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Gedde, Ulf W
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Publications (10 of 17) Show all publications
Wei, X.-F., De Vico, L., Larroche, P., Kallio, K., Bruder, S., Bellander, M., . . . Hedenqvist, M. S. (2019). Ageing properties and polymer/fuel interactions of polyamide 12 exposed to (bio) diesel at high temperature. npj Materials Degradation
Open this publication in new window or tab >>Ageing properties and polymer/fuel interactions of polyamide 12 exposed to (bio) diesel at high temperature
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2019 (English)In: npj Materials Degradation, ISSN 2397-2106Article in journal (Refereed) Published
National Category
Engineering and Technology Textile, Rubber and Polymeric Materials
Identifiers
urn:nbn:se:kth:diva-260464 (URN)
Available from: 2019-09-30 Created: 2019-09-30 Last updated: 2019-09-30
Moyassari, A., Gkourmpis, T., Hedenqvist, M. S. & Gedde, U. W. (2019). Molecular dynamics simulation of linear polyethylene blends: Effect of molar mass bimodality on topological characteristics and mechanical behavior. Polymer, 161, 139-150
Open this publication in new window or tab >>Molecular dynamics simulation of linear polyethylene blends: Effect of molar mass bimodality on topological characteristics and mechanical behavior
2019 (English)In: Polymer, ISSN 0032-3861, E-ISSN 1873-2291, Vol. 161, p. 139-150Article in journal (Refereed) Published
Abstract [en]

Blending different molar mass fractions of polyethylene (PE) in order to obtain materials with higher fracture toughness has previously proven beneficial. Our approach has been to use coarse-grained (CG) molecular dynamics (MD) simulations to obtain semicrystalline polyethylene systems on a nanoscale, and then draw them in order to mimic tensile testing. The CG potentials were derived, validated and utilized to simulate melt equilibration, cooling, crystallization and mechanical deformation. Crystallinity, tie chain and entanglement concentrations were continuously monitored. During crystallization, the low molar mass fraction disentangled to a greater degree and ended up with a lower entanglement density than the high molar mass fraction, although the tie chain concentration was higher for the low molar mass fraction. The deformation behavior of semicrystalline PE above its glass transition temperature was then assessed in a uniaxial tensile deformation simulation. The low-strain mechanical properties (i.e. elastic modulus, yield stress and strain) were in accordance with the literature. The high-strain mechanical features and toughness were improved in bimodal systems. The presence of a high molar mass fraction in bimodal systems was shown to affect the crystallinity and tie chain concentration during the strain hardening, leading to tougher model systems. Finally, the bimodal system with equal shares of the molar mass fractions showed the highest toughness and the best ultimate mechanical properties while having a concentration of tie chains and entanglements intermediate between the values for the other systems. This was a clear sign of the non-exclusive role of tie chains and entanglements in the mechanical behavior of bimodal PE and more generally of semicrystalline polymers at high strains.

Place, publisher, year, edition, pages
ELSEVIER SCI LTD, 2019
Keywords
Semicrystalline polyethylene, Coarse-grained molecular dynamics, Tie chains and entanglements
National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-241308 (URN)10.1016/j.polymer.2018.12.012 (DOI)000454931700016 ()2-s2.0-85059303277 (Scopus ID)
Note

QC 20190125

Available from: 2019-01-25 Created: 2019-01-25 Last updated: 2019-01-25Bibliographically approved
Wei, X.-F., Kallio, K. J., Bruder, S., Bellander, M., Kausch, H.-H., Gedde, U. W. & Hedenqvist, M. S. (2018). Diffusion-limited oxidation of polyamide: Three stages of fracture behavior. Polymer degradation and stability, 154, 73-83
Open this publication in new window or tab >>Diffusion-limited oxidation of polyamide: Three stages of fracture behavior
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2018 (English)In: Polymer degradation and stability, ISSN 0141-3910, E-ISSN 1873-2321, Vol. 154, p. 73-83Article in journal (Refereed) Published
Abstract [en]

Polyamides (PAs) frequently experience diffusion-limited oxidation (DLO) under elevated temperatures due to their combination of relatively high oxygen barrier properties and high susceptibility to, and rate of, oxidation; under DLO conditions, oxidation is uneven and limited to a thin surface layer. In this study, the reduced extensibility/embrittlement of unstabilized PA6 under DLO conditions was understood by revealing DLO-induced fracture behavior. The DLO was induced by thermally ageing PA6 samples at 180 degrees C; the built-up of the thin oxidized layer by ageing was revealed by infrared microscopy. Notably, the formation of the thin oxidized layer significantly reduced the strain-at-break. Depending on whether the oxidized layer was brittle, two types of surface behavior (voiding and cracking) occurred during the tensile tests, which in turn lead to three types (stages) of tensile fracture behavior. In particular, in the early stage (Stage I) of ageing, the fracture was caused by a long crack formed by the coalescence of adjacent surface voids, leading to a decrease in the strain-at-break from 300% to 30%. In Stage II, multiple surface cracks, which initiated in the oxidized layer, was arrested by the interface between the oxidized and unoxidized material, leading to an almost constant strain-at-break (at or close to the necking strain). Maximum brittleness occurred in Stage III, where a more extensive oxidation of the oxidized layer initiated cracks with high propagation rate, causing the interface to be unable to arrest the cracks. 

Place, publisher, year, edition, pages
ELSEVIER SCI LTD, 2018
Keywords
Diffusion-limited oxidation, Polyamide, Surface-induced embrittlement, Fracture behavior, Cracks, Mechanical properties
National Category
Other Materials Engineering Textile, Rubber and Polymeric Materials
Identifiers
urn:nbn:se:kth:diva-234202 (URN)10.1016/j.polymdegradstab.2018.05.024 (DOI)000441488100008 ()2-s2.0-85047652570 (Scopus ID)
Note

QC 20180907

Available from: 2018-09-07 Created: 2018-09-07 Last updated: 2019-09-30Bibliographically approved
Lo Re, G., Engström, J., Wu, Q., Malmström, E., Gedde, U. W., Olsson, R. & Berglund, L. (2018). Improved Cellulose Nanofibril Dispersion in Melt-Processed Polycaprolactone Nanocomposites by a Latex-Mediated Interphase and Wet Feeding as LDPE Alternative. ACS Applied Nano Materials, 1(6), 2669-2677
Open this publication in new window or tab >>Improved Cellulose Nanofibril Dispersion in Melt-Processed Polycaprolactone Nanocomposites by a Latex-Mediated Interphase and Wet Feeding as LDPE Alternative
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2018 (English)In: ACS Applied Nano Materials, ISSN 2574-0970, Vol. 1, no 6, p. 2669-2677Article in journal (Refereed) Published
Abstract [en]

This work reports the development of a sustainable and green one-step wet-feeding method to prepare tougher and stronger nanocomposites from biodegradable cellulose nanofibrils (CNF)/polycaprolactone (PCL) constituents, compatibilized with reversible addition fragmentation chain transfer-mediated surfactant-free poly(methyl methacrylate) (PMMA) latex nanoparticles. When a PMMA latex is used, a favorable electrostatic interaction between CNF and the latex is obtained, which facilitates mixing of the constituents and hinders CNF agglomeration. The improved dispersion is manifested in significant improvement of mechanical properties compared with the reference material. The tensile tests show much higher modulus (620 MPa) and strength (23 MPa) at 10 wt % CNF content (compared to the neat PCL reference modulus of 240 and 16 MPa strength), while maintaining high level of work to fracture the matrix (7 times higher than the reference nanocomposite without the latex compatibilizer). Rheological analysis showed a strongly increased viscosity as the PMMA latex was added, that is, from a well-dispersed and strongly interacting CNF network in the PCL.

Place, publisher, year, edition, pages
American Chemical Society (ACS), 2018
National Category
Materials Chemistry
Identifiers
urn:nbn:se:kth:diva-241449 (URN)10.1021/acsanm.8b00376 (DOI)000461400700029 ()
Note

QC 20190123

Available from: 2019-01-22 Created: 2019-01-22 Last updated: 2019-04-23Bibliographically approved
Wei, X.-F., Kallio, K. J., Bruder, S., Bellander, M., Gedde, U. W. & Hedenqvist, M. S. (2018). Long-term performance of a polyamide-12-based fuel line with a thin poly(ethylene-co-tetrafluoroethylene) (ETFE) inner layer exposed to bio- and petroleum diesel. Polymer degradation and stability, 156, 170-179
Open this publication in new window or tab >>Long-term performance of a polyamide-12-based fuel line with a thin poly(ethylene-co-tetrafluoroethylene) (ETFE) inner layer exposed to bio- and petroleum diesel
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2018 (English)In: Polymer degradation and stability, ISSN 0141-3910, E-ISSN 1873-2321, Vol. 156, p. 170-179Article in journal (Refereed) Published
Abstract [en]

The long-term performance of a polyamide-12 (PA12)-based (bio)diesel fuel line/pipe with a thin poly(ethylene-co-tetrafluoroethylene) (ETFE) inner layer was investigated in “close to real” and high-temperature isothermal conditions with fuel on the inside and air on the outside of the pipe. The inner carbon-black-containing ETFE layer resisted fuel attack, as revealed by the small fuel uptake, the very low degree of oxidation, and the unchanged electrical conductivity, glass transition and melting behaviour. The properties of the ETFE layer remained the same after exposure to all the fuel types tested (petroleum diesel, biodiesel and a blend of 80% diesel with 20% biodiesel). Because of the presence of the ETFE layer on the inside, the fuel pipe experienced noticeable changes only in the outer PA12 pipe layer through migration of plasticizer, annealing and slight oxidation. The evaporation of plasticizer was found to be diffusion-controlled and it led to an increase in the glass transition temperature of PA12 by 20 °C. This, together with a small annealing-induced increase in crystallinity, resulted in a stiffer and stronger pipe with an increase in the flexural/tensile modulus and strength. The oxidation of PA12 remained at a low level and did not lead to an embrittled pipe during the simulated lifetime of the vehicle. This study reveals that fluoropolymers have a great potential for use as fuel-contacting materials in “demanding” motor vehicle fuel line systems. 

Place, publisher, year, edition, pages
Elsevier Ltd, 2018
Keywords
Ageing, Biodiesel, Diesel, Fuel pipe, Plasticizer loss, Poly(ethylene-co-tetrafluoroethylene), Polyamide, Carbon black, Diesel fuels, Ethylene, Fluorine containing polymers, Gasoline, Glass, Oxidation, Plasticizers, Polyamides, Reinforced plastics, Electrical conductivity, Fuel pipes, High temperature, Isothermal conditions, Long term performance, Tetrafluoroethylene, Glass transition
National Category
Environmental Engineering
Identifiers
urn:nbn:se:kth:diva-236649 (URN)10.1016/j.polymdegradstab.2018.09.003 (DOI)000448091400017 ()2-s2.0-85053044298 (Scopus ID)
Funder
Swedish Energy Agency, 32519-3
Note

Export Date: 22 October 2018; Article; CODEN: PDSTD; Correspondence Address: Wei, X.-F.; KTH Royal Institute of Technology, School of Engineering Sciences in Chemistry, Biotechnology and Health, Fibre and Polymer TechnologySweden; email: xinfengw@kth.se; Funding details: 32519-3; Funding text: The financial support from the Swedish Energy Authority (project no. 32519-3 ), Volvo Cars AB (Göteborg, Sweden) and Scania CV AB (Södertälje, Sweden) is gratefully acknowledged. QC 20181113

Available from: 2018-11-13 Created: 2018-11-13 Last updated: 2019-09-30Bibliographically approved
Xu, X., Gaska, K., Karlsson, M. E., Hillborg, H. & Gedde, U. W. (2018). Precision electric characterization of LDPE specimens made by different manufacturing processes. In: CHVE 2018 - 2018 IEEE International Conference on High Voltage Engineering and Application: . Paper presented at IEEE International Conference on High Voltage Engineering and Application (ICHVE), SEP 10-13, 2018, Athens, Greece. Institute of Electrical and Electronics Engineers (IEEE), Article ID 8641846.
Open this publication in new window or tab >>Precision electric characterization of LDPE specimens made by different manufacturing processes
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2018 (English)In: CHVE 2018 - 2018 IEEE International Conference on High Voltage Engineering and Application, Institute of Electrical and Electronics Engineers (IEEE), 2018, article id 8641846Conference paper, Published paper (Refereed)
Abstract [en]

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.

Place, publisher, year, edition, pages
Institute of Electrical and Electronics Engineers (IEEE), 2018
Series
International Conference on High Voltage Engineering and Application, ISSN 2381-5043
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-249919 (URN)10.1109/ICHVE.2018.8641846 (DOI)000462278900021 ()2-s2.0-85063094743 (Scopus ID)978-1-5386-5086-8 (ISBN)
Conference
IEEE International Conference on High Voltage Engineering and Application (ICHVE), SEP 10-13, 2018, Athens, Greece
Note

QC 20190502

Available from: 2019-05-02 Created: 2019-05-02 Last updated: 2019-05-02Bibliographically approved
Liu, D., Pallon, L. K. H., Pourrahimi, A. M., Zhang, P., Diaz, A., Holler, M., . . . Gedde, U. W. (2017). Cavitation in strained polyethylene/aluminium oxide nanocomposites. European Polymer Journal, 87, 255-265
Open this publication in new window or tab >>Cavitation in strained polyethylene/aluminium oxide nanocomposites
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2017 (English)In: European Polymer Journal, ISSN 0014-3057, E-ISSN 1873-1945, Vol. 87, p. 255-265Article in journal (Refereed) Published
Abstract [en]

The incorporation of metal oxide (e.g. Al2O3) nanoparticles has a pronounced positive effect on low-density polyethylene (LDPE) as an insulating material for high-voltage direct-current (HVDC) cables, the electrical conductivity being decreased by one to two orders of magnitude and charge species being trapped by the nanoparticles. The risk of debonding between the nanoparticles and the polymer matrix leading to electrical treeing via electrical discharges in the formed cavities was the motivation for this study. Scanning electron microscope (SEM), small-angle X-ray scattering (SAXS) and X-ray ptychographic tomography were used to study a series of LDPE nanocomposites which contained Al2O3 nanoparticles treated with silanes having terminal alkyl groups of different lengths (methyl, octyl and octadecyl). When specimens were subjected to a tensile strain (a typical specimen stretched beyond the onset of necking consisted of three zones according to SEM of specimens that were studied after removal of the external force: an essentially cavitation-free zone with low local plastic strain, a transitional zone in which local plastic strain showed a marked increase and the revealed concentration of permanent cavities increased with increasing plastic strain and a highly strained zone with extensive cavitation), the cavitation occurred mainly at the polymer-nanoparticle interface according to SEM and X-ray ptychographic tomography and according to SEM progressed with increasing plastic strain through an initial phase with no detectable formation of permanent cavities to a period of very fast cavitation and finally almost an order of magnitude slower cavitation. The polymer/nanoparticle interface was fractal before deformation, as revealed by the profile of the Porod region in SAXS, presumably due to the existence of bound polymers at the nanoparticle surface. A pronounced decrease in the interface fractal dimension was observed when the strain exceeded a critical value; a phenomenon attributed to the stress-induced de-bonding of nanoparticles. The strain-dependence of the interface fractal dimension value at low strain levels between composites containing differently treated nanoparticles seems to be an indicator of the strength of the nanoparticle-polymer interface.

Place, publisher, year, edition, pages
Elsevier, 2017
Keywords
Aluminium oxide, Cavitation, Low-density polyethylene, Nanocomposites, Aluminum, DC power transmission, Electric discharges, Fractal dimension, Fractals, HVDC power transmission, Low density polyethylenes, Metal nanoparticles, Metals, Nanoparticles, Plastic deformation, Polyethylenes, Scanning electron microscopy, Silanes, Tomography, X ray scattering, Electrical conductivity, Electrical discharges, Fractal-dimension value, High voltage direct current, Low density polyethylene(LDPE), Nanoparticle surface, Polymer nanoparticles, Tensile strain
National Category
Polymer Technologies
Identifiers
urn:nbn:se:kth:diva-201939 (URN)10.1016/j.eurpolymj.2016.12.021 (DOI)000395210900022 ()2-s2.0-85008230710 (Scopus ID)
Note

Funding text: The Swedish Foundation for Strategic Research (grant EM11-0022) is thanked for the financial support.

QC 20170307

Available from: 2017-03-07 Created: 2017-03-07 Last updated: 2017-11-29Bibliographically approved
Pourmand, P., Hedenqvist, M. S., Furo, I. & Gedde, U. W. (2017). Deterioration of highly filled EPDM rubber by thermal ageing in air: Kinetics and non-destructive monitoring. Polymer testing, 64, 267-276
Open this publication in new window or tab >>Deterioration of highly filled EPDM rubber by thermal ageing in air: Kinetics and non-destructive monitoring
2017 (English)In: Polymer testing, ISSN 0142-9418, E-ISSN 1873-2348, Vol. 64, p. 267-276Article in journal (Refereed) Published
Abstract [en]

The effects of air ageing at different temperatures between 110 and 170 degrees C on cable transit seals based on highly filled EPDM rubber used in nuclear power plants were studied. The changes of the macroscopic mechanical properties (Young's modulus, indentation modulus and strain-at-break) were in accordance with the Arrhenius equation with an activation energy of 110 kJ mol(-1). Profiling to assess the structure and property gradients within aged blocks was performed via IR spectroscopy, micro-indentation, gravimetric analysis of n-heptane-extracted samples and non-invasive portable NMR spectroscopy. A previously developed methodology was used to separate the deterioration into three different processes: polymer oxidation that was diffusion-limited at all temperatures, migration of low-molar-mass species to the surrounding media and anaerobic changes to the polymer network. The methodology allowed the assessment of the kinetics (rate as a function of time and temperature) of the different processes. It was noticed that polymer oxidation yielded more crosslinking at higher temperatures than at lower temperatures. The data obtained by both the portable NMR (a non-invasive method) and the indentation modulus profiling showed correlations with strain-at-break data, indicating their usefulness as condition monitoring methods.

Place, publisher, year, edition, pages
ELSEVIER SCI LTD, 2017
Keywords
EPDM rubber, Air ageing, Structure and property profiling, Portable NMR, Deterioration mechanism separation, Condition monitoring
National Category
Polymer Chemistry
Identifiers
urn:nbn:se:kth:diva-220844 (URN)10.1016/j.polymertesting.2017.10.019 (DOI)000418221500032 ()
Note

QC 20180111

Available from: 2018-01-11 Created: 2018-01-11 Last updated: 2018-01-11Bibliographically approved
Kömmling, A., Jaunich, M., Pourmand, P., Wolff, D. & Gedde, U. W. (2017). Influence of Ageing on Sealability of Elastomeric O-Rings. In: MACROMOLECULAR SYMPOSIA: . Paper presented at International Scientific Conference on PolyMerTec held together with the 15th Meeting on Deformation and Fracture Behaviour of Polymers, JUN 15-17, 2016, Univ Appl Sci Merseburg, Merseburg, GERMANY. Wiley-VCH Verlagsgesellschaft, 373(1), Article ID UNSP 1600157.
Open this publication in new window or tab >>Influence of Ageing on Sealability of Elastomeric O-Rings
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2017 (English)In: MACROMOLECULAR SYMPOSIA, Wiley-VCH Verlagsgesellschaft, 2017, Vol. 373, no 1, article id UNSP 1600157Conference paper, Published paper (Refereed)
Abstract [en]

At BAM, which is the federal institute for materials research and testing in Germany, it is one of our tasks to evaluate the safety of casks designed for transport and/or storage of radioactive material. This includes the assessment of the service lifetime of elastomeric seals that are part of the container lid system with regard to the requirements for long-term safety (40 years and more) of the containers. Therefore, we started an accelerated ageing programme with selected rubbers often used for seals (HNBR, EPDM and FKM) which are aged at four different temperatures (75 degrees C, 100 degrees C, 125 degrees C and 150 degrees C) up to 1.5 years. In order to assess sealability, O-rings are aged in compression by 25% (corresponding to the compression during service) between plates as well as in flanges that allow leakage rate measurements. For comparison, uncompressed O-rings are aged as well. Further methods characterising seal performance are compression stress relaxation (CSR) reflecting the loss of sealing force of a compressed seal over time, and compression set (CS) which represents the recovery behaviour of a seal after release from compression. Additionally, hardness is measured for information about the change of mechanical properties. The experimental results indicate that while hardness, CSR and CS show considerable degradation effects, the leakage rate stays relatively constant or even decreases until shrinkage combined with the loss of resilience of the aged seal leads to leakage. This demonstrates that static leakage rate, which is the only available direct seal performance criterion, has only limited sensitivity towards the degradation of the seal material. CS data is extrapolated using time-temperature shifts and Arrhenius graphs. An exemplary CS of 50% would be reached after approx. 1.2, 17 and 29 years at 60 degrees C for HNBR, EPDM and FKM respectively.

Place, publisher, year, edition, pages
Wiley-VCH Verlagsgesellschaft, 2017
Keywords
compression, degradation, leakage, lifetime, rubber
National Category
Polymer Chemistry
Identifiers
urn:nbn:se:kth:diva-211028 (URN)10.1002/masy.201600157 (DOI)000404021100019 ()2-s2.0-85021164997 (Scopus ID)
Conference
International Scientific Conference on PolyMerTec held together with the 15th Meeting on Deformation and Fracture Behaviour of Polymers, JUN 15-17, 2016, Univ Appl Sci Merseburg, Merseburg, GERMANY
Note

QC 20170712

Available from: 2017-07-12 Created: 2017-07-12 Last updated: 2017-07-12Bibliographically approved
Liu, D., Hoang, A. T., Pourrahimi, A. M., Pallon, L. K. H., Nilsson, F., Gubanski, S. M., . . . Gedde, U. W. (2017). Influence of Nanoparticle Surface Coating on Electrical Conductivity of LDPE/Al2O3 Nanocomposites for HVDC Cable Insulations. IEEE transactions on dielectrics and electrical insulation, 24(3), 1396-1404
Open this publication in new window or tab >>Influence of Nanoparticle Surface Coating on Electrical Conductivity of LDPE/Al2O3 Nanocomposites for HVDC Cable Insulations
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2017 (English)In: IEEE transactions on dielectrics and electrical insulation, ISSN 1070-9878, E-ISSN 1558-4135, Vol. 24, no 3, p. 1396-1404Article in journal (Refereed) Published
Abstract [en]

LDPE/metal oxide nanocomposites are promising materials for future high-voltage DC cable insulation. This paper presents data on the influence of the structure of the nanoparticle coating on the electrical conductivity of LDPE/Al2O3 nanocomposites. Al2O3 nanoparticles, 50 nm in size, were coated with a series of silanes with terminal alkyl groups of different lengths (methyl, n-octyl and n-octadecyl groups). The density of the coatings in vacuum was between 200 and 515 kg m(-3,) indicating substantial porosity in the coating. The dispersion of the nanoparticles in the LDPE matrix was assessed based on statistics for the nearest-neighbor particle distance. The electrical conductivity of the nanocomposites was determined at both 40 and 60 degrees C. The results show that an appropriate surface coating on the nanoparticles allowed uniform particle dispersion up to a filler loading of 10 wt.%, with a maximum reduction in the electrical conductivity by a factor of 35. The composites based on the most porous octyl-coated nanoparticles showed the greatest reduction in electrical conductivity and the lowest temperature coefficient of electrical conductivity of the composites studied.

Place, publisher, year, edition, pages
IEEE, 2017
Keywords
HVDC cable insulation, LDPE/aluminum oxide nanocomposites, particle coating chemistry, particle dispersion, electrical conductivity
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-211613 (URN)10.1109/TDEI.2017.006310 (DOI)000405000300012 ()2-s2.0-85022181728 (Scopus ID)
Funder
Swedish Foundation for Strategic Research , EM11-0022
Note

QC 20170810

Available from: 2017-08-10 Created: 2017-08-10 Last updated: 2017-08-11Bibliographically approved
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