Compostable Degradation Testing: Standards, Methods, and Technical Requirements

Compostable degradation testing is the scientific evaluation process that verifies whether plastics, packaging, and other materials biodegrade safely and completely under composting conditions. Governed by internationally recognized standards such as EN 13432, ASTM D6400, and ISO 14855, this testing is essential for manufacturers seeking compostability certification, regulatory compliance, and credible environmental claims. This article explains the sample types, test items, methodologies, and acceptance criteria involved in a complete compostability evaluation program.

Technical Overview

Compostable degradation testing, also known as compostability testing, is a laboratory-based evaluation designed to demonstrate that a material will break down in a composting environment at a rate consistent with known compostable materials, without leaving visible residue or harmful substances in the finished compost. The evaluation is built on three scientific pillars: ultimate aerobic biodegradation, in which microorganisms convert organic carbon into carbon dioxide, water, and biomass; disintegration, in which the material physically fragments so that no recognizable residue remains; and compost quality safety, which confirms the absence of negative effects on plant growth, soil organisms, and heavy metal contamination.

Testing is typically performed by accredited third-party laboratories in accordance with frameworks such as EN 13432 and EN 14995 in Europe, ASTM D6400 and ASTM D6400-aligned methods in North America, ISO 18606 for packaging, and corresponding GB/T standards such as GB/T 19277.1 for the Chinese market. These specifications simulate industrial composting conditions—typically 58 ± 2 °C, high humidity, and active aeration—over a maximum period of 180 days for biodegradation and 12 weeks for disintegration. A material may only be marketed as compostable when it satisfies all biodegradation, disintegration, and ecotoxicity requirements of the applicable specification, not merely a single degradation measurement.

Testing Samples

Compostability evaluation can be applied to a wide range of bio-based and biodegradable materials and finished articles. Sample preparation and form selection significantly influence test outcomes, because biodegradation rates depend on surface area, thickness, crystallinity, and formulation.

Polymer Resins, Pellets, and Masterbatches

Raw materials such as PLA, PBAT, PBS, PHA, PCL, and starch-based blends are commonly tested as powders or granules to maximize microbial access. Formulation documentation—including additives, plasticizers, inorganic fillers, pigments, and processing aids—must accompany the submission, since every organic component contributes to the biodegradation balance and every inorganic component affects residue analysis.

Films and Flexible Packaging

Shopping bags, organic waste collection bags, produce bags, agricultural mulch films, e-commerce mailers, overwraps, and lidding films are tested at their final commercial thickness. Thin films generally disintegrate rapidly, but printed layers and adhesives must be evaluated as part of the complete article.

Rigid and Molded Products

Cutlery, straws, cups, trays, plates, coffee capsules, plant pots, and injection-molded or thermoformed containers are tested in their end-use configuration. Because thickness is the limiting factor for disintegration, the thickest section of the product is used as the worst-case condition.

Multi-Material Articles and Components

Coated paperboard, laminates, labels, inks, tapes, and fiber-based composites require evaluation of the complete construction. Certification programs generally require that every component of the article, including inks and adhesives, meets the same compostability criteria as the substrate.

Testing Items

A complete compostability evaluation according to EN 13432, ASTM D6400, or equivalent specifications includes the following core test items:

• Dry solids and volatile solids content of the test material
• Elemental carbon, hydrogen, and nitrogen analysis for calculating theoretical carbon dioxide (ThCO2)
• Regulated heavy metals and hazardous elements: Zn, Cu, Ni, Cd, Pb, Hg, Cr, Mo, Se, As, and fluorine
• Ultimate aerobic biodegradation rate determined by carbon dioxide evolution over a maximum of 180 days
• Disintegration degree in pilot-scale or laboratory-scale composting over 12 weeks, expressed as the mass fraction retained on a 2 mm sieve
• Ecotoxicity of the resulting compost, including seed germination rate, plant biomass yield, and soil organism toxicity
• Optional supplementary tests: anaerobic biodegradation, soil biodegradation, marine biodegradation, and home composting suitability

Testing Methods

Ultimate Aerobic Biodegradation (ISO 14855-1, ISO 14855-2, ASTM D5338, GB/T 19277.1)

The reference method uses mature, active compost as the microbial inoculum in aerated test vessels maintained at 58 ± 2 °C with moisture content around 50–55%. Test material is mixed with the compost at a defined ratio, and the reactors are continuously supplied with carbon-dioxide-free air. Evolved CO2 is quantified either by infrared gas analysis, alkaline absorption with titration, or gravimetric measurement in small-scale closed-vessel systems per ISO 14855-2. Cumulative biodegradation is expressed as a percentage of the theoretical CO2 derived from the material's carbon content, blank-corrected against compost-only reactors. The test system must include microcrystalline cellulose as a positive control, which must exceed the validity threshold (typically 60–70% biodegradation) for results to be accepted. The acceptance criterion under EN 13432, ASTM D6400, and ISO 18606 is a minimum of 90% biodegradation within 180 days, either in absolute terms or relative to the cellulose reference.

Disintegration Testing (ISO 16929, ISO 20200, GB/T 19811)

Disintegration is evaluated at pilot scale under ISO 16929 or at laboratory scale under ISO 20200, in which specimens of defined size are composted at elevated temperature for 12 weeks. At the end of the exposure period, the compost is dried and sieved through a 2 mm mesh. The test passes when less than 10% of the original dry mass of the test material remains as fragments larger than 2 mm, meaning at least 90% of the material has physically disintegrated beyond recognizable fragments.

Ecotoxicity and Compost Quality Assessment

The finished compost from the disintegration test is blended with a reference substrate and used to grow higher plants in accordance with plant growth test methods such as ISO 11269-2, using species such as cress, radish, or barley. Germination rate and plant biomass must each reach at least 90% of the values obtained with blank compost. Where required, earthworm acute toxicity testing per ISO 11268-1 may be added to confirm the absence of adverse effects on soil fauna.

Chemical Characterization and Regulated Substances

Elemental analysis establishes carbon content for ThCO2 calculation, while volatile solids confirm that the material is substantially organic. Heavy metal content is compared against strict limits, for example under EN 13432: Zn 150, Cu 50, Ni 25, Cd 0.5, Pb 50, Hg 0.5, Cr 50, Mo 1, Se 0.75, As 5, and F 100 mg/kg of dry sample. Exceeding any individual limit disqualifies the material regardless of its biodegradation performance.

Supplementary Degradation Scenarios

Depending on the intended disposal route and marketing claims, additional tests may be performed, including soil biodegradation under ISO 17556 or ASTM D5988, marine biodegradation under ISO 19679 or ASTM D6691, anaerobic digestion under ISO 15985, and home composting suitability under frameworks such as AS 5810, NF T 51-800, or EN 17427. These environments are colder and less biologically active than industrial composting, so their pass thresholds and durations differ from the industrial standards.

Applications

Compostable degradation testing supports a broad range of commercial, regulatory, and technical objectives across the sustainable materials value chain:

• Industrial compostability certification of packaging, foodservice ware, and consumer products for the European, North American, and Asia-Pacific markets
• Compliance with packaging and single-use plastics regulations that mandate compostability for specific product categories such as organic waste collection bags
• Substantiation of environmental claims on labels and marketing materials in line with self-declared environmental claims guidance such as ISO 14021
• Research and development screening of new biopolymer formulations, additives, and processing methods
• Incoming quality control and supplier verification for brand owners specifying compostable inputs
• Supporting documentation for e-commerce platforms, retailers, and municipal composting facilities that require proof of end-of-life performance

FAQ

What is the difference between biodegradable and compostable?

Biodegradable describes any material that can be broken down by microorganisms over an indefinite timescale, whereas compostable is a defined performance claim. A compostable material must biodegrade at least 90% within 180 days under controlled composting conditions, disintegrate so that no more than 10% of its mass remains above 2 mm after 12 weeks, and leave compost that is non-toxic to plants and within heavy metal limits.

How long does a complete compostability test program take?

Biodegradation testing runs for up to 180 days, disintegration testing takes 12 weeks, and plant toxicity testing adds approximately 3–4 weeks after compost maturation. Because some items proceed in parallel and chemical analysis can be performed at the start, a full evaluation typically requires 6 to 9 months from sample submission to the final report.

What sample quantity is required for testing?

Requirements vary with reactor size and test configuration, but as a practical guide, laboratories generally request 100–500 g of test material for biodegradation, several dozen square specimens of 5 × 5 cm for disintegration, and additional material for chemical characterization. Submitting 1–2 kg of the final commercial article is usually sufficient for a complete program.

Do industrial and home composting tests use the same conditions?

No. Industrial composting tests operate at approximately 58 °C with optimized aeration and humidity. Home composting tests simulate colder, less controlled conditions, typically in the range of ambient temperature to 30 °C, and therefore demand longer test durations. Passing an industrial standard such as EN 13432 does not by itself qualify a product for home composting claims.

Which standards apply to which markets?

EN 13432 governs compostable packaging in Europe, ASTM D6400 is the primary specification in the United States, and GB/T standards aligned with ISO methods apply in China. Because the underlying test methods are largely harmonized, a single well-designed test campaign can often support submissions under multiple specifications, though each certification scheme maintains its own documentation and administrative requirements.

Why must the test include cellulose and blank controls?

The cellulose positive control demonstrates that the compost inoculum is biologically active enough to support rapid biodegradation, validating the entire test system. The blank compost reactor quantifies the background CO2 generated by the inoculum itself, which is subtracted from all sample measurements. Without these controls, biodegradation percentages would be scientifically meaningless.