Increasing the effectiveness of a liquid biocide component used in antifungal waterborne paints by its encapsulation in mesoporous silicas

Abstract

SBA-15 and MCF mesoporous silicas were used as solid porous adsorbent for supporting a liquid commercial biocide, and the biocidal activity of the so-obtained loaded solids was checked after being incorporated in a waterborne paint. Starting from an acrylic latex free of biocidal agent, three series of paint formulations were obtained: two series were prepared by adding increasing amounts of the different biocide compounds (one series using SBA-15 and the second using MCF supported biocide) and a third series where the nonsupported, liquid biocide was added instead. Afterwards, the biocidal activity against Alternaria alternata of the different coatings prepared was measured by means of the current standard procedures used for dry coating sample evaluation. An increase in the inhibitory activity and a lower development of the fungal mycelium were generally observed when the concentration of the encapsulated biocide was increased. The film samples, corresponding to the two coatings formulated using a 2 wt.% of biocide loaded in MCF silica, showed a total inhibition of fungus growth after 1 month, in spite of the clear deterioration observed when the liquid biocide at 2 wt.% was incorporated. These two paints were selected for being tested under more severe deterioration conditions in the presence of Aspergillus fumigatus, Alternaria alternata and Chaetomium globosum spores. The paint films incorporating MCF loaded silica exhibited optimal efficiency, presenting a null development of the inoculated strains after 9 months. This behavior could be associated with the shape and pore size of the MCF particles, which favor biocide intraparticle diffusion, and also with the low density of this disordered material, which promotes its location close to the top surface of the dry paint.