A comprehensive study on the oxidative stabilization of mesophase pitch-based tape-shaped thick fibers with oxygen

Tape-shaped pitch fibers with a transverse cross-sectional size of 400 μm width and ∼30 μm thickness, melt-spun from mesophase pitch, were adopted as a model for treatment in oxygen using various temperatures and durations to investigate their stabilization behavior. Several characterization techniques were used to systematically analyze the functional group species, oxygen content and distribution, local composition, thermal pyrolysis behavior and micro-structural changes in the various stabilized tapes. After oxidative stabilization treatment, the tape-shaped fiber exhibits uniform shrinkage behavior during subsequent heat treatments thereby maintaining its tape shape and structural integrity. The ∼30 μm thick tapes can be stabilized completely by treatment in oxygen at 220 °C for ∼10 h and this indicates a high efficiency of stabilization, which is, perhaps unexpectedly, higher than that of corresponding ∼30 μm diameter round-shaped fibers. Thermal decomposition pathways varied with the degree of stabilization and have obvious effects on the microstructure of the resulted tapes, which in turn strongly influences their final physical properties. Pitch tapes oxidized under mild conditions offered relatively higher mechanical performance. Tensile strength and Young's modulus of 2500 °C graphitized tapes, previously oxidatively stabilized at 220 °C for 20 h, were measured to be about 2 and 250 GPa, respectively.

After oxidative stabilization at 220 °C for ∼10 h, the concentration and distribution of oxygen along the thickness direction on the transverse cross-section of stabilized tape (ca. 30 μm in thickness) are nearly equivalent. The subsequently carbonized (1000 °C) and graphitized (2500 °C) tape-shaped thick fibers completely maintain their morphology and structural integrity, and exhibit good mechanical performance.213