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Inhibition of biofilm formation on silicone rubber samples using various antimicrobial agents
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.ORCID iD: 0000-0002-2139-7460
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.ORCID iD: 0000-0002-5394-7850
2011 (English)In: International Biodeterioration & Biodegradation, ISSN 0964-8305, 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.

Place, publisher, year, edition, pages
2011. Vol. 65, no 8, 1111-1118 p.
Keyword [en]
High voltage silicone rubber insulator, Biofilm, Biofouling, Antimicrobial agents, Biodegradation
National Category
Materials Engineering
URN: urn:nbn:se:kth:diva-50044DOI: 10.1016/j.ibiod.2011.09.001ISI: 000297889000001ScopusID: 2-s2.0-80053376565OAI: diva2:460903
QC 20111205. Previous title: Biofilm formation on silicone rubber samples containing different antimicrobial agentsAvailable from: 2011-12-01 Created: 2011-12-01 Last updated: 2015-10-02Bibliographically approved
In thesis
1. Biofilm adhesion on silicone materials
Open this publication in new window or tab >>Biofilm adhesion on silicone materials
2011 (English)Licentiate 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.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2011
National Category
Textile, Rubber and Polymeric Materials
urn:nbn:se:kth:diva-50053 (URN)
QC 20120120Available from: 2012-01-20 Created: 2011-12-01 Last updated: 2012-01-20Bibliographically approved
2. Prevention of Biofilm Formation on Silicone Rubber Materials for Outdoor High Voltage Insulators
Open this publication in new window or tab >>Prevention of Biofilm Formation on Silicone Rubber Materials for Outdoor High Voltage Insulators
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.
TRITA-CHE-Report, ISSN 1654-1081 ; 2015:51
High voltage insulator, silicone rubber, biofouling, biofilm, biocide, superhydrophobicity, self-cleaning, hierarchical roughness
National Category
Polymer Technologies
urn:nbn:se:kth:diva-174091 (URN)978-91-7595-694-7 (ISBN)
Public defence
2015-10-23, K1, Teknikringen 56, KTH, Stockholm, 10:00 (English)

QC 20151002

Available from: 2015-10-02 Created: 2015-09-30 Last updated: 2015-10-02Bibliographically approved

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Atarijabarzadeh, SevilStrömberg, EmmaKarlsson, Sigbritt
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