German researchers optimise synthetic rubber for less tread loss

Truck tyres are subject to heavy loads and travel over long distances – resulting in similarly heavy wear and tear. The treads of the tyres are manufactured primarily from natural rubber from rubber trees and to date has demonstrated the best abrasion characteristics.

But the security of supply for rubber raw material is endangered; a widespread fungus is destroying whole plantations in Brazil, the original home of the rubber tree. If the fungus crosses over to Asia, where major cultivation areas are located today, the global production of rubber will be threatened.

While artificially manufactured rubber has previously been unable to match the performance of natural rubber, researchers at the Fraunhofer Institutes for Applied Polymer Research (IAP), Germany, have now developed a new type of synthetic rubber, BISYKA,  a German abbreviation for “biomimetic synthetic rubber, which can achieve 30-50% less abrasion than natural rubber.

The Fraunhofer researchers investigated rubber from dandelions, of which 95% consists of polyisoprene and trace organic components such as proteins or lipids. The advantage: dandelion rubber has a generation succession of just three months as opposed to seven years for tree rubber – dandelion rubber provides an ideal start to investigate the influence of organic components on rubber characteristics. After identifying the important organic components for abrasion behavior, the researchers synthesised the BISYKA rubber out of functionalised polyisoprene with high microstructural purity and the respective biomolecules. Their colleagues then investigated the characteristics of the rubber variants obtained via extensional crystallization: if one stretches natural rubber to three times its length, crystalline regions form, the rubber hardens.

In testing, four car tyres manufactured with a tread made from BISYKA were compared with tyres with a tread made from natural rubber. The tests were carried out directly on a car that drove 700 circuits each in opposite directions. The natural rubber tyre was 850 grams lighter after the test with 0.94 millimeters of tread loss, while the BISYKA tire lost merely 600 grams and 0.47 millimeters of tread.

According to Dr Ulrich Wendler, who leads the project at the Fraunhofer Pilot Plant Centre for Polymer Synthesis and Processing (PAZ) in the German municipality of Schkopau: “The extensional crystallisation of BISYKA rubber equals that of natural rubber; synthetic tyres lose 30% less mass and about only half tread loss than equivalent tyres made of natural rubber. Synthetic rubber therefore offers an excellent alternative to natural rubber, as industrial-scale production can make use existing plants and equipment.”

Wendler has explained that initial tests with the BISYKA tyre blend were extremely promising, and will further adapt the formula of the tread compound for high-performance truck tyres.

Production of truck tyres usually mixes rubber and carbon black, which is where the black color comes from. However, manufacturers are adding silicates to the mixture instead – Fraunhofer scientists thus investigate how new kinds of silica fillers can lead to optimum alternatives to natural rubber in the automotive industry.

The researchers will present their results in April 2019 at the annual conference of the German Rubber Society in Merseburg, Germany.