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Biofilms on silicone rubber insulators; microbial composition and diagnostics of removal by use of ESEM/EDS - Composition of biofilms infecting silicone rubber insulators
KTH, Superseded Departments, Fibre and Polymer Technology.
KTH, Superseded Departments, Fibre and Polymer Technology.ORCID iD: 0000-0002-5394-7850
2004 (English)In: Polymer degradation and stability, ISSN 0141-3910, E-ISSN 1873-2321, Vol. 85, no 2, 841-846 p.Article in journal (Refereed) Published
Abstract [en]

Silicone rubber high voltage insulators are sometimes reported to be colonised by microorganisms. When the hydrophobic polymeric surface is covered by a hydrophilic biofilm, the isolating properties of the insulator are reduced. However, cleaning the surface can restore the function of the insulator. In this study biofilms colonising insulators from Tanzania, Sri Lanka and Sweden were investigated. Results showed that the examined biofilms shared several properties. Small unicellular green algae associated with bacteria and filamentous fungi dominated all samples. Environmental scanning electron microscopy (ESEM) with X-ray energy disperse spectroscopy (EDS) is proposed as a new method to determine if an infected surface can be cleaned.

Place, publisher, year, edition, pages
2004. Vol. 85, no 2, 841-846 p.
Keyword [en]
silicone rubber, high voltage insulation, biofilm, algae, fungi, ESEM/EDS
National Category
Engineering and Technology
URN: urn:nbn:se:kth:diva-5033DOI: 10.1016/j.polymdegradstab.2004.02.014ISI: 000223254300012ScopusID: 2-s2.0-3042647452OAI: diva2:7661
QC 20100901 Available from: 2005-04-18 Created: 2005-04-18 Last updated: 2011-09-26Bibliographically approved
In thesis
1. Biofilms on silicone rubber for outdoor high voltage insulation
Open this publication in new window or tab >>Biofilms on silicone rubber for outdoor high voltage insulation
2005 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

Silicone rubber high voltage insulators are sometimes colonised by microorganisms which form a biofilm on the surface of the infected unit. In this work insulators exposed to the outdoor environment in Sweden, Sri Lanka and Tanzania respectively have been studied. The biofilms colonising the insulators were shown to be of roughly the same composition regardless of their origin. Algae in association with bacteria dominated the biofilms and provided nutrition to mold growth. The isolated microorganisms were further used to study the effect of a biofilm on different silicone rubber materials. New tools for diagnosing biological growth on polymeric materials were developed and used to analyse the silicone rubber samples.

No evidence of biodegradation of the polydimethylsiloxane (PDMS) molecule has been found in this work. However, this does not mean that PDMS rubbers used in high voltage insulators can be called bioresistant. Silicone insulating materials always contain additives and these may promote or hinder growth. For this reason, an extensive test program was developed, in order to evaluate the effect of different additives on the degree of biological growth. The program spanned from fast and easy methods, useful for screening large amount of samples, to the construction of specially designed microenvironment chambers in which mixed biofilms, similar to those formed on the surface of silicone rubber insulators in the field, were successfully grown.

The test program showed that the flame retardant zinc borate protected the materials, whereas alumina trihydrate (ATH) did not hinder biological growth. On the contrary, environmental scanning microscopy (ESEM) in combination with X-ray energy dispersive spectroscopy (EDS) showed that the surface roughening caused by the addition of ATH to the silicone rubber matrix made the materials more difficult to clean.

Furthermore when the hydrophobic surface of a silicone rubber insulator is covered by a hydrophilic biofilm this leads to a reduction of the surface hydrophobicity of the material. This may alter the electrical properties of the insulator. It is therefore important to develop methods to identify biofouled units. In this work, laser-induced fluorescence (LIF) spectroscopy was explored as a tool for the detection of biofilms on silicone rubbers. The experiments revealed that weak traces of algae or fungal growth, even those not visible to the naked eye, could be detected by this technique. In addition, it was shown that photography and subsequent digital image analysis could be utilised to estimate the area covered by biofilm growth. The results obtained indicate that LIF spectroscopy in combination with image analysis could be used for field diagnostics of biological growth on insulators in service.

Trita-FPT-Report, ISSN 1652-2443 ; 2005:13
Chemical engineering, polymer technology, Kemiteknik
National Category
Chemical Engineering
urn:nbn:se:kth:diva-171 (URN)91-7283-999-6 (ISBN)
Public defence
2005-04-21, Kollegiesalen, KTH, Valhallavägen 79, Stockholm, 13:00
Available from: 2005-04-18 Created: 2005-04-18 Last updated: 2012-03-21Bibliographically approved

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