Evonik AG has developed a process that, it said, enables the use of up to four times more recycled rubber in new tires than is possible with existing methods. The level of rubber recyclate incorporated into tires has been very limited up to now as the polymer structure hampers interaction with other materials, noted an Evonik release.

In particular, it said, the sulphur bonds formed under heat and pressure with the long carbon chains result in a highly robust, three dimensional network. As a result, there is an upper limit of about 5% when it comes to introducing ground tire rubber from end-of-life-tires into new tires, noted Evonik. According to Evonik, its research team led by Christian Mani has now succeeded in reversing the vulcanization more effectively than previously possible.

"By adding a special formulation containing vinyl silanes, the firm bonds in the recycled rubber can be split", Mani explained in a 17 Sept statement. The process, he said, 'cleaves the sulphur bridges in the rubber, yet leaves as many of the long carbon chains as possible untouched". In trials, recyclate levels in the rubber blend could be increased to up to 20%, said Evonik, which is now set to start next stage testing and trials.

"The aim is to find a solution that customers could use in industrial production and to prove the process "convincing on a large, commercial scale", stated Mani. "Rubber is far too valuable a raw material to be used only once in tires. We want to incorporate it into a circular system", the led researcher concluded.