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  • 1.
    Atari Jabarzadeh, Sevil
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymeric Materials.
    Prevention of Biofilm Formation on Silicone Rubber Materials for Outdoor High Voltage Insulators2015Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Microbial colonization on the surface of silicone rubber high voltage outdoor insulators often results in the formation of highly hydrated biofilm that influence the surface properties, such as surface hydrophobicity. The loss of hydrophobicity might lead to dry band formation, and, in the worst cases, flashover and failure of the insulator.

    In this work, the biocidal effects of various antimicrobial compounds in silicone rubber materials were determined. These materials were evaluated according to an ISO standard for the antimicrobial activity against the growth of aggressive fungal strains, and microorganisms that have been found colonizing the surfaces of outdoor insulators in several areas in the world. Several compounds suppressed microbial growth on the surfaces of the materials without compromising the material properties of the silicone rubber. A commercial biocide and thymol were very effective against fungal growth, and sodium benzoate could suppress the fungal growth to some extent. Thymol could also inhibit algal growth. However, methods for preservation of the antimicrobial agents in the bulk of the material need to be further developed to prevent the loss of the compounds during manufacturing. Biofilm formation affected the surface hydrophobicity and complete removal of the biofilm was not achieved through cleaning. Surface analysis confirmed that traces of microorganisms were still present after cleaning.

    Further, surface modification of the silicone rubber was carried out to study how the texture and roughness of the surface affect biofilm formation. Silicone rubber surfaces with regular geometrical patterns were evaluated to determine the influence of the surface texture on the extent of microbial growth in comparison with plane silicone rubber surfaces. Silicone rubber nanocomposite surfaces, prepared using a spray-deposition method that applied hydrophilic and hydrophobic nanoparticles to obtain hierarchical structures, were studied to determine the effects of the surface roughness and improved hydrophobicity on the microbial attachment. Microenvironment chambers were used for the determination of microbial growth on different modified surfaces under conditions that mimic those of the insulators in their outdoor environments. Different parts of the insulators were represented by placing the samples vertically and inclined. The microbial growth on the surfaces of the textured samples was evenly distributed throughout the surfaces because of the uniform distribution of the water between the gaps of the regular structures on the surfaces. Microbial growth was not observed on the inclined and vertical nanocomposite surfaces due to the higher surface roughness and improved surface hydrophobicity, whereas non-coated samples were colonized by microorganisms.

  • 2.
    Atari Jabarzadeh, Sevil
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymeric Materials.
    Mendoza Álvarez, Ana Isabel
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymeric Materials.
    Hillborg, Henrik
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymeric Materials. ABB, Corporated Resarch, Sweden.
    Karlsson, Sigbritt
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymeric Materials. Univ Skovde, S-54128 Skovde, Sweden.
    Strömberg, Emma
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymeric Materials.
    Design of nanocomposite surfaces with antibiofouling properties for outdoor insulation applicationsManuscript (preprint) (Other academic)
  • 3.
    Atari Jabarzadeh, Sevil
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymeric Materials.
    Nilsson, Fritjof
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymeric Materials. ABB, Corp Res, S-72178 Vasteras, Sweden.
    Hillborg, Henrik
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymeric Materials. ABB, Corp Res, S-72178 Vasteras, Sweden.
    Karlsson, Sigbritt
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymeric Materials. Univ Skovde, S-54128 Skovde, Sweden.
    Strömberg, Emma
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymeric Materials.
    Image Analysis Determination of the Influence of Surface Structure of Silicone Rubbers on Biofouling2015In: International Journal of Polymer Science, ISSN 1687-9422, E-ISSN 1687-9430, article id 390292Article in journal (Refereed)
    Abstract [en]

    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.

  • 4.
    Atari Jabarzadeh, Sevil
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymeric Materials.
    Salas Lacamprett, Carla
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymeric Materials.
    Karlsson, Sigbritt
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymeric Materials. Univ Skovde, S-54128 Skovde, Sweden.
    Strömberg, Emma
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymeric Materials.
    Use of essential oils for the prevention of biofilm formation on silicone rubber high voltage insulators2015In: Polymers from Renewable Resources, ISSN 2041-2479, Vol. 6, no 4, p. 119-136Article in journal (Refereed)
    Abstract [en]

    The prevention of biofilm formation on high voltage insulators is important to avoid changes in the surface properties of the material and the subsequent failure of the application. Antimicrobial silicone rubber samples were prepared by the addition of thymol and eugenol to Sylgard 184 to determine the possibility of using natural antimicrobial agents present in essential oils in materials used for high voltage insulators. The antimicrobial effects of thymol and eugenol were studied for different fungal strains and for green algae identified in the biofilms formed on insulators in Tanzania, Sri Lanka and Sweden. It was successfully demonstrated that samples containing high amount of eugenol and different concentrations of thymol could inhibit the fungal growth of strains from Sri Lanka and Tanzania and the growth of green algae. The growth of strains from Sweden was also suppressed. The addition of eugenol to the material resulted in a noncrosslinked system and therefore, the antimicrobial effect of the additive in the material could not be assessed. The addition of thymol did not significantly influence the thermal and mechanical properties of Sylgard184. Although thermal analysis revealed that a large amount of the antimicrobial agent was lost during sample preparation, the materials were effective against microbial growth, even at low thymol concentrations.

  • 5.
    Atarijabarzadeh, Sevil
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymeric Materials.
    Biofilm adhesion on silicone materials2011Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    Silicone composite high voltage insulators are sometimes contaminated by microorganisms in outdoor applications, which results in the insulator becoming conductive and thereafter failure of the insulators. In this work, it has been tried to develop silicone materials with antimicrobial properties. Silicone was blended with various antimicrobial agents. Affectivity and appropriate concentration of the biocides were decided through a fast test prior to the manufacturing of the samples.

    Samples were aged according to an international biodegradation test. To study the extent of the growth on the samples’ surface visual analysis and scanning electron microscopy (SEM) were performed. Samples were studied for changes in surface properties and surface chemical composition with carrying out dynamic contact angle measurements and Fourier transform infrared spectroscopy respectively. Results from the biodegradation test showed some biocides could inhibit the fungal growth comparing the results for the reference samples. Biofilm formation resulted in changes in surface hydrophobicity and surface chemical composition.

    Further, silicone materials were compounded with clay nanoparticles, which were modified with different organic compounds. Reference samples were manufactured with clay nanoparticles modified with a siloxane surfactant to make the dispersion of the particles into the silicone matrix easier. Clay nanoparticles were also grafted with two organic compounds with antimicrobial effect in order to synthesis organoclays, which have antimicrobial properties. Furthermore, grafting clay with these two compounds was also aimed to make the easy dispersion of the particles into silicone possible.

    Nanocomposites compounded with antimicrobial clay nanoparticles as well as reference nanocomposites were tested with quick test for microbial growth. Changes in the clay particles morphology were examined with x-ray diffraction as well as SEM. Manufactured nanocomposites were also examined with x-ray and SEM to study the dispersion of nanoparticles into the silicone matrix. Changes in clay morphology were observed due to modification with organic compounds. Microbial growth was inhibited on some samples due to presence of antimicrobial organoclays.

  • 6.
    Atarijabarzadeh, Sevil
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymeric Materials.
    Strömberg, Emma
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymeric Materials.
    Karlsson, Sigbritt
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymeric Materials.
    Biofilm formation on silicone materials containing various antimicrobial agents2010Conference paper (Refereed)
    Abstract [en]

    The colonisation of microorganisms and subsequent biofilm formation on the surface of polymeric high voltage insulators affect the surface properties and can lead to failure of the insulators.  In this study, silicone materials were prepared with different antimicrobial agents. The materials were analysed for the changes in the physical, chemical, surface and mechanical properties before and after biological growth test.

     

    Microorganisms used for the biological tests were fungi defined in the international standard test ISO 846 for electrical applications (Aspergillus niger van Tieghem, Penicillium funiculosum Thom, Paecilomyces variotii Bainier, Chaetomium globosum Kunze: Fries, Aspergillus terreus Thom, Aureobasidium pullulans (de Bary) Arnaud & Penicillium ochrochloron Biourge) and algae isolated from insulators in Sri Lanka and Tanzania (Chlorella vulgaris var. Autotrophica + various bacterial strains). Fungi growth test was performed by inoculation of the fungi on the surface of the materials and incubation in an oven at 28°C and 98% humidity for a specific period. Algae growth test was performed by inoculation on the material surface and subsequent incubation in room temperature under a constant fluorescent lamps for a specific period.

     

    The results indicated that some of the samples could prevent the biofilm formation on the surface of the materials while the microbial growth was unaffected on the pure silicone rubber.

  • 7.
    Atarijabarzadeh, Sevil
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymeric Materials.
    Strömberg, Emma
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymeric Materials.
    Karlsson, Sigbritt
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymeric Materials.
    Biofilm formation on silicone nanocomposites containing different antimicrobial agents2010Conference paper (Refereed)
    Abstract [en]

    In this study three types of clay/silicon nanocomposites were prepared. Clay was modified with two different antimicrobial agents (p-aminobenzoic acid and partially aminated poly(vinylbenzyl chloride) and used for preparation of the nanocomposites, which aimed to show antimicrobial properties and also easy dispersion of the clay into the polymeric matrix. Reference nanocomposites were made through the modification of the clay with a siloxane surfactant to make an easy dispersion of the clay into the silicone rubber. Nanocomposites were studied for resistancy against biological attack according to the international standard tests. Growth test results indicated that some of the nanocomposites can inhibit biological growth more than pristine nanocomposites. Modified clay was studied with x-ray diffraction technique. Materials were also studied with scanning electron microscopy before and after biological growth to analyse the biofilm formation on the surface.

  • 8.
    Atarijabarzadeh, Sevil
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Strömberg, Emma
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Karlsson, Sigbritt
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Design of antimicrobial silicone nanocomposites for high voltage insulationManuscript (preprint) (Other academic)
  • 9.
    Atarijabarzadeh, Sevil
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
    Strömberg, Emma
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
    Karlsson, Sigbritt
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
    Inhibition of biofilm formation on silicone rubber samples using various antimicrobial agents2011In: International Biodeterioration & Biodegradation, ISSN 0964-8305, E-ISSN 1879-0208, Vol. 65, no 8, p. 1111-1118Article in journal (Refereed)
    Abstract [en]

    High-temperature-cured silicone rubber samples (silicone rubber (SIR) based on polydimethylsiloxane (PDMS)) and SIR samples containing three different antimicrobial agents, sodium benzoate (NaB), DCOIT (4,5 Dichloro-2-octyl-2H-isothiazolone-one) and p-aminobenzoic acid (PABA) were inoculated with fungal spore suspensions and incubated for 28 days at 29 +/- 1 degrees C and >= 90% humidity, according to the ISO 846:1997(E) protocol. Prior to the biodegradation test, a powder test was conducted to study the efficacy of the chosen antimicrobial compounds and to determine the correct concentration of the compounds for sample preparation. The extent of the microbial growth was studied visually and by Scanning Electron Microscopy (SEM). Changes in surface hydrophobicity and surface chemical composition were studied by contact angle measurements and Fourier Transform Infrared (FTIR) spectroscopy, respectively. Microbial growth and biofilm formation were observed on the surface of reference samples. DCOIT was the most effective antimicrobial agent, as demonstrated by the lack of microbial growth and unaltered surface hydrophobicity. On the surface of samples containing NaB, an initiation of microbial growth and therefore a slight change in surface hydrophobicity was observed. PABA did not inhibit the fungal growth.

  • 10. Fiege, Kathrin
    et al.
    Luensdorf, Heinrich
    Atarijabarzadeh, Sevil
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Mischnick, Petra
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Cyanoethylation of the glucans dextran and pullulan: Substitution pattern and formation of nanostructures and entrapment of magnetic nanoparticles2012In: Beilstein Journal of Organic Chemistry, ISSN 2195-951X, E-ISSN 1860-5397, Vol. 8, p. 551-566Article in journal (Refereed)
    Abstract [en]

    Cyanoethylglucans with a degree of substitution in the range of 0.74 to 2.40 for dextran and 0.84 to 2.42 for pullulan were obtained by Michael addition of acrylonitrile to the glucans under various conditions. Products were thoroughly characterized, comprising elementary analysis, NMR and ATR-IR spectroscopy, and analysis of the substituent distribution in the glucosyl units by GC-FID and GC-MS of the constituting monosaccharide derivatives. Nanostructuring of the highly substituted cyanoethylpolysaccharides was performed by dialysis against a non-solvent. In the presence of ferromagnetic iron-oxide nanoparticles, multicore cyanoethylglucan-coated ferromagnetic nanoparticles were formed by selective entrapment. The specific interaction between cyano groups and iron could be proven. The size distribution and morphology of the nanoparticles were analyzed by dynamic light scattering (DLS), scanning electron microscopy (SEM) and energy-filtered transmission electron microscopy (EF-TEM) with parallel electron energy loss spectroscopy (PEELS).

  • 11. Wang, Jing
    et al.
    Gubanski, Stanislaw M.
    Blennow, Jörgen
    Atarijabarzadeh, Sevil
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Strömberg, Emma
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
    Karlsson, Sigbritt
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
    Influence of Biofilm Contamination on Electrical Performance of Silicone Rubber Based Composite Materials2012In: IEEE transactions on dielectrics and electrical insulation, ISSN 1070-9878, E-ISSN 1558-4135, Vol. 19, no 5, p. 1690-1699Article in journal (Refereed)
    Abstract [en]

    In this research, three kinds of silicone rubber based composite materials, SIR, NSIR and DSIR, were prepared. SIR is the reference silicone rubber without addition of antimicrobial biocide. Two different antimicrobial agents at a concentration of 3 wt% were added to the reference silicone rubber to form the other two types of materials. The materials were inoculated with a fungal spore suspension containing nutrients. Fungal growth could be observed visually in form of spots by naked eye, and biofilm was formed and detected by SEM observation on the surfaces of SIR and NSIR samples, whereas DSIR samples were completely free of the fungal growth. Then the electrical performance of both clean and biofilm contaminated samples, including the surface and volume conductivity, surface flashover voltage and leakage current before flashover, were measured. The obtained results indicate that as compared with SIR base material, the biocides have not changed the surface conductivity and surface flashover voltage of NSIR and DSIR materials. At the same time, the volume conductivity of NSIR remains almost the same as SIR, while that of DSIR increases by about two orders of magnitude. Biofilm could increase the surface conductivity and decrease the surface flashover voltage significantly. The time domain and frequency domain analyses of the leakage currents flowing before flashover event provide useful information on the severity of contamination by biofilm and the eventual risk for surface flashover.

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