Tire Environmental Issues

Chemicals

The need to produce safer, cleaner environments is driving the generation of new ‘environmentally friendly’ materials. Many potentially harmful materials such as nitrosamine generating chemicals have been eliminated from the ingredient basket of tire companies. Heavy metal elements have all but been eliminated, with zinc as the next possible target for reduction or elimination. As an activator, zinc oxide has seen a long history in the rubber industry but from where will its successor come? More recently attention has been paid to finding alternatives to polycyclic aromatic oils to reduce the possible risks of cancer. The use of solvents is also being reduced or eliminated to produce a cleaner working environment. The work will inevitably continue as each ingredient in turn comes under the environmental microscope.

Rubber Recovery from Scrap Tires


When rubber ingredients are mixed, processed and cured, the products or any cured scrap produced along the way cannot be just put back into the mixer and reprocessed like some thermoplastics. As the old saying goes, ‘you can’t unbake a cake into its constituent
ingredients of flour, eggs and so on’.

Millions of tires are removed from vehicles every year producing an estimated 2.5 million tonnes of scrap in Europe alone. This has provoked a growing interest in recycling within the industry . The whole subject of end-of-life tires has been studied in depth and reported in a Rapra Industry Analysis Report in January 2001 .




Prior to 1986 there was, apart from truck tire retreading, virtually no scrap tire recycling industry.

Conventionally tires were disposed of by landfill or burning. Tires present a valuable source of materials and also, tire-derived fuel contains a high calorific source of energy. At the end of their lives, tires can be burnt although the process has raised concerns over further pollution problems . Many tires are still dumped in landfill sites but this has led to serious problems such as fires raging out of control for years. Whole tires have also been successfully used to build coastal sea defences, but again it has been suggested, although not substantiated, that there could be risks that chemicals may leach out or that biological infestation may occur.

Burning and landfill techniques may no longer be allowed in the not too distant future, since there is to be more stringent control over emissions from incinerators and a total ban on landfill, even of shredded tires, by 2006. The industry is therefore addressing the problem of how to dispose of scrap tires with even greater urgency, with reclaim now becoming a more favoured option. There is also a growing interest in the EU end-of-life vehicle directives and how to dispose of scrap tires from old cars, as well as the many other components on a vehicle. This has led to a growing emphasis being placed on the whole subject of material usage by the
industry, government bodies and environmental monitoring groups.

There is an opportunity for tires to be ground into a fine mesh crumb . Devulcanisation , ultrasonics , bioreactions , cryogenics or pyrolysis may break a compound down to its constituent parts. Reclaimed rubber crumb has already found many novel applications. These include a bitumen additive for road surfaces , when coated in a trans-polyoctenamer (TOR), flooring, sports surfaces, and even as a raw material to be recycled back at fairly small loadings into new tire or other components . Rubber crumb is an inert filler, but it may be possible to activate the crumb to provide a more chemically integrated addition. Whilst on the subject of end-of-life tires, an interesting final question which may be asked is not ‘why do tires fail?’, but ‘why do some tires last so long?’ Evolution in the natural world is believed to arise through survival of the fittest. If a compounder were to study all the attributes of these long life tires, taking into consideration the operating environment, then perhaps much could be learnt to produce other tires with the same longevity characteristics.