Disposal of plastic items can be a problem. Poly(ethene is very resilient
and may remain intact for well over 100 years. This is much longer than
the time between manufacture and disposal, which may be no more than
a few months.
In these applications, there is a strong case for degradable polymers. To find out why poly(ethene) is not easily degraded, click here.
Poly(ethene) (PE) eventually becomes brittle in sunlight as some depolymerisation takes place. When buried, however, this cannot happen, and so in landfill the plastic will persist for many years. This is because the microbes in the soil are unable to process the long polymer chains. Sealed PE refuse sacks will also reduce significantly the rate at which their contents degrade when put in landfill tips.
There are several fully degradable polymers that could theoretically replace PE, but the volume of PE produced is so high that it would require massive investment to change to these to produce such volumes. Several companies have instead developed degradable PE.
Drinks in aluminium cans are often sold as a multi-buy pack. In some areas the plastic structure used to hold the cans together has become a litter problem, and there have been concerns over the effect on wildlife - birds and hedgehogs can become trapped in the rings.
Many are now made from a degradable poly(ethene), which has light-sensitive carbonyl groups inserted into the polymer chain. On exposure to light the chains will begin to disintegrate, leaving short sections that can now be "processed" by microbes.
Methods for incorporating starch into the polymer structure have been developed that produce a plastic that is as strong as LDPE but uses less petrochemical feedstock, is cheaper (starch costs less than PE), and will degrade when buried.
How it works
For more information about d2w, see the Symphony Environmental Ltd web site.