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ASTM D5338: Composting of Plastics - CO2 Evolution

ASTM D5338 determines the degree and rate of aerobic biodegradation of plastic materials on exposure to a controlled-composting environment under laboratory conditions, at thermophilic temperatures (58 °C) by measuring CO2 evolution.

The test substances are exposed to an inoculum that is derived from compost from municipal solid waste. The aerobic composting takes place in an environment where temperature, aeration and humidity are closely monitored and controlled.

The test normally lasts for 45 days but can be extended. This method is equivalent to ISO 14855.

ASTM D5338 Key Summary

The ASTM D5338 uses respirometry to determine the biodegradability by measuring the CO2 formation during the biodegradation process for normally 45 days. As the plastic material decomposition process primarily result in the formation of CO2 and H2O, the measurement of generated CO2 can well reflect the biodegradation of the test material. With the measured and the theoretical CO2 amount, one can easily calculate the degradation percentages over a specified incubation time.

This method is designed to yield the optimum rate of biodegradation of a plastic material in mature compost by controlling the humidity, aeration ratio and temperature in the composting vessel. It also aims to determine the ultimate biodegradability of the test material by using a small-scale reactor. The degradation rate is periodically measured by determining the mass of the evolved CO2 using COabsorption bottle filled with Ba(OH)2. The test material is mixed with an inoculum derived from mature compost and with an inert material such as sea sand.

▶ Materials that can be tested:
     ➢ All plastic materials, which are intended to be composted in facilities that achieve thermophilic temperatures.
▶ Test substance requirement:
     ➢ Organic carbon content is required in order to calculate the ThCO2;
     ➢ May be in the form of films, formed articles such as dog bones, granules, or powder;
▶ Measurement: CO2 evolution;
▶ Temperature: 58 °C;
▶ Positive control substance: a well-defined biodegradable polymer (e.g., thin-layer chromatography (TLC) grade microcrystalline cellulose with a particle size of less than 20 µm);
▶ Negative control substance: polyethylene;
▶ Reactor size: preferred at 2-5 L (No more than about 3⁄4 of the volume of the test vessel should be filled with test mixture);
▶ Test substance dosage: normally 100 g of total dry solids;
▶ Inoculum: two to four months old well-aerated compost coming from the organic fraction of municipal solid waste and sieved on a screen of <10 mm;
▶ Inoculum dosage: 600 g of total dry solids;
▶ Stir the compost weekly to prevent extensive channelling and to ensure uniform attack by the microorganisms on the test material.
▶ Number of reactors: 3 for blank control, 3 for reference (positive) control, 3 for negative control, and 3 for test substance;
▶ Duration: normally 45 days, but can be extended.

Requirement and Applicability

Different testing methods are applicable for materials with different properties. Below is a summary of the applicability of ASTM D5338. Please check our Method Selection Guide to select the most appropriate method for your materials. You can also find the applicability for many other methods on Aropha Resource Center

TestAnalytical methodSample info required *Poorly solubleVolatileAdsorbing
ASTM D5338CO2 evolutionOrganic carbon content *+-+

*"Sample info required" is the information needed to calculate the biodegradation percentages. This must be available for a selected method.
*"Organic carbon content" is the ratio of the organic carbon weight to the weight of the sample. It can be calculated by the sample formula (e.g., acetic acid C2H4O2, carbon content is 12*2/(12*2+1*4+16*2)=40%). Try our Online C% Calculator. If the formula is unknown, we can send the sample out to a third party lab for you for analysis (normally $110 with a 10-day turnaround time).

Aropha Resource Center

To learn more about different types of biodegradation tests, their applicability, biodegradation mechanisms, and many other information such as case studies, publications, and blogs, please check our Aropha Resource Center

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