Surface modification and its effect on the interfacial properties of model aramid-fibre/epoxy composites

Abstract The micromechanical behaviour of model Kevlar/epoxy composites made by using as-received fibres with a poly(vinyl alcohol) size was compared to that of fibres where the size was removed, and to the behaviour of model composites containing fibres modified by the introduction of amine groups which were able to take part in the reaction of the epoxy with the hardener. Raman spectroscopy was used to measure the fibre strains in the model composites as a function of distance along the fibre as the matrix load was increased, thus enabling the interfacial behaviour of the model composites to be deduced. The model composites containing the as-received fibres showed an elastic response up to 1% matrix strain with failure occurring through debonding at the interface near the ends of the fibres. Model composites containing fibres which had been washed to remove the size showed different behaviour with an elastic response to 1.5% matrix strain. In this case failure was through matrix yielding. Finally, the model composites containing fibres with pendant amine groups did not fail at the maximum matrix strain (2.25%) used in these experiments, this being interpreted in terms of an increase in the strength of the interface.