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Development and comparison of test methods for evaluating formation of biofilms on silicones
KTH, Superseded Departments, Polymer Technology.
KTH, Superseded Departments, Polymer Technology.ORCID iD: 0000-0002-5394-7850
2002 (English)In: Polymer degradation and stability, ISSN 0141-3910, E-ISSN 1873-2321, Vol. 78, no 2, 257-262 p.Article in journal (Refereed) Published
Abstract [en]

Silicone rubber formulations used for outdoor high voltage insulation are sometimes reported to be colonized by microorganisms. Different formulations show different sensitivity towards biological growth. In this study five rubbers were tested. Two standard practices were used, ASTM G21-90 and IEC 68-2-10. In addition a new method was developed to measure the rate of colonisation of a sample by biological growth. Results showed that the tested rubbers supported fungal growth when an external carbon source was available. Thus none of the silicones can be called bio-resistant. However the materials are not biodegradable either. This was clearly shown when mould spores were added to the samples in clean water, when none of the rubbers was contaminated. Some of the materials did, however, support growth when only nutrient salts, no carbon source, was added. The most bioresistant formulations contained the flame retardant zinc borate, indicating that this additive suppresses fungal growth. Further investigation with the new method supported that theory.

Place, publisher, year, edition, pages
2002. Vol. 78, no 2, 257-262 p.
Keyword [en]
Biofilm, Biological growth, Flame retardants, Fungus, High voltage insulation, Silicone rubber
National Category
Chemical Engineering
URN: urn:nbn:se:kth:diva-5032DOI: 10.1016/S0141-3910(02)00140-4ISI: 000178534800007OAI: diva2:7660
QC 20100908. Uppdaterat från In press till Published (20100908)Available from: 2005-04-18 Created: 2005-04-18 Last updated: 2010-09-08Bibliographically 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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Wallström, StinaKarlsson, Sigbritt
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