CO2-oxidation and Void Structure of Kevlar-and Kynol-based Carbon Fibres

An investigation was carried out on oxidation behaviour of Kevlar- and Kynol-based carbon fibres in a carbon dioxide atmosphere.A relationship was established between the void structure and either the precursor or the conditions of oxidation.Significant oxidation took place from 650°C for Kevlar and from 750°C for Kynol.The oxidation mechanism differed depending on the precursor and, in the case of Kevlar, on the oxidation conditions. Void structure, as characterized by a purpose-made procedure based on x-ray small angle scattering, also differed accordingly.Kynol-based products contained one type of voids i.e. small voids.Kevlar-based products contained other types of voids i.e.larger or longer voids, in addition to the same type of voids as found in the Kynol-based products.When Kevlar was brought to a lower oxidizing temperature, e.g.700°C, through a slower heating rate, e.g.0.5°C/min, the preferential type of voids to develop was oblong voids extending along the fibre axis.In other cases, it was the type of void commonly seen in Kynol-and Kevlarbased products.Depending on the degree of the oxidation, variation was observed in void size distribution within each type of the voids.