New insights into the radial structural differences of polyacrylonitrile fibres during thermal stabilization by the synchronous processing adjustment of time and temperature.

In this study, the synchronous effects of time and temperature on the radial structural differences of polyacrylonitrile (PAN) fibres during thermal stabilization were investigated. For each sample to achieve equal densities (∼1.36 g cm), PAN fibres were thermally stabilized for various times between 8-32 min and at corresponding temperatures of 279-252 °C, which was considered to give a synchronous processing adjustment as a time-temperature integral (TTI). Besides, a previously developed mathematic model was utilized to quantitatively evaluate the differences in the radial heterogeneous structures of the stabilized PAN fibres as a function of TTI. It was found that several structural parameters (, the stabilization degrees, the present crystallinities, and the orientation degrees) of PAN chains in the skin regions that mainly determine the fibres' overall performances were dramatically different from those in the core regions. Meanwhile, based on the TTI model, these skin-structure parameters demonstrated a strong correlation with the tensile properties of the resultant carbon fibres. However, while the stabilized PAN fibres had equal densities, their structural parameters, as well as the properties of the resultant carbon fibres, were obviously different.