Surface Chemical Modification and Analysis of Carbon Fibers - The Key to Novel Composites
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SURFACE CHEMICAL MODIFICATION AND ANALYSIS OF CARBON FIBERS - THE KEY TO NOVEL COMPOSITES
PETER M.A. SHERWOOD Department of Chemistry,
Kansas State University, Manhattan,
KS 66506
ABSTRACT making various Carbon fibers are finding increasing application in It is found that such composites have composites with special properties. The properties that can be markedly effected by the carbon fiber surface. effects of surface modification by electrochemical and plasma oxidation is The interaction of the discussed and the surface chemical changes described. matrix with the fiber surface is a subtle mixture of physical and chemical effects. The paper discusses work in the author's laboratory using surface studies with core and valence band X-ray photoelectron spectroscopy (XPS) and other techniques.
INTRODUCTION materials are attractive for high-temperature Carbon and graphite They also applications since they maintain strength and stiffness above 2500K. are amongst the lightest refractory materials known and possess low thermal Carbon fibers can be expansion and high thermal and electrical conductivity. produced with desirable properties including high modulus and high strength. These fibers can be used to reinforce various matrices, including carbon and polymeric matrices. Carbon-carbon composites (CFRC) are an arrangement of carbon fibers in various configurations held together in a rigid carbon matrix. Polymeric matrix composites (CFRP) have the carbon fibers held in a plastic The carbon fibers lead matrix (typically epoxy resin or cyanate ester resin). to improved impact strength and fracture toughness for the composite by resisting cracks which would otherwise propagate through the matrix. CFRP materials have been prepared most often using an epoxy resin matrix. These materials have been widely used as structural materials, especially in the aircraft and space industries, where the strength-to-weight ratio of such From the early days in the development of such composites is very important. materials the most severe problem was the weak fiber-resin bond, which resulted in very poor mechanical properties (e.g. the interlaminar shear strength (ILSS) was poor). In fact it was found that the properties were worse for high modulus fibers. Surface treatment of carbon fibers has been found to lead to a substantial improvement in fiber mechanical properties and the surface chemistry of the the final fibers has been found to be one of the key factors that 2effects 0 Surface treatmentl- and references therein mechanical properties of the composite. to alter the inert nature of carbon fiber surfaces has been examined using a number of methods. These methods are mainly oxidative in nature. They include chemical "wet" methods (e.g., treating carbon fiber surfaces with nitric acid, potassium permanganate, chromic acid, or sodium hypochlorite, etc.); chemical "dry" methods (e.g., catalytic oxidation, oxidation by air, oxygen, or ozone, radio-frequency plasma treatment, etc.); electrochemical methods (e.g., anodic oxidation in va
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