and the grafted NPs self-assembled into various morphologies inside the silicone matrices. The morphologies in the semi-compatible nanocomposites could be tuned by steering the graft length of poly(n-butyl methacrylate) via entropic matrix-graft wetting using surface-initiated atom-transfer radical polymerization. Image analysis models were developed to calculate the radius of primary NPs, the fraction of aggregates, the dispersion, and the face-to-face distance of NPs. The dielectric properties of the nanocomposites were related to the morphology and the face-to-face distance of the NPs. The dielectric losses, above 100 Hz, for nanocomposites with grafted NPs were approximately one decade lower than those of pristine NPs. The isotropic nanocomposites increased the resistivity up to 100 times compared to that of neat silicone rubber, due to the trapping of charge carriers by the interphase of dispersed NPs and nanoclusters. On the other hand, the resistivity of anisotropic nanocomposites decreased 10–100 times when the inter-particle distance in continuous agglomerates was close to the hopping distance of charge carriers. The electrical breakdown strength increased for compatible isotropic nanocomposites, and the temperature dependence of the resistivity and the activation energy were ∼50% lower in the nanocomposites with grafted NPs. These flexible dielectric nanocomposites are promising candidates for low-loss high-voltage transmission cable accessories, mobile electronic devices, wearables and sensors.
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| 47. |
- Xu, Xiangdong, 1984, et al.
(författare)
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Precision electric characterization of LDPE specimens made by different manufacturing processes
- 2018
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Ingår i: 2018 IEEE International Conference on High Voltage Engineering and Application (ICHVE). - : Institute of Electrical and Electronics Engineers (IEEE). - 2474-3852 .- 2381-5043. - 9781538650868
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Konferensbidrag (refereegranskat)abstract
- This work introduces two measurement techniques for precision determination of ultra-low conductivity and accurate characterization of dielectric frequency response for the assessments of polymeric materials used in HVDC insulations. To demonstrate the proposed methods, electrical properties of four different low density polyethylene (LDPE) specimens, obtained by different manufacturing processes were characterized. Results obtained from dc conductivity measurements revealed clear separation of the conduction current levels in the studied specimens. Dielectric losses obtained from the frequency response measurements agrees well with the differences observed in the measured conductivities. This study concludes that the different manufacturing processes have a significant impact on materials electric properties and these parameters can be characterized with precision beyond the existing instruments' specification by using the proposed methods.
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| 48. |
- Xu, Xiangdong, 1984, et al.
(författare)
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Robust measurements of electric conductivity in polyethylene based materials: measurement setup, data processing and impact of sample preparation
- 2017
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Ingår i: 25th Nordic Insulation Symposium on Materials, Components and Diagnostics.
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Konferensbidrag (refereegranskat)abstract
- In this work, a measurement setup and an algorithm are introduced that allow for obtaining and processing the current data during standard measurements of electric conductivity in polymeric insulation materials. Robustness of this setup is demonstrated through dc conductivity measurements of low density polyethylene (LDPE) specimens that were prepared by two different techniques, i.e. compression molding and extrusion, at two independent laboratories (at Chalmers and KTH) from the same raw pellets. The results resented in this paper reveal that the implemented data processing algorithm allows for clear separation of the conduction current level and the external noise and thus for good differentiation between the conductivity levels in the investigated material specimens. In addition, a high reproducibility of the results is obtained for the independently manufactured specimens, suggesting the proposed measurement technique is well suitable for characterization of low conducting dielectrics.
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