There are 5 main options to handle plastic waste material:
There are two types of plastics that are recycled:
1. Pre consumer Waste
This is scrap material from the manufacturing process. Over 90% of manufacturing scrap in New Zealand is recycled back into the plastics process. Some NZ manufacturing companies have virtually eliminated their waste stream.
2. Post consumer Waste
This is waste plastic material after it has been used by the final consumer.
Recycling can exist at two different levels:-
1. Physical Recycling
This is a physical process where the used plastics are treated with heating and pressure to convert them into new plastic products (Most recycling in New Zealand is physical, because there is insufficient plastic material in New Zealand to justify the capital expense of setting up a chemical recycling plant).
2. Chemical Recycling
This is sometimes called feedstock recycling - and involves chemical processes to release the chemicals locked up inside the plastics. There are 4 main methods used.
All thermoplastics can be softened by heating and reformed into new plastic objects. Thermosets however will not soften on reheating, and therefore can not be reformed into new objects by remoulding. This limits their potential tor recycling.
Stages in Recycling
PROBLEMS WITH RECYCLING PLASTICS
There are a number of problems associated with recycling
SOME INNOVATIONS IN PLASTICS RECYCLING.
Figures from the Auckland Regional Council indicate that plastics make up 8% of the solid waste stream.
Plastics are very high in energy. Plastic packaging can often be very bulky as well. In some countries plastics are being converted to energy in incinerators to save on space in landfills and to save on using fuel oil. Recent experiments indicate that the gases and particles released from the incineration of plastics, in “state of the art” facilities, are not significantly greater than those released when wood burns.
|Material||Energy content in kJ/kg|
|brown coal briquettes||18,800|
|firewood(air dried) or paper||18,700|
Source: Association of Plastics Manufacturers of Europe
Some plastics can be made to break down in the presence of light or as a result of biological activity.. These plastics will have some specialised uses, but will not solve the waste problem. Products that have decomposed are not available for recycling, or for use as a fuel.
When a “cradle to the grave”, or whole life cycle analysis is carried out on plastics products, their use of energy, and other non-renewable resources, compares very favourably with alternative products.
Material processing temperatures:
|Iron and Steel||800-1000 °C|
If a polystyrene cup is compared with a cardboard cup from the perspective of resource use in its manufacture, the following figures emerge.
A paper cup uses:
It is estimated that if a conventional plastic shopping bag was replaced by a paper equivalent, the paper bag would:
It is estimated that 50% of food in developing countries is wasted. The figure in western countries is around 2-5%. That discrepancy is a manifestation of the differences in packaging used.
In 1970 a yoghurt pot weighed around 12g. By 1985 the weight of a yoghurt pot had been reduced to around 5g. This is known as lightweighting. It is achieved by innovative plastics engineering. There are many other examples.
In 1970 a detergent bottle weighed 60g. By 1990 the weight had shrunk to around 38g. Plastic supermarket bags are now only 15 microns (micron = 1/1000 of a millimetre) thick, compared to a thickness of 45 microns 15 years ago, without any loss of physical properties.
In almost every sector of the community plastics are being used as substitutes for other materials. In cars the use of 100kg of plastic parts can replace about 200kg to 300kg of conventional materials — thereby reducing fuel consumption by 750 litres during the life of the car. The use of plastics in car design is expected to grow steadily at an average rate of 2.5% over the next 15 years.
It is estimated that each international plane saves around $15,000 per year in fuel costs by using plastics beverage bottles rather than glass ones as before.