31/05/2011

Recycling + retreading - when the useful life of a tyre ends

“But o dear, o dear, o deary, when the end comes sad and dreary”. This quote from the Wilhelm Busch story “Max and Moritz” would be an appropriate way to describe the life of a tyre too. Because for many years, until only recently, most old tyres simply ended up on landfill sites – or were dumped illegally following the introduction of collection charges.

The mountain of discarded, worn-out tyres had in the meantime reached a height that, all in all, would definitely have represented an interesting challenge for some mountain climbers. Simple disposal without any further processing came to an end in 2006, however. The storage and disposal of old and shredded tyres and tyre residue on landfill sites is now prohibited by European regulations.

A look at recent figures confirms that old tyres could have been used to build impressive slopes for quite a few Winter Olympics: at the conference held by the European Tyre Recycling Association (ETRA) in Brussels in 2007, it was estimated that a total of about 300,000,000 or even more old tyres reach the end of their useful life every year in the 27 member states of the European Union. Further estimates indicate that the quantities in North America, Latin America, Asia and the Middle East are similar, so that total global contamination probably exceeds the equivalent of 1,000,000,000 car tyres per year. An incredible number! The conclusion about these old tyres is that they need to be recycled in some form, i.e. have to be used for the production of new raw materials or as fuel, if retreading is not an option.

They can be transformed into suitable raw materials by pyrolysis and a great deal has in fact been achieved in research projects here in order to enable old tyres to be put to a sensible use. While undesirable by-products were still the problem in the obtainment of raw materials from old tyres in the early days, the latest research findings indicate that the quality is acceptable, with considerable success being achieved where soot production is concerned, for example.

Another common method of recycling is incineration in cement plants. Manufacturers like to chop tyres up small and then use them as additives and fuel, because they improve the quality of certain kinds of cement. Old tyres are also chopped up small for roadbuilding applications (road beds) or for artificial turf. While other old tyres end up again on asphalt too – but as soles for hiking boots and not as tyres. An albeit small proportion of old tyres, finally, finds a permanent new home in the agricultural community: we have all seen piles of pungent natural fertiliser covered with plastic film, which is weighed down with old tyres to make sure that the film is not blown away by the wind.

The cleverest way to dispose of tyres in an environmentally sound way would be if the tyres were made from a material that was decomposed in the course of time by microorganisms without leaving any residue. The problem is, however, that the tyres have to disintegrate when they are worn out and no longer needed rather than while they are still being used on cars. Chemists and engineers still have plenty of development work to do here.
Tyres are, however, given a new life via retreading before they are scrapped completely. As much as is possible is really made of them.

Apropos...