handbook of carbon, graphite, diamond and fullerenes

1.5 State of the Art
Carbon Fibers 173
Carbon fibers currently in production can be divided into three categories
based on the precursor materials: PAN (polyacrylonitrile), pitch, and
rayon, each with its own characteristics and special advantages.
• PAN-based fibers constitute the largest segment of the
industry. These fibers have high strength and modulus
and, as mentioned above, their cost is continually
decreasing.
• Pitch-based fibers can be divided in two groups: (a) the
isotropic pitch fibers, which have low mechanical
properties and relatively low cost, and (b)the mesophasepitch
fibers, which have very high modulus but are more
expensive. Pitch-based fibers are produced by a simple
process and their cost should eventually rival that of
glass fibers. Their potential is yet to be fully realized.
• Rayon-based fibers are not as strong as PAN-based
fibers. They are used in insulation and some carboncarbon
and ablative applications because of a good
match of properties with the carbonized matrix.
In addition to these, several other categories are being developed.
These include the vapor-phase (CVD) fibers which offer promise for the
development of whiskers, and fibers based on other precursors, such as
polyvinyl chlorides, Saran and polyphenylenebenzobisthiazoleJ 101 These
fibers are still experimental and have yet to reach the production stage.
2.0 CARBON FIBERS FROM PAN
2.1 PAN as Precursor
Polyacrylonitrile (PAN) is the most favored precursor at this time for
the production of high-performance fibers. PAN-based fibers are in the
medium price range (- $40/ kg in 1992). They have the highest tensile
strength of all carbon fibers and a wide range of moduli and are readily
available in a variety of tows.