For what purpose do manufacturers add silica to the rubber mixes of their tires

Silicon dioxide is used as a filler in many industries, and for example, in the construction industry, it is used in the production of concrete and brick. It is mainly obtained from quartz sand, but the crystalline silica produced in this way is not suitable for use in tire production, and instead, companies purchase technically processed "amorphous" silica, and this material has been used in the industry relatively recently.

In the mid-1990s, Continental became one of the first tire manufacturers to realize the potential of silica as a filler for rubber compounds. At the beginning of that decade, the company conducted the first experiments, which proved to be extremely promising. The properties of the material are activated during the rubber mixing process, when silica reacts with silane, acting as a bonding agent. At the next stage, i.e. during vulcanization, the rubber compound is subjected to pressure at temperatures from 120 to 160°C, and thanks to special molds, the tire takes on its shape. Sulfur is used to convert the polymer and silica mixture into elastic rubber, which forms bridges between the long-chain molecular threads of rubber during vulcanization. At the same time, silica, when interacting with silane, forms additional bonds, creating a very strong network of rubber molecules, which improves such tire properties as wet grip, resistance to abrasion and fuel efficiency. At the same time, tires also better withstand extreme loads.

"The addition of silica to rubber compounds has been a revolution in the tire industry, allowing us to almost halve the braking distance on wet roads," says Professor Burkhard Wies, who in the 1990s developed the first tires with silica content, and is now heading the department of applied research and innovation at Continental. "Silica also reduces environmental harm, as it reduces rolling resistance, increasing the range of electric vehicles and reducing fuel consumption of internal combustion engine vehicles."

The first road tests of tires made using the new filler in 1994 showed a significant increase in braking efficiency on wet surfaces and a decrease in rolling resistance compared to tires produced using only technical carbon. A year later, Continental first used silica in the production of a serial tire, which became the Continental ContiEcoContact CP, and in 1996, the ContiWinterContact TS 770 winter tire with silica in its composition was released.

"In combination with the use of passive safety means, such as anti-lock braking systems and seat belts, the introduction of silica has helped to significantly reduce the number of road casualties," notes Wies.

Now, tire manufacturers are working to make silica, like other materials used, more environmentally friendly, and one of the sources of raw materials has become rice husk ash, which makes it possible to obtain silica with the necessary properties. Rice husk is a by-product of rice production that cannot be used as food or animal feed. At the same time, the production of silica from rice husk ash is more energy-efficient compared to traditional raw materials, such as quartz sand. Now, "green" silica is already being used in the production of car tires, such as the Continental UltraContact NXT, which is the most environmentally friendly product from the German concern to date.