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Feature

Plastic Versus Paper

Environmental campaigns aiming to get manufacturers to shift from plastic packaging to paper may be misguided.

By Dr G P Savage

The environmental debate over the relative merits and demerits of plastic versus paper packaging has tended to concentrate on plastic as the villain. Campaigns to shift packaging from plastic to paper have proved successful -- the McDonalds fast food chain recently changed to paper packaging in response to consumer demands.

However, it now appears that paper is no more environmentally friendly than plastic. Its use can require more energy, produce more waste and present just as many problems of disposal as plastic counterparts.

At a recent nutrition conference, some of these concerns were raised by Peter Sutton of the Consumers' Institute and David Warbuton of the Plastics Environmental and Advisory Council. They outlined the role the food industry, in particular, has in being environmentally responsible and the problems of public perception of plastics versus paper.

Why is plastic less of an environmental problem than the public perceive it to be? It is necessary to look at the manufacturing processes, the amount of raw material and energy used and also the distribution and disposal of the product.

To make a polystyrene cup weighing only 1.5 grams, 3.2 g of oil and 0.05 g of other chemicals are required. A paper cup holding the same volume of liquid weighs 10.1 g and needs 33 g of wood, 4.1 g of oil and 1.8 g of chemicals to make it. To make things worse, the manufacture of paper cups requires more energy and water than plastic ones.

Chemical waste from the manufacture of the two cups also needs to be considered. The manufacture of polystyrene uses metal salts which are then discharged into the waste water, but making paper also requires chemicals such as chloride and sulphides. Making a paper cup involves the discharge of more than twice the amount of waste into the environment than its polystyrene equivalent.

Life Cycle Analysis

In all environmental issues, it is important to carry out a life-cycle analysis of each process being considered. Consideration of environmental issues should take all aspects of the manufacture, use and disposal of a product into account. For example, paper cups are much heavier, so transport costs are greater. If a more concerted effort was made to recycle these materials, then the costs and effect on the environment would not look so bad, but plastic would still have an overall advantage over paper.

It is understood that McDonalds is not going to change back to using plastics at this stage because of consumer perception that plastic is not good for the environment. Once public opinion changes, the company may revert to its original position.

There is definite consumer resistance to excessive packaging of food products. In Germany, legislation requires traders to remove excessive packaging from any products before they are put on display in supermarkets. Not only does the consumer have to cart less around, but the manufacturers and traders are forced to think about how much they should put on if it has to be taken off before display.

The same legislation states that if a consumer brings packaging back to the shop, the trader is responsible for disposing of it. This sort of approach in New Zealand would make manufacturers really start to think about the amount of packaging they use. Their packaging would become efficient, reduced to what is really needed, rather than being used for marketing purposes.

Beneficial Aspects

The enormous beneficial effect that plastic packaging has had on the food industry should not be overlooked. Plastic wrapping on food should be regarded as an energy- and resource-saving feature. It allows food that would otherwise deteriorate quite quickly to remain in excellent condition for longer, and to be consumed rather than wasted.

It is clear that if manufacturers decided not to use plastic wrapping on food, the high standards of hygiene currently achieved would slip. The main issue should be with the amount of extra packaging that is used over and above that required to present fresh and wholesome food.

At present, about 30% of total world production of plastic is used as packaging, with a major proportion being used in the food industry.

It is interesting to note that there has been a significant reduction in the amount of material being used to manufacture some plastic food containers. A good example is plastic milk bottles -- the original ones used in New Zealand contained 45-47 g of plastic, now they contain only 40 g. This has been made possible by a reduction in wall thickness. There is a great deal to the design of a plastic package. It must not only meet structural constraints, it must look attractive as well.

Manufacturers are happy to reduce costs and lower the amount of plastic they use. Once the package has been used it may be reused, recycled, incinerated or consigned to a landfill site. In New Zealand, incineration of waste is not carried out, but it is a process that is widely used elsewhere in the world and is being considered by a number of local authorities here.

Landfill Problems

Recently, Dr William Rathje, an American archaeologist-"garbologist", has provided some useful data on the structure and composition of US landfills. He has estimated that over the last 20 years plastics have increased on a volume base in landfills from 11% to 12%. The volume of paper has risen from about 36% to 57%, making it the fastest growing material in landfills. It is not all packaging, but includes phone books, computer printouts, journals and newspapers.

Rathje also noticed that considerable effort is put into compacting rubbish tips to reduce the volume. Consequently, the centre of the site contains very little air or moisture. Under these conditions, few micro-organisms can survive, so only a very slow degradation of paper and waste food, and almost none of plastics, occurs. Rotting almost ceases after 15 years. In a tip in Phoenix, Arizona, it was possible to read some of the newspapers dating back to 1952.

Degrading Plastics

Plastic waste evokes strong emotions. Most people are incensed by plastic litter on roadsides and at the beach. Environmentalists blame the litter problem on the long life of synthetic polymers that make up plastic.

It must be remembered that this longevity was initially seen as a virtue. Stabilisers were added to plastics to make them more durable, but concern about inappropriate longevity has led to some changes.

The plastic six-pack yokes used to hold cans of beer together were once extremely durable. Pictures of fish and marine mammals with these yokes stuck around their limbs or necks was the trigger for change. This problem has now been reduced by ensuring that the plastic used for this purpose contains additives which make it easily photodegradable, so that it breaks down in the presence of sunlight. The real problem is that people throw litter in inappropriate places.

Plastics can be made which will degrade under exposure to sunlight or micro-organisms. A photodegradable plastic is manufactured with a co-polymer, such as carbon monoxide, in the polythene chain which makes it sensitive to sunlight. Addition of this co-polymer allows recycling with little difficulty, which is not always the case for the other radicals that can be added.

Another way is to add iron or nickel dithiocarbamates to a plastic. These compounds are called photosensitisers. On exposure to sunlight they become extremely reactive, and release free radicals which oxidise the polymer and begin a series of chain reactions which leads to its destruction.

In general, synthetic polymers resist biodegradation. A plastic can be made more biodegradable by adding starch into the plastic film. This is not so suitable for the packaging of food, but can be used to make articles such as shopping bags.

The main problem is that the addition of starch to a plastic reduces its overall strength, so the thickness of the film has to be increased. This results in more plastic being used for each item. Furthermore, the lack of biodegradation in landfills limits the value of this option.

As a resource, plastic should be reused. If plastic is manufactured to be degradable then the possibility of re-using this material is considerably reduced. The added materials reduce the value of the plastic and the range of possibilities for its re-use.

The other problem is that plastic is, in fact, a range of materials which need to be properly sorted in any recovery system before they can be re-used. The identification, sorting and cleaning of the plastic waste materials are the main problems of an effective recovery system.

Dr Savage is a senior lecturer in biochemistry at Lincoln University.