Evolution of synthetic rubber: bio-based raw materials and new types of rubber

Synthetic rubber is indispensable today, especially for car tires and technical rubber goods. Until now, the raw materials for its production have largely been obtained from fossil sources. Under the leadership of the Fraunhofer Institute for Applied Polymer Research IAP, four Fraunhofer Institutes are now developing alternative, biobased raw material sources for synthetic rubber, which will enable completely new types of rubber for car tires. The three-year project is being funded by Fraunhofer with 3.25 million euros and starts in April 2024.

In order to meet these challenges, a team from four Fraunhofer Institutes is developing biobased raw material sources for synthetic rubber as part of the project "Sustainable biomonomers for synthetic rubbers with application-related adjustable viscoelastic properties NaMoKau". The Fraunhofer Institutes for Applied Polymer Research IAP, for Microstructure of Materials and Systems IMWS, for Industrial Mathematics ITWM and for Environmental, Safety and Energy Technology UMSICHT are involved.

"In the project, we are producing the rubber monomers butadiene, isoprene and dimethylbutadiene from biobased alcohols," explains Dr. Barbara Zeidler-Fandrich from Fraunhofer UMSICHT. "For this process to work, it is essential to use a catalyst that is as active and selective as possible. We are developing innovative materials based on clay minerals for this purpose."

"The production of sustainable dimethylbutadiene in particular is an outstanding feature of the project, as this monomer has not been available on a technical scale to date and is therefore not used in rubber production," adds NaMoKau project manager Dr. Ulrich Wendler, polymer expert at the Fraunhofer IAP. "We will make dimethylbutadiene accessible for rubber synthesis. Combined with the synthetic building blocks butadiene and isoprene, we will synthesize novel polymer structures with unique mechanical and thermal properties. This will create completely new types of biobased rubber with material properties that were previously impossible to achieve and can be adjusted extremely systematically," says Wendler.

One of the major challenges in the development of car tires is to find an ideal balance between the three factors of rolling resistance, wet grip and abrasion. To improve these parameters, fillers, processing aids and other additives are added to the rubber. These have a significant influence on the tread of the car tire. "Our aim is to develop new compounds for car treads with so far unprecedented property profiles based on the rubber types that we will be researching in the project. This will open up new perspectives for the tire industry," explains Professor Mario Beiner from the Fraunhofer IMWS.

In order to achieve the market launch of the rubber as quickly as possible, the use of digital methods in material design is essential - for example to predict the properties of the complex rubber composites. "Using data-supported simulations, we make the most targeted suggestions possible for synthesis and material characterization tests. To this end, we are developing a software prototype for model-based prediction, uncertainty evaluation and test planning," says Professor Michael Bortz from Fraunhofer ITWM.

Ultimately, the developed materials will be used to create a fully testable tire demonstrator. "The entire value chain from the monomer to the polymer to the rubber compound used in the demonstrator will be accompanied by a life cycle assessment. This systematic analysis enables us to determine the ecological footprint in accordance with ISO and contribute to green chemistry," explains Dr. Markus Hiebel from Fraunhofer UMSICHT.