Fiber Finishes for Improving Interfacial Thermo-Oxidative Stability in PMR-II-50 Matrix Composites

摘要

The interface has been shown to be a preferential site for thermo-oxidative degradation in carbon/polyimide composites. This study entails the development and demonstration of improved T650-35 carbon/PMR-II-50 polyimide composites through the use of high-temperature finishes. The finishes are based on a family of novel difunctional coupling agents that have been shown to form chemical bonds with a variety of organic, inorganic, and metallic materials. The finishes consist of a mixture of these coupling agents, PMR-II-50 carrier, surfactant, and solvent. A solvent dip process is used to apply the finishes. Subsequent application of heat dries the solvent and initiates reaction between the finish and the fiber. As applied, the finishes form a uniform 0.5 micrometer coating on each fiber that cannot be removed by a methanol wash and remain flexible for subsequent processing. When incorporated into a polyimide matrix composite, the finish reacts with the matrix resin during processing to form chemical bonds in the interphase. This approach has the potential to dramatically improve thermo-oxidative stability (TOS) of the interface in polyimide-matrix composites. The addition of these finishes to fiber surfaces serves the dual purpose of protection of the fiber during handling and alteration of the interphase in the cured composite. Initial results show that the finishes are compatible with PMR-II-5O processing and bond well to carbon fibers. The finishes display excellent TOS. Aged composites with these finishes show good retention of mechanical properties. Microinfrared spectroscopy indicates that oxidation of the carbon fiber surfaces is reduced in composites containing finished fibers.