O.P. Bahl

Effect of load on the mechanical properties of carbon fibres from pan precursor

Abstract A detailed study of the effect of tension during low temperature stabilisation on the mechanical properties of carbon fibres (HTT 1000°C) has been carried out. Best properties are attained even where the fibre has an ultimate shrinkage of about 7 percent, a result in contrast with the previous belief of obtaining maximum mechanical properties only with ultimate elongation during early stabilisation. To explain this behaviour, various other experiments with varying load conditions have been performed and are described here.

Characterisation of acrylic fibres used for making carbon fibres

Abstract Various PAN fibres have been characterised by using different techniques such as; mechanical testing, X-ray studies and molecular weight distribution analysis. A direct relationship between the primary Youngs modulus of the precursor and the Youngs modulus of the carbon fibre developed therefrom has been established for the first time.

Role of oxygen during thermal stabilisation of pan fibres

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.

Infrared spectral studies of preoxidized PAN fibres incorporated with cuprous chloride additive

Abstract Polyacrylonitrile (PAN) fibres, pretreated with cuprous chloride have been converted into carbon fibres with mechanical properties much higher than those obtained from untreated precursor. Infrared spectroscopy has been used to characterize the oxidized fibres in order to understand the reasons for superior performance of CuCl treated PAN fibres.

Treatment of pan fibres with SO2 and development of carbon fibres therefrom

Abstract High performance carbon fibres have been obtained by low temperature treatment of polyacrylonitrile (PAN) fibres in an atmosphere of SO 2 , before pyrolysis to 1000°C. The shrinkage behaviour, aromatisation index and the mechanical properties have been critically examined. These results are compared with those of the air-treated fibres. The process has been found to be much quicker and the strength of the carbon fibres so obtained is about 25% higher than that those prepared by the conventional air-pretreatment method.

Reducing treatment of overoxidized PAN fibres for making carbon fibres

Abstract The tensile strength of carbon fibres developed from overoxidized PAN fibres and later reduced with pyrogallol solution has been found to be 25% better than that obtained by conventional methods. There is, however, no effect of such treatment on the Youngs modulus of the fibres. Infrared analysis of the stabilized fibres shows a considerable decrease in the intensity of the oxygen-containing functional groups after reducing treatment of the fibres. The new model proposed for overstabilized PAN fibres agrees satisfactorily with the observations.

A novel method of improving the Young's modulus of carbon fibres

Abstract Carbon fibres possessing a Youngs modulus of about 24 × 106 psi have been made from PAN fibres by heating up to 1000°C. The conventional method of improving the modulus further is to heat treat the fibres to higher temperatures which adds to the cost of the fibres because of the high energy consumption. A novel method has been devised wherein the Youngs modulus can be improved by about 20%. The energy consumed in this method is about 5 Wh as compared to about 200 Wh to achieve a similar increase for the same amount of the fibre following the conventional method of thermal heating. These fibres have been characterised by infrared spectroscopy.