Strain-induced density changes in PAN-based carbon fibres

A series of density measurements has been carried out on PAN-based carbon fibres, which had been hot stretched under various processing regimes. It was found that all three process variables, namely temperature, stretching stress and dwell time, were important in determining the final density and that no simple factor related to the processing conditions could be used to characterise the density uniquely. Both Young’s modulus and tensile strength of the fibres were found to increase with increasing density but again the relationships depended on the specific combination of temperature, stretching stress and dwell time. On the other hand, it was found that both the preferred orientation and the apparent crystallite size, Lc, increased with increasing density, and both were directly related to density, independent of the precise combination of processing conditions.