Properties,end applications,comparison of carbon fiber with other fibers, classification and processes involved in making of carbon fiber,

1. CARBON FIBER
PRODUCTION METHODS, PROPERTIES AND
COMPOSITE APPLICATIONS

2. INTRODUCTION
• Carbon fibres have been under continuous
development for the last 50 years.
• There has been a progression of feedstocks, starting
with rayon, proceeding to polyacrylonitrile (PAN), on
to isotropic and mesophase pitches, to hydrocarbon
gases, to ablated graphite and finally back to carbon
containing gases.

3. CHEMICAL STRUCTURE
• The word ‘graphite’ is much misused
in carbon fibre literature. The word
refers to a very specific structure, in
which adjacent aromatic sheets
overlap with one carbon atom at the
centre of each hexagon
• The high-performance carbon fibres
are made up of large aromatic sheets,
these are randomly oriented to each
other, and are described as
‘turbostratic’
Irregular stacking of aromatic sheets; turbostratic carbon
Regular stacking of aromatic sheets in graphite
Some allotropes of carbon: a) diamond; b) graphite; c) lonsdaleite; d–f)
fullerenes (C60, C540, C70); g) amorphous carbon; h) carbon nanotube.

4. MECHANICAL PROPERTIES OF
SELECTED CARBON FIBRES

5. METHODS OF PRODUCING
CARBON FIBER
• All commercial C.F.’s from 3 processes:
• Rayon (cellulose)
• Polyacrylonitrile (PAN)
• Accounts for 90% of commercial C.F.’s
• 93-95% acrylonitrile units
• Pitch Based
• Isotropic pitch
• Mesophase pitch
• New method for C.F.
• Vapor Growth (high performance application)

6. PAN PROCESS
• Polyacrylonitrile (PAN) fibres are made by a variety of methods.
• The polymer is made by free-radical polymerisation, either in
solution or in a solvent–water suspension.
• The polymer is then dried and redissolved in another solvent for
spinning, either by wet-spinning or dry-spinning.
• Wet spinning: the spin dope is forced through a spinneret into a
coagulating liquid and stretched
• Dry spinning: the dope is spun into a hot gas chamber, and
stretched

7. CHEMISTRY OF CARBON FIBER
PRODUCTION
The strength of fibers spun in this way
and subsequently heat treated was
found to improve by >80% over
conventionally spun fibres.
The mechanism is presumed to be
removal of small impurities which can
act as crack initiators.
This technology is believed to be critical
for production of high strength fibres
such
as Toray’s T800 and T1000.

8. PRODUCTION OF CARBON FIBER
FROM PAN
• Heating/Stretching
• Pre-carbonization
• Carbonization
• Surface Treatment

9. HEATING/STRETCHING
• Stretching (500-1300%)
• 220-270oC for 30min to 7hrs
• Temp./Time dependent on composition/diameter
of Precursor
• Chemical changes
• Cyclization of nitrile groups
• Dehydration of saturated C-C bonds
• Oxidation
• Generates CO2 and HCN
• Large furnace + Drive rollers
• Controlled tension essential for alignment
• PAN carbon content: 54%
The first critical step in making
carbon fibre from PAN fibre is
causing the pendant nitrile
groups to cyclise. This process
is thermally activated and is
highly exothermic.
The next step is to make the
fibre infusible: this is
accomplished by adding
oxygen atoms to the polymer,
again by heating
in air

10. CARBON FIBERS
PAN based Carbon Fiber
StabilizationProcess
 The stabilization process is highly exothermic, the
heatreleased has adverse effecton
final properties of fibers.
 The process should be modified in such away
thateitherthe heatreleased during
stabilization should be reduced or it should be
dissipatedproperly
 The heat of stabilization can be reduced by using
comonomers during PANsynthesis.

11. PRE-CARBONIZATION
• After diffusion (tens of minutes),
about 8% oxygen by weight has
been added, the fibre can be heated
above 600 °C without melting.
• At such temperatures, the processes
of de-nitrogenation and
dehydrogenation take place, and
above 1000 °C large aromatic sheets
start to form,

12. CARBONIZATION
• 1300oC – 2800OC
• The precursor is drawn into long strands or fibers and then heated to a very
high temperature with-out allowing it to come in contact with oxygen.
• Without oxygen, the fiber cannot burn. Instead, the high temperature causes
the atoms in the fiber to vibrate violently until most of the non-carbon atoms
are expelled.
• This process is called carbonization and leaves a fiber composed of long,
tightly inter-locked chains of carbon atoms with only a few non-carbon atom
remaining.
• As the non-carbon atoms are expelled, the remaining carbon atoms form
tightly bonded carbon crystals that are aligned more or less parallel to the
long axis of the fiber.
• Final C content: 80% to >99%

13. CARBON FIBERS
PAN based Carbon Fiber
Graphitization Process
 This step involves heating thecarbonized fiber undertensionatabout
1200- 3000 °C in an inertatmosphere.
 This leads toan increase in the sizecrystals resulting inenhanced
mechanical properties.

14. SURFACE TREATMENT
• After carbonizing, the fibers have a surface that does not bond
well with the epoxies and other materials used in composite
materials.
• To give the fibers better bonding properties, their surface is
slightly oxidized.
• The addition of oxygen atoms to the surface provides better
chemical bonding properties and also etches and roughens the
surface for better mechanical bonding properties.
• Oxidation can be achieved by immersing the fibers in various
gases such as air, carbon dioxide, or ozone; or in various liquids
such as sodium hypochlorite or nitric acid.

15. PAN PRECURSOR FIBER PROCESS

16. C.F.’S FROM PAN PRECURSOR
FIBERS

17. CARBON FIBERS
Type Modulus
Ultra-high-modulus(UHM) >450 Gpa
High-modulus (HM) 350-450 Gpa
Intermediate-modulus (IM) 200-350 Gpa
Low modulus and high-tensile(HT) modulus < 100 GPa, tensile strength>
3.0 GPa
Super high-tensile(SHT) tensile strength > 4.5GPa
PAN based Carbon Fiber
 PAN based carbon fibers areclassified according to the tensilepropertiesand
the heat treatment temperatureas follows.
Classification based onProperties

18. CARBON FIBERS
PAN based Carbon Fiber
Classification based on Final Heat TreatmentTemperature
Type Name Treatment
Temperature
Modulus/Strength
Type-I High heat treated(HHT) above 2000 °C High-modulus
Type-II Intermediate heat treated (IHT) above 1500 °C High-strength
Type-III Low heattreated 1000 °C Low modulusand
low strength
materials

19. CARBON FIBERS
Carbonization temperature
& properties
High strength High modulus Ultra high modulus
Carbonization temperature (°C) 1200-1400 1800-2500 2800-3000
Carbon % in the fiber 92-96 99 99
Filament diameter (μm) 5.5- 8.0 5.4-7.0 8.4
Density (g/cm3) 1.75-1.80 1.78-1.81 1.96
Tensile strength (MPa) 3105-4555 2415-2555 1865
Tensile modulus (GPa) 228-262 359-393 (483-690), 577
Elongation at break (%) 1.3-1.8 0.6-0.7 0.38
PAN based Carbon Fiber
Classification and Typical Properties of PAN based CarbonFibers

20. ISOTROPIC PITCHES
• These pitches are prepared from high-boiling fractions
of petroleum feedstocks, usually heavy slurry oils
produced in catalytic cracking of crude oil.
• A typical commercial pitch is Ashland Aerocarb 70,
which has a softening temperature of 208 °C and a
viscosity of 1Pa s at 278°C.
• Pitches may be subjected to additional treatments to
reduce low-molecular weight components selectively

21. CENTRIFUGAL SPINNING
• Centrifugal spinning is practised
commercially in the production of glass
fibres. It was adapted for carbon fibre
production by the Kureha Company in
Japan in the 1970s.
• In this process, molten pitch is forced
through small holes in a rotating bowl.
The pitch stream is attenuated into a
fibre by centrifugal forces, and is
directed against a cutter by a stream of
air

22. MELT BLOWING
• Melt blowing was originally developed for the
manufacture of fibres from polypropylene, but was
adapted for pitch by Ashland Oil Co in the 1970s.
• It is a very high productivity process, giving production
rates per spinneret hole of the order of 10 times
conventional melt spinning.
• In this process, a molten stream of pitch is extruded into
a high velocity stream of forwarding gas, which rapidly
attenuates the fibre

23. MESOPHASE PITCH PRECURSORS
• Pitch is a viscoelastic material that is composed of aromatic hydrocarbons.
Pitch is produced via the distillation of carbon-based materials, such as plants,
crude oil, and coal
• Pitch-based fibres satisfy the needs of niche markets, and show promise of
reducing prices to make mass markets possible
• Same general process as PAN
• Low tensile strength of precursor fibers
• Melt-spin is used
• Do not require stretching process to maintain preferred alignment
• General purpose fibres are prepared by two different spinning methods,
centrifugal spinning and melt blowing.

24. PAN AND PITCH PROCESSING

25. CARBON FIBER PROPERTIES
COMPARISON

26. FINAL CARBON FIBERS
• Woven, Braided, or Wound
• Unidirectional lay-ups
• Multi-directional weaves
• Strength limiting factors
• Purity of precursor
• Precursor void content
• Temperature
• Tension

27. C.F.’S FROM DIFFERING
PROCESSES

28. CARBON VS. STEEL
Material Tensile
Strength
(GPa)
Tensile
Modulus
(GPa)
Density
(g/ccm)
Specific
Strength
(GPa)
Standard Grade
Carbon Fiber
3.5 230.0 1.75 2.00
High Tensile Steel 1.3 210.0 7.87 0.17

29. CARBON FIBER MODULUS
http://www.carbonfiber.gr.jp/english/index.html

30. CARBON-CARBON COMPOSITES
• Carbon substrate in Carbonaceous Matrix
• Same element does not simplify composite behavior
• each constituent has a wide
range of forms
• Carbon fibers continuous and woven
• Disadvantages
• High fabrication cost
• Poor oxidation resistance
• Poor inter-laminar properties

31. FABRICATION OF C-C
COMPOSITES
• Liquid phase impregnation (LPI)
• Hot isostatic pressure impregnation carbonization
(HIPIC)
• Hot pressing
• Chemical Vapor Infiltration (CVI)

32. APPLICATIONS OF C-C
COMPOSITES
• Aircraft Brakes
• Heat Pipes
• Reentry vehicles
• Rocket motor nozzles
• Hip replacements
• Biomedical implants
• Tools and dies
• Engine pistons
• Electronic heat sinks
• Automotive and motorcycle bodies
• Bicycles

33. FURTHER READING
• Buckley, John D. and Dan. D. Edie, eds. Carbon-
Carbon Materials and Composites Noyes
Publications: Park Ridge, NJ 1993
• Chung, Deborah. Carbon Fiber Composites.
Butterworth-Heinemann, Boston 1994
• Japan Carbon Fiber Manufacturer’s Association
http://www.carbonfiber.gr.jp/english/index.html