Supplies of post-industrial carbon fibers are in greater supply now that Boeing is fully engaged in the production of its new 787 aircraft, of which, 50% is composite material. In addition to scrap from the production of new planes, many aircraft that are being decommissioned have scrap material that could be reclaimed. According to Gaw, estimates place the number of aircraft that will be retired over the next 20 years at 5900, with 40% of those to be mothballed in North America.
For its purposes, Boeing is buying the highest grades of carbon fibers available: AS4, IM7, T8005, which can cost anywhere from $5-$50/lb as virgin materials. Of the amount it buys however, much of it ends up as scrap. Gaw said the buy-to-fly ratio for materials is less than 33%, meaning that 2/3 end up as production waste. Pyrolysis is one method used to extract the fibers from their epoxy matrices, and the process can affect the fibers' surface properties. Gaw says the residual carbon fibers about 7 µm in diameter.
The company has worked with engineering material compounding company RTP on creating compounds with the scrap fibers. According to Gaw, tests of the compounds showed that you get essentially the same properties from virgin carbon fiber as you do from scrap. The RTP compounds with scrap fiber exhibited similar stiffness or modulus, with the "ultimate strength" slightly weaker. No changes in conductivity were detected. In their testing, Boeing and RTP created PEEK and PEI compounds with 30% recycled carbon fiber content. —Tony Deligio