Porcelain stoneware tiles with antimicrobial action

This work reports the development of extruded porcelain stoneware tiles that show antimicrobial (to act as a barrier to the bacteriaʹs growth during a long period of time), and anti-stain (easy to clean) actions, and possess high chemical resistance. The antimicrobial action was proven through the reduction of Gram-positive Staphylococcus aureus and Gram-negative Escherichia coli bacteria. Staining and chemical resistance were tested according to ISO 10545-14 and 10545-13 standards, respectively. The tiles promote a population reduction of over 77% and 81% for the S. aureus and the E. coli bacteria, respectively. The optimized product was obtained by adding 2.5 wt% of a black ceramic pigment to the industrially-prepared paste, followed by the application of a small quantity of glaze (by jet spraying). Chemical (solution of 98 wt% NaNO3 and 2 wt% AgNO3) and thermal (2 h at 430 °C) treatments were finally applied to get the active surface. In terms of anti-staining characteristics the tiles belong to class 5, while their chemical resistance is excellent (UA, ULA and UHA) against almost all aggressive agents, except for chloridric acid, 18% (v/v), for which a small surface attack (UHB) was observed. Furthermore, the treatments used (chemical and thermal) do not change the surface aspect of the product, and thus fulfil the industrial/commercial requirements.