Biodegradable Plastics Natural Degradation Testing: Standards, Methods, and Technical Requirements

Biodegradable plastics natural degradation testing evaluates how plastic materials break down under real-world environmental conditions such as soil burial, freshwater, marine exposure, and outdoor weathering. This testing is essential for manufacturers, brand owners, and regulatory authorities who need to verify environmental claims, confirm compliance with international standards such as ISO 17556, ASTM D5988, and ISO 14855, and support market access for sustainable materials. Accredited third-party laboratories offer comprehensive degradation assessments covering biodegradation rate, disintegration behavior, and ecological safety.

Technical Overview

Natural degradation testing of biodegradable plastics assesses the breakdown behavior of polymeric materials under environmental conditions that reflect real-world disposal scenarios. Unlike controlled laboratory composting, natural degradation tests expose materials to variable temperature, humidity, UV radiation, and microbial communities found in soil, freshwater, seawater, and open-air environments. The objective is to quantify the degree and rate of biodegradation, document physical disintegration, and confirm that degradation products do not harm the surrounding ecosystem.

During natural degradation, microorganisms colonize the plastic surface and secrete extracellular enzymes that cleave polymer chains into oligomers and monomers. These fragments are then metabolized by microbes, ultimately converting the carbon in the material into carbon dioxide, water, and biomass under aerobic conditions, or into carbon dioxide, methane, and biomass under anaerobic conditions. Testing typically tracks this process through respirometric measurement of evolved carbon dioxide, gravimetric mass loss, reduction in molecular weight, deterioration of mechanical properties, and changes in surface morphology and chemical structure.

The results of natural degradation testing support product certification against standards such as EN 13432, ASTM D6400, and GB/T 20197, and provide scientific evidence for environmental marketing claims, research and development optimization, and regulatory submissions.

Testing Samples

Natural degradation testing can be applied to a wide range of biodegradable polymer materials in various physical forms, including films, sheets, injection-molded articles, fibers, powders, and granules.

PLA-Based Materials

Polylactic acid (PLA) is a bio-based polyester derived from fermented plant starch. It is widely used in rigid packaging, food service ware, and 3D printing filaments. PLA degrades relatively slowly at ambient temperature and typically requires testing programs that run for extended durations to capture its natural degradation profile.

PBAT-Based Films

Polybutylene adipate terephthalate (PBAT) is a flexible, compostable copolymer frequently used in mulch films, shopping bags, and cling films. Its aliphatic ester segments are susceptible to enzymatic hydrolysis, making it a common subject for soil burial and agricultural field degradation studies.

PBS and PBSA Materials

Polybutylene succinate (PBS) and polybutylene succinate adipate (PBSA) offer good heat resistance and processability. These materials are used in packaging, agricultural products, and disposable articles, and they exhibit measurable biodegradation in soil environments.

PHA and PHB Materials

Polyhydroxyalkanoates (PHA), including polyhydroxybutyrate (PHB), are microbial polyesters that biodegrade readily in soil, marine, and freshwater environments. They are often selected for applications where environmental persistence must be minimized, such as marine-degradable packaging.

Starch Blends and Composites

Thermoplastic starch blended with PBAT, PLA, or PCL provides a cost-effective biodegradable option. Testing evaluates how starch content, compatibilizers, and fillers influence the overall degradation rate and disintegration behavior.

PCL and Other Aliphatic Polyesters

Polycaprolactone (PCL) is a low-melting biodegradable polyester used in medical devices, adhesives, and blends. It degrades through hydrolysis of ester linkages followed by microbial assimilation of the fragments.

Testing Items

Comprehensive natural degradation testing programs typically include the following evaluation parameters:

• Biodegradation rate and ultimate biodegradation percentage, determined by monitoring carbon dioxide evolution or oxygen consumption relative to the theoretical carbon content of the sample.
• Mass loss and weight retention measured at defined intervals throughout the exposure period.
• Disintegration degree, assessed by visual inspection and sieving to quantify fragmentation of films or molded articles.
• Molecular weight distribution analysis using gel permeation chromatography (GPC) to detect chain scission.
• Changes in chemical structure identified by Fourier-transform infrared spectroscopy (FTIR), including carbonyl index and crystallinity variation.
• Tensile strength, elongation at break, and other mechanical properties measured before and after exposure.
• Surface morphology characterization using scanning electron microscopy (SEM) to observe erosion, pitting, and biofilm formation.
• Thermal property changes determined by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA).
• Ecotoxicity assessment using seed germination tests, plant growth tests, and earthworm or daphnia acute toxicity tests on degradation residues.
• Heavy metal and regulated element content analysis to confirm compliance with concentration limits specified in EN 13432 and ASTM D6400.

Testing Methods

Test methods are selected according to the intended disposal environment of the material. Accredited third-party laboratories conduct these tests under controlled laboratory simulations or genuine outdoor field exposure conditions.

Soil Burial Biodegradation Testing

Soil burial tests evaluate biodegradation in natural or defined soil media at ambient temperature. International standards include ISO 17556, which measures ultimate aerobic biodegradability by respirometry, and ASTM D5988, which determines aerobic biodegradation in soil by carbon dioxide evolution. Chinese national standard GB/T 19275 provides corresponding procedures. Test specimens are buried in soil beds, and evolved carbon dioxide is captured and quantified over exposure periods ranging from several months to more than one year.

Controlled Composting Biodegradation Testing

Although composting represents an accelerated environment rather than a natural one, it is frequently combined with natural degradation studies to establish ultimate biodegradability. Key methods include ISO 14855-1, ASTM D5338, and GB/T 19277.1, which determine carbon dioxide evolution under controlled composting conditions at approximately 58 degrees Celsius. EN 13432 and ASTM D6400 define the full acceptance framework for compostable packaging.

Aqueous Aerobic Biodegradation Testing

Freshwater degradation is assessed using ISO 14851, which measures oxygen demand in a closed respirometer, and ISO 14852, which measures carbon dioxide evolution in an aqueous medium with activated sludge or river water inoculum. These methods are relevant for products that may enter freshwater systems after disposal.

Marine Biodegradation Testing

Marine environment testing evaluates materials exposed to seawater and marine sediment. ASTM D6691 determines aerobic biodegradation of plastics in the marine environment by a defined microbial consortium, while ISO 19679 addresses biodegradation at the seawater-sediment interface. ASTM D7473 covers weight loss in marine sediments under anaerobic conditions. These tests are critical for fishing gear, marine-degradable packaging, and coastal applications.

Outdoor Weathering and Field Exposure Testing

Natural weathering tests place specimens on exposure racks outdoors to evaluate the combined effects of sunlight, temperature cycles, rainfall, and humidity. Reference procedures include ISO 877 for direct solar exposure and ASTM D1435 for outdoor weathering of plastics. Laboratory-accelerated weathering using xenon arc lamps (ISO 4892-2, ASTM G155) or fluorescent UV lamps (ISO 4892-3, ASTM G154) is often performed in parallel to correlate natural and simulated exposure. Field trials for agricultural mulch films follow protocols aligned with GB/T 35795 for biodegradable mulching film.

Anaerobic Biodegradation Testing

For materials destined for anaerobic digestion or landfill, ISO 15985 and ASTM D5511 measure biogas evolution under high-solids anaerobic digestion conditions, while ISO 14853 evaluates anaerobic biodegradation in an aqueous system.

Applications

Natural degradation testing serves multiple industries and regulatory purposes across the biodegradable plastics value chain:

• Agricultural mulch films and plant protection products, where degradation in soil after harvest must be verified to avoid residual plastic accumulation in farmland.
• Flexible and rigid packaging, including shopping bags, food wraps, bottles, and trays, supporting compostability and biodegradability certifications for consumer goods.
• Food service items such as cutlery, plates, straws, and coffee capsules that require compliance with EN 13432 or ASTM D6400 for composting claims.
• Marine and fishery applications, including fishing nets, lines, and bait packaging, where seawater biodegradability reduces ghost fishing and ocean pollution risks.
• Medical and hygiene products, such as surgical sutures, drug delivery carriers, wipes, and sanitary products, where controlled degradation performance is essential.
• Research and development programs comparing formulations, additives, processing conditions, and bio-based fillers to optimize degradation performance.
• Government procurement and eco-labeling schemes that require independent laboratory evidence of environmental claims.

FAQ

How long does a natural degradation test take?

Test duration depends on the environment and the material. Controlled composting tests typically run 45 to 180 days. Soil burial and marine tests may run from 6 months to 2 years because ambient temperatures and microbial activity are lower and more variable. The test continues until the biodegradation curve reaches a plateau or the required pass threshold, such as 90 percent relative to cellulose within 180 days under composting conditions.

What is the difference between biodegradable and compostable?

Biodegradable describes the inherent ability of a material to be broken down by microorganisms under one or more environmental conditions. Compostable is a stricter claim that requires complete biodegradation, disintegration, and absence of ecotoxic effects within a defined timeframe under composting conditions, verified against standards such as EN 13432 or ASTM D6400. All compostable plastics are biodegradable, but not all biodegradable plastics qualify as compostable.

What sample quantity and form are required?

Respirometric biodegradation tests generally require 100 to 500 grams of material per replicate, preferably as powder or small pieces to maximize surface area. Field exposure tests require film sheets or finished articles of defined dimensions. The laboratory confirms exact sample size and form after reviewing the test plan and applicable standard.

Which reference materials and controls are used?

Positive controls typically include cellulose powder or thin-layer cellulose as a biodegradable reference, while non-biodegradable polyethylene serves as a negative control. Blank inoculum vessels without test material correct for background carbon dioxide evolution, and results are validated only when reference materials exceed 70 percent biodegradation by the end of the test.

How are results reported and interpreted?

The final report presents the biodegradation percentage versus time curve, cumulative carbon dioxide production, mass loss data, disintegration observations, and any requested physicochemical characterizations. A material is generally considered to demonstrate effective biodegradability when it achieves at least 90 percent of the maximum degradation of the cellulose reference, or an absolute value of at least 60 percent for mineralization, within the specified test period.

Can testing be performed on finished products rather than raw resin?

Yes. Testing can be conducted on raw pellets, processed films, molded components, and end-use products. Testing finished products is recommended when certification of the final article is required, since pigments, inks, adhesives, and additives can significantly influence degradation behavior and compliance with regulatory limits.