Plastic Breakdown

There are many forms of plastic degradation spoken about these days and it is giving rise to confusion about how plastic breaks down. Here are some of the facts that you can safely drop into conversations at the pub or dinner parties:

Compostable Plastic

Compostable materials are capable of undergoing biological decomposition in a compost site, to the extent that they are not visually distinguishable and break down to carbon dioxide, water, inorganic compounds, and biomass, at a rate consistent with known compostable materials (e.g. cellulose). Compostable materials leave no toxic residue which means the resulting humus is a safe and healthy contribution to soil.

In order to be classified compostable, the degradation must meet certain specified criteria such as rate biodegradation, maximum residue of material left at a specific point in time and a requirement for the material to have no harmful impact on the final compost or the composting process. All compostable plastic is, therefore, also biodegradable. The most commonly used standards for compostable plastic are the American standard ASTM #D6400-99, the European standard EN-13432 and DIN V-54900.

The important thing to remember with a compostable plastic bag is that when you can no longer re-use it, you can recycle what’s left in the compost.

Biodegradable Plastic

Biodegradable materials will degrade from the action of naturally occurring micro-organisms, such as bacteria, fungi, etc. Biodegradable material is not necessarily compostable, as the residue may be toxic and cannot be considered compostable. For biodegradation to take place the micro-organisms also need oxygen and moisture.

Biodegrade sounds good, doesn’t it? However, there are three important things to remember when a bag is labelled ‘biodegradable’:

  • The conditions have to be RIGHT for a bag to biodegrade. If the conditions are not right—the bag wil not biodegrade well. Conditions are generally not right include: your bin; landfill sites; the local river; the sea; or up a tree. Typically it can take years for biodegradation to occur in a landfill, if it happens at all.
  • If a bag biodegrades (and that is a big IF) it may still leave a toxic residue.
  • ‘Biodegradable’ plastic is bad news for recycling. It is not recommened to mix ‘biodegradable’ plastic with ‘normal’ plastic. If plastic recycling is contaminated with ‘biodegradable’ plastic the subsequent product could be corrupted and weakened.
  • ‘Biodegradable’ bags are not the answer to environmental plastic bag litter because the conditions required for full biodegradation are not met.

Plastic that Photo-degrades

This is plastic that breaks down by the action of natural daylight. Plastic that can only be broken down in this way just breaks into smaller and smaller pieces but still remains a plastic.

Degradable Plastic

A confusing term because it is used in different ways. All of the above processes are forms of degradation. If someone says that they have a degradable product, ask them how it degrades. It may be that you’ve found a great product which composts. On the other hand it may well degrade—but take a few hundred years to do it. Degrade just means to break something down. You can degrade something by tearing it up into smaller and smaller pieces. So, most things are degradable.

Where this term is used, it needs justification. On its own, this term says nothing about how long the process may take or what is left after degredation. When it comes to plastic, this generally means a lot of very small pieces of plastic.


i.e.fix