ASTM G21-15: Testing Resistance of Synthetic Polymeric Materials to Fungi

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Purpose: 
This standard evaluates the resistance of polymeric materials (e.g., plastics, coatings) to fungal growth. It assesses the material's ability to resist: 

• Surface discoloration. 
• Physical degradation. 
• Changes in optical, mechanical, or electrical properties. 

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Scope: 
- Applicable to plastic materials with additives (e.g., plasticizers, stabilizers) that may support fungal growth. 
- Simulates environments favorable for fungal activity (temperature: 28-30°C; relative humidity: 85%+). 

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Test Procedure Overview: 

1. Preparation: 

• Test Specimens: 
      - Standard size: 50x50 mm (2x2 in.) or 50 mm diameter pieces. 
  
• Nutrient-Salts Agar: 
      - Sterilized medium providing essential nutrients. 
  
• Fungal Suspension: 
      - Mixture of five fungal species: 
        1. *Aspergillus brasiliensis* 
        2. *Talaromyces pinophilus* 
        3. *Chaetomium globosum* 
        4. *Trichoderma virens* 
        5. *Aureobasidium pullulans* 
      - Spore concentration: 1,000,000 ± 200,000 spores/mL. 
  

2. Inoculation: 
- Specimens placed on agar and sprayed with fungal suspension. 
- Dishes are sealed to maintain humidity. 

3. Incubation: 
- Conditions: 28-30°C with 85%+ humidity. 
- Duration: Typically 28 days. 

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Evaluation and Ratings: 

Visual Growth Ratings: 

Rating	Growth Observed
0	None
1	Trace (<10% surface)
2	Light (10-30% surface)
3	Medium (30-60% surface)
4	Heavy (60-100% surface)

Changes in Material Properties: 
After incubation, specimens are tested for: 

• Optical Properties: Transparency, haze. 
  
• Physical Properties: Stiffness, tensile strength. 
  
• Electrical Properties: Insulation resistance, dielectric strength. 
  

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Applications: 
- Plastic Components: Films, molded parts. 
- Cable Sheaths: Resistance in humid, fungal-prone environments. 
- Industrial Coatings: Prevent fungal discoloration and degradation. 
- Healthcare Equipment: Sterile polymeric materials. 

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Limitations: 
- Fungal attack depends on **random factors**, such as nutrient dispersion. 
- Results may require additional conditioning tests for real-world performance (e.g., weathering, UV exposure). 

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Reporting: 
The report should include: 

• Fungal species used. 
• Incubation time and conditions. 
• Visual growth ratings. 
• Changes in optical, physical, or electrical properties. 

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