BIODEGRADABILITY | TESTING
Understanding standards and testing, and keeping up with changes, are crucial for suppliers of biodegradable plastics. Jennifer Markarian reports on new test methods and accelerated screening aiding development
Putting biodegradable plastics to the test
Biodegradability is an important property to measure for some plastics applications, such as agricultural mulch films or for bags, containers, or packages designed to be composted at their end of life. Because “biodegradability” is a broad term that has potential for misuse and confusion, it is important to understand the standards and test methods that are required in this market and what claims are allowed. In some states in the US, for example, the term “biodegradable” is considered misleading and is prohibited in product claims. Companies can, however, demonstrate the conditions under which the product has been tested and use the corresponding term (eg industrially compostable). Technically, biodegradation occurs in two steps:
disintegration (fragmentation into small particles) and mineralization, which is conversion by biologi- cal mechanisms to water, carbon dioxide, and humus in an aerobic environment (and also methane, if in an anaerobic environment). Standard specifications, such as ASTM International’s D6400
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for industrial compostability of single-layer prod- ucts, require passing both disintegration and mineralization lab tests, as well as tests for ecotoxic- ity, explained Kelvin Okamoto, Chair of the ASTM D20.96 Subcommittee on Environmentally Degra- dable Plastics and Biobased Products and President of consultancy Green Bottom Line. The mineraliza- tion test begins with material in a powder form, but disintegration begins with the actual product and is affected by product geometry and thickness. All materials generate particles during the disintegra- tion step, but materials that fully mineralize will not create persistent microparticles, Okamoto noted. The ASTM D6400 standard, which currently
states that complete biodegradability requires 90% of the organic carbon to be converted to carbon dioxide, is often misunderstood to mean that 10% residue of degraded polymer will remain. In reality, however, these numbers relate to the experimental threshold of +/- 10% in the mineralization test. “The rise of microplastics as a concern has forced the [long-held] misunderstanding into a brighter
May 2026 | COMPOUNDING WORLD 15
Main image: The behaviour of biodegrad- able plastics should ideally be tested in the field, say experts
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