The Disposal and Recycling of Polymers

It is a sobering thought to think that the very first disposable nappies are still in existence. This is because the material that they are made from is not degradable.
Much of our waste is buried in landfills, but sites are getting harder to find, which is increasing the costs associated with waste disposal.
Alternatives to dumping are available. Incineration, recycling, or even the use of degradable plastics are beginning to look like more economical methods of waste disposal.
Most plastics don’t break down because bacteria do not have the enzymes required to decompose them. However, there are two important kinds of plastic that are degradable:
1. Biopolymers- polymers made by living organisms.
2. Synthetic plastics that are designed to break down naturally (photodegradable plastics, synthetic biodegradable plastics and soluble plastics.)

Biopolymers

Poly(hydroxybutyrate) (PHB) is a natural polyester made by bacteria, which is used by them as a source of energy.
Micro-organisms found in the soil and natural water sources are able to decompose the polymer.
PHB decomposition usually takes around nine months; however PHB is around 15 times more expensive than polythene.

Carbonyl groups (C=O) absorb radiation in the wavelength range 270-360 nm.
This corresponds to the UV region of the spectrum.
These groups can be incorporated into polymer chains, where they can act as “energy trappers”.
The trapped energy leads to fission of the bonds in the neighbourhood of the carbonyl group; thus the polymer can break down into short fragments which can be biodegraded.

Polythene can be made to have starch molecules incorporated into its structure.
The starch is digested by micro-organisms in the soil when the plastic is buried. The very small pieces left over have a large surface area to volume ration, which results in an increased rate of biodegradation.
A lot of energy is required to produce plastics; it should be an energy saving option recycling plastics; however the situation is more complex than this.
There are costs involved in sorting and recycling plastics, and sometimes the applications for the recycled plastic are inappropriate; how would you feel knowing that the clingfilm you wrapped your sandwiches in was originally part of a nappy?
There are now almost a hundred companies in the UK recycling around 150,000 tonnes of plastic per year between them. Two-thirds of the recycled plastic comes from industrial waste.
It is not currently economical to sort through domestic waste, but perhaps in the future when it is, plastic may be retrieved from landfills and used once again. It may be a wise idea to bury plastic waste separately, so that in the future, we may be able to retrieve the plastic without too much trouble and use it again.