ISO 846: 2019. Plastics. Evaluation of the action of microorganisms.

Test accredited by ENAC (Spanish National Accreditation Entity).

Under certain climatic and environmental conditions, microorganisms can settle on and colonize the surface of plastics or plastics products. Their presence and/or their metabolic products might not only damage the plastic itself, but can also affect the serviceability of building materials and systems containing plastic parts. The ISO 846 standard specifies 4 methods (methods A-D) for determining the deterioration of plastics due to the action of fungi, bacteria or microorganisms present in the soil. These tests are applicable to all plastics that have a non-porous flat surface.

The 4 tests described by the standard will be selecting according to the intended application for the plastic and the type of resistance to be evaluated. Method A is used to determine the inherent resistance of plastics to fungal attack in the absence of any other organic substance. On the other hand, method B allows to evaluate the fungistatic or fungicidal efficacy of a biocide incorporated in a plastic material, comparing the fungal growth in samples with and without biocide. The resistance of plastics to bacteria is determined by method C (this method does not evaluate antibacterial / hygienic properties, if you want to evaluate the antibacterial performance of a plastic material treated with a biocide, this should be tested according to the Standard ISO 22196). Lastly, the resistance to soil microorganisms of plastics used in permanent contact with the soil is determined using method D. The latter, method D, is not performed in our laboratory.

In the tests using methods A, B and C, plastic specimens are exposed to the action of certain strains of fungi and bacteria for a minimum of 4 weeks, at 29ºC ± 1ºC and a relative humidity of 95% ± 5%. At the end of the exposure, the specimens are evaluated by visual examination and determination of the change in mass. For each sample, three series of tests are prepared: with test specimens inoculated with the test microorganisms (Series I), with non-inoculated reference or control specimens (Series 0) and with sterilized non-inoculated specimens (series S). The results obtained with the specimens exposed to microorganisms are compared with those obtained in the reference specimens or in sterilized specimens, kept under identical conditions. In the case of fungistatic properties tests (method B), samples with biocide and samples free of biocides must be inoculated with the test microorganisms to demonstrate the effect of a biocide in a qualitative way, therefore, series I must include both types of test specimens.

The plastic specimens must be provided by the manufacturer and must be square pieces of 50 mm ± 1 mm on each side, with a recommended thickness of 0.5 mm to 2 mm. For methods A or C, the minimum number of pieces for the visual evaluation and the evaluation of the change in mass is 29 plastic specimens, thus 58 specimens are requested to carry out the tests, in case a result confirmation or a test repetition is needed. For method B, a minimum of 29 plastic specimens with biocide and 11 specimens without biocide is required, therefore 58 plastic specimens with biocide and 32 plastic specimens without biocide are requested, in case a result confirmation or a test repetition is needed. Specimens with and without biocide must be identical, except for their biocide content.

Fungi used for methods A and B: according to the standard, for the tests with plastics without electronic application, a spore suspension of the strains of Aspergillus niger, Penicillium pinophilum, Paecilomyces variotti, Trichoderma virens and Chaetomium globesum will be used; while for tests with plastics with electronic application, a spore suspension of the strains of Aspergillus niger, Penicillium pinophilum, Paecilomyces variotti, Trichoderma virens, Aspegillus terreus, Hormoconis resine and Scopulariopsis brevicaulis will be used. Other test microorganisms can be used.

Bacteria used for method C: according to the standard, the tests are carried out with the bacterium Pseudomonas aeruginosa. Other bacteria can be tested.

For the evaluation of the results in the tests with fungi, a visual assessment, with a stereoscopic microscope if needed, is performed, assigning a gradation from 0 to 5, according to the absence or intensity of the growth degree. To determine the variations in mass, the pieces are weighed before and after the test to determine if the mass of the specimens has varied significantly.