Plastic aerobic composting biodegradation testing is the internationally recognized method for evaluating how plastics break down under controlled composting conditions, measuring carbon dioxide evolution to quantify biodegradation rates. This testing is essential for manufacturers seeking compostability certifications under standards such as ISO 14855, ASTM D5338, and EN 13432. This article provides a comprehensive technical overview of sample requirements, test parameters, methodologies, and practical applications of aerobic composting degradation testing for plastic materials.
Technical Overview
Aerobic composting biodegradation testing simulates the thermophilic composting environment to determine the ultimate aerobic biodegradability of plastic materials. During the test, plastic specimens are mixed with mature compost inoculum and incubated under controlled conditions, typically at 58°C with optimal humidity and aeration. Microorganisms metabolize the organic carbon in the plastic, converting it into carbon dioxide, water, mineral salts, and new microbial biomass. The evolved carbon dioxide is continuously monitored and compared against the theoretical carbon content of the material to calculate the biodegradation percentage.
The test typically runs for up to 180 days, during which the biodegradation curve is plotted to track the progress of degradation. To be classified as compostable under major international standards, materials generally must achieve a minimum biodegradation rate of 90% (relative to cellulose reference) or 60% absolute biodegradation within the test period. This testing forms the scientific foundation for compostability claims on products such as biodegradable bags, food packaging, and disposable tableware.
Testing Standards
- ISO 14855-1: Determination of the ultimate aerobic biodegradability of plastic materials under controlled composting conditions by analysis of evolved carbon dioxide
- ISO 14855-2: Gravimetric measurement of the amount of carbon dioxide evolved
- ASTM D5338: Standard test method for determining aerobic biodegradation of plastic materials under controlled composting conditions
- EN 13432: Requirements for packaging recoverable through composting and biodegradation
- ASTM D6400: Standard specification for labeling of plastics designed to be aerobically composted in municipal or industrial facilities
- GB/T 19277.1: Chinese national standard for determining ultimate aerobic biodegradability under controlled composting conditions
- OECD 217/208: Biological and ecotoxicity assessment methods supporting compostability evaluation
Testing Samples
Biodegradable Polymer Resins
Raw polymer materials including polylactic acid (PLA), polybutylene adipate terephthalate (PBAT), polybutylene succinate (PBS), polyhydroxyalkanoates (PHA), and starch-based blends. Resin samples are typically ground or cut into small particles to increase surface area for microbial attack, ensuring representative and reproducible degradation behavior.
Finished Products and Packaging
Consumer and industrial products such as compostable shopping bags, garbage bags, food packaging films, coffee capsules, disposable cutlery, plates, cups, and food service ware. These finished goods must be tested in their final commercial form because additives, inks, adhesives, and lamination layers can significantly influence overall biodegradation performance.
Natural Fiber Composites and Coated Materials
Materials combining synthetic biodegradable polymers with natural fibers, such as bagasse fiber tableware, bamboo fiber composites, and paper products coated with biodegradable barrier layers. Testing verifies that both the substrate and coating degrade completely within the composting timeframe.
Agricultural Films
Mulch films and other agricultural plastics designed for soil or compost degradation, tested to confirm their suitability for composting streams after their service life ends.
Testing Items
- Ultimate aerobic biodegradation rate: percentage of theoretical carbon dioxide evolved relative to total organic carbon in the test material
- Disintegration degree: mass ratio of fragments retained on a 2 mm sieve after composting, with a pass threshold of no more than 10% retained
- Volatile solids content: determination of organic matter fraction in the test material
- Elemental carbon content and carbon-to-nitrogen ratio: essential for calculating theoretical CO2 production
- Heavy metal content: concentrations of regulated elements including zinc, copper, nickel, cadmium, lead, mercury, chromium, molybdenum, arsenic, and fluorine
- Ecotoxicity assessment: plant germination and biomass growth tests using compost output, and earthworm acute toxicity testing
- Positive control validation: cellulose reference material must achieve at least 70% biodegradation to confirm inoculum activity
Testing Methods
Test Setup and Inoculation
The test employs either a static or dynamic composting system. Mature compost inoculum aged between 2 and 4 months is sieved and characterized for pH, volatile solids, water content, and microbial activity. Test material is mixed with the inoculum at a defined ratio, typically 100 grams of total solids per vessel, with the test material constituting a specified fraction of total dry solids. The mixture is adjusted to approximately 50-55% moisture content and placed in test vessels connected to humidified, CO2-free air supply.
Incubation Conditions
Vessels are incubated at 58 ± 2°C in temperature-controlled chambers to simulate the thermophilic phase of industrial composting. Continuous aeration supplies oxygen to sustain aerobic microbial metabolism. The test is run in triplicate alongside blank vessels containing only inoculum, positive control vessels containing cellulose, and optionally negative control vessels containing non-biodegradable polyethylene.
Measurement of Evolved Carbon Dioxide
Carbon dioxide in the exhaust air from each vessel is measured using infrared gas analyzers, gas chromatography, or captured in alkaline absorption solutions and quantified through titration or conductivity measurement according to ISO 14855-1. The gravimetric method in ISO 14855-2 captures CO2 in absorption columns weighed periodically. Net biodegradation is calculated by subtracting the average CO2 production of blank vessels from the test vessel values and expressing the result as a percentage of theoretical CO2 based on the material's measured carbon content.
Disintegration and Ecotoxicity Testing
Following the biodegradation phase, disintegration is assessed by sieving the composted residue and determining the mass fraction of fragments larger than 2 mm. The resulting compost is then used in plant growth tests with species such as cress, barley, or ryegrass, comparing germination rates and biomass yield against control compost to confirm the absence of phytotoxic effects.
Applications
- Compostability certification support: generating data packages required for certification schemes based on EN 13432, ASTM D6400, and regional regulations for industrial composting claims
- Regulatory compliance: demonstrating conformity with the EU Single-Use Plastics Directive, packaging ordinances, and national compostability labeling requirements
- Product research and development: comparing biodegradation performance of new formulations, additives, and material thicknesses to optimize compostable product design
- Quality control: verifying batch-to-batch consistency of biodegradable raw materials and finished goods in manufacturing environments
- Market access and labeling: substantiating compostable claims, seedling logos, and OK-to-compost markings through accredited third-party laboratories
- Academic research: studying structure-biodegradation relationships of novel bio-based polymers and polymer blends
FAQ
How long does the aerobic composting biodegradation test take?
The standard test duration is up to 180 days, although the test may conclude earlier once the biodegradation curve reaches its plateau phase. Including sample preparation, inoculum characterization, and post-test ecotoxicity assessment, a complete evaluation typically requires 6 to 9 months.
What is the pass criterion for biodegradation?
Under EN 13432 and ASTM D6400, materials must achieve at least 90% biodegradation relative to the cellulose positive control, or 60% absolute biodegradation of theoretical CO2, within 180 days. The cellulose reference itself must reach at least 70% biodegradation for the test to be considered valid.
What sample quantity is required for testing?
Typically 100 to 500 grams of test material is sufficient for the biodegradation phase depending on vessel size and replication requirements. Additional material is needed for characterization tests such as carbon content, heavy metals, and disintegration assessment.
What is the difference between biodegradable and compostable?
Biodegradable is a broader term describing materials that can be broken down by microorganisms, while compostable specifically requires demonstrated biodegradation, disintegration, and ecotoxicity compliance under defined composting conditions within a specified timeframe. Aerobic composting testing provides the scientific evidence supporting the stricter compostable designation.
Does passing this test mean the material degrades in home compost or open environments?
No. This test simulates industrial composting conditions at elevated temperatures around 58°C. Home composting occurs at lower ambient temperatures, and natural environments such as soil or marine water require separate testing under ISO 17556, ISO 14852, or ASTM D5988 for verification.