Enhanced activity of commercial biocides by encapsulation in mesoporous silicas

LUCAS E. MARDONES; M. SOLEDAD LEGNOVERDE; NATALIA BELLOTTI; ELENA I. BASALDELLA

Santa Fe

Conferencia; VI San Luis Conference on Surfaces, Interfaces, and Catalysis; 2018

The use of two typesof nanostructured materials as new hosts for stabilizingisothiazolinone-based biocides was investigated. SBA-15 mesoporous silica wasprepared according to the methodology described by Zhao1 and mesocellularsiliceous foam (MCF) was obtained employing a procedure described by Schmidt-Winkel2.The physicochemical properties of the silicas (structure, textural properties)were evaluated in order to determine their ability to encapsulate, stabilizeand subsequently release a commercial biocide used for latex preservation3(CMIT/MIT). CMIT/MIT consists of an aqueous solution of the active ingredientsCMIT (5-chloro-2-methyl-4-isothiazolin-3-one) and MIT(2-methyl-4-isothiazolin-3-one), present in a CMIT/MIT: 3/1 weight ratio4.The successful loading of biocide in the mesoporous silica materials wasevidenced by the decrease of pore diameters, pore volumes, and BET surface areasafter the CMIT/MIT mixture adsorption. The SBA-15 support exhibits a loweradsorption capacity of biocide molecules than MCF, which may be attributed toboth higher MCF pore volume and pore size. It was observed by FTIR that thebiocide can be encapsulated in both silica frameworks without sufferingstructural damage. The formulation of the waterborne coating was made, and thendifferent batches of the same paint were separated. Different quantities of theliquid biocide, the solids without biocide and the solids with adsorbed biocide,were separately added to each batch. A batch was also left without any type ofbiocidal protection. The different coating batches were applied over glasssubstrates. The antifungal activity against Alternariaalternata (AA) of these dry paint films was determined. After four weeks thefree biocide coating and the coating with the materials without encapsulated biocideshowed no antifungal activity. The formulations including the non-supportedliquid biocide and the biocide encapsulated onto SBA-15 showed a moderate fungusgrowth. The encapsulated biocide onto MCF paint showed a total inhibition ofthe microorganism growth. A second essay was carried out with this coating. Thesample was placed in an environmental chamber with controlled relative humidityfor 6 months. Relative humidity and temperature were regulated inside thechamber by 99% and 21 ± 1ºCrespectively. Thepaint was inoculated with a spore suspension of Aspergillus fumigatus, Alternariaalternata and Chaetomium globosum. The coating with the biocide encapsulated onto MCFshowed an optimal efficiency, without development of any of the inoculated fungi.Results indicate that the biocide encapsulation onto MCF silica could be abeneficial tool for improving the resistance of waterborne coating formulationsto the deleterious microbiological attack.