The surface of carbon fibres continuously treated by cold plasma

Abstract

The surface of carbon fibres prepared from polyacrylonitrile (PAN) precursor have been continuously treated by means of a cold plasma. The interlaminar shear strength of carbon fibre reinforced epoxy composites containing fibres so treated was increased from about 60 MPa to 100 MPa. There are four possible mechanisms for this increase: 1. (1) Higher reactivity between fibre surface and matrix as a result of an increase of ▪ groups on the fibre surface. 2. (2) The surface constitution was changed by the plasma treatment so as to improve the wetting properties of fibre surface. The contact angle θ between water and the carbon fibre was decreased from 75° to 61°. 3. (3) Electron micrographs of the surface of carbon fibre show that the surface striations and surface roughness were changed increasingly on fibre surfaces after plasma etching. This increases the interfacial adhesion and the effect of mechanical interlocking. 4. (4) The strength of the carbon fibre was decreased very little (about 1·6%) by this surface treatment method. Analysis of fracture morphology by scanning electron microscopy (SEM) indicates that debonding and fibre pull-out between fibre and matrix do not occur in the treated carbon fibre reinforced epoxy composite. These results all show that adhesion between fibre and matrix is very strong. In addition, the plasma treatment technology is very simple and the cost is low. This treatment process produces no environmental pollution and has promising future for engineering applications.