ASTM G 21 - Standard method to determine the resistance of synthetic polymeric materials to fungi.

Test not accredited by ENAC.

The ASTM G 21 test determines the effect of fungi on the properties of synthetic polymeric materials in the form of molded and fabricated articles, tubes, rods, sheets and film-forming materials. Changes in optical, mechanical and electrical properties can be determined by following the corresponding ASTM standards.

The component corresponding to the synthetic polymer of these materials is generally resistant to fungi. This is because the synthetic polymeric material itself does not provide or act as a carbon source for fungi, which is what promotes their growth. Most of the time, those responsible for the growth of fungi in plastic materials are other components such as plasticizers, cellulosics, lubricants, stabilizers and dyes.

After the colonization of the materials by the fungi the following effects could be caused: the attack of their surface, the discoloration, the loss of optical transmission, and the removal of plasticizers, modifiers and susceptible lubricants, giving rise to an increase in rigidity, changes in weight, dimensions and other physical properties, and the deterioration of electrical properties such as insulation resistance, dielectric constant, power factor and dielectric strength. Other effects include preferential growth caused by non-uniform dispersion of plasticizers, lubricants and other processing additives.

The ASTM G 21 method is carried out by inoculating a high combined suspension of spores from five species of fungi: Aspergillus brasiliensis, Penicillium funiculosum, Chaetomium globosum, Trichoderma virens and Aureobasidium pullulans in the culture medium and the pieces subjected to the test. Subsequently, the test pieces, and the positive control (viability control) are maintained for 28 days at a suitable temperature and humidity, before evaluating the effect produced.

The test may only include visual assessment of fungal growth. Additionally, the physical, optical or electrical characteristics of the pieces can be evaluated to determine the change of these properties.

In the IVAMI we only evaluated the observation of the visible effect caused by the development of the fungi on the pieces evaluated after four weeks of confrontation, coding the effects from 0 to 4, with the value 0 corresponding to the absence of growth, and the value 4 to intense growth (on at least 60% of the surface). The report includes images corresponding to the observed effects.

Requirements of test samples for the ASTM G21 test

To perform the test, it is necessary to analyze three pieces. Each replica can be a piece of 50 by 50 mm, a piece of 50 mm in diameter or a cut of a piece (rod or tube) of at least 76 mm of the material to be tested. Film-forming materials, such as coatings, can be tested in the form of films of a size of at least 50 by 25 mm.

 If the sample is different on both sides, three samples will be evaluated for each face.