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Prevention of Biofilm Formation on Silicone Rubber Materials for Outdoor High Voltage Insulators
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymeric Materials.ORCID iD: 0000-0001-7223-3549
2015 (English)Doctoral 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.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2015. , xi, 67 p.
Series
TRITA-CHE-Report, ISSN 1654-1081 ; 2015:51
Keyword [en]
High voltage insulator, silicone rubber, biofouling, biofilm, biocide, superhydrophobicity, self-cleaning, hierarchical roughness
National Category
Polymer Technologies
Identifiers
URN: urn:nbn:se:kth:diva-174091ISBN: 978-91-7595-694-7 (print)OAI: oai:DiVA.org:kth-174091DiVA: diva2:857787
Public defence
2015-10-23, K1, Teknikringen 56, KTH, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

QC 20151002

Available from: 2015-10-02 Created: 2015-09-30 Last updated: 2015-10-02Bibliographically approved
List of papers
1. Inhibition of biofilm formation on silicone rubber samples using various antimicrobial agents
Open this publication in new window or tab >>Inhibition of biofilm formation on silicone rubber samples using various antimicrobial agents
2011 (English)In: International Biodeterioration & Biodegradation, ISSN 0964-8305, E-ISSN 1879-0208, Vol. 65, no 8, 1111-1118 p.Article in journal (Refereed) Published
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.

Keyword
High voltage silicone rubber insulator, Biofilm, Biofouling, Antimicrobial agents, Biodegradation
National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-50044 (URN)10.1016/j.ibiod.2011.09.001 (DOI)000297889000001 ()2-s2.0-80053376565 (Scopus ID)
Note
QC 20111205. Previous title: Biofilm formation on silicone rubber samples containing different antimicrobial agentsAvailable from: 2011-12-01 Created: 2011-12-01 Last updated: 2017-12-08Bibliographically approved
2. Use of essential oils for the prevention of biofilm formation on silicone rubber high voltage insulators
Open this publication in new window or tab >>Use of essential oils for the prevention of biofilm formation on silicone rubber high voltage insulators
2015 (English)In: Polymers from Renewable Resources, ISSN 2041-2479, Vol. 6, no 4, 119-136 p.Article in journal (Refereed) Published
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.

Place, publisher, year, edition, pages
Rapra Technology Ltd., 2015
Keyword
Algae, Biofilms, Elastomers, Electric insulation, Electric insulators, Essential oils, Microorganisms, Phenols, Rubber, Silicones, Thermoanalysis, Anti-microbial effects, Biofilm formation, High voltage insulators, Microbial growth, Natural-antimicrobials, Sample preparation, Silicone rubber, Thermal and mechanical properties
National Category
Polymer Chemistry
Identifiers
urn:nbn:se:kth:diva-174283 (URN)2-s2.0-84952893692 (Scopus ID)
Note

QC 20170111

Available from: 2015-10-02 Created: 2015-10-02 Last updated: 2017-03-24Bibliographically approved
3. Image Analysis Determination of the Influence of Surface Structure of Silicone Rubbers on Biofouling
Open this publication in new window or tab >>Image Analysis Determination of the Influence of Surface Structure of Silicone Rubbers on Biofouling
Show others...
2015 (English)In: International Journal of Polymer Science, ISSN 1687-9422, E-ISSN 1687-9430, 390292Article in journal (Refereed) Published
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.

National Category
Polymer Chemistry
Identifiers
urn:nbn:se:kth:diva-170710 (URN)10.1155/2015/390292 (DOI)000356264100001 ()
Note

QC 20150707

Available from: 2015-07-07 Created: 2015-07-03 Last updated: 2017-12-04Bibliographically approved
4. Design of nanocomposite surfaces with antibiofouling properties for outdoor insulation applications
Open this publication in new window or tab >>Design of nanocomposite surfaces with antibiofouling properties for outdoor insulation applications
Show others...
(English)Manuscript (preprint) (Other academic)
National Category
Polymer Chemistry
Identifiers
urn:nbn:se:kth:diva-174284 (URN)
Note

QS 2015

Available from: 2015-10-02 Created: 2015-10-02 Last updated: 2015-10-02Bibliographically approved

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Atari Jabarzadeh, Sevil

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