Scope:

Oxo-biodegradable plastics are those plastics that degrade by a combination of thermal or photo-oxidation and biodegradation. The ASTM D6954 guide provides a roadmap for evaluating degradation progress and resulting ecological impacts of degraded plastics in soil, landfill, compost, land-cover and agricultural environments. Plastics that are classified as Oxo-biodegradable will decompose at a faster rate than conventional plastics, though subsequent eco-impacts may be adverse. The guide organises various existing ASTM test methods in three tiers to first simulate abiotic oxidation followed by microbial degradation and finally eco-impact evaluation in controlled conditions. The data generated for different polymers under standard ASTM test conditions allow for relative ranking, facilitating decision-making on material selection, product development and plastics disposal issues.

Test Procedure:

The samples are first subjected to Tier-1 accelerated thermal and/or photo-oxidation tests using prescribed ASTM methods. The humidity and temperatures are chosen to represent conditions in soil, landfill or composting. Equipment includes laboratory oven for thermal test and UV light for photo-oxidation. Parameters monitored include molecular weight distribution, volatiles percentage, mechanical strength and weight loss with respect to time and temperature. When the Tier-1 process produces a residue that is demonstrably biodegradable (as measured by ASTM biometer test for CO₂  evolution), the procedure shifts to the prescribed Tier-2  tests for biodegradability. The intent of Tier-2 is to measure biodegradability in conditions similar to actual disposal or use environments. This is done by standard biometric test methods that can provide the rates and degree of biodegradation over a period of several months. The procedure involves inoculating the residue from Tier-1 with aerobic composting microbes and monitoring conversion of carbon to CO₂ in a reactor set-up with CO₂ free air supply. The residue after the oxidation and biodegradation stages is then subjected to Tier-3 tests that deal with terrestrial and aquatic toxicity tests conducted as per prescribed ASTM standards.

Specimen size:

Specimen size is not prescribed. It may be noted that in addition to samples of various plastics that need testing, various other samples such as representative soil, composting inoculum, seeds for germination tests are required.

Result:

The result is provided in the form of a report of all the tests covering the 3-tiers. Overall ranking can be done based on the tests.