2. Structurally, carbon fibers contain a blend of
amorphous carbon and graphitic carbon , high
tensile modulus results from the graphitic
form, in which the carbon atoms are arranged in
a crystallographic structure of parallel planes or
layers

3. Carbon fibers are manufactured from two types
of precursors (starting material) namely,
1) Textile precursor
Polyacrylonitrile (PAN)
2) Pitch

5. The molecular structure of PAN contains highly polar CN groups
that are randomly arranged on either side of chain,
The filaments are wet spun from a solution of PAN and stretched
at an elevated temperature during which the polymer chains
are aligned in the filament direction
The stretched elements are then heated in air at 200C – 300C for
a few hours ,during this stage the CN groups located on the
same side of the original chain combine to form a more stable
and rigid ladder structure and some of the CH2 groups are
oxidized
Next step PAN filaments are carbonized by heating them at a
controlled rate at 1000C -2000C in an inert atmosphere.

6. Tension is maintained on the filaments to prevent shrinking as well
as to improve molecular orientation
With the elimination of oxygen and nitrogen atoms ,the filaments
now contain mostly carbon atoms ,arranged in aromatic ring
patterns in parallel planes
Carbonized filaments are subsequently heat treated at or above
2000C their structure becomes more ordered and turns toward
graphitic form with increasing heat treatment temperature.

7. POLYACRYLONITRILE (PAN)
Wet spinning and stretching
PAN FILAMENT
Carbonization Heating and stretching at 1000C -2000C in an inert
atmosphere for 30 min
RELATIVELY LOW MODULUS (BETWEEN 200 & 300 GPa)
HIGH STRENGTH CARBON FIBERS
Heating above 2000C with or without stretching
Graphitization
WITH OUT STRETCHING :RELATIVELY HIGH MODULUS (BETWEEN
500 & 600 GPa )CARBON FIBERS WITH STRETCHING :CARBON
FIBERS WITH IMPROVED STRENGHT

8. Pitch is a byproduct of petroleum refining or coal cocking
Carbon atoms in pitch are arranged in low molecular weight
aromatic ring patterns ,
Heating to temperature above 300C polymerizes these molecule
into long , two dimensional sheet like structures .
The highly viscous state of pitch at this stage is referred to as
mesophase
Pitch filaments are produced by melt spinning mesophase
passing through a spinneret die , the mesophase pitch
molecules become aligned in the filament direction

9. The filaments are cooled to freeze the molecular orientation and
subsequently heated between 200C and 300C in an oxygen
containing atmosphere to stabilize them and make make
them infusible
Next step filaments are carbonized at temperatures around
2000C.
The rest of the process of transforming the structure to graphitic
form similar to that followed for PAN precrsors.

10. PITCH (ISOTROPIC)
Heat treatment at 300C-500C
MESOPHASE PITCH (ANISOTROPIC)
Melt spinning & drawing followed by heat stabilization at 200C-300
PITCH FILAMENT
Heating and stretching at 1000C -2000C in an inert atmosphere
Carbonization for 30 min
RELATIVELY LOW MODULUS (BETWEEN 200 & 300 GPa)
HIGH STRENGTH CARBON FIBERS
Graphitization Heating above 2000C with or without stretching
WITH OUT STRETCHING :RELATIVELY HIGH MODULUS (BETWEEN 500 &
600 GPa )CARBON FIBERS WITH STRETCHING :CARBON FIBERS WITH
IMPROVED STRENGHT