The biodegradability of plastics is a topic that often comes up when discussing bioplastics. The term “biodegradable plastic” is widely used, but it is also often misunderstood.
What does that mean?
A material is said to be “biodegradable ” when it can be broken down by microorganisms (bacteria, fungi, etc.) into simple components such as:
- Water
- Carbon dioxide (CO2)
- Methane in the absence of oxygen (CH4)
- Biomass.
The chemical structure of the material is the main factor that determines whether a polymer is biodegradable.
Some of its characteristics—such as its thickness or shape—will also have an impact.
However, this deterioration does not depend solely on the material. It is also related to the conditions in which it is found, namely:
- Temperature
- Humidity
- The presence of microorganisms
- pH
- Available oxygen.
- Etc.
All of these factors will therefore influence the rate at which these materials biodegrade.
Various environments
Biodegradation therefore depends heavily on the environment in which the material will reach the end of its life.
Certain environments can be simulated and subjected to standardized test protocols to evaluate the biodegradability of materials in those environments:
Industrial compost (EN 13432 standard)
In dedicated facilities, conditions are controlled (high temperature, humidity, microbial activity). This allows materials that comply with the standard to biodegrade within a few months.
Home composting (NF T 51-800 standard)
In home settings, conditions are less stable, with little or no monitoring, and temperatures are lower. Not all materials that are compostable in an industrial setting are necessarily compostable at home, as biodegradation can take up to 1 year even for certified products.
Anaerobic Digestion This is a process carried out in the absence of oxygen in an industrial setting. The material is converted into biogas (methane) and digestate (residues of bacteria and organic matter).
Natural environments (soil, freshwater, marine environment)
Conditions in these environments vary widely and are often less favorable (lower temperatures, limited control over environmental parameters). Biodegradation generally occurs more slowly in these environments.
A common misconception
So, just because a plastic is labeled as biodegradable doesn’t mean it will break down quickly if left in the natural environment.
Without the right conditions, biodegradation can be very slow. In some cases, it is virtually nonexistent on a human timescale.
In other words, biodegradable plastic should not be considered a solution to the problem of waste disposal in the environment.
Biodegradability should be viewed as a property that can be useful in a number of applications:
- Contaminated items and packaging that facilitate the collection of organic waste (for composting, for example)
- Agricultural and horticultural plastics that make waste management easier for the user.
- Or products for fishing and aquaculture that help combat marine pollution affecting wildlife.
It is therefore an interesting property, but it must be part of a comprehensive approach that includes reduction and reuse, and should be used to supplement recycling when the latter is not—or is no longer—possible.