Compost Degradation Testing for Packaging Materials: Standards, Methods, and Certification Requireme

Compost degradation testing evaluates whether packaging materials can biodegrade completely and safely within a controlled industrial composting environment, verifying compliance with internationally recognized standards such as ISO 14855, ASTM D5338, and EN 13432. This technical article outlines the testing scope, sample requirements, evaluation items, analytical methods, and typical applications of compost degradation testing for packaging. By understanding these requirements, manufacturers, brand owners, and exporters can achieve regulatory compliance and support credible compostability claims in global markets.

Technical Overview

Compost degradation testing, also known as compostability or aerobic biodegradation testing, is a laboratory evaluation that measures the extent and rate at which packaging materials are converted into carbon dioxide, water, mineral salts, and new microbial biomass by microorganisms under controlled composting conditions. The test simulates the thermophilic environment of an industrial composting facility, typically maintained at 58 ± 2 °C with high relative humidity and mature compost serving as the microbial inoculum.

The evaluation is governed by a family of internationally recognized standards, and a complete assessment verifies four essential attributes:

• Aerobic biodegradation of the organic carbon content of the material
• Disintegration of the material into fine fragments within a defined composting period
• Absence of negative effects on the composting process and the quality of the resulting compost
• Absence of hazardous substances and ecotoxic effects on plants and soil organisms

The principal standards applicable to packaging materials include:

• ISO 14855-1 and ISO 14855-2 – Determination of the ultimate aerobic biodegradability of plastic materials under controlled composting conditions
• 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 and ISO 17088 – Specifications for labeling plastics designed to be aerobically composted in municipal or industrial facilities
• ISO 18606 – Packaging and the environment: organic recycling
• GB/T 20197 and GB/T 41010 – Chinese national standards for degradable plastics and compostable plastic products

Testing Samples

Biodegradable Plastic Films and Bags

Flexible packaging produced from biodegradable polymers and their blends, including PLA, PBAT, PBS, PHA/PHB, PPC, and starch-based compounds. Typical articles include shopping bags, courier and express delivery bags, waste bags, agricultural mulch films, and laminated multilayer films.

Rigid and Semi-Rigid Packaging

Injection-molded and thermoformed articles such as food containers, trays, clamshells, cups, bottles, caps, straws, and disposable cutlery made from biodegradable resins or fiber-plastic composites.

Paper-Based and Coated Packaging

Paper cups, paperboard food containers, and other cellulosic packaging laminated or coated with biodegradable polymers, where the coating layer must be evaluated together with the substrate.

Packaging Auxiliary Materials

Adhesives, printing inks, tapes, labels, cable ties, cushioning materials, and closure systems that enter the organic recycling stream together with the primary package and may influence overall compostability.

Sample Preparation Requirements

For biodegradation testing, specimens are usually cryogenically milled to a particle size below 5 mm to ensure homogeneous contact with the inoculum. The dosage is calculated on the basis of total organic carbon (TOC), typically 100–200 mg of TOC per test vessel. For disintegration testing, whole articles or representative sections of the finished packaging are tested in their end-use form.

Testing Items

A complete compost degradation assessment for packaging materials generally includes the following items:

• Ultimate aerobic biodegradation rate – cumulative carbon dioxide evolution expressed as a percentage of the theoretical carbon dioxide (ThCO2) derived from the TOC of the material
• Disintegration degree – mass fraction of the material that fragments and passes through a 2 mm sieve after a defined composting period
• Ecotoxicity – plant seedling emergence and biomass growth tests on compost containing the degradation residues, and where required earthworm acute toxicity testing
• Chemical characterization – content of regulated heavy metals and other elements, including As, Cd, Co, Cr, Cu, Hg, Mo, Ni, Pb, Se, Zn, and F
• Basic parameters – dry solids, volatile solids, ash content, and total organic carbon of the test material and inoculum
• Optional supplementary items – anaerobic biodegradation (ISO 15985), aqueous aerobic biodegradation (ISO 14851/14852), or marine biodegradation (ASTM D6691) for specific environmental claims

Representative acceptance criteria under EN 13432 and ASTM D6400 are:

• Biodegradation of at least 90% of the theoretical CO2 within 180 days, or at least 90% of the cellulose reference material under equivalent conditions
• Disintegration of at least 90% of the test mass into fragments smaller than 2 mm within 84 days
• Seedling germination rate and plant biomass of at least 90% relative to the blank control compost
• Heavy metal concentrations below the tabulated limits, for example Zn below 150, Cu below 50, Ni below 25, Cd below 0.5, Pb below 50, Hg below 0.5, Cr below 50, and As below 5 mg/kg dry substance

Testing Methods

Aerobic Biodegradation Test (ISO 14855-1 / ASTM D5338)

Test vessels containing mature compost inoculum and the milled test material are incubated at 58 ± 2 °C with moisture maintained above 50% of the dry mass. Carbon dioxide-free air is passed continuously through the vessels, and the evolved CO2 is quantified by infrared gas analysis, gas chromatography, or titration after absorption in alkaline solution. The test typically runs for up to six months. Validity requires that the cellulose positive control achieves more than 70% biodegradation within 45 days, and the mean CO2 evolution of the blank inoculum vessels remains within specified limits. Biodegradation is calculated after subtracting the blank contribution and expressing net CO2 as a percentage of ThCO2.

Gravimetric CO2 Measurement (ISO 14855-2)

This small-scale variant uses sealed reactors in which carbon dioxide is captured by absorption columns filled with soda lime or alkaline solution. The mass increase of the columns is weighed periodically, allowing a gravimetric determination of cumulative biodegradation suitable for laboratories with limited access to gas analysis instrumentation.

Disintegration Test (ISO 16929 / ISO 20200 / EN 13432)

Whole packaging articles or cut sections are mixed with a synthetic or genuine organic waste matrix and composted under controlled temperature and aeration. ISO 16929 describes a pilot-scale procedure while ISO 20200 describes a laboratory-scale procedure using synthetic solid waste. After the composting period, the matrix is dried and sieved through a 2 mm mesh, and the fraction retained on the sieve is reported as non-disintegrated material.

Ecotoxicity and Chemical Analysis

Compost recovered from the disintegration test is blended with a defined ratio of reference soil and used as the plant growth medium in terrestrial plant tests following OECD Guideline 208, with a minimum of two plant species such as barley and radish. Germination rate and biomass yield are compared against a blank compost control. Heavy metals are quantified by ICP-MS or atomic absorption spectrometry after microwave acid digestion of the test material.

Quality Assurance

Testing should be performed by accredited third-party laboratories operating under ISO/IEC 17025 management systems. Each study includes replicate test vessels, a blank inoculum control, a cellulose positive control, and where appropriate an inactive reference material, ensuring statistically defensible and internationally acceptable results.

Applications

Compost degradation testing supports a wide range of commercial and regulatory objectives across the packaging value chain:

• Compostability certification and eco-labeling – generating the technical dossier required to obtain recognized industrial compostable logos and to substantiate marketing claims
• Market access and regulatory compliance – meeting EN 13432 for the European market, ASTM D6400 for North America, AS 4736 for Australia, and GB/T standards for the Chinese market
• Research and development – verifying the influence of resin grades, masterbatches, plasticizers, inks, and adhesives on the degradation performance of new formulations
• Supplier qualification – evaluating incoming biodegradable materials and finished packaging from upstream vendors against contractual compostability specifications
• Sector-specific programs – e-commerce and express delivery packaging, food service ware and food contact packaging, disposable tableware, and agricultural mulch films subject to plastic restriction policies
• Corporate sustainability reporting – providing auditable laboratory evidence for environmental, social, and governance disclosures and circular economy commitments

FAQ

How long does a compost degradation test take?

The aerobic biodegradation phase runs for up to 180 days, the disintegration phase for up to 84 days, and ecotoxicity testing requires an additional several weeks. A complete assessment project, including chemical characterization and reporting, typically spans six to nine months.

What is the difference between biodegradable and compostable packaging?

Biodegradable describes the general capability of a material to be decomposed by microorganisms, without a defined timeframe or environment. Compostable is a stricter claim requiring verified biodegradation, disintegration, and ecological safety within a specified period under industrial composting conditions, as demonstrated through standardized testing.

Which standard should my product be tested against?

The applicable standard depends on the target market: EN 13432 for Europe, ASTM D6400 for North America, AS 4736 for Australia, and the relevant GB/T standards for China. ISO 14855 or ASTM D5338 typically serve as the underlying biodegradation methods within these certification schemes.

What sample quantity is required for testing?

Biodegradation testing generally requires material milled to below 5 mm in sufficient quantity to provide the required TOC dosage across replicate vessels, while disintegration and ecotoxicity testing require whole articles or representative finished packaging. In practice, several kilograms of sample are recommended to cover all test items.

Does a high biodegradation rate alone prove compostability?

No. A material is considered compostable only when it passes all four elements of the assessment: biodegradation, disintegration, absence of adverse effects on the composting process, and compliance with limits for regulated substances and ecotoxicity.

Can the test results be used directly for marketing claims?

Results from accredited third-party laboratories provide the technical basis for compostability claims, but most markets additionally require certification against the relevant standard before a compostable logo or label may be applied to the product. Unsupported self-declarations carry significant regulatory and reputational risk.