Transverse shape, texture, and the degree of preferred orientation along the fiber axis in mesophase pitch fibers were studied by varying spinning temperature and spinning nozzle to clarify the influences of the structure of mesophase pitch. The mesophase pitch derived from methylnaphthalene (mNP) showed much larger Lc(002) and smaller d002 than that from naphthalene (NP), indicating larger and better ordered stacking of the aromatic planes in the former pitch, although their softening points, melt viscosities, spinning temperatures, and molecular weight distributions were much the same. MNP provided a higher degree of preferred orientation in the round shaped fiber, which led to an open wedge in the radial texture in a particular spinning temperature range, and larger width/ thickness ( W T) ratio of tape spun through the slit-shaped spinning nozzle. Addition of NP to mNP in their melt states decreased Lc(002), lowering the degree of orientation and decreasing W T ratio according to the added amount. Such structural factors of fiber and tape are related to the stacking of aromatic molecules in the mesophase pitches. The higher stacking may emphasize the dimensional anisotropy of molecular assembly, influencing the viscoelastic flow of the mesophase pitch in the spinning nozzle. Larger anisotropy may also contribute to the better alignment of molecular assembly along the spinning nozzle wall.
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