Recycling Carbon Fibers
Scientists at Siemens AG have developed a solvolytic recycling process to reclaim carbon fibers from composites. At a temperature of 200°C and in the presence of water under pressure, the resin component is converted into low-molecular-weight soluble alcohols during this process. The fabric in the composite part retains its form with intact fibers and can be processed again immediately. The mechanical properties of the fibers are almost unchanged. Next, the researchers hope to find ways to use the reclaimed fibers again in new parts having a different shape.
The process is well-suited for processing production waste that arises in the course of trimming or in the form of rejects during production of composite plastic parts with carbon fiber reinforcement (CFP). Until now, such materials were pyrolyzed in special systems at a temperature of about 1000 °C in the absence of oxygen. The matrix resin is converted into a gas, leaving the pure carbon fibers behind. Reuse of the fabric is not possible with this method, however, because the fibers become knotted together and must be chopped up.
To produce carbon fibers, carbon-containing starting materials are converted into a graphite-like form of carbon at elevated temperatures. Most of the high-performance fibers used today are produced from polyacrylonitrile by pyrolysis under an inert gas. Because of the complex production process, carbon fibers are considerably more expensive than, for instance glass fibers. Recycling of carbon fibers is thus interesting from both an economic and ecological standpoint. Because of their low weight and exceptional mechanical properties, CFP currently find use primarily in wind turbine rotor blades, in the aircraft and aerospace industries and in sporting goods. Current estimates place the worldwide demand for carbon fibers in 2012 at about 40 000 t.