Recycling Increase the recycled content in car tires by fourfold

Related Vendors

Evonik Industries AG

FAULHABER Drive Systems

Wuxi InfiMotion Technology Co., Ltd.

Until now, ground old rubber has only been suitable to a limited extent for the production of new car tires because its chemical structure complicates interaction with new tire materials. A research team from Evonik has significantly advanced a process to use up to four times as much recycled material in new tires as previously common.

Vulcanization typically creates tire rubber from rubber, sulfur, and other components. Through heat and pressure, sulfur forms bonds with the long carbon chains in rubber, resulting in a robust, three-dimensional network. Rubber powder from old tires is also made this way: as an already vulcanized material, however, it has different properties than non-vulcanized rubber. Consequently, tire recycling industry associations specify that adding about five percent ground recycled material is the maximum allowable in the production of new car tires.

Rubber is too valuable a resource to only use once in tires. We aim to incorporate it into a cycle.

Christian Mani

Most of the old rubber is used, for example, in the production of protective elements on playgrounds or for running tracks. Many used tires also end up in thermal recycling—used as fuel for energy production. However, Christian Mani, Project Manager of Circularity at Evonik, is convinced: "Rubber is too valuable a raw material to be used only once in tires. We want to integrate it into a cycle."

Separating the solid network in the recycled material again

He and his research team have now succeeded in largely reversing the vulcanization in rubber material: "By adding a special formulation with vinyl silanes, we can separate the solid cross-linking in the recycled material. We break the sulfur bonds in the rubber while keeping as many of the long carbon chains intact as possible," the expert explains.

The research team has successfully used these vinyl silanes for devulcanization: In experiments, the proportion of recycled material in the rubber mix could be increased to up to 20 percent—instead of the previously mentioned technical threshold of about five percent.

In the end, our approach must also be convincing on a large, commercial scale.

Christian Mani

Evonik is now aiming for the next milestones with series of tests and trials. The goal is to provide a solution that customers can use in industrial production in the foreseeable future. "In the end, our approach must also be convincing on a large, commercial scale," says Mani.

2000 new car tires per minute

The sustainability benefits of such a circular solution would be enormous: There are more than 1.3 billion passenger cars worldwide. Every minute, more than 2000 new car tires are produced. The demand shows no signs of abating—because cars with electric or hydrogen drives will also roll on rubber tires into the future. The annual turnover from car tires worldwide exceeds 100 billion euros. Evonik's own development project also supports the diverse sustainability initiatives of tire manufacturers.

“This article was first published on our sister portal "konstruktionspraxis" (German Edition), Vogel Communications Group.“