2. • Although a strict definition of high-
performance fibers does not yet exist, the
term generally denotes fibers that give higher
values in use in a range of applications.
• It commonly refers to fibers with some unique
characteristics that differentiate them from
commodity fibers such as nylon, polyester, and
acrylic fibers.
• Synonyms are specialty fibers and high-
functional fibers.
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3. • Commodity fibers are typically used in a highly competitive
price environment which translates into large scale high
volume programs in order to compensate for the (often) low
margins.
• Conversely, high performance fibers are driven by special
technical functions that require specific physical properties
unique to these fibers.
• Some of the most prominent of these properties are:
• tensile properties
• operating temperature
• chemical resistance
• Each fiber has a unique combination of the above properties
which allows it to fill a niche in the high performance fiber
spectrum.
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4. Commodity vs. High Performance Fibres
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5. Basic properties- an overview
High-performance fibers can be classified
broadly into three categories according to their
applications:
1. High-Modulus and High-Strength fibers (HM-
HS);
2. Heat-resistant fibers, including flame-
retardant ones;
3. Chemically resistant
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6. • Tensile strength is often the determining
factor in choosing a fiber for a specific need. A
major advantage of high strength fibers over
steel, for example, is the superior strength-to-
weight ratio that such fibers can offer.
• Para-aramid fiber (e.g. Kevlar) offers 6-8 times
higher tensile strength and over twice the
modulus of steel, at only one-fifth the weight.
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7. High Tenacity- High Modulus fibres
• Two methods have proved effective in preparing
high modulus, high tenacity (HM-HT) polymer
fibres:
(a) perfecting the drawing technique of precursor
fibres to attain draw ratios far above ten, as in the
polyethylene Dyneema® and Spectra®.
(b) manipulating rigid rod-like molecules into fibres
that are already very highly oriented in the as-
spun state, as in PPTA fibres (Kevlar ®).
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9. • Temperature resistance often plays an integral role in
the selection of a fiber. Heat degrades fibers at
different rates depending on the fiber type,
atmospheric conditions and time of exposure. The
key property for high temperature resistant fibers is
their continuous operating temperature.
• Fibers can survive exposure to temperatures above
their continuous operating temperatures, but the
high heat will begin to degrade the fiber. This
degradation has the effect of reducing the tensile
properties of the fiber and ultimately destroying its
integrity.
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10. • A common mistake is to confuse temperature
resistance with flame retardant ability. Flame
retardant ability is generally measured by the
Limiting Oxygen Index.
• LOI is the amount of oxygen needed in the
atmosphere to support combustion. Fibers
with a Limiting Oxygen Index (LOI) greater
than 25 are said to be flame retardant, that is
there must be at least 25% oxygen present in
order for them to burn.
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11. • Just as heat can degrade a fiber, chemical
exposure, such as contact with acids or alkalis,
can have a similar effect. Some fibers, such as
PTFE (i.e. DuPont’s Teflon), are extremely
resistant to chemicals.
• Others lose strength and integrity quite
rapidly depending on the type of chemical and
the degree of concentration of the chemical or
compound.
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13. Aramids
• Aromatic polyamides first appeared in the
patent literature in the late 1950s and early
1960s, when a number of compositions were
disclosed by researchers at DuPont.
• These polymers were made by the reaction of
aromatic diamines with aromatic diacid
chlorides in an amide solvent. Over 100
examples of aromatic polymers and
copolymers described in patents.
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Para-phenylenediamine PPD Terephthaloyl chloride
14. • Sixty years later, after the expenditure of much
time and money, the number of commercially
important aromatic polyamide polymers has
been reduced to three:
• two homopolymers, poly(m-phenylene
isophthalamide) (MPDI- commercial name
Nomex) and poly(p-phenylene terephthalamide)
(PPTA- commercial name Kevlar),
• and one copolymer, copoly(p-phenylene/3,4-
diphenyl ether terephthalamide) (ODA/PPTA-
commercial name Technora).
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15. • Simple AB homopolymers may be synthesised
according to the scheme below:
A is the amine group
B is the carboxylic group
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16. • AABB aromatic polyamides are prepared from
various aromatic diamines and diacids or
diacid chlorides. The early AABB polymers
contained predominantly meta-orientated
linkages.
• The earliest representative of this class is
m-phenyleneisophthalamide, which was
commercialised by DuPont in 1967 as Nomex®
aramid fibre.
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17. • Kevlar® aramid fibre was launched by DuPont
in 1971; the corresponding chemical formula
is given below:
Kevlar® fibres are poly (p-phenylene terephthalamide)
(PPTA), the simplest form of AABB para-orientated
polyamide.
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18. • Because fibers from these aromatic polyamides
have properties that differ significantly from the
class of fibers known as polyamides, the United
States Federal Trade Commission adopted the
following definition to describe aromatic
polyamide-based fibres : ‘a manufactured fibre in
which the fibre-forming substance is a long chain
synthetic polyamide in which at least 85% of the
amide (—CO—NH—) linkages are attached
directly to two aromatic rings’.
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19. • The important properties of this class of polymers
include thermal and chemical stability and the
potential for high strength and modulus.
• Aliphatic polyamides melt at temperatures below
300◦C, whereas most aromatic polyamides do not
melt or melt above 350◦C.
• Aramids also exhibit greater chemical resistance
and low flammability. These properties derive
from the aromatic character of the polymer
backbone that can provide high chain rigidity.
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20. • Aromatic polyamide fibers can have very high strength
and modulus, and these properties persist at elevated
temperatures.
• Because of their low density, aromatic polyamides have
higher specific strength and modulus than steel or
glass.
• In recent years, design engineers have been able to
utilize these unique properties to create products
which protect personnel from fire, bullets, and cuts,
reduce the weight of aircraft and automobiles, and
hold oil drilling platforms in place.
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21. 15/10/2012 21
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Caution: Capacity dates back to 1974.
22. Meta-oriented aramid fibre
• The polymer is prepared by low-temperature
solution polymerization or interfacial
polymerization according to the following
reaction:
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23. Solution polymerisation
• In this technique, the aromatic diamine is dissolved in an amide
solvent (N,N-dimethylacetamide DMA or N-Methyl-2-pyrrolidone
NMP ) and a stoichiometric quantity of the aromatic diacid chloride
is added to the diamine solution while stirring vigorously.
• Since the reaction between an acid chloride and an amine is highly
exothermic, the heat generated can significantly increase the
temperature of the polymerizing solution. The extent of the
temperature rise will depend on the diamine concentration and the
degree of cooling.
• High temperature can lead to side reactions that produce
unreactive ends, thus the reaction must be carried out at low
temperature (0°C).
• The resulting polymer remains in solution.
NMP
CH3
CH3
CH3
DMA
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24. Interfacial polymerisation
• In interfacial polycondensation, the two fast-reacting intermediates
are dissolved in a pair of immiscible liquids, one of which is
preferably water.
• In this technique the isophthaloyl chloride – ICL- is dissolved in a
solvent with limited water solubility (i.e. tetrahydrofuran) and then
added to an aqueous solution of the m-phenylene diamine –MPD-
with vigorous stirring.
• The aqueous solution contains a base that neutralizes the HCl that
is generated.
• Polymer formation takes place at or near the liquid–liquid interface
when the two solutions are brought in contact or stirred together.
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THF
25. • Interfacial polymerization gives higher
molecular weight than the solution
polymerization technique and therefore,
improved fiber properties. This is the process
that Teijin uses to produce the polymer for
their MPDI product, Teijinconex®.
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26. • In both the solution and the interfacial
methods, the following factors are important
for the preparation of a high molecular mass
polymer:
• Use of high-purity monomers
• Stoichiometric balance of the two parent
monomers.
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27. Commercial Polymerisation process of m-aramid
• U.S. Pat. 3287324 (Nov. 22,
1966), W. Sweeny (to E. I. du
Pont de Nemours & Co.,
• Inc.)
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Solution polymerization
28. • The diamine noted in the figure is actually a 9%
solution of m-phenylene diamine (MPD) in DMA in
the patent example, and the diacid chloride is molten
isophthaloyl chloride (ICL)- melting temperature
45°C.
• The MPD solution is cooled to −15◦C, while the
molten ICL is supplied at 60◦C. The heat of reaction
brings the temperature of the effluent from the
mixer to 74◦C.
• This effluent is then cooled before Ca(OH)2 is added
to neutralize the HCl formed in the polymerization
reaction. Finally, the polymer solution is blended,
deaerated, and filtered before being pumped to
storage for use in spinning.
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29. Interfacial polymerization
• H. Fujie,
Nikkakyo
Geppo
40, 8
(1987)
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30. Spinning of MPDI
• Most of the aromatic polyamides have high
melting points that prevent the type of melt
processing common to aliphatic polyamides,
polyolefins, and other polymers.
• Thus, most applications are based on forms of
the polymer that can be prepared from solutions
of the polymers. These would include fiber, films,
and pulp.
• Techniques for processing polymer solutions are
well known and include wet spinning and dry
spinning of fibers.
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31. Wet spinning of m-aramid
• H. Fujie,
Nikkakyo
Geppo
40, 8
(1987)
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32. • The process involves dissolving the dry, salt-
free polymer in an organic solvent at low
temperature and then heating the dispersion
to near 100◦C to form a clear solution.
• This solution is wet spun into an aqueous
solution containing a high concentration of an
inorganic salt.
• The coagulated fiber is washed, and then
drawn and post-treated.
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33. • The dry spinning of MPDI from a DMF solution
into an air column maintained at 225◦C has also
been described - U.S. Pat. 3063966 (Nov. 13,
1962), S. L. Kwolek, P. W. Morgan, and W. R.
Sorenson (to E. I. du Pont de Nemours & Co., Inc.)
• After the fibers thus formed are drawn 4.75× and
the remaining solvent and salt removed by
extraction in hot water, they exhibit a tenacity of
0.6 GPa and an elongation of 30%.
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34. Post-Spinning Processes.
• Significant portion of the aramid fiber sold in
recent years has been in the form of staple, floc,
or pulp products that are produced by the fiber
manufacturer.
• Short fiber products are produced by cutting
continuous filament yarn into lengths that range
from about 1 mm to over 100 mm. Products in
the 1- to 6-mm length range are referred to as
floc, while the longer products are called staple.
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36. To convert strength and modulus values to
cN/dTex, multiply GPa by 10.0 and divide by
density (g/cm3)
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38. • Most of the mechanical properties of PMIA fibers
are about the same as those of commodity fibers.
• Fibers from wholly aromatic polymers are, in
general, highly sensitive to light exposure and
poorly dyeable.
• Intrinsic color is a defect of wholly aromatic
polymers, particularly when they are used for
textile materials. Only PMIA is colorless and can
thus be employed in dyed textiles.
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39. • Because PMIA exhibits high crystallinity and
strong intermolecular cohesion due to hydrogen
bonding, it has a high melting point and a high
decomposition temperature. Accordingly, PMIA
fibers have better thermal properties than
commodity fibers.
• At elevated temperature, PMIA fibers offer better
long-term retention of mechanical properties
than commodity fibers; they also have good
dimensional stability.
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40. The physical properties
of Teijinconex, a typical PMIA fiber
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41. • MPDI fibers have found a substantial market as the fiber used to produce
garments designed to protect workers from the hazard of fire. Obviously
this includes firefighters and race car drivers, but it is also becoming
standard clothing for workers who operate in chemical factories and other
places where the danger of flash fires is real.
• Key properties include its inherent flame resistance; abrasion, wear, and
chemical resistance which allows clothing to be washed and worn many
times; and high elongation and low modulus which allows the design of
comfortable clothing.
• Antistatic properties and other characteristics can be incorporated by use
of fiber blends.
• MPDI fabrics have also been used as a fire blocking material in aircraft seat
upholstery, where regulations require such functionality. They are finding
increasing use as a fire block in hospitals and as upholstery where fire
resistance is important.
• Another major market for MPDI fabrics is as bag filters for a number of
industries, such as power plants, cement factories, and steel factories,
where the ability to withstand hot, corrosive gases is critical.
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42. • Because of the excellent properties of PMIA fibers (e.g., high
thermal and chemical resistance, as well as radiation resistance),
their end uses are growing.
• Typical applications follow:
• Clothing. Meta-oriented aramid fibers do not ignite, flare, or melt
and stick to the skin. This makes them suitable for heat-resistant
clothing material in the following areas:
– 1.Heated furnaces: work uniforms, aluminized coats and pants, capes
and sleeves, gloves and mitts, leggings, and spats;
– 2. Emergency services: aluminized proximity suits, turnout coats and
jumpsuits, station uniforms, rescue uniforms, fire-fighting and aviation
garments, riot police uniforms, ranger uniforms, gloves, underwear,
leggings, and spats;
– 3. Fuel handling: work uniforms, rubber coats, gloves, socks,
underwear, etc.
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43. • Interior Fittings. Materials from PMIA are used in aircraft
interiors (for increased safety and enhanced flame
retardance).
• Industrial Materials. Uses here include filtration fabrics
(especially filter bags for hot stack gases); high-temperature
heat insulants (especially replacing asbestos); reinforcement
in fire hoses, V-belts, and conveyor belts; threads for high-
speed sewing; and cut-fiber reinforcement for rubber
composites.
• Electrical Insulation. High-temperature paper insulation for
electric motors, dynamos, transformers, and cables; braided
tubing for wire insulation; and dryer belts for papermaking
are among the uses of PMIA fibers.
• Miscellaneous Uses. Home ironing-board covers and kitchen
gloves are also made from PMIA fibers.
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44. • Most meta-oriented fibers are heat-resistant; they are
regarded as the first generation of high performance fibers.
Para-oriented fibers are considered the second generation
of high-performance fibers; they are composed mainly of
para-substituted residues, instead of the meta-substituted
residues of the first generation.
• Du Pont initiated the second generation with Kevlar, a
successor to the first-generation Nomex. Compared to
meta-oriented fibers, highly sophisticated polymerization
and production techniques are needed for the para-
oriented type to overcome difficulties caused by their rigid
molecular structure.
• Para-aramids, such as Kevlar, belong to the family of rigid-
rod polymers.
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