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ASTM G21
Standard Method for Determining Resistance of Synthetic Polymeric Materials to Fungi
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ASTM G21 – Antifungal Resistance Test
ASTM G21 is a standard test method used to determine the resistance of synthetic polymers and plastic materials to fungal growth. Synthetic polymers, in themselves, are generally resistant to fungi because they do not provide the necessary nutrients for fungal growth. However, ingredients that are added during the production of these materials like plasticizers, lubricants, stabilizers, cellulose and colorants can enhance the growth of fungi. Therefore it is essential to check the resistance of these materials to fungal growth thus ensuring the material’s durability and longevity.
Why test for antifungal resistance?
The growth of fungi on plastic materials accelerates the rate of plastic deterioration whereby the strength and performance of the material is affected. This is a major concern when these products are used in areas that are exposed to moisture and organic load which may trigger fungal growth. Antifungal testing helps identify susceptible materials and allows manufacturers to improve their formulations ensuring long-lasting products.
ASTM G21 Test Requirements
Test Specimens
The ASTM G21 test requires specific specimens to be tested for fungal resistance:
- Standard specimens – Typically, specimens with dimensions of 50mm×50 mm are selected.
- Rod or tube specimens – Specimens with a minimum size of 76 mm are used.
- Film-forming materials – Films with dimensions of 50mm×25 mm (2 inches×1 inches) are selected.
- Differing surfaces – If a specimen has different surfaces three specimens are tested each with different surface orientations (face up and face down).
ASTM G21 Testing organisms
Aspergillus brasiliensis, Aureobasidium pullulans, Chaetomium globosum, Trichoderma virens, Penicillium funiculosum are the test organisms. These fungi are chosen due to their prevalence in various environments and their ability to grow on a wide range of materials including materials containing plasticizers, cellulose, lubricants, stabilizers, and colorants as food sources.
ASTM G21 Test methodology
Preparation and inoculation
- The test specimens are placed on the solidified surface of nutrient salt agar and inoculated with a spore suspension. This setup mimics real-world conditions where fungi encounter the materials in a nutrient-rich environment.
- Control specimens which are untreated are also inoculated and incubated alongside the test specimens to provide a baseline for comparison.
Incubation
- The inoculated specimens are sealed and incubated at a temperature range of 28°C to 30°C under 90% relative humidity conditions.
- The standard incubation period is 28 days but the test can be terminated earlier if the test specimens exhibit significant fungal growth typically indicated by a growth rating of two or more.
Evaluation and rating
After the incubation period, the specimens are evaluated based on a rating scale from 0 to 4 which reflects the extent of fungal growth:
Rating Scale | Description |
0 | No growth on the specimen |
1 | Traces of growth on the specimen (less than 10 %) |
2 | Light growth (10 to 30 %) |
3 | Medium growth (30 to 60 %) |
4 | Specimens completely covered with growth (60 %) |
This rating scale provides a clear and quantifiable measure of the antifungal efficacy of the tested materials.
Importance of ASTM G21
Ensuring material longevity and durability
The test is highly useful in assessing the durability of any synthetic polymer as well as plastic material. Fungal growth on such products can greatly reduce their structural durability and visual appeal thus affecting the product’s integrity.
Enhancing safety and hygiene
Several industrial sectors including healthcare and food packaging can be negatively affected by fungal presence. Fungal growths on medical devices, packaging material or any surface that comes into contact with foods lead to contamination and spread of infections. This test makes sure that the materials used for these vital applications will not support the growth of fungi hence increasing safety and sanitation. This is particularly important in sterile environments where even minimal fungal contamination can have severe consequences.
Compliance with industry standards
Compliance of fungi resistant polymers and plastics with this standard provides them access to the market and brings credibility.
Supporting innovation and development
This standard is a good tool for research and development in material science. Understanding how different additives and formulations affect fungal resistance can help researchers develop new materials with unique improved properties. This test provides key information necessary for the formulation of new plastics and polymers that have higher resistance to fungal degradation while at the same time being durable, biodegradable, and sustainable.
Versatility in application
This test is applicable to a wide range of materials and products. From coatings and films right through to tubes, rods and fabricated articles, the test can be applied to various types of synthetic polymers and plastics.
Enhancing consumer confidence
Quality assurance of products plays a significant role in determining the confidence levels of consumers. Hence it is crucial to understand that certification for fungal resistance testing helps build consumer confidence regarding quality, safety and durability of the product.
Supporting sustainable practices
The test contributes to sustainability by encouraging the use of strong and fungus-resistant products that helps to avoid their rapid deterioration by fungi thus reducing regular replacements. This serves to reduce waste and conserve the available resources to the maximum possible extent.
Real-world applicability
The test method effectively simulates real-world conditions making it a reliable predictor of how materials will perform during actual use. This is particularly important for industries where the material can be exposed to environments that favor fungus growth such as the marine sector, construction and healthcare sectors.
At Microbe Investigations (MIS), we test the efficacy of antifungal plastic finishes using ASTM G21 test and other standard test methods like AATCC-30. With a team of experts and advanced technology capabilities, MIS provides a comprehensive suite of quality antiviral, antibacterial, and antifungal testing services worldwide.
Contact our experts here to know about pricing, turnaround times, and other related queries.
FAQs
ASTM G21 is a standard test method that is used to qualitatively assess the resistance of synthetic polymer materials to fungal growth.
A wide range of materials can be tested using this standard. These include but are not limited to molded and fabricated articles, tubes, rods, coatings, pipes, marine plastics, sheets and film materials. This wide range of applicability makes it an important test for various industries.
It takes approximately 4-6 weeks to complete this test. This period allows for the thorough incubation and growth of the test specimens thus ensuring accurate and reliable results.
At MIS, Aspergillus niger (ATCC-16888) is tested for ASTM G21. However, additional strains like Penicillium funiculosum, Chaetomium globosum, Gliocladium virens, Aureobasidium pullulans can be included based on the customer’s specific testing requirements.
To prepare the fungal spore suspension, streak the fungal culture on the agar medium and allow it to sporulate. Harvest the spores by flooding the Petri dish with sterile water or saline and filter the suspension through sterile gauze or cheesecloth to remove the mycelial fragments. Dilute the spore concentration by adding sterile water or saline followed by enumeration.
This test includes temperature and humidity parameters which usually range between 28-30°C and the humidity of around 90-100%. Samples are incubated at 28 days and test materials are exposed to a spore suspension of the selected fungi.
This test is used to measure the ability of synthetic polymeric materials to resist fungal growth using a standard fungal culture which is known to decompose plastics. It sets specific conditions of temperature, humidity, and incubation time, and visually evaluates the degree of fungal growth on a scale, which defines material resistivity.
This test identifies fungal susceptibility to improve formulations for better material durability and longevity and ensures quality assurance through standardized methods. This shall enable manufacturers to enhance their product quality and consistently ensure improved quality of their products.
Product samples for testing can be prepared by cutting the samples into the required size—usually 50×50 mm, cleaning them, labeling them with appropriate identification marks, and then placing them inside a sterile container so as not to contaminate them. Detailed documentation of material specifications and handling instructions is to be provided, together with test requirements.
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