Abstract
PAN fibres are to be heated in the presence of an oxidising atmosphere before carbonisation. Infra-red spectra of heat treated PAN fibres show variation in the intensities of some old peaks and development of new peaks suggesting that three main reactions take place namely cyclisation, dehydrogenation and uptake of oxygen in the form of hydroxyl, carbonyl and carboxyl groups. Initiation as well as propagation of these reactions depends on the nature of the polymer as well as on the experimental conditions. For copolymer fibres heated in the presence of oxygen, it has been found that cyclisation and dehydrogenation go on simultaneously while in the presence of air and for homopolymer fibres, dehydrogenation precedes cyclisation. This is further confirmed by DTA studies and the mechanical properties of oxidised fibres. The length of the ring sequence for fibres oxidised in the presence of oxygen is found to be shorter than that of air and nitrogen treated fibres.
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