Second Life

According to the Environment Agency’s Tyre Watch Programme, every year in the UK around 450,000 tonnes of used tyres are produced and require some form of reuse or disposal. That is the equivalent of some 50 million car tyres, and with vehicle ownership expected to grow between 30 and 60 per cent over the next two decades the potential environmental threat posed by waste tyres will become more acute – unless a suitable solution is embraced.

At Swansea University engineers are seeking such a solution through their research into new methods of recycling tyres. This Knowledge Transfer Partnership (KTP) project, made possible by Department for Trade and Industry funding, is being conducted by the university’s School of Engineering Materials Research Centre under the overall supervision of Dr David Isaac, a Reader at the Centre. Dr Isaac has been working as part of a research group studying various aspects of polymers and composites.

“Some materials, such as metals and thermoplastics, can be melted down and reformed into new components without significant loss in properties or integrity,” reports Dr Isaac. “Tyre rubber, however, is a ‘thermosetting’ material, which means that it does not melt but, if heated, the constituent chains degrade, lose their elastic properties and eventually burn and release energy.” He added that the combustible properties of tyres has led to their adoption as fuel in cement kilns, but believes that this application can be seen as “wasteful of a limited resource.”

While recycling is deemed a more acceptable use for scrap tyres, the end product of such recycling is at present only suitable for use in products in which the consistency of rubber quality is not a vital concern. However the team at Swansea University believe that such restrictions can be overcome. “Since 65 per cent of rubber produced worldwide is used by the tyre industry, the focus of our research is investigating how to reincorporate old tyres into new tyres,” said Dr Isaac. “However, we have to treat the old rubber before it is mixed with the new rubber otherwise the two types won’t bond correctly, which could lead to imperfections. Such defects would not be significant in flooring products, but could be potentially dangerous in tyres.”

This obstacle can potentially be overcome by treating rubber crumb with a type of ionised gas that acts upon the surface of the rubber and improves its bonding properties. This possible solution has been developed in collaboration with Welsh company Haydale Limited, who hold a number of patent applications related to the use of recycled rubber/polymer materials. The Swansea University project team think that this and similar techniques will enable the manufacture of new tyres containing a substantial proportion of recycled rubber to standards that meet the established criteria for road tyres.

“Although each manufacturer uses slightly different mixes of many components to make tyres, and the precise composition is carefully guarded, very little, if any, recycled rubber is incorporated into road car tyres. For some low speed off-road applications, some tyres are already being produced with between 5 per cent and 10 per cent recycled rubber,” said Dr Isaac.

“But I believe that there is a great deal of room for improvement. This technology has the potential to make a huge impact on the amount of rubber wasted each year – but we do need to prove to manufacturers that the process is reliable and consistent and will not cause imperfections in the finished product.”

The Swansea University research is currently the subject of trials being conducted by a global tyre manufacturer to determine whether the techniques developed by the project group are both commercially viable and safe.