Compostability testing is the scientific evaluation of whether a material or finished product can biodegrade, disintegrate, and leave no ecotoxic residues under controlled composting conditions. Governed by internationally recognized standards such as EN 13432, ASTM D6400, and ISO 14855, these tests are essential for manufacturers of biodegradable plastics, packaging, and disposable products who need credible environmental claims and access to regulated markets. This article explains the scope, sample types, test items, methodologies, and practical applications of compostability testing.
Technical Overview
Compostability testing determines whether a material undergoes biological decomposition in a composting environment at a rate consistent with known compostable materials, converting into carbon dioxide, water, inorganic compounds, and biomass without leaving visually distinguishable or toxic residues. The evaluation is not a single measurement but a structured assessment built on four pillars: chemical characterization, ultimate aerobic biodegradation, disintegration, and ecotoxicity.
The principal international frameworks include EN 13432 for compostable packaging and EN 14995 for compostable plastics in Europe, ASTM D6400 and ASTM D6868 for plastics and coated-paper products in North America, and the ISO method standards ISO 14855 (biodegradation under controlled composting conditions), ISO 16929 (pilot-scale disintegration), and ISO 20200 (laboratory-scale disintegration). In China, corresponding GB/T standards, such as GB/T 19277.1 and GB/T 19811, adopt the same technical principles together with GB/T 41010 for marking and labeling of degradable plastics.
Most industrial compostability tests simulate thermophilic composting at approximately 58°C with active mature compost as the inoculum, reflecting the conditions of well-managed municipal and industrial composting facilities. Testing is typically performed by accredited third-party laboratories operating under ISO/IEC 17025 quality management systems, ensuring that results are technically valid and acceptable for certification and regulatory purposes.
Testing Samples
Biodegradable Polymer Resins and Compounds
Pellet-form materials are submitted for formulation qualification before conversion into finished goods. Common materials include PLA, PBAT, PBS, PHA/PHB, PPC, PGA, starch blends, and their filled or modified compounds. Because certification applies to the final article, resins should be tested together with all intended additives, processing aids, colorants, and stabilizers.
Flexible Films and Bags
Compostable shopping bags, produce bags, garbage liners, mailers, shrink films, and agricultural mulch films are evaluated as complete multilayer structures, including inks, adhesives, and printed surfaces. Flexible packaging often relies on ASTM D6400 in North America and EN 13432 in Europe.
Foodservice Ware and Rigid Products
Cutlery, cups, lids, straws, plates, bowls, clamshell containers, trays, and coffee capsules are tested in their final commercial form. Thick or highly rigid articles usually receive specific attention in the disintegration test because geometry significantly affects fragmentation behavior.
Coated and Laminated Paper Products
Paperboard and molded pulp products with biodegradable barrier coatings are assessed under ASTM D6868, which specifies requirements for coatings bonded to compostable substrates. The coating, not the paper, is typically the critical component being qualified.
Fibers, Nonwovens, and Hygiene Products
Wet wipes, nonwoven fabrics, tea bag meshes, sanitary products, and other fiber-based disposables are increasingly subject to compostability requirements. Spunbond and meltblown nonwovens made from PLA or PBAT are among the most frequently submitted sample types.
Sample submissions should be representative of regular production batches and are typically supplied in quantities of several kilograms per material or article, allowing for biodegradation testing in replicate plus disintegration and ecotoxicity assessments. Full articles are preferred over coupons or trimmed sections whenever certification is the objective.
Testing Items
Chemical Characterization
The first stage verifies that the material is fundamentally organic and free of restricted substances. Key parameters include:
- Volatile solids content, which must be at least 50% of the dry mass for the material to qualify as compostable under EN 13432.
- Regulated heavy metals and other elements, with maximum limits such as zinc 150, copper 50, lead 50, chromium 50, nickel 25, arsenic 5, molybdenum 1, cadmium 0.5, mercury 0.5, and selenium 0.75 mg/kg dry weight, plus a fluorine limit of 100 mg/kg.
- Total organic carbon and elemental composition (C, H, N), used to calculate the theoretical carbon dioxide evolution required for the biodegradation calculation.
Ultimate Aerobic Biodegradation
The core test measures the conversion of organic carbon into carbon dioxide by the compost microbiome. Under EN 13432 and ASTM D6400, the material must achieve at least 90% biodegradation, either in absolute terms or relative to the cellulose positive control, within a maximum of 180 days.
Disintegration
The finished article must physically break down in active composting so that at least 90% of its dry mass passes through a 2 mm sieve after 12 weeks (84 days). This demonstrates that the product will not leave visible fragments that contaminate the final compost.
Ecotoxicity
Compost produced in the disintegration test, or extracts of the test material, is used to grow higher plants. Germination rate and plant biomass must each reach at least 90% of the blank compost control. Earthworm acute toxicity testing in accordance with ISO 11268-1 is a common supplementary endpoint for higher-tier assessments.
Testing Methods
Controlled-Composting Respirometry
Biodegradation is measured according to ISO 14855-1 or ASTM D5338. The test material, reduced to a defined particle size, is mixed with mature, active compost inoculum in insulated bioreactors of typically two to five liters. The reactors are aerated continuously with carbon-dioxide-free air and held at 58°C, with moisture and pH monitored throughout. Evolved carbon dioxide is quantified continuously or periodically using infrared analysis, gas chromatography, or alkaline absorption with titration. The test design includes a blank inoculum vessel, a cellulose positive control that must exceed 70% biodegradation for the run to be valid, and replicate test vessels. Net cumulative carbon dioxide, after blank correction, is divided by the theoretical carbon dioxide of the material to yield the percentage of biodegradation.
Pilot-Scale and Laboratory-Scale Disintegration
Disintegration is evaluated under ISO 16929 at pilot scale, where the test article is mixed with fresh organic waste and composted in insulated reactors for 12 weeks with controlled aeration and periodic turning, replicating realistic facility operation. ISO 20200 provides a laboratory-scale alternative using a defined synthetic solid waste matrix held at 58°C. In both methods, the final residue is sieved through 2 mm mesh, and dry fragments larger than 2 mm are weighed to calculate the disintegration percentage.
Ecotoxicity Assessment
Compost generated during the disintegration phase is blended with a reference growing substrate and used to cultivate at least one monocotyledonous and one dicotyledonous plant species per internationally recognized phytotoxicity protocols. Germination rate, survival, and biomass yield are compared statistically against the blank control. The material passes when both germination and biomass remain at or above 90% of control values.
Chemical Analysis
Elemental analyzers determine carbon, hydrogen, and nitrogen for theoretical carbon dioxide calculation. Heavy metals are quantified by ICP-OES or ICP-MS after microwave acid digestion, fluorine is measured by ion-selective electrode or ion chromatography, and volatile solids are determined gravimetrically by loss on ignition. All results are reported against the applicable limit values of EN 13432, EN 14995, ASTM D6400, or the relevant GB/T standards.
Applications
Compostability testing serves a wide range of commercial and regulatory purposes across the biodegradable materials value chain:
- Product certification and eco-labeling, where a complete test report from an accredited third-party laboratory is the technical basis for obtaining the right to display compostability marks on packaging and products.
- Regulatory compliance, including European packaging and single-use plastics requirements, national plastic restriction policies, and extended producer responsibility schemes that mandate verified compostability for specific product categories.
- Research and development, allowing formulators to compare polymer grades, plasticizers, fillers, and additive packages against quantified biodegradation kinetics.
- Incoming material and production quality control, detecting formulation drift or substitution of non-compliant resins before goods reach customers.
- Substantiation of environmental marketing claims, protecting brands against greenwashing disputes in an era of tightening advertising and consumer protection scrutiny.
- Waste management acceptance, providing composting facility operators with documented evidence that incoming articles will break down within their process windows.
FAQ
What is the difference between biodegradable and compostable?
Biodegradable is a broad term meaning that microorganisms can break down the material over an unspecified time and environment, whereas compostable is a precisely defined claim. A compostable product must biodegrade at least 90%, disintegrate almost completely within 12 weeks, and leave compost that supports plant growth, all verified under recognized standards such as EN 13432 or ASTM D6400.
How long does compostability testing take?
Biodegradation runs for up to 180 days, disintegration for 84 days, and ecotoxicity for several additional weeks. Because some tests can run in parallel, a complete evaluation package typically requires six to nine months from sample receipt to final reporting.
What sample quantity is required?
Laboratories generally request five to ten kilograms of finished product, or two to five kilograms of resin, to cover replicate biodegradation vessels, disintegration charges, ecotoxicity planting, and chemical analysis with sufficient retention material.
Does a passing industrial compostability result also cover home composting?
No. Standards such as EN 13432 and ASTM D6400 simulate industrial composting at approximately 58°C, where microbial activity is far higher than in a home heap at ambient temperature. Home compostability is assessed under separate regional and national schemes that apply cooler temperatures and extended exposure periods, and it must be demonstrated explicitly.
Can test reports be used directly for certification?
Yes, when the testing is performed by accredited third-party laboratories conforming to ISO/IEC 17025 and the test program fully matches the selected standard. Certification bodies review these reports, together with the quality management documentation of the manufacturer, before authorizing the use of compostability labels.
