New tyres from old rubber

Engineers at Swansea University are investigating new ways of recycling tyres to dramatically reduce the amount of rubber wasted each year.


Every year, nearly 50 million tyres, weighing almost half a million tonnes, are disposed of in the UK alone. Since July 2006 it has been illegal to landfill old tyres, even after shredding, and so new methods of reusing or disposing of the rubber need to be found.  And it isn’t simply a matter of melting the rubber down to be reformed.


‘Some materials, such as metals and thermoplastics, can be melted down and reformed into new components without significant loss in properties or integrity.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. Indeed one particular use of waste tyres has been as fuel in cement kilns, but this is now seen as wasteful of a limited resource,’ said Dr David Isaac, a Reader based in the Materials Research Centre, School of Engineering at the University.


The Swansea University team is looking at ways to take advantage of the very special elastic properties of rubber, by incorporating waste rubber into new products. This can be achieved by first grinding the tyres into “crumb rubber” and then mixing the crumb with new material.


One application that is already meeting with some success is rubber flooring. But even with high market penetration, this would utilise just a very small fraction of the tyres wasted annually.


‘Since 65% 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.’


A possible solution has been found in collaboration with a local company, Haydale. Treating the crumbed rubber with a plasma, a type of ionized gas, activates the surface of the rubber and improves its bonding properties.


It is believed that such techniques will allow new tyres containing a substantial proportion of recycled rubber to be manufactured to meet current road tyre standards.


‘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% and 10% 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 research is now being put into practice as part of coordinated trials with a tyre manufacturer, and it is hoped that the results of the trials will show that the techniques developed in Swansea are both commercially viable and safe.