A Multitechnique Investigation of the Chemical and Physical Properties of Carbon Fibre Surfaces.

The oxidative surface treatment of carbon fibres is of great technical importance. It is widely recognised that the interface between the fibre and matrix resin can have a large effect on the mechanical properties of the composite. However this empirical understanding is not sufficient to allow either the prediction of the effect of new surface treatments, or to tailor the interfacial region for particular applications. The work described in this thesis attempts to improve this understanding by rigorous analysis of the changes arising at the fibre surfaces as a function of surface treatment. The effect of surface oxidation was followed by a wide range of surface sensitive techniques, providing a picture of the changes in surface chemistry and physics. The experimental parameters affecting the degree of surface oxidation were investigated on both on a laboratory and commercial scale. The effect of surface treatment on mechanical performance was assessed by laminate tests. Surface oxidation has been shown to increase the number of chemically reactive groups on the surface, as well as increasing the depth of oxidation. A large number of surface analyses by XPS allowed the development of a self consistent curve fitting protocol to quantify the carbon-oxygen functionality after treatment. There is no conclusive evidence that oxidation radically alters the morphology of the fibre surfaces. Increasing the level of surface oxidation changes the mechanical response of composites, and is resin dependent. In conclusion, this systematic study has shown that, contrary to some of the mechanisms proposed in the literature, the question of how the state of the fibre surface affects the interface in composite materials is extremely complex. This work has, however, provided a broad base upon which further work can be attempted to reach the ultimate goal of engineering the interface