By Ilya SHMURAK, Dr. Sc. (Tech.), head of department, Federal State Enterprise "Scientific Research Institute of Tyre Industry"
Using a bike, motorcycle, car or truck and even a plane, you cannot avoid dealing with tyres. These pneumatic devices ensure grip on the road for your vehicle, protecting it from knocks and bumps. This has always been so and there is really no significant changes of the situation in sight. In recent time, however, Geologists sounded the alarm. It turns out that tyres in their traditional forms are a threat to the environment.
Г lie negative impact of tyres upon I the atmosphere, soil, vegetation, .Ж. animals and humans comes from their resistance to rolling which, in its turn, determines fuel consumption and the volumes of exhausts containing such biologically dangerous components as lead, carbohydrates, sulfur dioxide, carbon dioxide, carbon monoxide and so on and so forth. Tyres of a moving vehicle "rub off' against the road, scattering highly dispersed solid wastes and gases harmful for human health. The latter can be released even by the tyres of a parked car.
As experts point out, the main "source" of the aforesaid negative phenomena is the tread-the surface rubber layer of a tyre. It is responsible in cars for 35-50 and in trucks, for 50 to 70 percent of the tyre resistance to roll and for practically the entire volume of the products of tyre wear. Figuratively speaking, in order to make a "green", or environment-friendly tyre, it was necessary to solve two problems: reduce as much as possible the first factor, while increasing tyre resistance to wear and bringing down the volume of its "discharges".
And it turns out that this is not "baying for the moon" to use the popular expression.
Resistance to roll as such depends on dynamic hysteresis*, which is responsible for mechanical losses and heat release from cyclic stress upon tyre. That means that in order to minimize such losses protectors should be made of some appropriate materials in which technical carbon should be balanced with colloidal silicon dioxide (CSD). As proved by experiments: a replacement of 45-75 percent of the former by the latter material can bring down hysteresis losses by 30-50 percent. An indispensable condition for getting such results is what we call the degassing of CSD particles and interaction between their surfaces and the raw rubber (caoutchouc) of the rubber mixture. With this aim in mind they introduce into the latter special additives and the most common of them is Si-69 (or A-1289). The ethoxysilane groups of these substances react with silanolic ones on the surface of CSD. In the process of rubber vulcanization the tetrasulfide bonds of the additives are broken and the free radicals produced* are attached to the sulfur net which promotes the disaggregation of CSD particles, forming a strong bond between them and raw rubber. And all of these things are having a positive effect, or no effect upon the elasticity, durability, wear- resistance and the grip of the tyre on the road.
Unfortunately, the Si-69 product is very expensive and chemical experts try to reduce its consumption. One of the ways of reaching this objective, in the opinion of our Institute researchers (like Dr. Yulia Azarova), consists in spraying of this component in a pseudoliquified CSD layer. Similar results, as has been demonstrated by a team of Dr. Oleg Sigov (Voronezh Branch of the Federal Institute of Synthetic Rubber), can be obtained by the modification of butadiene orbutadienstyrol rubbers** through
* Hysteresis-retardation of the effect when the forces acting upon a body are changed (from viscosity or internal friction). -Ed.
* Free radicals-chemical compounds with an "uncoupled" electron, which makes them highly reactive.- Ed.
** Synthetic rubbers, first produced in 1932 by the method of Acad. Sergei Lebedev.- Ed.
their polymerization in solutions with the use of replaced lithiumorganic catalysts or using the same polymerization but in aqueous medium and with the use of reactive monomers. Of special interest among such rubbers is a copolymer of butadiene, styrol and methylmetacrylat which makes rubber, as had been established by Dr. Naum Sakhnovsky and others, highly wear resistant and resistant to ageing as compared with the conventional butadienestyrol rubbers.
Tyre resistance to rolling can also be reduced by reducing its mass. The way we see it, the most promising method in this respect consists in replacing the traditional cord (long slender flexible material consisting of several strands, as of thread, positioned in a tyre from edge to edge in a parallel pattern and making the tyre strong, flexible and elastic) by that made of high-strength capron fiber.
Being as strong as the conventional products of this kind, the "novelty" has a smaller diameter-which means lesser weight. Another version of the same approach features high-strength capron strands of the same diameter as the conventional ones. They make it possible to reduce the number of cord layers in the carcass of a tyre which means making it much lighter.
The worst source of environmental pollution caused by tyres are the amins-products of "boosters" of vulcanization. Getting into the atmosphere, they react with nitric oxides, producing carcinogens. To reduce the volumes of such discharges Oleg Sigov and his colleagues from Voronezh suggested using rubbers which produce no volatile discharges and specialists from our own Institute have designed what we call protector rubbers on their basis.
And there are also other ways of reducing amins pollution. They include using vulcanization boosters which do not release amins reacting with nitric oxides, and the aforesaid copolymer of butadiene, styrene and methylmetacrylat. Fragments of the latter can bind the amines released from vulcanization boosters.
Summing it up, an environment-friendly tyre is becoming a reality. In France, for example, new Michelin tyres are now successfully winning their share of the market.