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ISO 14855: Composting of Plastics - CO2 Evolution

ISO 14855 is an aerobic biodegradability test that determines the ultimate aerobic biodegradability of plastic materials under controlled composting conditions (58 °C) by measuring CO2 evolution. The test normally lasts for 45 days but can be continued for up to 6 months. This method is equivalent to ASTM D5338.

This method consists of two parts:
Part 1: General method
Part 2: Gravimetric measurement of CO2 evolved in a laboratory-scale test

Part 2 (i.e., ISO 14855-2) is more widely used and therefore discussed below.

ISO 14855 Key Summary

The ISO 14855-2 uses respirometry to determine the biodegradability by measuring the CO2 formation during the biodegradation process up to 6 months. 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 an absorption column filled with soda lime and soda talc on an electronic balance. 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:
     ➢ Natural and/or synthetic polymers, copolymers or mixtures of these;
     ➢ Plastic materials that contain additives such as plasticizers or colorants;
     ➢ Water-soluble polymers;
     ➢ Materials that, under the test conditions, do not inhibit the microorganisms present in the inoculum.
▶ Test substance requirement:
     ➢ Organic carbon content is required in order to calculate the ThCO2;
     ➢ Preferably in powder form with maximum size of 250 um diameter;
▶ Measurement: CO2 evolution;
▶ Temperature: 58 °C;
▶ Reference: a well-defined biodegradable polymer (e.g., thin-layer chromatography (TLC) grade microcrystalline cellulose with a particle size of less than 20 µm);
▶ Reactor size: preferred at 500 mL;
▶ Test substance dosage: normally a minimum of 10 g of total dry solids containing 4 g of TOC is required per 500 mL-vessel;
▶ Inoculum: well-aerated compost from a properly operating aerobic composting plant;
▶ Inoculum dosage: 60 g of total dry solids;
▶ Ammonia is absorbed by a bottle filled with 1 M sulfuric acid before CO2 absorption;
▶ 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 control, and 3 for test substance;
▶ Duration: normally 45 days, but can be continued for up to 6 months.

ISO 14855 Requirement and Applicability

Different testing methods are applicable for materials with different properties. Below is a summary of the applicability of ISO 14855. 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
ISO 14855CO2 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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