Better Handled With Innovative Plasma Technology to Cheaper Carbon Fibers

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Carbon fibers are currently produced from the plastic polyacrylonitrile (PAN) in ovens in a relatively complex and expensive process, says FH Aachen University of Applied Sciences. But it can also be done much more easily ...

Carbon fibers are the reinforcements for composites (fiber-reinforced plastics (FRP)) found in aircraft and vehicle construction or in rotors for wind turbines, to name just a few examples. Until now, considerable effort has been required to produce carbon fibers. However, at the Aachen University of Applied Sciences, it has been discovered that a special plasma treatment can achieve results faster. The fibers, as the raw material for carbon, are produced from the thermoplastic PAN—manufactured by Bayer, it is also commonly known as Dralon or Dolan from Hoechst. This process takes place in two phases: the stabilization of the fibers and the subsequent carbonization, as explained by the researchers in Aachen. During stabilization, the PAN fibers are usually fed millimeter by millimeter through an industrial oven that, as emphasized, is immense, around 30 meters long. There, they are heated to approximately 300°C (572°F) for 60 minutes, which of course consumes an enormous amount of energy. Additionally, the costs for the large building housing the oven are significant. However, this stabilization phase can now take place entirely differently using free-standing plasma:

A Remarkable Breakthrough in Plasma Technology

During the course of their research, there were attempts to treat the surface of the PAN with a plasma beam. The plasma easily provided enough energy, it is stated. However, the energy from the beam-shaped plasma inevitably acted too locally on the fibers, causing them to simply burn through, as Dr. Christoph Schopp, a research associate at the Institute for Microwave and Plasma Technology (IMP) at FH Aachen, explains. Until now, artificially generated plasma was also bound to a component, such as an electrode. However, the researchers have now achieved an exciting breakthrough! "We have managed to decouple the plasma from the electrode and can even shape it freely according to our needs," adds colleague Prof. Dr. Holger Heuermann, head of the IMP. The result is plasma with a cylindrical shape that is detached from the elements forming the plasma. This free-standing plasma was made usable as a tool in an innovative device, allowing the PAN fibers to pass through the plasma without direct contact. The heat now acts evenly on the fibers, so there is no longer any burning through, and everything can be stabilized in a controlled manner.

PAN Fibers Can be Stabilized in just One-Tenth of the Usual Time

With the new method, the PAN passes through the oven at a speed of one millimeter per second—resulting in a total processing time of just seven minutes (instead of the previous 60 minutes) to achieve complete stabilization, the researchers emphasize. The energy demand for the stabilization phase is thus reduced by a substantial 80 percent. Additionally, the production line is now only around four meters long, instead of 30 meters. This approach can even be further developed into an additionally optimized, industrially applicable setup. According to the specialists, this would involve positioning 16 of the innovative plasma devices in parallel in a 4×4 matrix. This would reduce the processing time of the fibers in the oven to six minutes! The researchers are also optimistic that further optimization to a minimum of four minutes is possible.