The objective of this project is to develop a new composite based on the second generation of Naval Research Laboratory (NRL)-developed phthalonitrile resins as a non-methylene dianiline (MDA)-based material with superior high temperature and flammability properties, which is easily processed into shaped component by low-cost composite manufacturing methods and has the potential to be fabricated into shaped composites by non-autoclave techniques. The research efforts will focus on developing a polymeric material/composite database on (1) the optimization of the composite processing parameters, (2) thermo-oxidative properties, (3) mechanical properties of the fiber reinforced composite under various heat treatments and humidity and aircraft fluid exposures, (4) flammability and toxicity studies, and (5) final development of a procedure with the help of industrial sources for the fabrication of composite engine component(s) and other aircraft components by out-of-autoclave (OOA) techniques. The initial work between NRL and the Naval Air Warfare Center Aircraft Division will involve the fabrication of carbon fiber composite panels from prepreg consolidation and characterization/evaluation of machined samples thereof.

This collaborative effort will involve the material property development of the non-polyimide, low melting NRL PEEK-like phthalonitrile polymer/composite for Department of Defense (DoD) weapons and platform applications such as for aircraft and jet engine uses and potential marine applications. Due to the unique properties exhibited by the phthalonitrile resin, the fabrication of composite panels and the characterization and evaluation studies are vital in understanding the full capabilities of this new resin system and could reveal their importance in composite components fabricated from this superior resin. If microcracking became an issue in the fabrication of the composite panels/test coupons, adjustments would be made, as needed, in the curing and post-curing thermal parameters such as heating rate and thermal exposure at various temperatures to eliminate or release any thermal stresses within the composite that might arise. A slow heating rate and soaking at various temperatures during the curing cycle would eliminate any mismatch in the temperature on the outside versus the middle of a panel or thick composite component, which could contribute to microcracking due to internal stresses. Physical properties of the resin/prepolymer, in the presence of several amine curing additives based on their reactivity, will be ascertained prior to prepreg formulation and composite panel fabrication.

The NRL-developed PEEK-like phthalonitrile resin addresses the need to replace composite materials containing MDA, a known carcinogen, in the fabrication of engine components and other aerospace applications. Composite components can be readily manufactured using cost-effective techniques such as resin transfer molding (RTM), resin infusion molding (RIM), filament winding, prepreg consolidation, and potentially by automated composites manufacturing techniques. When fully cured at temperatures up to 400°C, the polymer does not exhibit glass transition temperatures (Tg), does not burn in a flame environment, and shows superior high temperature performance. (Anticipated Project Completion - 2015)