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Structure/Property Correlations Of Several Polyimide Optical Fiber Coatings For Embedding In An Epdxy Matrix

To be effective in high temperature environments, optical fibers require coating materials which maintain their integrity over their lifetimes of intended use. Polyimide-based fiber coatings are suitable for temperatures up to 350°C. These fibers, used as embedded sensor elements, would remain undamaged during the cure cycles of low temperature composites. To enhance the utility of such sensor elements, an understanding of the structure/property correlations related to adhesion and composite matrix integrity is essential. Several commercially available polyimide coating/glass fiber systems were compared in uniform adhesion tests. The primary concern was the characterization of adhesion between these materials and the surrounding epoxy matrix. Factors to be considered were the effect of coated versus uncoated fibers, the performance of cured versus uncured coatings, and the method of fiber pretreatment. Specific analytical techniques were used to determine the relationship between molecular structure and physical properties. Fiber pullout tests were performed using a tensile stage attached to a light microscope. Failure modes were verified via infrared microspectrometry (FTIRMA) and optical microscopy.