Preferred orientation of pitch precursor fibers

Spinning condition dependences of the microstructures of a pitch precursor fiber which is a raw material for carbon fiber preparation were studied in detail. The degree of preferred orientation of the molecules in a pitch precursor fiber along the fiber axis was higher when spinning was done at a lower mesophase pitch viscosity. An intermediate diameter gave the highest degree of preferred orientation. The degree of preferred orientation of the molecules in an extruded pitch rod was especially low. The crystallite size L_c(002) of the pitch precursor fiber also was varied by controlling the spinning conditions, and exhibited a good correlation with the degree of preferred orientation. Mesophase pitch at a higher temperature possessed a smaller L_c(002) and a larger d₀₀₂. The small L_c(002) observed at high temperature was maintained by a rapid cooling to room temperature, but the large d₀₀₂ relaxed to a small value at room temperature, even with rapid cooling. A qualitative model for the formation of a preferred orientation through spinning is proposed.