One of the major concerns of the fast moving consumer goods segment is the level of pollution related to post consumer packaging (PCT). In a linear economy model, PCT generate waste. However, by moving to a circular model, is it expected to transform waste into value. To date, different alternative routes have been investigated in order to alleviate waste. As such, biodegradability and compostability have gained noticeable attention for the past couple of years. But are they really effective in addressing the circularity of the economy? Should they be considered as a sensible options?
What is biodegradability?
Biodegradability refers to the capacity of a material to be degraded through a biological mechanism. The European Commission defines a biodegradable plastic as one that can be broken down and taken up by microbes without harming the environment (1). This implies the use of living organisms capable of decomposing the material into smaller units down to biomass. As a consequence, the process generates carbon dioxide (or methane) and water. Biodegradability depends therefore on the nature of the material and the environmental conditions in which the degradation occurs (temperature, humidity, water content, etc).
What is compostability?
Compostability is a sub-class of biodegradability. It relates to the ability of a material to degrade under controlled process conditions (temperature, humidity, exposure time). The European norms EN 13432 and 14995 bring precisions on compostability conditions:
- After 3 months, the mass of residues has to be less than 10% of the original mass.
- 90% biodegradation must be reached within 6 months.
- Absence of negative effects on the composting process.
- Amount of heavy metals has to be below given maximum values, and the final compost must not be affected negatively.
It is understood that compostability of a material should lead to a true nutritional benefit for the compost environment.
In simple words, compostability corresponds to biodegradation under controlled conditions, with a focus on the end result. So a compostable product is biodegradable, but the reverse is not necessarily true.
Biodegradability / compostability of plastic materials
A limited number of plastics are qualified today as biodegradable or compostable. They can either be fossil based or produced from renewable resources (usually referred to as biosourced). For example, the most common biodegradable / compostable plastic materials are made from polylactic acid (PLA), polyhydroxybutyrate (PHB), polybutylenesuccinate (PBS) just to name a few.
Biodegradability / compostability is totally independent from the origin of the plastics. A biosourced plastic material is not necessarily biodegradable / compostable, and vice-versa. But unfortunately there’s an ongoing confusion on this point. In addition, a majority of suppliers don’t deliver a clear communication / guidance either.
Are biodegradable or compostable plastic materials good choices for the circularity of the economy?
From the above, it appears clear that biodegradation and compostability are very similar in nature. This accounts for the misuse between the 2 terms.
As biodegradability happens in a non controlled environment, it is not an acceptable option for a circular economy. Simply put, biodegradability is a licence to pollute!
Compostability is also a tricky concept. Whilst domestic composting appears to be an « eco-responsible » approach, in reality it’s far from being an effective solution. The lack of control upon transformation could lead to a long process time (perhaps a couple of years) before even the degradation starts.
Industrial compostability, on the other hand, could be a viable alternative. In this situation, process conditions could remain under control. The whole operation becomes reproducible in an acceptable time frame. For illustration purpose, the chart below shows the degradation time for PLA under different temperature and humidity conditions.
One last point related to the compostability: the current value chain of plastic production doesn’t allow to separate compostable and non compostable plastic materials. As such, compostable alternatives tend to negatively impact the recycling process of the latter. To date, this is a major bottleneck.
So what to conclude on biodegradability and compostability of plastic materials?
There’s a big focus on quick substitution of fossil based plastics by biodegradable / compostable alternatives. Unfortunately the technical landscape is not yet ready for this switch. Technical innovation efforts in fine-tuning plastic properties for enhanced compostability in both industrial and domestic conditions should remain a priority. But the more concerning issue, in a very similar way to fossil based plastics, is the lack of infrastructure for collecting and sorting compostable plastics. This needs to be conducted in a collaborative way through the whole value chain, otherwise, the industry is making the same good old mistake of designing without integrating the end of life!
(1) Biodegradability of plastics in the open environment, December 2020
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