MECHANISM OF ANISOTROPY OCCURRENCE IN A PITCH PRECURSOR OF CARBON-FIBERS .3. HOT STAGE MICROSCOPY OF PITCH-B AND PITCH-C

Two anisotropic pitches, B and C, were heat-treated by using a hot-stage. The optical microscopy study shows that only pitch C is a true thermotropic material, whereas pitch B reversibility is hindered by the mixture with an isotropic phase, rich in Brooks and Taylor mesophase single spheres. In the latter, the development of irreversible Brooks and Taylor mosaics at least partly overcomes the sol-gel transformation. On the contrary, after softening, pitch C develops an overall anisotropy without germination growth. The mosaic-like domains are formed by disclinations annealing.