Novel, oxidation-stable, carbon-based multifibrillar fibers with exceptional mechanical properties via electrospinning

• Applicants: Professor Dr. Andreas Greiner; Dr. Günter Motz
• Subject Area: Polymer Materials
• Term: since 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 455984818

The mechanical properties of carbon and ceramic fibres are determined primarily by defects. Unlike polymer and metal fibres, a defect in brittle materials leads to catastrophic failure. Therefore, the theoretically possible strength values are not even approximately reachable. An opportunity presents itself on one side to improve fibre production with regard to defect avoidance, and on the other side to decrease the fibre diameter. Then the defect frequency per fibre length diminishes. Improvement is expected when such nanofibres are aligned ideally parallel to one another and combined into bundles with continual pyrolysis. At the Chair for Macromolecular Chemistry II at the University of Bayreuth such a procedure has been developed to produce extremely high-strength, multifibrillar polymer nanofibres from electrospinning modified PAN. Since PAN is the precursor most often used to produce carbon fibres, the first research focus is the production of low-defect carbon fibres made of many nanofibrils via electrospinning, curing and, lastly, continual carbonisation. The disadvantage of carbon fibres is the beginning of oxidation already at 400 °C. Therefore, the findings from the synthesized carbon fibres should be used to achieve the main project goal: the production of a high-strength and significantly oxidation-resistant multifibrillar fibre. These investigations are based on previous works from the Chair of Ceramic Materials Engineering at the University of Bayreuth, where PAN was combined with silazanes. The multifibrillar carbon / SiCN fibers, again produced by electrospinning, should consist of carbon and passivating Si3N4 after curing and continual pyrolysis, and should have very high strength values and be sufficiently stable to oxidation. Such continuously produced fiber types are unknown for either carbon or ceramic fibers. They represent a new generation and are said to exceed the mechanical properties of commercial carbon and SiC fibers. The necessary expertise in synthesis and modification of corresponding polymers, their processing into multifibrillar fibers via electrospinning, curing and pyrolysis are available at the two research chairs involved at the University of Bayreuth and are documented in the corresponding publications. This complementary knowledge should be brought together and combined in the proposed project. Finally, the potential of the multifunctional carbon fibers, which are easy to process in terms of textile technology, for the reinforcement of plastics and that of carbon / SiCN fibers for ceramics reinforcement, are to be examined and evaluated.

• DFG Programme: Research Grants