Compostable Plastics Testing: Standards, Test Items, Methods, and Applications

Compostable plastics testing is the scientific process of verifying that plastic materials and products fully biodegrade, disintegrate, and leave no toxic residues under composting conditions. Guided by internationally recognized standards such as EN 13432, ASTM D6400, and ISO 14855, this testing is essential for manufacturers seeking compostability certification and access to regulated markets. This article explains the sample types, key test items, testing methods, and typical applications involved in compostable plastics evaluation.

Technical Overview

Compostable plastics are polymeric materials designed to be converted by microorganisms into carbon dioxide, water, inorganic minerals, and biomass within a defined composting environment. Unlike conventional plastics, which can persist in the environment for decades, a compostable plastic must meet strict scientific acceptance criteria before any environmental claim can be made. Compostability is therefore a verifiable performance property, not a marketing label.

Internationally harmonized standards frameworks govern the evaluation of these materials. In Europe, EN 13432 for packaging and EN 14995 for plastics define the acceptance criteria. In the United States, ASTM D6400 covers compostable plastics and ASTM D6868 covers compostable coatings on paper and board substrates. At the international level, ISO 14855, ISO 16929, and ISO 20200 specify the corresponding laboratory methods. In China, GB/T 19277 and GB/T 20197 establish the national requirements for biodegradation and degradability claims.

Across all of these frameworks, compostability verification rests on four technical pillars:

• Chemical characterization of the material, including heavy metals and organic constituents.
• Ultimate aerobic biodegradation measured by respirometry.
• Physical disintegration during a controlled composting cycle.
• Ecotoxicity assessment of the resulting compost.

Only when a material satisfies all four pillars, as verified by accredited third-party laboratories, can it support certification schemes, ecolabeling, and regulatory compliance in target markets.

Testing Samples

Compostability evaluation can be performed at different stages of the product lifecycle, from raw material development through finished goods. The sample type determines the applicable test conditions and acceptance criteria.

Resins, Masterbatches, and Raw Materials

Polymer resins such as PLA, PBAT, PBS, PHA, and starch-based blends are tested during formulation development to screen biodegradation potential and chemical safety before commercialization. Testing at the resin stage helps material producers demonstrate compostability to converters and brand owners.

Finished Products

End-use items such as carrier bags, food waste bags, cutlery, plates, cups, food containers, coffee capsules, and cotton bud sticks are tested in their final commercial form, including all components such as labels, seams, and closures. Certification schemes typically require the complete article, not just the base polymer, to comply.

Multilayer Films, Coatings, and Laminates

Multilayer packaging structures and coated paperboard are evaluated as complete constructions under ASTM D6868 and EN 13432, ensuring that every layer contributes to overall compostability.

Inks, Adhesives, Pigments, and Additives

Ancillary materials such as printing inks, adhesives, colorants, and processing additives must also fall within permissible limits for heavy metals and volatile solids, and in many cases require their own supporting biodegradation data.

Testing Items

A complete compostability evaluation consists of four categories of test items, each with quantified pass criteria defined by EN 13432, EN 14995, ASTM D6400, and related standards.

Chemical Characterization

The material is analyzed for regulated substances and composition. Key items include:

• Heavy metals and trace elements: limits apply to zinc, copper, nickel, cadmium, lead, mercury, chromium, molybdenum, arsenic, selenium, and fluorine on a dry-weight basis.
• Volatile solids: a minimum of 50 percent volatile solids is required to demonstrate sufficient organic content for microbial breakdown.
• Declared organic components and additives with supporting biodegradation evidence where applicable.

Ultimate Aerobic Biodegradation

The material must achieve at least 90 percent biodegradation, expressed as the ratio of evolved carbon dioxide to the theoretical maximum, within 180 days under controlled composting conditions. ASTM D6400 additionally accepts reaching 90 percent of the biodegradation level of the cellulose reference material. This requirement excludes simply fragmenting into microplastics without true microbial conversion.

Disintegration

After a composting cycle of up to 12 weeks, at least 90 percent of the test material must pass through a 2 mm sieve, demonstrating that the product physically breaks apart and does not remain visibly distinguishable in the final compost.

Ecotoxicity and Compost Quality

Compost produced during the disintegration test is mixed with soil and used to grow seedlings of at least two plant species. Germination rate and plant biomass must each reach at least 90 percent of the values obtained with blank control compost, confirming that the degraded material leaves no phytotoxic residues. Additional ecotoxicity assays may include aquatic or invertebrate screening depending on the certification scheme.

Testing Methods

The test items described above are executed through standardized laboratory procedures simulating industrial composting conditions of approximately 58 degrees Celsius, high humidity, and active microbial inoculum.

Controlled Composting Biodegradation Test

ISO 14855-1 and ASTM D5338 are the primary respirometric methods. Test materials are mixed with mature compost inoculum in closed vessels, and carbon dioxide evolution is continuously monitored and compared against blank and cellulose reference reactors until the plateau phase is reached, for a maximum of six months. ISO 14855-2 offers a gravimetric measurement variant of the same principle.

Laboratory-Scale Disintegration Test

ISO 16929 defines a pilot-scale disintegration procedure, while ISO 20200 defines a laboratory-scale simulation of an industrial composting environment. Test specimens are composted in defined synthetic waste, and after the exposure period the residue is sieved through a 2 mm mesh to quantify the fraction of material that has fragmented.

Supporting Biodegradation Methods

ISO 14852 and ISO 14851 measure aerobic biodegradation in an aqueous medium and are frequently used for screening during research and development, or to build a technical dossier supporting the controlled composting data.

Plant Germination and Growth Test

The ecotoxicity assessment uses the compost generated in the disintegration test. Seeds are cultivated in mixtures of test compost and reference soil under controlled light, temperature, and humidity, and germination rate and biomass yield are statistically compared with control groups.

Instrumental Chemical Analysis

Heavy metal content is determined using techniques such as inductively coupled plasma optical emission spectrometry or mass spectrometry after acid digestion, while volatile solids are measured gravimetrically by furnace ignition at 550 degrees Celsius.

Applications

Compostable plastics testing supports product development, regulatory compliance, and commercial claims across a wide range of industries:

• Flexible and rigid food packaging, including films, trays, and barrier-coated paperboard certified under EN 13432 and ASTM D6868.
• Food service items such as cups, cutlery, straws, and takeaway containers supplied to catering and hospitality sectors.
• Organic waste collection bags designed to break down together with food waste in industrial composting facilities.
• Agricultural products such as biodegradable mulch films and plant pots that are incorporated directly into soil after use.
• Consumer and hygiene articles, including coffee capsules, tea bags, wipes, and cotton bud sticks.
• Regulatory submissions and ecolabel applications where verified compostability data from accredited third-party laboratories is a mandatory entry requirement.

By grounding environmental claims in standardized test data, manufacturers reduce greenwashing risk, satisfy increasingly strict plastic regulations, and build credibility with retailers, municipalities, and end consumers.

FAQ

What is the difference between biodegradable and compostable?

Biodegradable describes any material that can be broken down by microorganisms over an unspecified timescale and environment. Compostable is a much stricter claim: the material must biodegrade at a defined rate, disintegrate, and produce compost with no toxic effects within a specified composting environment, as demonstrated through standardized testing.

How long does a complete compostability evaluation take?

The biodegradation test alone runs up to six months. Including disintegration testing, ecotoxicity assessment, and chemical analysis, a full evaluation typically requires six to nine months, so manufacturers should plan certification timelines accordingly.

Does compostability testing cover home composting?

Standard frameworks such as EN 13432 and ASTM D6400 are based on industrial composting conditions of approximately 58 degrees Celsius. Home composting occurs at lower and more variable temperatures, so additional evidence under ambient-temperature conditions is generally required to support home compostability claims.

What samples are required for testing?

Laboratories generally require finished commercial products, including all attached components, along with material safety data, formulation information, and sufficient quantity to run parallel biodegradation, disintegration, and chemical test reactors. Exact sample requirements are defined in the test proposal issued by the laboratory.

Is compostability testing legally required?

Requirements vary by market. In many jurisdictions, environmental claims about compostability must be substantiated by testing to recognized standards, and certification is often a practical prerequisite for access to retail and municipal procurement programs. Engaging an accredited third-party laboratory ensures the resulting data is technically valid and broadly accepted.