ASTM D5338 Testing: Determining Aerobic Biodegradation of Plastic Materials Under Controlled Composting Conditions
As sustainability becomes a central priority across manufacturing and packaging, the ability to verify the compostability of plastic materials through standardised laboratory testing has never been more important. ASTM D5338 is the primary standard test method for determining aerobic biodegradation of plastic materials under controlled composting conditions incorporating thermophilic temperatures. This blog provides a complete overview of the ASTM D5338 test method — its purpose, procedure, applications, and significance for manufacturers committed to environmental responsibility.
What Is ASTM D5338?
ASTM D5338 is a standardised laboratory procedure used to evaluate the ability of plastic materials to biodegrade aerobically in a simulated composting environment. The test exposes plastic materials to a thermophilic composting matrix under controlled temperature and humidity conditions, measuring the percentage of the test material’s carbon that is converted to carbon dioxide (CO₂) by microbial activity over a defined test duration, typically a minimum of 90 days.
The test yields reproducible and repeatable outcomes under stated parameters and is widely used to assess whether plastics conform to compostability standards, most notably as a core component of ASTM D6400, the standard specification for compostable plastics.
Purpose and Significance
Biodegradation of a plastic within a composting system is an important phenomenon because it can affect the decomposition of surrounding organic matter and the quality of the resulting compost. ASTM D5338 measures the rate and degree of aerobic biodegradation of plastic materials by exposing them to a particular temperature under a controlled composting environment inside the laboratory. This procedure was developed to permit rapid and reproducible determination of aerobic biodegradability under conditions that resemble an optimally operated industrial composting process where thermophilic temperatures are achieved.
ASTM D5338 is essential for manufacturers developing biodegradable products that must conform to environmental regulations, and for waste management organisations seeking to verify material compostability before processing.
Key Test Parameters
Specimen Quantity: The dry weight of the test material should range between 50 grams and 100 grams.
Material Form: Test material is typically shredded or granulated into particles smaller than 2 mm. Smaller particle sizes maximise surface area exposure and promote microbial decomposition.
Temperature: Thermophilic temperatures — typically 58°C ± 2°C — are maintained throughout the test to replicate professionally managed industrial composting conditions.
Test Duration: A minimum of 90 days, with results reported as percentage net gaseous carbon generation at the conclusion of the test.
Reference Material: Cellulose is typically used as a positive control to validate composting inoculum activity.
Test Procedure Overview
The test matrix consists of mature compost inoculum combined with the shredded or granulated test material. The mixture is maintained under aerobic, temperature-controlled, and moisture-controlled conditions in sealed bioreactors. CO₂ evolved during the test is continuously measured, and the percentage of the theoretical maximum CO₂ production — based on the total carbon content of the specimen — is calculated as the biodegradation percentage.
Applications Across Industries
Packaging and Consumer Goods: Verifying the compostability claims of flexible packaging films, bags, food service containers, and single-use items.
Automotive: Evaluating bio-based components in vehicle interiors for compostability at the end of product life.
Electronics: Assessing biodegradable housing materials for consumer electronics.
Textiles: Testing fibres and coatings for aerobic biodegradability in composting environments.
Research and Development: Enabling scientists and engineers to study the biodegradation behaviour of novel biopolymers and formulations.
Relationship to Other Biodegradability Standards
ASTM D5338 is often used in conjunction with complementary standards:
- ASTM D5511: Anaerobic biodegradation under high-solids landfill conditions.
- ASTM D5988: Aerobic biodegradation in soil environments.
- ASTM D6400: Overall compostability specification for plastics (incorporates D5338 as a core component).
- ISO 14855: International equivalent for aerobic biodegradability under controlled composting.
Conclusion
ASTM D5338 provides a scientifically rigorous method for assessing the aerobic biodegradation of plastic materials under controlled composting conditions. Measuring CO₂ evolution, the test accurately reflects the conversion of organic carbon to carbon dioxide, simulating real-world composting processes.
The method is thus an essential tool for manufacturers, researchers, and regulatory organisations that intend to verify compostability by applying international standards and fostering sustainability in product design.
Ultimately, ASTM D5338 plays a critical role in the transition toward a circular economy, enabling the shift whereby plastics are designed to safely return to nature through industrial composting.
Why Choose Infinita Lab for ASTM D5338?
Infinita Lab is a leading provider of ASTM D5338 and streamlined material testing services, addressing the critical challenges faced by emerging businesses and established enterprises. With access to a vast network of over 2,000+ accredited partner labs across the United States, Infinita Lab ensures rapid, accurate, and cost-effective testing solutions. The company’s unique value proposition includes comprehensive project management, confidentiality assurance, and seamless communication through a Single Point of Contact (SPOC) model. By eliminating inefficiencies in traditional material testing workflows, Infinita Lab accelerates research and development (R&D) processes.
Looking for a trusted partner to achieve your research goals? Schedule a meeting with us, send us a request, or call us at (888) 878-3090 to learn more about our services and how we can support you.
Frequently Asked Questions (FAQs)
What is the purpose of ASTM D5338 testing? ASTM D5338 evaluates the aerobic biodegradation of plastic materials when exposed to controlled composting conditions, simulating industrial composting environments. It measures how effectively the carbon in the test material is converted into carbon dioxide (CO₂) by microorganisms, indicating its compostability and environmental performance.
What does the test measure? ASTM D5338 measures the amount of CO₂ evolved during composting, which corresponds to the extent and rate of biodegradation of the plastic material. The results are expressed as a percentage of total organic carbon converted to CO₂, indicating the extent to which the plastic decomposes under composting conditions.
What are the control and reference materials in this test? Control: Compost without any added plastic material, used to measure background CO₂ production. Reference Material: Cellulose powder, which is readily biodegradable and serves as a positive control to validate microbial activity and test reliability.
How long does the ASTM D5338 test take? The duration typically ranges from 45 to 180 days, depending on the material’s degradation behavior. The test continues until the biodegradation curve stabilizes, meaning microbial activity has significantly decreased and no additional CO₂ evolution is observed.
What temperature is used in ASTM D5338 testing? The test uses thermophilic temperatures, typically 58°C ± 2°C, which simulate conditions found in professionally managed industrial composting facilities.
