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Graphite Fiber Surface Treatments.

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The objective of this program was the development of new and improved surface treatments for graphite fibers in order to provide optimum bonding to structural resins. Experiments conducted with Fortafil 5-Y, a polyacrylonitrile based graphite yarn, demonstrated that short time exposures to liquid systems containing a strong oxidizing agent, such as sodium chlorate, in refluxing aqueous sulfuric acid, could increase the shear strength of epoxy composites containing these fibers to levels in excess of 10,000 psi. Other combinations of oxidizing agents and oxygen acids were also effective there was evidence that intercalation reactions played a role in these rapid treatments. Air oxidation also was found to improve composite shear strength but at a cost to other fiber and composite properties. Continuous gas phase and other types of surface treatment experiments were performed. There was indication that silane or other types of chemical coupling agents affected the bonding of oxidized fibers to epoxy resins. Dark field electron microscopy studies indicated the retention, after surface treatment, of the high degree of orientation at the surface of the fiber. Electron photomicrographs of replicas of the fiber surface showed some pitting resulting from surface treatment as well as some etching away of surface features. Measurements of surface area and oxygen content also showed the effect of surface oxidation, both of these being increased by surface treatment. Author, modified-PL

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Summary technical rept. 1 Apr-30 Sep 70,

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Prepared in cooperation with Rensselaer Polytechnic Inst., Troy, N. Y.



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