Rheological Behavior of Liquid Crystal Pitch and Its Effect on the Structure of Carbon Fiber

The viscosity and viscoelasticity of a molten liquid crystal pitch were investigated by a cone‐plate type rheometer at various temperatures. The molten material’s viscous behavior was characterized by WLF‐type temperature‐dependence and pseudoplastic flow. Furthermore, the material’s viscoelastic behavior was marked by two relaxation mechanisms at different angular frequencies. The mechanism with a longer relaxation time was observed in the lower angular frequency. It was presumed that this was due to some higher order structures in the liquid crystal pitch resulted from the dependences of the dynamic storage modulus on the temperature, the shear history and the degree of the heat treatment etc. The other mechanism with a shorter relaxation time, τ, was observed in the higher angular frequency that corresponded to the glass transition. To investigate the effect of τ on the property of carbon fiber, the spinning process of the pitch fiber was simulated. It was found that the Deborah number ND, defined by t...