Meso-scale texture of mesophase pitch and its spun fiber

The mesoscopic textures of the mesophase pitch and its spun fiber were examined in the as-prepared and solvent extracted forms using high resolution scanning electron microscopy (HR-SEM). HR-SEM revealed spherical or elliptical grains of 10-50 nm size. Such units were defined as microdomains in the insoluble fraction of the mesophase pitch. The solvent of high dissolving activity reduced the size of the grains, while maintaining their basic shape. No porosity was found in the surface of the microdomain. The as-spun fiber showed a flat textureless plane on its surface along the fiber axis. The solvent extraction closed up the spherical micrograin of 10 nm, as viewed perpendicular to the surface. A tilt angle of 10 degrees to the surface of the fiber revealed the pleat alignment of insoluble microdomains. The carbonization after the stabilization of the fiber provided pleat alignment of microdomains on the surface when the fiber was tilted to be observed. Pleat microdomains observed on the surfaces of as-extracted and carbonized fibers were basically the same. The insoluble fraction in the mesophase pitch forms the particular microdomains in the extracted pitch. Thus, the insoluble microdomains in the pitch were deformed into the pleat unit through the spinning. The soluble fraction which coats the mesoscopic units of the insoluble fraction to give the textureless surface of the as-spun fiber may shrink during carbonization to follow the shapes of the insoluble microdomains. The unique shape of the insoluble fraction may reflect the channel structure observed in polymer blends, since microdomains in the fiber reflect the shape and size of those in the pitch after the spinning. The shape, size and arrangement of microdomains in the fiber may be one of the key factors in finding ways to control the mechanical properties of mesophase pitch-based carbon fibers. (C) 1997 Elsevier Science Ltd.