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Silicone sealants are widely used within the construction industry, where they are appreciated for their thermal and chemical stability. However, sealant joints can be susceptible to microbial growth, especially in warm and humid environments, such as kitchens and bathrooms. Apart from not being very hygienic, the microbial growth on sealants can cause permanent staining and/or etching and shorten the lifespan of joints.
For these reasons, the standards underpinning the CE marking required for products marketed within the European Union are extra-stringent for sealants used in these settings.
“Previous studies seemed to suggest that naphthenic extender oils could have the ability to suppress microbial growth. Therefore, we decided to study the potential effect in a sealant,” says Emma Öberg, Development Engineer at Nynas.
In order to conduct a comparative study, Emma Öberg prepared silicone sealant samples extended with either naphthenic specialty oil or other alternatives in the market.
“So as not to interfere with the study results, no biocide was included in any of the samples,” she points out.
The sealants were then examined at a specialist lab, where standard procedures were used to establish the relative microbial growth in the samples.
“In essence, the procedure involved leaving the samples in separate agar discs at a regulated temperature for the duration of 28 days,” explains Emma Öberg.
The results showed that a transparent RTV-1 acetoxy curing silicone sealant extended with 20 wt% naphthenic specialty oils had a lower level of microbial growth compared with the sealant samples containing other alternative extenders.
“The study results confirmed our initial hunch that our specialist extender oil could have an impact on the bacterial growth in silicone sealants,” says Emma Öberg.
Zero microbes in sight
• To achieve a CE marking, a sealant needs to meet the standards of EN ISO 15651-(1-5):2017, depending on area of application. Sealant materials applied in sanitary joints are tested for microbial growth according to EN ISO 846, where the growth intensity is evaluated visually according to a rating scheme from 0 to 5, Table 1.
• The sealant samples formulated with Nynas’ extender oil NYFLEXΠ 2120B showed no microbial growth even under the microscope, giving these an intensity rating of zero, Table 2. However, sealant samples using an alternative paraffinic (PAR 4 cSt) extender oil had microbial growth visible to the naked eye and rated 2 on the evaluation scale. This rating indicates that up to 25% of the test surfaces or the surrounding agar were covered by microbial growth, relating to fungi or bacteria respectively.
Emma Öberg is a Development Engineer, Chemical Manufacturing Industry, Nynas. She joined Nynas in 2016.