ISO 16929: Determination of the Degree of Disintegration of Plastic Materials under Defined Composting Conditions in a Pilot-Scale Test

ISO 16929 Key Summary

The methodology evaluates the breakdown of test materials in a laboratory environment, mimicking the conditions of a robust aerobic composting process. The testing incorporates either the biowaste from the input material of a composting plant or a synthetic solid waste matrix enriched with mature compost obtained from a municipal or industrial composting facility. Plastic test pieces, presented as large pieces and/or powder (depending on the study's objectives), undergo a 12-week composting cycle within the formulated solid matrix at temperatures ranging from 45-75°C. Post-composting, the degree of breakdown is determined by passing the resulting matrix through a 2 mm sieve to isolate any remaining undecomposed residues. The reduction in the mass of the test sample is considered disintegrated material and forms the basis for calculating the extent of disintegration.

▶ Artificial biowaste (if used rather than the input material of a composting plant):
     ➢ freshly mixed fruit and vegetable waste.
     ➢ rabbit feed (seeds and extruded dried-vegetable pellets).
     ➢ mature compost.
     ➢ sufficient water to attain a good moisture content.
     ➢ a bulking agent (such as wood chips or bark with a particle size of 10-50 mm) (100-600 g/kg).
  Ensure: 
     ➢ C/N of 20:1 to 30:1. 
     ➢ >50% of water content. 
     ➢ >50% of volatile solids content. 
     ➢ pH above 5. 
     ➢ maximum particle size of 50 mm.
▶ Composting reactors shall: 
     ➢ have a minimum volume of 35 L. 
     ➢ consist of a sturdy, heat-resistant and non-biodegradable material. 
     ➢ not affect the composting process or the quality of the compost.
▶ Number of reactors: 2 for blank, and 2 for each test substance.
▶ Test substance size and dosage: use the test material in an identical form (e.g. shape, thickness) as for the intended final use at a dosage of 10 g/kg. Reduce large materials in size to 10 cm × 10 cm for films and 5 cm × 5 cm for other products. Optionally, if purpose of the test includes production of compost for ecotoxicity tests, additionally add test material in the form of fine powder or granules (size < 500 µm) at a dosage of 90 g/kg (i.e., in total 10 g/kg large pieces with 90 g/kg powder). It is believed that the fine powder or granulates, if reduced in particle size to <500 µm, will not affect the disintegration of the test material. If the purpose is only ecotoxicity test (no disintegration), then use 100 g/kg of powder.
▶ Turning: Turn the biowaste mixture regularly to break down lumps and to remix water (maintain water content > 40%), microorganisms and substrate. Do this weekly during the first 4 weeks and then every 2 weeks until the end of the test.
▶ Temperature: temperature changes from high to low depending on the incubation phases (five phases in total: days 2-7, 8-28, 29-56, 57-70, and 71-84). Temperature also varies depending on the purpose of the tests.
▶ Duration: 12 weeks.
▶ Measurement after testing: sieve the mixtures after composting with 10 mm, 5 mm, and 2 mm sieves to collect the remaining test substance. Wash and dry the test substance and determine its weight. Also determine compost dry solids content, volatile solids, pH, ammonium nitrogen, nitrite and nitrate nitrogen, total nitrogen, and compost maturity (by volatile fatty acids or the “Rottegrad”).
▶ Test validity criteria: 
     ➢ the temperature during incubation meet the requirements. 
     ➢ the pH increases to a value above 7 during the test and does not fall below 5. 
     ➢ the biowaste compost of the blank control has a maturity (Rottegrad) of IV to V after 12 weeks and/or the volatile fatty acid content is <500 mg/kg.

▶ When ISO 16929 is used as part of ASTM D6400 or ISO 17088, a plastic product is considered to have demonstrated satisfactory disintegration if after twelve weeks (84 days) in a controlled composting test, no more than 10 % of its original dry weight remains after sieving on a 2.0-mm sieve.remains after sieving on a 2.0-mm sieve.

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