Antioxidant Fiber Finishes for Polyimide-Matrix Composites

John H. Glenn Research Center, Cleveland, Ohio

Polyimide-matrix/carbon-fiber composite materials with enhanced thermo-oxidative stability can be made from carbon fibers that have been coated with suitably formulated reactive finishing materials. These finishing materials were developed out of a need to increase thermo-oxidative stability of composite materials for high-temperature applications, and in response to the observation that thermo-oxidative degradation of polyimide-matrix/carbon-fiber composites is dominated by phenomena that occur at matrix/fiber interfaces.

A Reactive Finish is applied to a carbon fiber, with which it forms a chemical bond. During the subsequent incorporation of the fiber into a composite material, the finish forms a chemical bond with the matrix.

The figure schematically depicts the coating of a carbon fiber with a reactive finish and the subsequent incorporation of the fiber into a polyimide-matrix/carbon-fiber composite. Reactive coupling agents in the finishing material chemically bond to both the carbon fibers and the polyimide resin. The fiber/finish and finish/matrix chemical bonds increase the durability of the composite material by strongly resisting attack by oxygen, moisture, and solvents. The chemical bonds also increase interfacial strength and resistance to fatigue.

The finishing material includes a resin carrier compatible with the matrix resin. By selection of different carrier resins, it should be possible to formulate other reactive finishes and tailor interfacial properties, not only for polyimides, but also for a variety of other matrix materials, including epoxies, bismaleimides, phenolics, vinyl esters, and polyesters.

This work was done by James K. Sutter of Glenn Research Center and Ronald E. Allred and Larry A. Harrah of Adherent Technologies, Inc. For further information, access the Technical Support Package (TSP) free on-line at www.nasatech.com/tsp under the Materials category.

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