Structure and properties of thin, slit-shaped carbon fibers prepared from mesophase pitch

A mesophase pitch of 100% anisotropy prepared from methylnaphthalene using HF/BF₃ was spun through the slit-shaped nozzle in a temperature range of 260-275°C. Very thin fibers were obtained, about 2-5 μm in thickness and 10-18 μm in width, according to spinning temperature. The slit-shaped transversal section of tape was observed under optical microscope, scanning and transmission electron microscopes. The symmetric Double Layer is proposed as a model of the cross-sectional texture, which carried radial orientation at the semicircular edges, onion-skin at the flat edges, alignments perpendicular to the flat edges in the intermediate parts and alignments parallel to the major axis at the central part of the ellipse fiber. Present carbon fibers exhibited better mechanical properties, as compared to those of round fibers spun through conventional circular nozzles. The fibers after graphitization at 2500°C showed excellent tensile strength and modulus as high as 340-395 Kg/mm² and 84-92 ton/mm², respectively. The particular shape and texture of transversal section appears principally responsible for such tensile properties.