SEIR liner technology offers improved air retention
The greatest environmental impact associated with the tyre life cycle occurs during the tyre’s on-road use, and therefore rolling resistance and the role it plays in fuel consumption is an increasing focus for tyre makers and consumers. Yet important as it may be, rolling resistance is only one of a number of factors that require consideration during the development of a ‘green’ tyre.
According to Prof. & Dr. Yang Weimin from the Beijing University of Chemical Technology, three key principles are attached to green tyres. The first is that rolling resistance mainly depends on turning momentum, therefore the key to its reduction is to maintain a tyre’s pressure and shape. The second principle is that reducing the weight of the tyre can reduce the moment of inertia and therefore enhance fuel efficiency – to emphasise the importance of tyre weight, Yang comments that wearing shoes weighing 20 kilogrammes is much harder than carrying a 20 kilogramme weight. The third principle is that maintaining tyre pressure can reduce wear on the crown and sidewall flexing, thus prolonging the tyre’s working life.
Maintaining tyre pressure – the protagonist in two of the above principles – has gained Prof. & Dr. Yang’s attention through his role as vice-director of the Triangle Group-run National Engineering Laboratory for Radial Tire Design and Manufacturing Technologies (NEL). Yang’s and the NEL’s work has focused on the development of new inner liner technologies. Yang notes that although butyl rubber, which was adopted for the first generation of inner liner technology, has an air permeability less than ten per cent of natural rubber, it is still not that good at retaining air: “instant noodle packaging has much better permeability than butyl rubber,” he commented during a presentation on green tyre technology in April. Halobutyl rubber has superior air retaining qualities to butyl rubber and binds well with casing rubber during curing, and these factors led to its widespread use in second generation inner liner technology.
A third generation of inner liner technology is now being developed. Exxon Mobil has worked with Yokohama Rubber on DVA (Dynamic Vulcanization Alloy) resin, a blend of specialty elastomer and nylon. This product will be manufactured under the Exxpro brand name. Yang opines, however, that the product the NEL and Beijing University of Chemical Technology is working on provides an even more effective means of retaining air within a tyre. It’s called SEIR (Super Efficient Inner Liner) and, like DVA, utilises nylon to reduce permeability. However, as can be seen from the diagram comparing SEIR and DVA, SEIR possesses a more standardised pattern and distribution. Therefore, says Yang, permeability is much lower.
In Chinese, SEIR is pronounced “sigher”, which means “better than IR”, or isoprene rubber. Yang says that SEIR is 30 times more airtight than natural rubber and three times more than BIIR (bromobutyl rubber). “If we can commercialise SEIR, BIIR will be completely replaced,” he stated.
Prototype SEIR tyres have been developed through cooperative research between the Triangle Group and the Beijing University of Chemical Technology. Yang reports that, compared with tyres containing a halobutyl rubber inner liner, the new material is 12 per cent better at retaining air pressure and enhances high speed performance by ten per cent. In addition to reduced rolling resistance, other stated advantages of SEIR are its durability, resistance to heat build up and that rapid decreases in tyre pressure are avoided should the liner be perforated.