Compostability testing evaluates whether plastics, packaging, and other organic materials 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 regulatory compliance, compostability certification, and verified environmental marketing claims. This article explains the sample types, test items, analytical methods, and application scenarios involved in a complete compostability evaluation.
Technical Overview
Compostability testing is a systematic laboratory evaluation that determines whether a material or product can be safely processed together with organic waste in a composting environment. Unlike general claims of "biodegradability," verified compostability requires demonstration across four technical pillars: chemical safety, ultimate aerobic biodegradation, physical disintegration, and absence of ecotoxic effects on plants and soil organisms. The most widely applied specifications include EN 13432 for packaging in Europe, EN 14995 for plastics in general, ASTM D6400 for compostable plastics in North America, and the corresponding GB/T standards used in China, such as GB/T 19277 series for biodegradation testing and GB/T 41010 for biodegradable product labeling.
A distinction must be made between industrial composting and home composting. Industrial facilities operate at elevated temperatures, typically around 58 °C with controlled moisture and aeration, and the reference biodegradation window is 180 days. Home composting occurs at ambient temperatures with less controlled conditions and typically requires demonstration over up to 12 months using modified, low-temperature test regimes. Because compostability claims are increasingly regulated by packaging directives, single-use plastics legislation, and consumer protection rules on environmental claims, testing through accredited third-party laboratories is a critical step before products enter regulated markets.
Testing Samples
Resins, Masterbatches, and Raw Materials
Base polymers and additive formulations submitted for characterization prior to conversion. Common material families include PLA, PBAT, PHA/PHB, PBS, starch blends, cellulose derivatives, and their compostable compounds, fillers, and colorants.
Films and Flexible Products
Carrier bags, organic waste collection liners, agricultural mulch films, cling films, laminates, and flexible packaging. Film samples are tested for biodegradation in film form and for disintegration after artificial weathering or representative use conditioning where applicable.
Rigid and Molded Products
Cutlery, cups, plates, trays, food containers, straws, coffee capsules, thermoformed parts, injection-molded items, and foamed products. Thick-walled or complex articles may require dimensional reduction according to the relevant standard to expose a representative surface area.
Coated Paper, Board, and Fiber-Based Products
Paper and board coated or laminated with bioplastics, molded fiber tableware, and composite structures. The coating layer and substrate are assessed together to confirm the finished article disintegrates and biodegrades as a whole.
Fibers, Nonwovens, and Hygiene Products
Compostable nonwoven wipes, tea bags, coffee filters, and hygiene articles where full biodegradation of every component, including stitching, adhesives, and inks, must be demonstrated.
Typical submission quantities range from several hundred grams to a few kilograms of homogeneous material, together with technical data sheets, formulation information, and declarations of composition, which are required for the chemical characterization stage.
Testing Items
A complete compostability assessment covers the following test items, each with defined acceptance criteria under EN 13432, EN 14995, and ASTM D6400.
- Chemical characterization: determination of dry solids and volatile solids, with volatile solids required to be at least 50% of the dry mass.
- Regulated heavy metals and toxic substances, with typical dry-weight limits (mg/kg): zinc ≤150, chromium ≤50, copper ≤50, nickel ≤25, molybdenum ≤1, arsenic ≤5, cadmium ≤0.5, lead ≤50, mercury ≤0.5, selenium ≤0.75, and fluorine ≤100.
- Ultimate aerobic biodegradation: at least 90% of the theoretical carbon dioxide must be released within 180 days, measured in absolute terms or relative to a cellulose reference.
- Disintegration: at least 90% of the test material must fragment to pieces smaller than 2 mm within 12 weeks in a composting environment.
- Ecotoxicity: seed germination rate and plant biomass of the resulting compost must each reach at least 90% of the corresponding blank compost control.
- Optional anaerobic biodegradation and biogas production assessment for materials intended for anaerobic digestion treatment streams.
Testing Methods
Chemical Characterization
Volatile solids are determined by ignition of the dried sample at 550 °C. Heavy metals are quantified after microwave acid digestion using inductively coupled plasma optical emission spectrometry (ICP-OES) or mass spectrometry (ICP-MS), with atomic absorption spectroscopy (AAS) as an alternative technique. Fluorine is typically determined by ion-selective electrode or combustion ion chromatography.
Aerobic Biodegradation Under Controlled Composting
The core biodegradation test follows ISO 14855-1, ASTM D5338, EN 14046, or GB/T 19277.1. Test material is mixed with mature, inoculated compost and incubated at approximately 58 °C with controlled moisture and aeration. Evolved carbon dioxide is monitored continuously by infrared analysis or by periodic titration, and the cumulative CO2 is compared against the theoretical amount calculated from the material's carbon content. ISO 14855-2 provides a simplified closed-vessel variant using small-scale reactors. A cellulose reference and an inert blank are run in parallel for validity and normalization.
Biodegradation in Aqueous Medium
For materials or products where an aqueous screening is required, ISO 14851 (oxygen demand measurement in a closed respirometer) and ISO 14852 (evolved carbon dioxide analysis) are applied using activated sludge or aqueous inocula at ambient temperatures. These methods support formulation development and comparative screening before full composting trials.
Disintegration Testing
Disintegration is evaluated at pilot scale using ISO 16929 or EN 14045 with a natural compost matrix, or at laboratory scale using ISO 20200 with a synthetic solid waste matrix held at 58 °C. GB/T 19811 is the corresponding national method. After the 12-week exposure, the residue is sieved and the mass fraction of fragments exceeding 2 mm is determined; this fraction must not exceed 10% of the original dry mass.
Ecotoxicity Bioassays
Compost produced in the disintegration test is mixed with a reference soil and used to grow indicator plant species under standardized conditions, following plant growth and emergence tests such as ISO 11269-2, with two or more species and replicate controls. Germination rate and plant biomass must remain within 10% of blank compost performance. Where required, earthworm acute toxicity testing per ISO 11268-1 supplements the plant bioassays for soil fauna protection.
Anaerobic Biodegradation
ISO 14853 measures biodegradation and biogas production under anaerobic aqueous conditions for materials destined for anaerobic digestion. This provides carbon conversion data supporting end-of-life declarations for digestion treatment routes.
Applications
Compostability test reports from accredited third-party laboratories are used across the full product lifecycle and value chain:
- Packaging compliance: demonstrating conformity with the essential requirements of packaging and packaging waste legislation, for which EN 13432 is the harmonized reference standard in Europe.
- Certification and labeling: providing the technical dossier required for compostability certification marks, seedling-type logos, and lawful "compostable" claims under advertising and green-claims regulations.
- Agriculture: verification of soil-biodegradable mulch films against EN 17033 and ISO 23517, enabling biodegradation in soil as an accepted end-of-life route in place of film retrieval and landfilling.
- Organic waste programs: qualification of waste bags, liners, and foodservice ware for municipal source-separated biowaste collection and industrial composting infrastructure.
- Research, development, and quality control: screening new biopolymer formulations, additives, inks, and adhesives, and monitoring batch-to-batch consistency of compostable raw materials.
- Procurement and tenders: objective evidence for retailers, brand owners, and public buyers specifying certified compostable inputs.
FAQ
How long does a full compostability test take?
The biodegradation test alone runs up to 180 days, disintegration requires approximately 12 weeks plus compost preparation, and ecotoxicity bioassays add several weeks of plant growth. Because some stages can be run in parallel while others depend on compost generated in the disintegration phase, a complete evaluation typically takes six to nine months from sample receipt to final reporting.
What is the difference between biodegradable and compostable?
Biodegradable describes a material's general capacity to be broken down by microorganisms, without a defined timeframe or environment. Compostable is a stricter claim that requires verified biodegradation within 180 days in a composting environment, physical disintegration, chemical safety within heavy metal limits, and no ecotoxic effects on plants or soil organisms.
What is the difference between industrial and home compostability testing?
Industrial testing is performed at approximately 58 °C with optimal moisture and aeration, simulating commercial composting facilities. Home compostability testing uses ambient temperatures and less controlled conditions, extends the evaluation to up to 12 months, and applies lower-temperature biodegradation and disintegration regimes. Materials certified for industrial composting should not be claimed suitable for home composting without separate testing.
How much sample is required for testing?
Biodegradation and disintegration trials generally require 0.5 to 2 kg of homogeneous material, while chemical characterization and ecotoxicity stages need smaller representative portions. Finished products should be submitted in their final formulation, including all coatings, adhesives, inks, and additives.
Can one test report cover multiple products or colors?
Where products share an identical material formulation and differ only in geometry, disintegration testing may be grouped, with the thickest or most challenging configuration tested as worst case. Different colors, additives, or resin grades normally require separate chemical characterization and may require separate biodegradation verification, subject to the certification body's grouping rules.
Which materials typically pass compostability testing?
Materials that routinely meet the criteria include PLA, PBAT, PHA, PBS, starch blends, cellulose-based plastics, paper and board, and plant fibers, provided that all additives, inks, adhesives, and coatings are also compostable and heavy metal limits are respected. Conventional polyethylene, polypropylene, and oxo-degradable plastics do not meet the biodegradation thresholds and cannot be certified as compostable.
