Fungal resistance of plastics and synthetic polymeric materials is determined by ASTM G21. The test polymeric materials can be in the form of fabricated and molded articles, sheets, tubes, rods, and film materials. The changes in mechanical, optical, and electrical properties are also determined. Usually, the synthetic polymeric materials are resistant to fungi but there might be additives used in the polymer such as stabilizers, colorants, and plasticizers that may not be resistant to fungi and may contribute to fungal growth. ASTM G21 is typically used to test the products that are made from plastics and foam but it can also incorporate a wide range of other products and materials.
For Fungus Testing by ASTM G21, the fungi are grown on solid apparatus. A pooled spore suspension is made from Chaetomium, Aspergillus, Penicillium, Aureobasidium, and Trichoderma spores. The spore suspensions are cleaned thoroughly, eluted in a solution having minimum salt, and then standardised. The test samples are placed in triplicate in a petri dish or other suitable containers with minimum salt agar before pooled spore is sprinkled on the test samples. This process is repeated for the negative control i.e., agar only and positive control i.e,. fungal growth control. These preparations are incubated for about 28 days in suitable humidity conditions. A performance score is given for the samples on the basis of fungal growth after 28 days and pictures of each test sample are taken at uniform intervals.
The simplest sample can be of 5050 mm (22 inches) piece, a diameter piece of 50 mm ( 2 inches), or a rod or tubing piece of 76 mm (3 inches) long for the ASTM G21 practice. The film-forming materials like coatings can be tested in the form of films having at least 5025 mm (21 inch) in size.
The visual rating of fungus growth
Magnification for rating
Table of progressive change