Improved surface interface of OPF and PAN carbon fibers for Carbon-Carbon processing

Specialized materials such as Carbon-Carbon (C-C) are required as primary structural and thermal protection elements to sustain the severe temperatures on the surface of Hypersonic Vehicles during high-speed flight. The C-C material currently qualified at Northrop in Hypersonic Glide-Bodies or “Aeroshells” consist of phenolic resin and a low fired, stretch broken polyacrylonitrile fiber (LFSP) and/or blended stretch broken polyacrylonitrile fiber (BSP) pre-preg. Both fiber solutions have been found to be suitable replacements for the rayon-based carbon phenolic used in tape wrapped rocket nozzles and 2D C-C components. The LFSP and the BSP input fibers originally made from TOHO (Rockfield, TN) are no longer available. The stretch breaking process employed to reduce the modulus and thermal conductivity of the Polyacrylonitrile (PAN) fiber has also changed ownership with key processes and technical know-how potentially lost. A domestically sourced PAN has been identified for the LFSP product, while domestic fibers needed for the BSP replacement are available yet still require further optimization. Each were developed as domestically sourced, industry standard products that would reduce the obsolescence risks associated with past and current Rayon fiber supply chains. Rayon fiber used in C-C applications would progress thru a series of cleaning, firing, and purification steps prior to resin coating. Due to this process, the sizing added by the fiber manufacturers to aid in handling and weaving is removed, alleviating potential interface issues with phenolic and pitch resins used in C-C processing. PAN fiber manufacturers are focused on epoxy and polyester based resin systems used in the automotive, aircraft, and sporting good markets. These resin systems are defined as addition-based reactions which produce little to no volatiles during curing. The sizing used on the PAN fiber for these resin systems are monomer or copolymer acetates which will not survive high temperature processing environments. Furthermore, some of these sizing solutions are soluble in water. Phenolic resin is a condensation reaction system which produces water during the curing and cross-linking process, potentially degrading the fiber-to-resin interface. The objective of this development is to remove the epoxy compatible sizing off the PAN fiber and re-size the PAN fiber with a chemistry that is compatible with phenolic and other high temperature capable resins used in C-C processes. Alkemix Corp. will employ a team-based development approach with the PAN and OPF fiber manufacturer and Oak Ridge National Laboratory to implement our solutions and validate our deliverables.