Fine ceramics (advanced ceramics, advanced technical ceramics) - Test methods for antibacterial activity of semiconducting photocatalytic materials. ISO 27447: 2019 Standard.

Test accredited by ENAC (Spanish National Accreditation Entity), except for viruses.

This standard determines the activity and antimicrobial efficacy of materials that contain photocatalytic products or photocatalytic films on their surface that cause oxidation and reduction reactions under the action of ultraviolet radiation. For this the reduction of the number of several species of bacteria deposited as inoculum on the surface of the test material.

There are two ways of testing: method of covering with glass sheet once inoculated the test material with bacterial suspensions for the tests of fabrics and textile products, and method of covering with transparent adherent sheet intended for the tests of flat sheets, boards and other materials with flat surface. The method of covering with glass sheet uses the bacteria Staphylococcus aureus and Klebsiella pneumoniae, and the method of covering with transparent adherent sheet uses the bacteria Staphylococcus aureus and Escherichia coli. In both methods, the test material is placed inside a Petri dish base on a support, inoculated with the bacterial suspension (0.2 mL with 1 x 105 cells/mL for method with glass slide and 0.15 mL with 6.7 x 105 to 2.6 x 106 cells/mL for adherent sheet method).

In both methods, pieces of the 50 ± 2 mm x 50 ± 2 mm x £ 10 mm thick test material must be used. The number of test pieces is 15, destined in the following groups: 3 units without photocatalytic product to quantify the inoculum control; 3 units with photocatalytic product and another 3 units without photocatalytic product to keep in the same test chamber without exposure to ultraviolet radiation; and 3 units with photocatalytic product and another 3 units without photocatalytic product to keep in the same test chamber with exposure to ultraviolet radiation.

Once the exposure of the test material to the inoculants and to the radiations has been carried out, the existing bacteria in each of the surfaces are quantified, comparing the amount of bacteria existing in the surfaces exposed to ultraviolet radiation with respect to the inoculated surfaces, but not exposed to ultraviolet radiation. For this count, the existing bacteria should be collected from each surface (in total 15 for each bacterium), perform 5 dilutions in base 10, and seed each dilution in duplicate (in total 300 cultures: 15 samples of test products x 2 bacteria x 5 dilutions x duplicate cultures for counting).

The number of pieces of test material would be a minimum of 30 (15 x 2 bacteria), 18 of them without active product, and 12 with the product to be tested, although it would be necessary to receive 60 (36 without the product and with the same surface finish + 24 with the test product), to dispose of them in case it was necessary to repeat a trial.

The client must specify the intensity of ultraviolet radiation at which the material must be irradiated in the tst, in order to simulate the circumstances where the materials are used. The standard proposes four levels of intensity (0.001 mW/cm2; 0.01 mW/cm2; 0.10 mW/cm2; y 0.25 mW/cm2), but the client can request any other intensity within the range. The test must be performed at a mandatory temperature of 25 ± 3ºC. The exposure time to ultraviolet radiation can be from 4 to 8 hours, so the applicant must choose it.

This test is not designed for powdered, granular, or porous photocatalytic materials.