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Microbiological growth testing of polymeric materials: an evaluation of new methods
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.ORCID iD: 0000-0002-2139-7460
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.ORCID iD: 0000-0002-5394-7850
2005 (English)In: Polymer testing, ISSN 0142-9418, E-ISSN 1873-2348, Vol. 24, no 5, 557-563 p.Article in journal (Refereed) Published
Abstract [en]

Biofilms growing on high voltage insulators made of silicone rubber cause changes in appearance and properties of the silicone material. This study presents the design and building of microenvironment chambers simulating outdoor environment and the use of these for long-term studies of the development of mixed biofilms on silicone rubber materials. Results from the microenvironment chambers are compared to standard test procedures used in combination with new methods to evaluate the effect of two common flame retardants, ATH and zinc borate, on the development of a biofilm. Algae, bacteria and fungi isolated from silicone rubber insulators collected from Tanzania, Sri Lanka and Sweden, respectively, were used in the tests performed. Results show that zinc borate has a protective effect against all the microorganisms tested.

Place, publisher, year, edition, pages
2005. Vol. 24, no 5, 557-563 p.
Keyword [en]
Algae; Biofilm; Fungi; Insulators; Silicone rubber; Zinc borate
National Category
Polymer Chemistry
Identifiers
URN: urn:nbn:se:kth:diva-5034DOI: 10.1016/j.polymertesting.2005.02.005ISI: 000229979000004Scopus ID: 2-s2.0-19144366150OAI: oai:DiVA.org:kth-5034DiVA: diva2:7662
Note
QC 20100811Available from: 2005-04-18 Created: 2005-04-18 Last updated: 2017-12-05Bibliographically 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.

Series
Trita-FPT-Report, ISSN 1652-2443 ; 2005:13
Keyword
Chemical engineering, polymer technology, Kemiteknik
National Category
Chemical Engineering
Identifiers
urn:nbn:se:kth:diva-171 (URN)91-7283-999-6 (ISBN)
Public defence
2005-04-21, Kollegiesalen, KTH, Valhallavägen 79, Stockholm, 13:00
Opponent
Supervisors
Available from: 2005-04-18 Created: 2005-04-18 Last updated: 2012-03-21Bibliographically approved
2. Long-term Properties of Sustainable Polymeric Materials: Mechanical Recycling and Use of Renewable Resources
Open this publication in new window or tab >>Long-term Properties of Sustainable Polymeric Materials: Mechanical Recycling and Use of Renewable Resources
2009 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

New strategies for management of the accumulating amounts of plastic waste are required, to achieve a sustainable development in terms of material production and use. After service life, the materials should be recovered and recycled efficiently to provide a valuable resource for future applications. Optimised use of amended recycled polymeric materials, e.g. reinforced with natural fibres, and polymers from renewable resources give rise to polymeric materials with lower environmental impact. The recovery of plastic waste by means of mechanical recycling is a favourable route for preservation of raw materials and energy. Deficient knowledge about the overall quality of the recyclates, such as the degree of degradation, mixing and contamination, has resulted in restricted subsequent application of the recycled materials. Therefore, quality assessment of the recycled polymers is required for guaranteed performance in future applications.

Recycling and service life of polyolefins (PP and HDPE) were modelled by multiple reprocessing and thermo-oxidation. The material properties of the polyolefins were affected by both thermo-oxidation and thermo-mechanical degradation. PP showed higher susceptibility to reprocessing and elevated formation of low molecular weight compounds compared to HDPE. Release of the compounds during service life is anticipated on account of the extensive migration of these volatiles during thermal ageing.

Microenvironment chambers simulating outdoor environmental conditions were designed to monitor biofilm formation on silicon rubber composite materials. Furthermore, the microenvironments were successfully used to determine the long-term properties of biocomposites, consisting of conventional or biodegradable polymeric matrices and natural fibres as reinforcement, by subjecting the materials to a hydrolytic environment and microbiological degradation. Facilitated surface colonisation due to the presence of cellulose fibres in the composites was mainly attributed to water uptake. Biodegradation of PP biocomposites influenced mainly the surface properties whereas for PLA the bulk properties were also highly affected.

PP-clay nanocomposites were subjected to simulated environmental degradation by thermo-oxidation, daylight photo-oxidation and exposure to forest soil. Increased crystallinity and surface oxidation were detected after thermo-oxidation of the materials. The presence of clay promoted formation of carbonyl compounds during photo-oxidation and water uptake during exposure to soil.

Place, publisher, year, edition, pages
Stockholm: KTH, 2009. 62 p.
Series
Trita-CHE-Report, ISSN 1654-1081 ; 2009:44
Keyword
Sustainable materials, mechanical recycling, polyolefin, reprocessing, accelerated ageing, chromatography, biofilm, microenvironment chamber, environmental degradation, biocomposite, nanocomposite
National Category
Polymer Chemistry
Identifiers
urn:nbn:se:kth:diva-10934 (URN)978-91-7415-402-3 (ISBN)
Public defence
2009-09-17, F3, KTH, Lindstedtsvägen 26, Stockholm, 10:00 (English)
Opponent
Supervisors
Note
QC 20100811Available from: 2009-09-03 Created: 2009-08-25 Last updated: 2010-08-11Bibliographically approved

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Strömberg, EmmaKarlsson, Sigbritt

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