Effect of thermal transformation and stability on the flammability of PAN precursors-based carbon fibres

Abstract

During the development of the carbon fibres and oxidized fibres, the aim was to get a material with extraordinary mechanical properties. Nowadays, it becomes more and more important to make it also fire resistant. To achieve the fire resistance of the raw material PAN, a multistage technology process is needed in which its microstructure and flammability are changed. These special properties can be achieved by heat treatment, during which the microstructures of the fibres change at each step. The thermal transformation involves thermal stability. The thermal transformation can be followed by measuring the limited oxygen index (LOI), and compare it to traditional testing methods, such as infrared and Raman spectroscopy and elementary analysis. The results show that the oxygen index of the samples is a very sensitive and characteristic parameter of flammability. It seems a good correlation between the LOI and the structural parameters of the samples. The structural transformations are not linear but abrupt. Considering the temperature treatment ranges which are responsible for the increasing oxygen indices, three distinct areas can be determined. It has been confirmed by measurements that LOI can express the grade of stability. Based on spectroscopic measurements, it has also been confirmed that the oxidized fibres dramatically decompose when burning in enriched air with more than 50% oxygen content.