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ASTM D5988: Ultimate Aerobic Biodegradability of Polymers in Soil

ASTM D5988 determines the degree and rate of aerobic biodegradation of plastic materials in soil under laboratory conditions by measuring oxygen consumption or CO2 evolution. This test method is designed to measure the biodegradability of plastic materials relative to a reference material in an aerobic environment. This test method is designed to be applicable to all plastic materials that are not inhibitory to the bacteria and fungi present in soil.

This ASTM test method is equivalent to ISO 17556.

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CONCEPT

The ASTM D5988 uses respirometry to determine the biodegradability by measuring the CO2 formation or oxygen consumption during the biodegradation process. As the plastic material decomposition process primarily result in the consumption of O2 and formation of CO2 and H2O, the measurement of consumed O2 or generated CO2 can well reflect the biodegradation of the test material.

This method is designed to yield the optimum rate of biodegradation of a plastic material in natural soil by controlling the humidity, C:N ratio, temperature and other conditions. It also aims to determine the ultimate biodegradability of the test material by using a small-scale reactor.

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ASTM D5988

ASTM D5988 Key Summary

▶ Materials that can be tested:
     ➢ All plastic materials that are not inhibitory to the bacteria and fungi present in soil.
▶ Test substance requirement:
     ➢ Organic carbon content is required in order to calculate the theoretical CO2 evolution (ThCO2) (alternatively, if oxygen consumption is measured to determine the biodegradability, then theoretical oxygen demand (ThOD) of the sample is required);
     ➢ May be in the form of films, pieces, fragments, powders, or formed articles, or in aqueous solution;
     ➢ Do not inhibit bacteria and fungi present in soil.
▶ Measurement: oxygen consumption or CO2 evolution;
▶ Temperature: 20-28°C;
▶ Reference: a well-defined biodegradable polymer (e.g., starch or cellulose);
▶ Reactor size: preferred at 2-4 L;
▶ Test substance dosage: approximately 200 mg to 1000 mg carbon for 500 g soil;
▶ Soil: natural, fertile soil less than 2 mm collected from the surface layers of fields and forests. Make a laboratory mixture of equal parts (by weight) of soil samples obtained from at least three diverse locations (for example, an agricultural field, a forest, and a pasture or meadow);
▶ Soil loading: 100-500 g of soil;
▶ Number of reactors: 3 for blank control, 3 for reference control, 3 for technical control, and 3 for test substance;
▶ Duration: Continue the incubation until no net carbon dioxide production is noted between consecutive measurements taken four weeks apart, from both the positive reference material and test material vessels.
▶ Test validity criteria:
     ➢ Reference substance reaches 70% of degradation in 6 months;
     ➢ The amounts of CO2 evolved from the blanks (or the BOD values for the alternative measurement of oxygen consumption) shall be within 20 % of the mean at the plateau phase or at the end of the test.

Requirement and Applicability

Different testing methods are applicable for materials with different properties. Below is a summary of the applicability of ASTM D5988. You can also find the applicability for many other methods on Aropha Resource Center
. 

TestAnalytical methodSample info required *Poorly solubleVolatileAdsorbing
Oxygen demand in a respirometerOxygenThOD*+++
CO2 evolutionCO2Organic carbon content*+-+

*"Sample info required" is the information needed to calculate the biodegradation percentages. This must be available for a selected method.
*"ThOD" can be easily calculated based on the chemical formula of the sample. Try our Online ThOD Calculator.
*"Organic carbon content" is the ratio of the organic carbon weight to the weight of the sample. It can be calculated by the chemical 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).

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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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