UNE-EN ISO 846: 1998. Plastics. Evaluation of the action of microorganisms.

Test accredited in our laboratory by ENAC (National Accreditation Entity).

This standard guideline determines the action of microorganisms (fungi, bacteria or soil microorganisms) on plastic materials, deteriorating them, either when their components are used as nutrients by microorganisms, or by altering their appearance due to the effect of some metabolites of microorganisms on the color or other characteristics of the plastic. In this test, plastic pieces are exposed to the action of fungi, bacteria, or a microbiologically active soil, for specified periods of time, and under defined conditions of humidity and temperature. After the exposure, the plastic pieces are evaluated before and/or after cleaning by a visual examination and/or determining any variation in the mass or other physical properties, comparing the pieces of plastic exposed to the biological attack with those not exposed. The plastic parts must be supplied by the manufacturer and shall be 0.5 mm maximum thickness and 30 to 60 mm side when variations in thickness must be measured; and from 0.5 to 2 mm thick and 30 to 60 mm side when variations of its mass must be measured. The minimum number of pieces, for the tests evaluated by visual examination should be 15, for each sample to be evaluated and for each method of assay (minimum 5 -five- species of fungi for methods A, B, B', and 1 -one - species of bacteria for method C), and 18 pieces when the variation in the mass must be determined. Resistance can be determined in several ways:

Method A: effect of fungi, exposing the plastic to fungal spores in an incomplete culture medium without a carbon source, whereby the fungi can only grow and develop mycelia at the expense of the plastic material;

Methods B and B': fungistatic effect of fungi, exposing the plastic to fungal spores in a complete medium in which the fungus develops, so that the metabolites of the fungus could degrade the plastic, if there is an inhibition of the fungus it should be to a fungistatic or fungicidal effect of the plastic on the fungus, the method B' differs from method B, in that it performs the exposure of the pieces when the culture is fully developed;

Method C: similar to method A, but using bacteria instead of fungal spores;

Method D: burying plastic pieces in a natural soil with a known water retention capacity.

Fungi used (minimum 5 species): Aspergillus niger, Penicillium funiculosum, Paecilomyces variotti, Gliocladium virens and Chaetomium globosum; other species chosen by the client can be used if necessary; for the effect on electronic components the four indicated first species should be used, and Aspergillus terreus, Aureobasidium pullulans, Penicillium ochrochloron and Scopulariopsis brevicaulis);

Bacteria used (Pseudomonas aeruginosa). The minimum follow-up time for the methods is 4 weeks, which can be increased according to the client's requirements. For the evaluation of the result in the tests with fungi, a visual examination is performed with a stereoscopic microscope, assigning a gradation from 0 to 5, according to the absence or intensity of the grade growth. For the mass variations, the pieces, once clean and dry, should be weighed to the nearest 0.1 mg, and the corresponding calculations should be made. The growth intensities obtained allow to establish an interpretation of the absence or presence, and in case of the amount, of nutritive substances for microorganisms in the plastic.