Influence of cure volume shrinkage on interfacial adhesion in carbon fiber-vinyl ester composites

Vinyl ester resins are commonly used in aerospace and aeronautics industries, military equipment, transportation, chemical engineering, sport and recreation goods⋯particularly because of their high resistance to moisture absorption, ambient curing, and resistance to corrosion. Nevertheless, the mechanical properties of carbon fiber-vinyl ester composites are low compared to carbon fiber-epoxy composites, mainly because of lower interfacial adhesion. The origins of that well known phenomenon were investigated. While there was a preferential adsorption of the matrix constituents (initiator, promoter, accelerator, styrene and vinyl ester monomers) to the carbon fiber surface, the mechanical properties of the interface and the interfacial adhesion did not appear to be significantly affected. However, the high cure volume shrinkage, which depended on the matrix composition and its thermal history during the cure, was shown to be the main parameter. To overcome this inherent issue, a partially cross-linked epoxy sizing was found to strongly improve the interfacial adhesion. The mechanisms involved in that enhancement resulting from the crosslinked epoxy sizing were characterized. The diffusion of styrene in the epoxy coating made it swell, which counteracted the residual stress generated by the cure volume shrinkage of the vinyl ester matrix.