Tyres of the future

Better tyres can considerably reduce the fuel consumption of a motor vehicle. With his research group, Prof. Jacques Noordermeer is closely involved in the development of energy-saving tyres and now his efforts have been rewarded with a prestigious international award: the American Chemical Society's George Whitby Award 2010.

Tyres can play an important role in reducing fuel consumption and lowering CO2 emissions from motor vehicles. Two thirds of the world's oil is consumed as fuel for transport. A great deal of research in this field is therefore geared towards finding ways of reducing the amount of fuel needed for this purpose. Prof. Jacques Noordermeer's Elastomer Technology & Engineering (ETE) research group is therefore closely involved in the development of energy-saving tyres to ensure that less fuel is consumed. "Our group has two primary focuses," explains Prof. Noordermeer. "The first is the development of energy-saving tyres and the second is finding the most effective way to recycle used tyres."

Rolling resistance
"In effect, a car utilizes 30% of the energy present in the fuel, one third of which disappears into the tyres in the form of rolling resistance," reveals Prof. Noordermeer."Obviously, the more we can reduce the level of resistance, the better the performance will be." In July 2012, new European legislation will come into force requiring that all new tyres be accompanied by an energy label, just as with cars and refrigerators. This will take into account rolling resistance, skid resistance and the noise generated by the tyre. "The problem is that if you try to reduce rolling resistance as much as possible, this results in poor skid resistance and vice versa. Striking the best possible balance between the two is a major challenge," Prof. Noordermeer asserts.

Tyre and road surface
Improvements to tyres cannot be viewed separately from improvements to the road surface. Lowering rolling resistance (lower CO2 emissions) can mean a decrease in traction, with inevitable consequences in terms of safety. For these very reasons, a number of research groups within the University of Twente have joined forces in the Tyre-Road Consortium, which together champion an integrated approach to the problem. This consortium of IMPACT research groups brings together the required expertise in the field of tyre behaviour, road behaviour and tyre-road interaction. The participating groups are Elastomer Technology & Engineering (ETE), Construction Management & Engineering (CME), Surface Technology & Tribology (STT) and Structural Dynamics & Acoustics (SDA). At this time, 14 PhD researchers are working within the Tire-Road consortium.

Replacing carbon black
Tyres are made of more than just rubber. In order to make them sturdy enough, between 30% and 40% carbon black is usually added. "The drawback of carbon black is that it increases rolling resistance by producing friction losses in the rubber on a nano scale. And despite its usefulness in processing rubber, it's filthy stuff!" Prof. Noordermeer exclaims. Silica (in the form of glass nanospheres) has proved to be a good alternative, its big advantage being that it can reduce rolling resistance by 30% without having a negative effect on skid resistance. However, the fact that silica is far more difficult to bind to rubber than carbon black presents a problem. As Prof. Noordermeer states: "This process requires special compounds." In his research group, two PhD candidates are currently working on this subject.

One drawback of working with silica technology is that, to date, it can only be applied in combination with synthetic rubber, while 45% of all tyres are still made of natural rubber. "Natural rubber is much stronger than synthetic rubber and has the additional advantage that rubber trees are themselves also CO2 absorbers." The application of silica technology to natural rubber is being studied by another three PhD researchers.

Rubber recycling
Wilma Dierkes works as an associate professor in Prof. Noordermeer's research group. One of her main projects is the recycling of rubber tyres. "One problem with car tyres is that they have a very low rate of biodegradability," Dr Dierkes observes. "To make an elastic tyre keep its shape, it is vulcanized with sulphur. The simplest way to recycle a tyre would be to reverse this process - devulcanize it - but that simply isn't possible. This is due to the sulphur bridges that have been formed."

At present tyres are ground up into the smallest possible pieces for recycling. All other substances, such as textile and metal, are removed leaving only the rubber. The result is a powder which can be used to make products such as the rubber tiles used in playgrounds. However, this powder is difficult to process for other applications because it is tough and dry. "The properties of the 'old' rubber are lost in the recycling process. Only a very small percentage can be mixed in to the manufacture of new tyres," Dr Dierkes recounts.

"We are now developing a chemical catalyst that can break down the sulphur bridges while leaving all other properties intact," she reveals. "The aim is to use 50% recycled material in the tyres of the future. For roofing materials and pond liner, we've already reached 100%, so we're confident we can achieve the same for tyres!"

Provided by University of Twente