Characterisation and development of antifouling coatings for metal surfaces in aquatic environments

Volschenk, Mercia (2015-04)

Thesis (MSc)--Stellenbosch University, 2015.

Thesis

ENGLISH ABSTRACT: Biofouling in cooling water systems lead to several problems resulting in reduced efficiency and financial losses. Antifouling coatings present an environmental friendly solution to prevent biofouling alternatively to the current use of toxic chemicals in cooling water systems. In this study biofilm growth in a cooling water system was simulated in a modified flow cell system to evaluate industrial antifouling coatings and biocide-enriched coatings as potential antifouling coatings for metal surfaces. The design of a novel antifouling coating was also attempted. Firstly, analytical methods for biofilm monitoring to evaluate selected antifouling coatings and biocides were optimised. Pseudomonas sp. strain CT07 was selected to grow biofilms in the biofilm studies. A metal alloy of stainless steel and mild steel (3CR12) showed no corrosion after a 24 h biofilm growth and was selected as metal surface for the biofilm growth discs. Sonification for 5 min was determined as the optimum biofilm removal method from the growth discs. After biofilm removal the metal growth discs were stained with the LIVE/DEAD® BaclightTM Bacterial Viability kit. Visualisation by confocal laser scanning microscopy and flow cytometry revealed auto fluorescence signals from metal discs that hindered quantitative and qualitative analysis of the metal substrate. The use of Pseudomonas sp. strain CT07::gfp to grow biofilms on the metal growth discs and the exclusion of the stain SYTO9 from the LIVE/DEAD® BaclightTM Bacterial Viability kit reduced auto fluorescence signals from the metal discs. The industrial coatings containing quaternary ammonium salt (QAC), triclosan (TC) and copper oxide (CUO) respectively, showed the highest antimicrobial activity in the disc diffusion test. The minimum inhibition concentrations for silver nitrate (SN) and copper sulphate (CS) were 432 ppm and 160 ppm respectively. A minimum of 6.25 % of furanone solution (FR) was biocidal in the dilution susceptibility test. Secondly, the metal growth discs were coated respectively with the three selected industrial coatings QAC, TC and CUO and the epoxy biocide-enriched coatings SN, CS and FR and chemically characterised before and after exposure to biofilm formation. The antifouling activity of these coatings was also characterized. Growth media inoculated with Pseudomonas sp strain CT07::gfp was circulated through the modified flow cell system via a multichannel peristaltic pump for 48 h before the coated metal discs were removed and washed to perform chemical or antifouling analysis. All the industrial coatings and biocide enriched epoxy coatings complied with the thermal stability requirements of a cooling water system. Scanning electron microscopy (SEM) imaging and Energy dispersive X-ray spectroscopy (EDX) analysis confirmed that the adhesion properties of industrial coatings TC and QAC in aqueous environments were insufficient and that the copper and silver ions leached out of the biocide-enriched epoxy coatings. The qualitative analyses of the attachment of bacteria on the surfaces of both the industrial and biocide enriched epoxy coatings was confirmed by SEM, CLSM. The attached bacteria were removed and analysed quantitatively through plate counts and flow cytometry. None of the industrial coatings or the biocide incorporated epoxy coatings that were used in this study would therefore be efficient for the use on metal surfaces in cooling water systems. Thirdly, several approaches were followed to synthesise a poly(styrene-alt-maleic anhydride) (SMA) coating, chemically bind a furanone derivative, 2,5-dimethyl-4-hydroxy-3-(2H)-furanone, to the polymer back bone of the SMA coating for the application as an antifouling coating for cooling water systems. The synthesis of SMA was confirmed through 1H NMR and SEC and the synthesis of tert-butyl 2-(2-hydroxyethoxy) ethylcarbamate and 4-(2-(2-(tert-butoxycarbonyl)ethoxy)ethoxy)-4- oxobutanoic acid was confirmed through 1H NMR and ES-MS+. The synthesis of the end furanone derivative product could however not be achieved.

AFRIKAANSE OPSOMMING: Bio-aanpaksels in waterverkoelingsisteme veroorsaak talle probleme wat lei tot verminderde doeltreffendheid en finansiële verliese. Antimikrobiese oppervlakbedekkings verskaf ‘n omgewingsvriendelike oplossing om bio-aanpaksels te voorkom en ‘n alternatief vir die huidige gebruik van giftige chemikalieë in waterverkoelingsisteme. Biofilm groei in waterverkoelingsisteme was nageboots in ‘n gewysigde vloeiselsisteem om industriële aanpakwerende en biopsied bevattende antimikrobiese oppervlakbedekkings as potensiële aanpakwerende beskermingslae vir metaaloppervlaktes te evalueer. Die ontwerp van ‘n nuwe aanpakwerende beskermingslaag is ook ondersoek. Eerstens is analitiese moniteringsmetodes vir bio-aanpaksels op geselekteerde aanpakwerende antimikrobiese oppervlakbedekkings en biosiedes geoptimiseer. Pseudomonas sp. stam CT07 was verkies om bio-aanpaksels te simuleer gedurende hierdie studie. ‘n Metaalalooi van vlekvrye staal en sagte staal (3R12) het geen korrosie getoon na 24 uur se groei van bio-aanpaksels nie en is vir hierdie rede gebruik as metaal vir die bio-aanpaksel groeiplate. Dit was vasgestel dat sonifisering die optimale verwyderingsmetode vir groeiplate was. Na verwydering van bio-aanpaksels was die metaal groeiplate bedek met die LIVE/DEAD® BaclightTM bakteriële lewensvatbaarheid-toestel. Visualisering deur middel van konfokale mikroskopie en vloeisitrometrie het outofluoreserende seine vanaf die metaal groeiplate onthul wat kwantitatiewe en kwalitatiewe analise van die metaal substraat verhinder het. Die gebruik van Pseudomonas sp. stam CT07:gfp om bio-aanpaksels te kweek op metal plate en die uitsluiting van SYT09 van die LIVE/DEAD® BaclightTM bakteriële lewensvatbaarheid-toestel, het die outofluoreserende seine van die metaalskywe verminder. Industriële beskerminglae, wat onderskeidelik Kwaternêre ammonium sout (QAC), triclosan (TC) en koperoksied (CUO) bevat, het die hoogste antimikrobiese aktiwiteit in die skyf-diffusie toets getoon. Die minimum inhibisiekonsentrasies vir silwernitraat (SN) en kopersulfaat (CS) was onderskeidelik 432 dpm en 160 dpm. ‘n Minimum konsentrasie van 6.25% van die furanoonoplossing (FO) is geklassifiseer as ‘n biosied in die oplossingstoets.Tweedens was die metaal groei-skywe bedek met drie industriële beskermingslae QAC, TC en CUO en die epoksie-biosied-verrykte lae SN, CS en FR en chemiesgekarakteriseerd voor en na die vorming van bio-aanpaksel. Die karaktereienskappe van die aktiwiteit van die beskermingslae was ook vasgestel. Opgeloste triptiese soja sop vermeng met Pseudomonas sp strain CT07: gfp was gesirkuleer in die gemodifiseerde vloeisel deur ‘n multikanaal peristaltiese pomp vir 48 uur voordat die beskermde metaalskywe verwyder en gewas is om chemiese en aanpakwerende analise uit te voer. Al die industriële beskermingslae en biosied-verrykte epoksie-beskermingslae het aan die vereistes van termiese stabiliteit van ‘n waterverkoelingsisteem voldoen. Skandeer elektronmikroskopie (SEM) en X-straal spektroskopie (EDX) analise het aangetoon dat die aantrekkingseienskappe van industriële beskermingslae TC en QAC in waterige oplossings onvoldoende was en dat die koper- en silwerione uit die biosiedverrykte epoksie-resin beskermingslae diffundeer. Die kwalitatiewe analise van die aanpaksel van bakterieë op die oppervlaktes van beide industriële en biosied -verrykte epoksie-beskermingslae was bevestig deur SEM en CLSM. Die aangepakte bakterieë was verwyder en kwantitatief geanaliseer deur middel van plaattellings en vloeisitrometrie. Nie een van die industriële beskermingslae of die biosied-bevattende epoksie beskermingslae wat in hierdie studie gebruik is, is dus gepas vir gebruik op metaaloppervlaktes in waterverkoelingsisteme nie. Derdens was verskeie pogings aangewend om ‘n poli(stireen-alt-maleic anhidried) (SMA) beskermingslaag chemies te bind tot ‘n furanoon afgeleide 2.5-demitiel-4-hidroksie-3-(2H)- furanoon, tot die polimeer-ruggraat van die SMA beskermingslaag vir aanwending as ‘n aanpakwerende beskermingslaag vir waterverkoelingsisteme. Die sintese van SMA was bevestig deur 1H NMR en SEC en die sintese van tert-butyl 2-(2-hirdoksie-etoksie) etielkarbamaat en 4-(2- (2-(tert-butoksiekarboniel)etoksie)etoksie)-4-oksobutanoiesesuur was bevestig deur 1H NMR en ES-MS+. Die sintese van die uiteindelike afgeleide furanoon kon egter nie behaal word nie.

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