TWI Knowledge Summary

Recycling of plastics

by Mehdi Tavakoli

Worldwide production of plastic material has increased considerably in recent years from something less than 5 million tonnes in the 1950s to over 80 million tonnes in recent years. The amount of plastic waste generated is considerably less than the amount consumed, indicating more plastics are used in long lifetime applications. The main plastic waste is generated from packaging applications, which has a service life of days or months rather than years.

There are two types of plastics recycling. The first is process scrap from industry. This is easy to recycle, as there is a regular and reliable source, uncontaminated by previous use. The second type of plastic recycling involves products which go through a full service prior to being reclaimed. This type of plastic waste requires collecting, sorting and in most cases cleaning and is therefore harder to recycle. The second type of recycling is on the increase.

In early 1992, Europe's first recycling plant for plastics was opened in Cheshire. This factory was able to recycle meat trays, fast-food boxes, egg cartons, vending cups, yoghurt pots and even disposable cameras.

New technology is also being used to sort plastics automatically, using techniques such as X-ray fluorescence and infrared spectroscopy. X-ray fluorescence can sort PVC bottles from bottles made from other plastics by identifying the chlorine content. Tests performed in the USA by the Environmental Protection Agency reported that accuracy levels of >99.9% can be achieved by automatic sorting systems over a range of different polymers.

In another use of recycled plastic, Subaru, the car manufacturer, has announced a breakthrough in car bumper recycling. Old bumpers can be recycled into new bumpers, thus avoiding recycling the plastic into a lower grade product.

Biodegradable polymers have a critical role in reducing waste and limiting plastic litter. Development of new generations of biodegradable or reworkable smart polymers, which contain specific functional groups (hydrolysable, bio-, photo- or thermally unstable), is of major interest for many new applications (e.g. medical) as well as for recycling. Recyclable and degradable polymers are being used or developed which will respond to reforming, remelting or converting to their basic original structure using a variety of techniques including depolymerisation and unzipping reactions, chemolysis, hydrolysis, pyrolysis, saponification, refinery cracking, photo-degradation and biodegradation.

Recycling of plastics is of interest not only to the packaging industry but also to the automotive, electronics, etc, sectors. There is a clear need for handling and recycling the mountain of electronics waste that is estimated to be over 100 million tonnes and increasing rapidly at a rate of several millions per year. The waste is in the form of end-of-life consumer equipment (e.g. microcomputers, audio-visual and telecommunications) and industrial systems (computers, communications and microprocessors).

Further information

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