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ASTM G21
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Quick understanding of the test
ASTM G21 - Fungal Resistance Test
- Aspergillus brasiliensis
- Talaromyces pinophilus
- Chaetomium globosum
- Trichoderma virens
- Aureobasidium pullulans
- Test specimens and controls are placed on nutrient-salt agar and are inoculated with spore suspension.
- Samples are incubated at specified temperatures for up to 28 days.
- Specimens are rated on a 0–4 scale based on fungal coverage.
- Helps manufacturers to improve material formulations for better antifungal efficacy.
- Assists in meeting industry and safety standards for antifungal properties.
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Overview of ASTM G21 fungal resistance test
ASTM G21 is an international standard that describes the test method for determining the resistance of plastics and polymers to fungal growth. In general, synthetic polymers are resistant to the growth of fungi as they do not provide the nutrients required for their growth. However, other components or additives (such as plasticizers, lubricants, stabilizers, cellulose, and colorants) used in the making of synthetic plastic materials trigger the fungal growth and deterioration process. Therefore, antifungal resistance tests are important to ensure the durability and lifespan of plastic materials that can be affected by fungal growth.
Why test for fungal resistance?
The growth of fungi on plastics enhances the rate at which they deteriorate, affecting the strength and performance of the material. This is a major concern for plastic products used in areas exposed to moisture and organic load that can stimulate the growth of fungi. Antifungal testing helps identify susceptible materials and allows manufacturers to improve their formulations, ensuring long-lasting products.
What types of products are tested with ASTM G21?
The ASTM G21 test is used to determine the resistance of synthetic polymeric materials against fungal growth. The ASTM G21 test is applicable for molded and fabricated products, tubes, rods, sheet, and film material.
Which fungi are used in ASTM G21 testing?
- Aspergillus brasiliensis
- Aureobasidium pullulans
- Chaetomium globosum
- Trichoderma virens
- Penicillium funiculosum
ASTM G21 test methodology
1. Preparation and inoculation
- The test specimens are placed on the solidified surface of nutrient-salts agar and inoculated with a spore suspension. This setup mimics real-world conditions where fungi encounter the materials in a nutrient-rich environment.
- Untreated control samples are also inoculated and incubated alongside the test specimens to provide a baseline for comparison.
2. Incubation
- The inoculated samples are then sealed and incubated at a temperature range of 28°C to 30°C, and under conditions of 90% relative humidity.
- The standard incubation period is 28 days but the test may be terminated earlier if the test specimens show considerable mycelial growth, usually indicated by a growth rating of two or more.
3. Evaluation and rating
Importance of ASTM G21 fungal resistance test
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.
Evaluates safety and hygiene
Particularly important for products used in healthcare, food packaging, and construction where fungal growth can compromise safety.
Supporting innovation and development
By assessing how additives and formulations influence fungal resistance, the test supports R&D efforts to create durable, sustainable, and biodegradable materials with improved antifungal properties.
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 the quality, safety, and durability of the product.
Aids Regulatory and Market Acceptance
Meeting ASTM G21 requirements strengthens credibility and supports regulatory submissions or international trade approvals.
Strengths of ASTM G21 test method
- ASTM G21 uses multiple fungal strains from diverse environments, each with different nutrient and enzyme requirements. This ensures a thorough assessment of the material’s antifungal performance.
- The ASTM G21 test uses a high spore concentration, which gives materials a tough and consistent fungal challenge to check how well they can withstand growth and damage.
- The test simulates real environmental conditions, providing a realistic measure of how materials perform in humid, marine, or construction settings prone to fungal exposure.
Limitations of ASTM G21 test method
- If the spore mixture isn’t prepared properly or contains leftover nutrients, it can encourage abnormal fungal growth and give misleading results.
- The results are based on visual scoring, which can vary between technicians.
- The 28-day incubation period can be quite long for manufacturers who need rapid screening or quick go-to-market decisions.
At Microbe Investigations (MIS), we test the efficacy of antifungal plastic finishes using the ASTM G21 test and other standard test methods like AATCC-30. With a team of experienced microbiologists and advanced technological capabilities, MIS provides a comprehensive suite of quality antiviral, antibacterial and antifungal testing services worldwide.
Contact our experts here to learn about the pricing, turnaround times and other related queries.
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