Synthetic Rubber Outperforms Natural Rubber

Natural rubber extracted from rubber trees is a raw material with limited supply. Synthetic rubber produced artificially, however, has not yet achieved the wear behavior of natural products, which has not made it suitable for truck tires. But now, for the first time, a new type of synthetic rubber has been developed that provides 30 to 50 percent less wear than natural rubber.

Truck tires carry very heavy loads: due to the heavy loads they transport every day and the long distances they cover, they are subject to excessive wear. For this reason, tire treads are made from natural rubber extracted from rubber trees, which has shown the best wear characteristics to date. Until now, artificially produced rubber has not reached the performance of natural rubber, at least in this respect. The problem with natural rubber is that the supply security of this important raw material is at risk. In Brazil, the homeland of the rubber tree, the fungus Microcyclus ulei is destroying all plantations. If the fungus spreads to Asia, where important cultivation areas are currently located, global rubber production will be endangered.

Biomimetic synthetic rubber with optimized wear behavior (BISYKA)
In response to this threat, researchers at the Fraunhofer Institute for Applied Polymer Research IAP, the Institute for Microstructure of Materials and Systems IMWS, the Institute for Molecular Biology and Applied Ecology IME, the Institute for Material Mechanics IWM, and the Institute for Silicate Research ISC optimized the properties of synthetic rubber. Dr. Ulrich Wendler, who directs the project at the Fraunhofer Polymer Synthesis and Processing Pilot Plant Center PAZ in Schkopau, Germany, says: "Our synthetic rubber called BISYKA – this is an abbreviation meaning 'biomimetic synthetic rubber' in German – actually has superior properties to natural rubber." Fraunhofer PAZ is a joint initiative of Fraunhofer IAP and Fraunhofer IMWS. "Tires made from synthetic rubber lose 30 percent less mass compared to equivalent tires made from natural rubber. Moreover, the tooth wear of synthetic tires is also half as much. Additionally, synthetic rubber can be produced on an industrial scale using existing facilities and equipment. This means that synthetic rubber is a perfect alternative to natural rubber – including in the field of high-performance truck tires."

Targeted analysis of dandelion rubber
How did researchers achieve this high performance? Scientists at Fraunhofer IME examined rubber obtained from dandelions. Like rubber from rubber trees, dandelion rubber also contains 95 percent polyisoprene, while the remaining percent consists of organic compounds such as proteins or lipids. The advantage of dandelion rubber over tree rubber is that the generation time in the former is only three months, whereas in the latter it is seven years. This makes rubber obtained from dandelions an ideal starting point for investigating the effect of organic compounds on rubber properties. For this purpose, Fraunhofer researchers strategically removed the relevant key organic compounds. After identifying the organic compounds important for wear behavior, Fraunhofer IAP researchers synthesized BISYKA rubber from functionalized polyisoprene and associated biomolecules with high microstructural purity. Colleagues at Fraunhofer IWM and IMWS investigated the properties of the resulting rubber variants. To do this, they used strain-induced crystallization: when you stretch natural rubber up to three times, crystalline regions form and the rubber hardens. Wendler explains: "The strain-induced crystallization of BISYKA rubber is equivalent to that of natural rubber." When manufacturing truck tires, rubber is usually mixed with carbon black, which is the source of the tire's black color. However, manufacturers are increasingly adding silicate instead of carbon black. The expertise of Fraunhofer ISC comes into play here: scientists at the institute are researching how new silica fillers can create the best alternatives to natural rubber in the automotive industry.

Synthetic rubber delivers impressive results in practical tests
Following the development of BISYKA rubber, it was tested: would it deliver the performance promised by strain-induced crystallization? Researchers posed this question to an external and therefore independent partner, Prüflabor Nord. For this purpose, four car tires with tread made from BISYKA were produced and compared with tires with tread made from natural rubber. The tests were carried out directly on an automobile consisting of 700 revolutions in one direction followed by 700 revolutions in the other direction. What was the result? After the test, the natural rubber tire lost 850 grams and lost 0.94 millimeters of tread, while the BISYKA tire lost only 600 grams and 0.47 millimeters of tread. The synthetic rubber's rolling resistance was also better: natural rubber received a C rating in traffic light labeling for rolling resistance, while BISYKA received the higher B rating. "So far we have only conducted initial tests with the BISYKA tire compound, but they are extremely promising. As a next step, we want to further optimize BISYKA rubber. This concerns above all the proportion and composition of organic compounds. At the same time, we will adapt the formula of the tread compound for truck tires to the new rubber," says Wendler. The researcher and his team are currently seeking cooperation partners to bring the product to market.

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