biodegradable or compostable? let's clarify

The term biodegradable refers to a material that, thanks to its chemical structure, is capable of undergoing a process in which microorganisms such as bacteria and fungi metabolise polymer chains, transforming them into water, carbon dioxide (or methane) and biomass under aerobic (or anaerobic) conditions.

From an application point of view, polymer products must be certified as biodegradable under specific conditions depending on the scenario envisaged for the end of their life cycle. For example, plastic cutlery or bags, designed to be disposed of in organic waste, must meet the biodegradability requirements described in standard EN13432 (industrial compostability). Similarly, mulch films must comply with standard EN17033 (degradation in soil under environmental conditions), while bioplastic objects that could end up in the sea should be certified as biodegradable in the marine environment according to standard ASTM D6691.

In these cases, the thickness of the bioplastic product and the conditions of biodegradation (time, temperature, oxygen and humidity levels) strongly influence the outcome of the certification. So we can have a bag made of bioplastic that is compostable and a thicker object (e.g. a shoe sole) made of the same biodegradable plastic that no longer meets the compostability criteria. In other words, the term biodegradable is a necessary condition for an object made of bioplastic to be certified, but it is not a sufficient condition.