The Study On Supercritical Carbon Dioxide Modified Of Carbon Fiber Surface

Because of the excellent mechanical properties, carbon fibres are developed for a variety of high technology applications. However, carbon fibres, without any surface treatment, consist of graphitic basal planes and edge sites. And the weak-bound crystallites left over from the grphitisation process on carbon fibres cause the weak adhesion to the matrix resin, so material properties are weak . Therefore, the surface treatments of carbon fibres are necessary. Supercritical carbon dioxide (SCCO2) has low viscosity and high diffusivity. Dissolvability and dielectric properties of the fluid are higher. Because of inert, non-toxic and environmentally acceptable, the study on the application of SCCO2 was focused in recent years. Base on the special properties of supercritical carbon dioxide, SCCO2 was employed to etch the surface of PAN based carbon fibres.The surface characteristics of PAN based carbon fibres were studied by atomic force microscopy (AFM), scanning electron microscopy (SEM). The changes between treated and untreated carbon fibres surface were observed and analysed. The surface composition and surface functional groups of carbon fibres were examined by X-ray photoelectron spectroscopy (XPS). It was found that the ratio of O/C on carbon fibres surface decreased due to the increase of temperatures. Deconvoluted peaks of the C1s spectrum were also used to analyze the chemical status of C element. When the carbon fibres were treated at the higher temperature, the oxygen functional groups on carbon fibres surface decreased. The X-ray diffraction analysis (XRD) had been used for investigating the effect of SCCO2 treatment on the structure of carbon fibres, in order to analyze the mechanics of the evolution of graphite microcrystallite structural parameters during the treatment-temperature increase. It was found that the interplanar distance of 002 crystal plane increased and the thickness (Lc) and the size (La) of graphite microcrystallite also increased with the treatment temperature. Therefore, the degree of graphitization of carbon fibres decreased when raising temperature. The surface of SCCO2-treated carbon fibres were observed by AFM, it was found that the grooves in the surface became deeper and the roughness increased with treatment temperatures. Besides, carbon fibres single tensile strength decreased by 4.4% at the 200℃SCCO2 treatment. The shear fractures of treated CF/epoxy composite were tested by ILSS, the maximum enhancement was 17.4% at the 200℃SCCO2 treatment, and the improvement of ILSS after SCCO2 treatment was obvious. After the SCCO2 treatment, the surface roughness of treated carbon fiber and the wettability increased. As a result, CF /expoxy interfacial properties were improved by supercritical carbon dioxide treatment. In summary, SCCO2 treatment on carbon fibres to improve the interfacial properties of CF/epoxy composites is a green and environment friendly approach.