Anisotropy and mesophase formation towards carbon fibre production from coal tar and petroleum pitches: a review

Mesophase is a key issue to design carbon materials towards its properties and microstructures. The understanding of this intermediate phase has changed since it was first discovered. The removal of light molecules is necessary to produce mesophase, but the yield can be improved if other techniques, such as pressure and oxidation, can be used before they are carried out of the system, with nitrogen or vacuum. Anisotropic pitches can be produced throughout the traditional Brooks and Taylor mesophase spheres, rich in alpha-resins, or, avoiding them, with other techniques, such as solvent extraction or strong agitation, to generate, almost exclusively, beta-resins. Anisotropic pitches exhibiting almost 100% beta-resins have been melt-spun at lower temperatures, producing pitch carbon fibres of higher quality. Recent studies were able to explain why the behaviour of the pitches is so different, towards the pitch carbon fibre production, when their compositions, in terms of alpha-resins and beta-resins, change.