Biodegradability is the ability of organic substances and materials to be broken down into simpler substances through the action of enzymes from microorganisms. If this process is complete, the initial organic substances are entirely converted into simple inorganic molecules such as water, carbon dioxide and methane.
Compostability is the capacity of an organic material to be transformed into compost through the composting process. This process exploits the biodegradability of the initial organic materials to transform them into a finished product called compost. Compost is therefore the result of disintegration and aerobic biodegradation (occurring in the presence of oxygen)
Composting: why Bioplastics.
Composting is currently applied to selected waste that only contains biodegradable organic matter. Traditional plastics are not included in composting, and when present are discarded because they resist biodegradation and therefore contaminate the finished compost. In contrast, biodegradable plastics can be included in composting, but only if they satisfy the criteria established by the standards that define compostable materials. Incompatible materials were composted in the past in the absence of rules and in a context of unregulated definitions and test methods. This caused significant damage, not least to the trust of users and technicians responsible for composting facilities. This is no longer possible thanks to EU standard EN13432 concerning organic recycling of packaging through composting, and its twin standard EN 14995 which applies the same criteria as EN13432 to the more general field of plastics.
Compostable Plastics are a new generation of plastics which are biodegradable through composting. They are derived generally from renewable raw materials like starch (e.g. corn, potato, tapioca etc), cellulose, soy protein, lactic acid etc., are not hazardous/toxic in production and decompose back into carbon dioxide, water, biomass etc. when composted. Some compostable plastics may not be derived from renewable materials, but instead derived made from petroleum or made by bacteria through a process of microbial fermentation.
Currently, there are a number of different compostable plastics resins available in the market and the number is growing every day. The most commonly used raw material for making the compostable plastics is corn starch, which is converted into a polymer with similar properties as normal plastic products. Other compostable resins are available made from potato starch, soybean protein, cellulose and as well from petroleum and petroleum by products. It is counter intuitive to think that compostable resins could be derived from petroleum, when all normal plastic products are derived from petroleum and are non compostable. However, there are certified compostable resins available in the market, derived from petroleum and the field of compostable plastics is constantly evolving with new materials and technologies being worked on and being brought to market. There is even research underway to make compostable plastics from carbon dioxide.
Biodegradability & Compostability
Bioplastics can take different length of times to totally compost, based on the material and are meant to be composted in a commercial composting facility, where higher composting temperatures can be reached and is between 90-180 days. Most existing international standards require biodegradation of 60% within 180 days along with certain other criteria for the resin or product to be called compostable. It is important to make the distinction between degradable, biodegradable and compostable. These terms are often (incorrectly) used interchangeably.
Compostable Plastic is plastic which is “capable of undergoing biological decomposition in a compost site as part of an available program, such that the plastic is not visually distinguishable and breaks down to carbon dioxide, water, inorganic compounds, and biomass, at a rate consistent with known compostable materials (e.g. cellulose). and leaves no toxic residue.” American Society for Testing & Materials (ASTM). In order for a plastic to be called compostable, three criteria need to be met:
- Biodegrade – break down into carbon dioxide, water, biomass at the same rate as cellulose (paper).
- Disintegrate – the material is indistinguishable in the compost, that it is not visible and needs to be screened out
- Eco-toxicity – the biodegradation does not produce any toxic material and the compost can support plant growth.
Biodegradable Plastic is plastic which will degrade from the action of naturally occurring microorganism, such as bacteria, fungi etc. over a period of time. Note, that there is no requirement for leaving “no toxic residue“, and as well as no requirement for the time it needs to take to biodegrade.
Degradable Plastic is plastic which will undergo a significant change in its chemical structure under specific environmental conditions resulting in a loss of some properties. Please note that there is no requirement that the plastic has to be degrade from the action of “naturally occurring microorganism” or any of the other criteria required for compostable plastics.
A plastic therefore may be degradable but not biodegradable or it may be biodegradable but not compostable (that is, it breaks down too slowly to be called compostable or leaves toxic residue).
some Bioplastics products in Sri Lanka