Independent thesis Advanced level (professional degree), 20 credits / 30 HE credits
Silicone rubber is an extensively used material for high voltage insulator applications. The material is occasionally affected by microbial attacks, i.e. microorganisms adhere to the surface and form a biofilm. Although biofilms do not affect the mechanical properties of silicone rubber, the high water content of the film may induce current leakage and failure of the application.
The focus of this study was to investigate the possibility of incorporating a natural/renewable or degradable antimicrobial (AM) agent into the silicone matrix, to prevent the adherence of microorganisms and thus the formation of biofilm. Biofilms have a diverse and complex composition, in this work fungi and algae found on outdoor insulators in Sweden, Sri Lanka and Tanzania were studied.
The efficacy of the antimicrobial agents (thymol, eugenol and THPS) was first studied through the tube dilution method and the minimal inhibitory concentration (MIC) test, to establish the lowest concentration of AM agent required to inhibit growth of algae and fungi respectively. The tube dilution method showed that all three AM agents successfully inhibited the growth of algae, independently of the concentration. Furthermore MIC showed that only thymol at a concentration of 10 wt% inhibits growth of all fungi tested. Due to the high capacity of thymol to inhibit fungi, the incorporation of the substance into the silicone matrix was studied. Disk diffusion test was performed to investigate thymol inhibitory capacity while embedded in the material. The test showed that depending on the manufacture procedure different concentrations of thymol could be retained in the material. Additionally it showed that the antimicrobial silicone is efficient at a concentration of 10 wt% and higher.
The antimicrobial silicone samples were also analysed with TGA and SEM. TGA showed that thymol degraded at 100 ⁰C, so the manufacture of the material is restricted to room temperature vulcanized rubber. It also indicated that thymol not only was lost during manufacture of the material, but also continued to leach out after the curing was completed. SEM showed that thymol crystallizes in the silicone matrix making the material porous.
It can be concluded that thymol is efficient in inhibiting fungi and algae. Due to the rapid leaching mechanism of thymol, the molecule can only be considered for short term applications.
2012. , 28 p.