Carbon Fiber Production from Pitch

The process under analysis comprises three major sections: (1) Pitch treatment and spinning; (2) Stabilization, carbonization and graphitization; and (3) Surface treatment and sizing.

Pitch treatment and spinning. The first step in the production of pitch-based carbon fiber consists in a pitch treatment, in which the petroleum pitch is converted into a liquid crystalline phase called mesophase pitch, with adequate spinnability. The treatment involves heating the pitch at 350-450°C using a mixture of oxygen and nitrogen for sparging. The mesophase pitch is cooled down and solidified, and then melt spun into pitch fibers. The mesophase pitch spinning is performed by termed melt extrusion.

Stabilization, carbonization and graphitization. The thermoplastic pitch fiber previously obtained is oxidized into infusible thermosetting fibers, by means of gas-phase oxidation, at 250 - 400°C. This stabilization aims to prevent softening and resulting deformation of the pitch fibers upon heating downstream. After stabilization, the pitch fibers are carbonized in a multi-zone furnace, under an inert atmosphere, in successive heating zones with temperatures increasing ranging from 700 to 2,000°C. The carbonization’s goal is to remove elements other than carbon from the fibers, and grows graphite crystals (graphitization). The carbonized fibers are then heated to higher temperatures (2,500 - 3,000°C), in order to increase carbon fiber’s tensile modulus of elasticity.

Surface treatment and sizing. The carbon fibers are submitted to anodic oxidation (electrolytic bath), so as to roughen filaments surface and introduce functional groups into the fiber surface (improving interfacial fiber/matrix bonding). The carbon fiber is then coated with a solution of resin, to protect it in downstream operations and keep filaments adhered together in individual tows. Finally, the carbon fiber is wound onto bobbins and stored.