Processing of PAN-based Carbon Fibers

The production process of PAN-based carbon fibers can be divided into the following five steps i l 

Spinning. Since PAN decomposes before melting, it is necessary to make a solution with a solvent such as dimethyl formamide in order to be able to spin the material into a fiber. The spinning operation is either dry spinning, where the solvent evaporates in a spinning chamber (Fig. 8.3 a) or wet spinning, where the fiber is piaced in a coagulating bath solution 

Of the two fibers, only the wet-spun PAN is used as precursor. It contains a co-polymer, such as itaconic acid or other proprietary compounds, that apparently catalyzes the cyclization in air and helps the carbonization process. The dry-spun fiber is not as suitable and is not used. 

Stabilization and Oxidation. During the carbonization process, the elimination of the non-carbon elements (hydrogen and nitrogen) is usually accompanied by chain scission and relaxation of the fibrillar structure. This is detrimental to the formation of high-strength and high-modulus fibers, but can be avoided by a stabilization process prior to carbonization. 

This stabilization consists of slowly heating the stretched fiber to 200 -280°C in an oxygen atmosphere (usuaily air) under tension to maintain the orientation of the poiymer skeleton and stabilize the structure (Fig. 8.4). The addition of ammonia to oxygen increases the rate of stabilization.i i 

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