End-of-life of bioplastics
The chemical nature of different bioplasticw allow of us to distinguish them and particularly classify them into two categories of biobased and/or biodegradable plastics. This distinction is also to be taken into consideration when discussing the end-of-life of these bioplastic materials.
Those materials which are structurally similar to existing polymers (PET or biobased PE for example) will have the same possibilities of reclamation through end-of-life recycling as their petroleum-based counterparts. In case of recycling plastic food packaging (mainly hollow bodies today), the distinction is not technically possible based on the currently used means for sorting after collection. These biobased versions will then be able to be recycled in the same way as traditional materials without affecting the quality of the recycled plastic.
On the contrary, bioplastic with new chemical structures will need to be considered on a case-by-case basis like new materials, since some of them also possess the capability of biodegradation. This allows, for example, for us to plan new methods of reclamation at the end-of-life, particularly through composting or anaerobic digestion.
Allowing for a reduction in the volume of plastic waste abandoned in nature, this property may also be seen as a functionality from which it is possible to benefit depending on the applications and uses of the materials.
Biodegradability and composting of bioplastic
The biodegradability of a polymer is a property that depends on its chemical structure.
ADEME has defined this in its data sheet http://www.ademe.fr/plastiques-biodegradables as follows:
A material is called biodegradable if it can be decomposed through the action of micro-organisms (bacteria, mushrooms, algae, etc.). The result is the formation of water, CO2 and/or methane and possibly other by-products (residue, new biomass) which are non-toxic as regards the environment.
It is particularly the ability to decompose which differentiates biodegradable polymers from those that are not.
The origin of a material must also be distinguished (whether or not it is biobased) along with its end-of-life properties (biodegradable or not); these are not connected in any manner. Thus, we have polymers which are biodegradable but are not biobased (like PBAT or PCL), and conversely, polymers obtained from biomass but are absolutely not biodegradable (biobased PE and PET, for example).
As for composting, it is a procedure for transformation of fermentable materials into compost, improving the soils by increasing fertility. Then, aerobic biodegradation takes place (in the presence of oxygen) in very specific conditions.
In the field of compostable plastics, two main types of composting are often mentioned:
- Domestic composting (also called Home Compost), which can be done by individuals in conditions which are barely controlled or not at all.
- Industrial composting, which is carried out on dedicated platforms with regulated conditions.
These two possibilities are primarily different based on the temperature of execution of biodegradation of the product, which induces different decomposition kinetics depending on the polymers as well as the presence or absence of micro-organisms, which allows their assimilation
A biodegradation process that takes place in anaerobic conditions (without oxygen) results in anaerobic digestion which produces biogas.
Standards and certifications of biodegradable and compostable plastics
Today there are several standards that allow for assessing the biodegradability of bioplastic in different conditions:
It defines four criteria to be respected (composition, biodegradation, disintegration and quality of the compost) for materials or packaging in order to be reclaimed through industrial composting.
This most recent standard concerns the ability of the materials to be reclaimed through domestic composting. It particularly serves as the basis for the laws that govern the use of disposable plastic bags intended for the packaging of goods at points of sale as well as wrapping film or other disposable cups and dishes.
Variants of these standards are also used today to assess the biodegradation of bioplastic in different conditions and environments such as soil, or sea water.
Based on the tests carried out as per the above-mentioned standards, it is possible to obtain certificates that provide increased visibility for the materials and products thus labelled.