Carbon Fiber—Vinyl Ester Interfacial Adhesion Improvement by the Use of an Epoxy Coating
With the use of composites expanding into larger structural applications, vinyl ester matrices which are not dependent on an autoclave cure and are more environmentally resistant to water absorption are being investigated. The degree of adhesion between the fiber and matrix has been recognized to be a critical factor in determining the performance of fiber-reinforced composites. The mechanical properties of carbon fiber–vinyl ester composites are low compared to carbon fiber–epoxy composites, partly because of lower interfacial adhesion. The origins of this limitation were investigated. The influence of preferential adsorption of the matrix constituents on the interfacial adhesion was not significant. However, the high cure volume shrinkage was found to be an important factor. An engineered interphase consisting of a partially cross-linked epoxy sizing that could chemically bond to the carbon fiber and form an interpenetrating network with the vinyl ester matrix was found to sharply improve the interfacial adhesion. The mechanisms involved in that improvement were investigated. The diffusion of styrene in the epoxy coating decreased the residual stress induced by the volume shrinkage of the vinyl ester matrix. The optimal value of the thickness was found to be a dominant factor in increasing the value of the interfacial shear strength according to a 2D non-linear finite element model.
KeywordsCarbon Fiber Interfacial Adhesion Vinyl Ester Interfacial Shear Strength Epoxy Coating
Ashland, Huntsman and Hexcel Co. are sincerely thanked for having donated samples of vinyl ester resins (Derakane 411-C50 and Derakane 510A-40), Jeffamine T-403 and AS4 carbon fibers respectively. Financial support for this research from the US Office of Naval Research (Y. Rajapakse) and Florida Atlantic University (R. Granata) is gratefully acknowledged.
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