Degradable, biodegradable or compostable – what do these terms mean when used in conjunction with plastic.
Degradable plastic could be plastic that falls apart into pieces of plastic -plastic that degrades OR plastic that has had a degradation initiator added to make it biodegradeable.
Bio -degradable plastic could be a compostable plastic that biodegrades naturally OR plastic that has had a degradation initiator added to make it bio-degrade.
Compostable Plastic – a plastic that biodegrades with out chemical addatives within a certain amount of time.
Confused? Read On…
Though there are some who disagree, plastic is not generally consdiered to be biodegradable. Even those who suggest it might be biodegradable, admit it would take a huge amount of time.
Biodegradable products break down as the result of the actions of naturally occurring microorganisms, such as fungi or bacteria, over a period of time. Basically it gets eaten
Plastic takes so long to break down because the long polymer, the basic building block, is man-made. Microorganisms do not recognise it as something they can they can eat so they leave it alone.
Of course plastic breaks, tears and cracks. It weathers and sunlight makes it brittle, It falls apart – it degrades – but only into smaller pieces of plastic.
This degrading process can go on indefinitely it seems.
Particles of plastic of 20 microns in diameter (a width thinner than a human hair) have been found in the oceans and are being found in increasing amounts.
But suppose there was a way of making plastic biodegradable? The industry argue that they can do just that by means of chemical adatives known as degradation initiators.
degradation initiators are added to the plastic mix in amounts of up to 2% of the total composition.
Very basically, these addatives break the long unnatural plastic polymers into shorter recognisable polymers that microbes can attack and digest – or biodegrade.
The process happens as follows.
- Microbes are attracted to the additive;
- They “crack” the long polymer allowing acces to other microbes and water.
- Eventually these will break down huge polymers into smaller and smaller bits.
- These smaller bits are then vulnerableto other microbes.
The difficulty is of course ensuring that the plastic doesnt start biodegrading in normal conditions so that the strength of the plastic product is not jeopodised. Biodegradation is designed to start in certain extreme conditions.
As 75% ofplastic ends up in landfill, most addatives are designed to work in landfill conditions though there is no reason to assume that other addatives could not be developed to respond to other conditions. Different addatives manipulate the microbes in different ways.
Products may start to degrade outside of the specified conditions but the process will take much longer
So, to become biodegradable, plastic has to be further chemically engineered. Obviously, this is by no means a natural process as biodegrading is normally understood to be rather it requires complex chemical eginerring.
The composition of these chemical addatives is secret and known only to the companies who produce them.
Types Of Degradable Plastics
The ISO (International Organization for Standardization) has defined six types of degradable plastics.
Degradable – breaks down in some way.
Photodegradable, broken down by light
Oxidatively degradable broken down by oxygen
Hydrolytically degradable. Broken down by water
Biodegradable – can be broken down by microbes to mass, water and co2 but with no indication of how long that might take. May also need chemical addatives to make this process possible.
Compostable – degrade at a rate that’s similar to other types of compostable materials, and they result, again, in water, carbon dioxide, humus, and inorganic compounds. Compostable plastics biodegrade naturally.They do not need additonal addatives to break down the polymers as they made from natural materials that microorganisms recognise.
Whatever the ins and outs of degradable plastic,and there are many issues, it seem rather dumb to me … why go to the effort of making degradable plastic bags when we already have naturally compostable products such as paper bags and cornstarch bags. Why not use plastic for things we don’t want to rot away like drainpipes and use naturally biodegrading materials for disposable packaging? Just a thought….
Useful stuff to know
Why leaves rot at How Biodegrading Works
Why most plastics dont at Why Plastic Doesnt Rot
Compostable plastic the factss.
Remember, not all bio- plastics can be composted and some are not as green as they sound>
Yup its confusing but try everything you ever wanted toknow about plastic.but were too scared to ask, to find out a lot more about plastic.
Inspired to give up plastic? Check these plastic-free products. Use them then compost them.
- Composting Standards (plasticisrubbish.wordpress.com)