Kevlar is a high-performance synthetic fiber made from para-aramid polymers. It is exceptionally strong for its weight, with high tensile strength and modulus. Kevlar fibers are produced through a solution spinning process using concentrated sulfuric acid and result in highly oriented molecular chains arranged in liquid crystalline domains. The fiber has high strength, stiffness, and heat resistance and is used in applications like bulletproof vests, composites, ropes, and tires due to its unique properties. Aramid fibers like Kevlar and Twaron are resistant to chemicals but can be degraded by strong acids and bases.

1. Aramid: High
Performance Fibres
Mukesh Kumar Singh
Professor, UPTTI Kanpur
stronger, lighter, safer

2. Commodity Fibres
Volume driven
Price oriented
Large scale
production
Continuous line
production
Hiperformance Fibres
Technically driven
Specialty oriented
Small scale Production
Batch type production

3. high temperature resistant fibers
synthetic fiber with a continuous operating
temperature ranging from 3750 F to 6000 F

4. High PERFORMANCE FIBRE
• A fibre that is specially designed and
manufactured to give some specific
performance characteristics under some
specific ambient conditions
Example HM-HT Fibre
Kevlar, UHMWPE Fibre, PBO
Thermal resistant
Nomex, Kevlar, PBO, Carbon

5. History
Nomex -1960
Kevlar- 1971
Twaron (by Teijin ) 1980 by Ozawa &Matsuda
Last 20 years: structure and properties of
Aramid

6. Definition
United States Federal Trade Commission
1974
• Aramid ia a manufactured fiber in which
the fiber forming substance is a long-chain
synthetic polyamide in which at least 85%
of the amide (-CO-NH-) linkages are
attached directly between two aromatic
rings.
• p-phenylene terephthalarnide
(PTA), of which Kevlar fibres are made

7. Aramid manufacturing
• By reaction between amine and carboxylic acid
halide group to synthesize AB homopolymer
nNH2 Ar COCl NH2 Ar CO
n
nHCl
A B
• Similarly AABB homopolymer can also be
synthesized

8. Polymerization
Polycondensation
NH2
NH2
Poly-phenylene diamine (PPD)
ClCO
ClCO
Terephthaloyl chloride (TCL)
Amide
solvent)
NH
NH CO
CO 2HCl
p-phenylene terephtalamides (PPTA)

9. Process
Dissolve PPD in a mixture of hexamythylphosphoramide (HMPA)
and N-methylpurrolidone (NMP)
Cooling in ice/ecetone to -15°C in N2 atmosphere
Add TCL with rapid stirring: paste like gel
Stand overnight with gradual warming to room temp
Resultant mixture is agitated with water to wash solvent and HCL
Polymer is collected by filteration

10. History of Aramid
• Aromatic polyamides were first introduced
in 1960s, with a meta-aramid fiber
produced by DuPont under the tradename
Nomex.
• Meta-aramid is also produced
Teijin: Conex
Kermel France: Kermel

11. Production
• World capacity of para-aramid production
is estimated at about 41,000 tons/yr in
2002 and increases each year by 5-10%. In
2007 this means a total production
capacity of around 55,000 tons/yr.

12. Aramid Fibre Production
Polymer solvent for spinning PPTA is generally 100% (water free)
sulfuric acid (H2SO4)
• The aromatic polyamide solution processing temperature is of the
order of 80°C for the highly concentrated solution in 100%
sulphuric acid
• At this temperature, the solution state corresponds to a pneumatic
crystalline phase
• The degree of orientation of these polymer chains depends on
solution temperature and polymer concentration. The radial
crystalline orientation can only be brought about using the dry-jet
wet spinning process
• Kevlar fibres have a very high molecular orientation, which has an
almost directly proportional relationship to fibre modulus and is
highly dependent on drying conditions, temperature and tension

13. • Monomers’ are made up of fourteen
Carbon atoms, two Nitrogen atoms, two
Oxygen atoms and ten Hydrogen atoms.
• A single Kevlar polymer chain could
possibly have anywhere from one to five
million monomers bonded together.

14. Kevlar
• Kevlar is the trade name (registered by
DuPont Co.) of aramid (poly-para-phenylene
terephthalamide) fibers.
• Kevlar fibers were originally developed as a
replacement of steel in automotive tires
• Kevlar is high impact resistance and low
density fibre

16. Spinning
• Solution is prepared by using H2SO4 as
solvent (100% free from water)
• Solution is heated to 80C
• Solution solid content 10%

17. Liquid crystalline domains
Spinneret
Air gap Elongational stretch
Coagulation bath

19. Gel spinning

20. Liquid crystalline solution


21. Semi-crystalline polymer
like nylon 6
Kevlar

22. Atomic configuration
a trans-amide
the peptide bond
carbonyl
carbon
amide
nitrogen
In the trans amide, the
Hydrocarbon group are on
opposite side of peptide bond
In the cis amide, the hydrocarbon
group are on the same side
of peptide bond
O
C
N
H

23. Properties of Kevlar Fibre
• High tensile strength (five times stronger per weight
unite than steel)
• High modulus of elasticity
• Very low elongation up to breaking point
• Low weight
• High chemical inertness
• Very low coefficient of thermal expansion
• High Fracture Toughness (impact resistance)
• High cut resistance
• Textile processibility
• Flame resistance (burning starts at 427C

24. 0 5 10 15 20
1
2
3
4
Elongation (%)
Specific
stress
(N/tex)
Polyamide
Polyester
Steel
S-Glass
Aramid
Carbon-HS
HDPE

25. Moisture attraction by Kevlar
• X-ray data have shown that the water
molecules from moisture uptake do not
enter the unit cell of the crystal lattice.
• Hence, the amide-water molecular
interactions are likely to be confined to the
polymer chains on the surface.
• Secondly, the presence of microvoids on
the surface

26. Limitations of Kevlar Fibre
• Very low moisture regain
• Very difficult to cut
• Low compressive strength

27. Physical properties of materials
MATERIAL
Ultimate Strength
MPa
Density
g/cm3
Spectra fiber (UHMWPE) 2300-3500 .97
Kevlar (ARAMID) 2757 1.44
Carbon Fibre 4137 1.75
Carbon laminate 1600 1.5
E Glass Fibre 3450 2.57
E Glass laminate 1500 1.97
Polypropylene 19.7-80 .91
S Glass Fibre 4710 2.47
Spider Silk 1000 1.3
Steel alloy ASTM A36 400 7.8
Epoxy 12-30 1.23
Nylon 75 1.15

28. Modulus of materials
Material
Young's Modulus
GPa
PTFE (Teflon) 0.5
Rubber (small strain) 0.01–0.1
PTFE (Teflon) 0.5
Low density polyethylene 0.2
UHMWPE (such as Dyneena or Spectra) .7
Polypropylene 1.5-2
Nylon 2–4
Pine wood (along grain) 8.963
Glass-reinforced plastic (70/30 by weight
fibre/matrix, unidirectional, along grain)
40–45
Carbon fiber (depends on direction and type) 300-400
Carbon fiber reinforced plastic (70/30
fibre/matrix, unidirectional, along grain)
181
Steel 200
Single-walled carbon nanotube 1,000+

29. Molecular requirement of Aramids
Improvement Polymeric composition
Thermal resistance Wholly aromatic polyamide, absence of
unstable linkage (urethane, urea, alkylene etc.)
Solubility Copolymer with dissymmetrical units inclusion
of –O-, -CO-, -SO2- etc., amides rather than
esters
Drawing potential High molecular weight
Enhanced chain flexibility by incorporating -O-,
-CO-, -SO2-, etc
Dimensional
stability
Rigid molecular chain, crystallinity

30. Chemical properties of Kevlar
Aramid Fibers are Chemically quite
Resistant
• Aramids are not sensitive to organic solvents or oil.
• Kevlar, Twaron and other Aramids are sensitive to strong acids, bases, and
certain oxidizers, like chlorine bleach* (sodium hypochlorite).
• Exposure to these cause degradation of the fiber.
• Regular chlorine bleach (e.g. Clorox®) cannot be used with Kevlar®, oxygen
bleaches such as sodium perborate (e.g. OxiClean®) can be used without
damaging the Aramid fiber.
• Hydrogen Peroxide cannot be used to whiten Aramid though.
• This is important for anyone cleaning boat ropes or sails containing Kevlar.
• Polyester (Dacron) is not particularly sensitive to bleach but Kevlar's
strength will be destroyed! Nylon is also attacked by bleach
• Most organic solvents (oil) have little effect on the material, and most salt
solutions (sodium chloride) have no effect on Kevlar fiber. However, strong
acids and bases (hydrochloric acid and sodium hydroxide) at high
concentrations or elevated temperatures are able to attack Kevlar fiber.

31. Types of Kevlar fibre
• Kevlar 29 – high strength (3600 MPa), low density
(1.44 g/cc3), used for bullet-proof vests, composite
armor reinforcement, helmets, ropes, cables,
asbestos replacing parts
• Kevlar 49 – high modulus (131 GPa), high strength
(3800 MPa), low density (1.440 g/cm³) used in
aerospace, automotive and marine applications
• Kevlar 149 – ultra high modulus (186 GPa), high
strength (3400 MPa), low density (1.470 g/cm³)
highly crystalline, used as reinforcing dispersed
phase for composite aircraft components.

32. a trans-amide a cis-amide

33. O
C N
H
O
C N
H
In Nomex the aromatic group are linked into the
Molecular chain through 1 and 3 positions
(i.e meta-linkage)
O
C N
H
O
C N
H
In Kevlar the aromatic group are linked into the
Molecular chain through 1 and 4 positions
(i.e para-linkage)
n

34. C
N
O
H
C
N
O
H
C
N
O
H
C
N
O
H
C
O
All trans polyamide stretches fully to form a
wonderful Aramid fibre, Kevlar

35. Fibre axis

36. Crystalline region
Amorphous region
Cross-linking

37. Applications of Kevlar
• Kevlar may protect carbon fibers and improve their
properties: hybrid fabric (Kevlar + Carbon fibers)
combines very high tensile strength with high impact
and abrasion resistance
•
• The most popular matrix materials for manufacturing
Kevlar (aramid) Fiber Reinforced Polymers are
Thermosets such as Epoxies (EP), Vinylester and
Phenolics (PF)
• Kevlar Fiber Reinforced Polymers are manufactured by
open mold processes, closed mold processes and
Pultrusion method

38. Aramid Brands
Nomex
Aramid fibre reinforced for sealing friction

39. Conveyor belts
Technora Sulfron
Aramid fibre: Kevlar

40. Aramid Brands
Aramid /PVC: Clad for optical fibre
Aramid fibre honeycomb
Aramid fibre braided sleeve “Sharx”

41. Fabrics for aircraft Aramid for shipbuilding Aramid fire blanket
Aramid fire retardant
clothing
Aramid: cut resistant gloves

42. Aramid: seat cover fabric
Aramid: aircraft tyres Aramid: brake
linings
Aramid: mooring
ropes

43. Aramid: clutch
facings
Aramid: vehicle cover Aramid: hoses for
Off-shore