Candid Cameron
Candid Cameron
I just read a short article about how the European Union has stipulated that after 2010, tires can no longer contain aromatic extender oils. What are aromatic extender oils and what do they do for tires? Will North America adopt this ruling, too? And what will that requirement mean for motorcycle tires—shorter or longer tire life, changes in performance with temperatures or something else? Joe White
Marion, Iowa
Ain chemistry, “aromatic” means “based on a carbon ring structure.” The most basic carbon ring is the 6-carbon structure benzene, and this is probably the key to the matter. Benzene is an excellent solvent for rubber, and it is also mildly carcinogenic. For example, its use in shoe manufacturing shops in Istanbul has been extensively studied, as it appears that about 10 years of daily exposure to benzene fumes will cause a fair number of excess leukemias.
Europe has reduced the legal percentage of benzene in gasoline to a small number, like 2 percent, for the above reason, and the U.S. has similar guidelines, I believe. It would therefore make sense that Europe might also seek to reduce the use of aromatic oils in rubber. Benzene is an excellent fuel, having a high anti-knock (octane) number, and there are many benzene-derived compounds still present in fuel, such as toluene and xylene.
Extender oils make up about 30 percent of a tire rubber compound. Such oils are used to enable rapid mixing of the elements in rubber compounds, and to impart desired properties to the rubber itself. These include adjustments of the all-important glass transition temperature (or “glass point”), which is the temperature at which the rubber loses its elastic properties. Racing rubber compounds have high glass points, as this gives properties not otherwise possible, such as grip in rain. The high glass point is also the reason race tires have to be heated In tire warmers before use. Some extender oils are not oils at all at room temperature but rather are waxes.
Switching to oils that are less soluble in rubber will probably require some research, but I’d expect that the industry will be able to cope. -Kevin Cameron
