The performance of a composite material depends strongly on the quality of the fibre-matrix interface. The interactions developed at the carbon fibre-epoxy matrix interface were studied using the acid/base or acceptor/donor concept. The surface characteristics of the reinforcing fibre and the polymer were determined using a tensiometric method and the inverse gas chromatography technique at infinite dilution. Following the approach of Gutmann, acid/base surface characteristics were obtained, allowing the interactions at the interface to be described by a specific interaction parameter. It was shown that the shear strength of the interface, that is, the capacity of the interface to transfer stress from the matrix to the fibre, as measured by a fragmentation test, is strongly correlated to this specific interaction parameter, demonstrating the great importance of acid/base interactions in fibre-matrix adhesion.The adhesion between reinforcing fibres and the polymer matrix is one of the important parameters governing the performance of a composite material. It is generally recognized that the interface or interphase is the third constituent of a composite material. However, high adhesive strength at the interface does not necessarily lead to optimum properties of the composite. For instance, good impact strength would require the formation of reversible physical bonds rather than high energy chemical links. In order to understand and predict the mechanical behaviour of the composite, it is necessary to gain better knowledge of the nature and level of interactions likely to be exchanged at the interface.In the case of physical bonds (London dispersion, Keesom orientation, and Debye induction forces), the energy of interaction or reversible energy of adhesion can be directly calculated from the surface free energies of the solids in contact.For years, it was assumed that the surface energy y s of a solid is the surriof two terms: a dispersive component Ys and a non-dispersive or polar component 75. However, recently, it appears that the non-dispersive term of interaction could be better described using the concept of electron acceptor/donor or Lewis acid/base characteristics of the solids.
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