Dealing With Plastics Wastes

Dealing With Plastics Wastes

Plastics waste management in developing countries needs proper collection schemes and effective technology to be successful. Lou Reade reports from a recent conference in Malaysia

An increasingly important problem for the plastics industry is how to deal with its products after they have completed their useful life. All plastics, whether used in life-saving medical products or simply for keeping food fresh, must eventually be thrown away.

Central to the issue is the ‘3R’ rule: reduce, re-use, recycle. But puffing this rule into practice can be difficult. For developing countries, effective technology may be too expensive; for developed countries it is often cheaper to bury the waste in landfill, so only environmental legislation makes recycling happen.

J S Anand, director of Indian research institute Cipet, says: ‘In Western countries, plastics recycling is a step towards curbing ecological problems. In India, it has more to do with economics.’

Dr Anand was speaking at the Technology Transfer Forum on Plastics Waste Management in Commonwealth Countries, organised by the Malaysian Plastics Manufacturers Association and held during Aseanplas 95. He believes that while India has a well developed waste collection system it needs better recycling technologies if it is to improve.

After collection and cleaning, there are two ways of recycling plastic waste:

mechanical recycling and feedstock or chemical recycling. India does lots of the former and some of the latter.

‘Mechanical recycling of separated waste plastics has an edge over other modes of waste disposal as it is ecofriendly and generates employment potential,’ says Anand.

All kinds of products are recycled using

this method, such as polyester filament yarn, PP/HDPE woven sacks and PP films.

Feedstock recycling, in which polymer is converted back to monomer and later re-polymerised, is gaining popularity in India. Three materials in particular have been studied: PET, Nylon 6 and PMMA. The technology is driven by manufacturers of these raw materials. They have developed their own technology, or upgraded existing technology, to improve the economic performance of their plants.

In a commercial Nylon 6 manufacturing plant about 5-6% is generated as fibre waste. Caprolactam, the raw material used for making Nylon 6, can be recovered in four stages. Nylon 6 is superheated with a catalyst, purified and distilled under high vacuum.

PET waste, from film, bottles and fibres, can be converted into dimethyl terephthalate (DMT) by methanolysis. PET is heated with methanol at 250°C in the presence of catalysts, filtered and then re-polymerised under vacuum.

‘In India, considerable work is being carried out on recycling of plastics,’ says Anand. This includes research into recycling mixed waste plastics, which usually make poor recycled products.

‘New compatibilisers can be developed for blending and alloying of polymers used in multi-layer products which cannot be conveniently separated,’ says Anand.

The recycling of PE/Nylon and PE/PET is a subject that has attracted the interest of a number of researchers. Anand believes that such technologies have great potential in India, and may be helped by a centre for PWM.

‘A joint venture of Cipet and renowned waste management institutes of the world would be a beginning for improving technology in India,’ he says.

Other countries are keen to develop their PWM structures. Malaysia, for example, is trying to introduce a labelling system for plastics, which will speed up the collection process. But Pakistan’s experience has shown that even knowing the identity of the plastic does not guarantee success. Things can come unstuck through simple problems.

Pakistan, like India, has effective ‘scavengers’ — self-employed people who collect scrap plastic and sell it to recyclers.Despite this, the problem of waste polyethylene bags remains. They are difficult to collect, have low scrap value and can cause problems.

‘This makes not only an ugly sight but is also an environmental nuisance,’ says Ahsan Siddiqi of the Plastics Technology Centre in Karachi. ‘The choking of sewers and resulting overflowing of sewage on the roads has been the worst menace caused by these bags.’

He suggests two alternative solutions:

a ban on the bags, which would affect the 40,000 people in the industry; or to incinerate them, which would be costly. Even if the bags can be collected, he points out, they can only be used for very low quality recycled products.

Professor Zhu Fuhua of Beijing University of Chemical Technology presented the results of a study into the feasibility of using ultrasonic technology to clean plastic films.

China’s agricultural industry uses about 1.5 million tonnes of plastic film each year. Because such film is very thin, recycling is made more difficult. After initial cleaning with water, plastic films are put into an ultrasonic cleaning tank. Water is circulated through it, and can also be recycled. The film is then cleaned again with water, and dried.

The best cleaning results are obtained with low energy consumption (the power is only 4 kW). The method can clean 100 kg/hour, which the group claims can lead to recycling rates of 250-450 tonnes per year. It was developed for agricultural films, but has been extended for use with pipes, bottles and moulded parts.

China’s annual plastic consumption is expected to rise from 5.5 million tonnes in 1995 to 7 million tonnes by the end of the decade. India’s is expected to double in the same period, to 2.8 million tonnes.

Technology to help control this waste explosion is an important factor, which could be improved by creating a network of PWM centres in each country.

Cipet’s Anand says: ‘This would help industries to develop newer and more useful products from the plastic waste.'

Source : Asian Plastics News May/June 1995

Back to Archive Page

Recycling Point Dot Com