Fully biodegradable mulch film testing verifies that agricultural cover films made from biodegradable polymers truly degrade in soil, maintain mechanical strength throughout the growing season, and remain safe for crops and the environment. By evaluating biodegradation rate, disintegration behavior, heavy metal content, and ecotoxicity against standards such as GB/T 35795, EN 17033, and ISO 23517, manufacturers, distributors, and regulators obtain objective evidence of product performance and compliance. This article explains the sample types, testing items, laboratory methods, and typical acceptance criteria involved in a complete biodegradable mulch film evaluation program.
Technical Overview
Fully biodegradable mulch film is a thin plastic covering material laid on agricultural soil to suppress weeds, conserve moisture, and moderate soil temperature. Unlike conventional polyethylene film that must be recovered and disposed of after harvest, biodegradable mulch film is designed to be plowed into the soil, where microorganisms convert the material into carbon dioxide, water, and new biomass, eliminating residual "white pollution" in farmland. These films are typically formulated from biodegradable polyesters and bio-based components such as PBAT, PLA, PBS, PHA, and thermoplastic starch blends.
Because a mulch film must satisfy two conflicting requirements, maintaining strength and barrier function during the crop season and then degrading reliably after incorporation into soil, comprehensive laboratory and field testing is essential. Testing also protects the market from misleading claims, since oxo-degradable products that merely fragment into microplastics can otherwise be sold under the "biodegradable" label.
The principal standards governing this product category include:
- GB/T 35795-2017, the Chinese national standard for fully biodegradable agricultural mulch film, covering dimensions, mechanical properties, biodegradation rate, heavy metals, and ecotoxicity.
- EN 17033, the European standard specifying requirements and test methods for biodegradable mulch films used in agriculture and horticulture.
- ISO 23517, the international standard for biodegradable mulch films, harmonized with the European approach.
- ISO 17556, GB/T 22047, and ASTM D5988, which measure ultimate aerobic biodegradability of plastics in soil.
- ISO 14855-1, GB/T 19277.1, and ASTM D5338, which measure biodegradability under controlled composting conditions, together with EN 13432 for compostability reference criteria.
Testing Samples
Raw Materials and Compounds
Resin pellets, masterbatches, and compounded granules are tested before film production to confirm polymer identity, melt flow behavior, thermal characteristics, and the absence of non-biodegradable polyethylene contamination. Material-level screening by FTIR spectroscopy, DSC, and biodegradation pre-testing helps formulators lock down a compliant recipe early in development.
Finished Film Products
Rolls of manufactured mulch film are sampled for dimensional verification, appearance inspection, and full mechanical characterization. Because film performance is highly sensitive to processing conditions, finished-product testing is the basis for factory quality control, product certification, and batch release.
Weathered and Field-Aged Samples
Film specimens exposed to artificial weathering chambers or retrieved from real field installations after part or all of a growing season are tested to measure retention of tensile strength and elongation. These samples demonstrate whether the film survives its intended service life and whether degradation begins on schedule after harvest.
Soil-Incubated and Compost Test Specimens
Film pieces buried in reference soil or composting vessels for biodegradation testing, together with the surrounding soil or compost recovered at the end of exposure, are used for respirometric measurement, disintegration assessment, and ecotoxicological evaluation of degradation products.
Testing Items
A complete evaluation of fully biodegradable mulch film typically includes the following groups of test items:
- Dimensions and appearance: average thickness, thickness deviation, width, length, and visual defects such as gels, pinholes, streaks, and uneven winding.
- Mechanical properties: tensile strength and elongation at break in both machine and transverse directions, right-angle tear strength, and property retention after aging.
- Biodegradation performance: relative biodegradation rate compared with a cellulose reference, degree of disintegration, fragmentation behavior, and decline in molecular weight during exposure.
- Ecotoxicity: seed germination rate, plant emergence and biomass growth in soil or compost containing degraded film residues, and, where required, soil invertebrate toxicity screening.
- Chemical safety: regulated heavy metals and other elements including arsenic, cadmium, chromium, copper, mercury, nickel, lead, selenium, zinc, fluorine, molybdenum, vanadium, and cobalt, plus volatile solids and ash content.
- Durability: artificial weathering by xenon-arc or UV fluorescent exposure and heat aging, followed by measurement of residual mechanical properties.
- Material characterization: infrared spectroscopy for polymer identification, melting and crystallization behavior by DSC, thermal stability by TGA, and melt flow rate for processability control.
Testing Methods
Soil Biodegradation Testing
The core test for "fully biodegradable" claims is laboratory soil biodegradation per ISO 17556, GB/T 22047, or ASTM D5988. Film specimens are mixed with defined reference soil in sealed respirometers, and microbial conversion of the material carbon to carbon dioxide is monitored continuously or periodically through CO2 evolution or oxygen demand. The cumulative CO2 is compared with that from a cellulose positive control and a blank soil inoculum, and the relative biodegradation percentage is calculated. Standards such as EN 17033 and ISO 23517 generally require at least 90% biodegradation within a maximum of 24 months of soil exposure at ambient temperature, while GB/T 35795 applies the same 90% relative biodegradation threshold as its acceptance criterion.
Composting Biodegradation and Disintegration
Where claims relate to compostability or where accelerated mineralization data are needed, testing follows ISO 14855-1, GB/T 19277.1, or ASTM D5338 at controlled thermophilic composting temperature around 58 degrees Celsius. Disintegration is assessed per ISO 20200 or ISO 16929 by sieving recovered material and determining the fraction remaining above 2 mm; the EN 13432 benchmark requires at least 90% disintegration into fragments smaller than 2 mm within 12 weeks.
Ecotoxicity Testing
Plant growth tests are performed in soil or finished compost blended with known amounts of degraded film residue. Seed germination percentage, emergence rate, and shoot or total biomass are compared with a blank control using methods aligned with ISO 11269 series procedures and the plant test requirements of EN 13432 and EN 17033. Typical acceptance requires germination and biomass values not lower than 90% of the blank control, confirming that degradation intermediates do not harm crops.
Heavy Metal Analysis
Specimens are microwave-digested in acid and analyzed by ICP-OES, ICP-MS, or atomic absorption spectroscopy. Measured concentrations of regulated elements are compared against the limit tables in GB/T 35795 and EN 13432, ensuring that tilled-in film does not accumulate hazardous substances in farmland.
Mechanical and Physical Testing
Tensile strength and elongation at break are measured on strip specimens according to GB/T 1040.3 or ISO 527-3, and right-angle tear strength is determined with standard film tear fixtures. Thickness is scanned at regular intervals across the web using precision contact gauges per GB/T 6672. Artificial weathering is conducted per GB/T 16422.2 or ISO 4892-2 using xenon-arc light with water spray cycles, after which mechanical retention values quantify service-life durability.
Applications
Testing services for fully biodegradable mulch film serve a wide range of practical needs across the agricultural value chain:
- Regulatory compliance: demonstrating conformity with GB/T 35795 for products sold in China and with EN 17033 or ISO 23517 for international markets.
- Product certification and eco-labeling: providing the technical file data needed for biodegradability marks, green product declarations, and compostability claims.
- Government procurement and subsidy programs: supplying the third-party test reports commonly required when agricultural authorities distribute degradable film to farmers.
- Manufacturer quality control: verifying each production batch for thickness, strength, and composition consistency before shipment.
- Research and development: comparing formulations, stabilizer packages, and weathering strategies during new product development and field demonstration projects.
- Export documentation: supporting customs, buyers, and overseas distributors with standardized performance evidence.
FAQ
What is the difference between fully biodegradable and oxo-degradable mulch film?
Fully biodegradable film is metabolized by soil microorganisms into carbon dioxide, water, and biomass, which is proven by respirometric mineralization testing. Oxo-degradable film is conventional polyethylene with additives that cause it only to fragment into small plastic particles; it cannot pass the soil biodegradation tests required by GB/T 35795, EN 17033, or ISO 23517 and is increasingly restricted.
Which standards apply to fully biodegradable mulch film?
In China, GB/T 35795-2017 is the dedicated national standard. In Europe, EN 17033 governs biodegradable mulch films, and ISO 23517 provides the corresponding international requirements. Biodegradation test methods are drawn from ISO 17556, GB/T 22047, and ASTM D5988 for soil, and ISO 14855-1 or ASTM D5338 for composting, while EN 13432 is used as the reference framework for compostability claims.
How long does biodegradation testing take?
Controlled composting tests usually run for 45 to 180 days, whereas soil biodegradation tests at ambient temperature may require up to 24 months, since standards allow a long window to reach the 90% relative biodegradation threshold. Test duration depends on film formulation, thickness, inoculum activity, and incubation temperature.
What are the typical acceptance criteria?
The most common thresholds are a relative biodegradation rate of at least 90% versus cellulose, disintegration of at least 90% into fragments smaller than 2 mm where applicable, heavy metal content within the standard limit tables, and seed germination and plant biomass at or above 90% of blank controls in ecotoxicity tests.
How much sample is required for testing?
Dimensional and mechanical testing generally requires several square meters of finished film taken from representative positions across the roll. Biodegradation testing typically consumes 100 to 500 grams of specimen material plus reference cellulose and blank soil, while weathering studies need additional sheet area for exposure racks and subsequent mechanical measurement. Accredited third-party laboratories confirm exact quantities based on the selected test program.
Must the film remain intact during the growing season?
Yes. A qualified biodegradable mulch film must balance durability and degradability. Artificial weathering tests and field service evaluations verify that tensile strength and elongation are retained through the crop season, after which degradation should progress once the film is incorporated into soil, avoiding both premature breakdown and persistent residue.