Effects of plasma oxidation on the surface and interfacial properties of ultra-high modulus carbon fibres

An ultra-high modulus (UHM) carbon fibre was submitted to an oxygen plasma treatment. The effects of this treatment on the physical and chemical prope rties of the carbon surfaces were investigated by using surface characteris ation techniques. SEM and STM studies were performed in order to determine the changes in the surface morphology. Observations on the nanometre scale lead to the conclusion that the plasma oxidation "cleaned" the original sur faces of carbonaceous impurities. XPS analysis of the treated fibres reveal ed a very significant increase of oxygen content. Single-fibre epoxy compos ites were prepared from as-received and plasma-treated fibres. and fragment ation tests were performed in order to characterise fibre/matrix interfacia l adhesion. Raman spectroscopy has been used to map the strain along the fi bre during tensile loading of the matrix, and the distribution of interfaci al shear stress has been obtained. The quality of the interface improved dr amatically after the surface treatment, supporting the ability of cold plas ma oxidation to enhance the adhesion of UHM carbon to epoxy matrices. It is concluded that the increase of the oxygen surface content and the removing of the outermost layers may contribute in a cooperative way to the improve ment on fibre/matrix adhesion. (C) 2001 Elsevier Science Ltd. All rights re served.