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Aramid Para-aramid structure Aramid fibers are a class of heat-resistant and strong synthetic fibers. They are used in aerospace and military applications, for ballistic rated body armor fabric and ballistic composites, in bicycle tires, and as an asbestos substitute. The name is a portmanteau of "aromatic polyamide". They are fibers in which the chain molecules are highly oriented along the fiber axis, so the strength of the chemical bond can be exploited. [edit]History Aromatic polyamides were first introduced in commercial applications in the early 1960s, with a meta-aramid fiber produced by DuPont as HT-1 and then under the trade name Nomex. [1] This fiber, which handles similarly to normal textile apparel fibers, is characterized by its excellent resistance to heat, as it neither melts nor ignites in normal levels of oxygen. It is used extensively in the production of protective apparel, air filtration, thermal and electrical insulation as well as a substitute forasbestos. Meta- aramid is also produced in the Netherlands and Japan by Teijin under the trade name Conex, [1] in China by Yantai under the trade name New Star, by SRO Group (China) under the trade name X-Fiper, and a variant of meta-aramid in France by Kermel under the trade name Kermel. Based on earlier research by Monsanto Company and Bayer, a fiber – para-aramid – with much higher tenacity and elastic modulus was also developed in the 1960s–1970s by DuPont and Akzo Nobel, both profiting from their knowledge of rayon,polyester and nylon processing. Much work was done by Stephanie Kwolek in 1961 while working at DuPont, and that company was the first to introduce a para-aramid called Kevlar in 1973. A similar fiber called Twaron with roughly the same chemical structure was introduced by Akzo in

Aramid Fiber

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Page 1: Aramid Fiber

Aramid

Para-aramid structure

Aramid fibers are a class of heat-resistant and strong synthetic fibers. They are used in

aerospace and military applications, for ballistic rated body armor fabric and ballistic

composites, in bicycle tires, and as an asbestos substitute. The name is

a portmanteau of "aromatic polyamide". They are fibers in which the chain molecules are

highly oriented along the fiber axis, so the strength of the chemical bond can be

exploited.

[edit]History

Aromatic polyamides were first introduced in commercial applications in the early 1960s,

with a meta-aramid fiber produced by DuPont as HT-1 and then under the trade

name Nomex.[1] This fiber, which handles similarly to normal textile apparel fibers, is

characterized by its excellent resistance to heat, as it neither melts nor ignites in normal

levels of oxygen. It is used extensively in the production of protective apparel, air

filtration, thermal and electrical insulation as well as a substitute forasbestos. Meta-

aramid is also produced in the Netherlands and Japan by Teijin under the trade name

Conex,[1] in China by Yantai under the trade name New Star, by SRO Group (China)

under the trade name X-Fiper, and a variant of meta-aramid in France by Kermel under

the trade name Kermel.

Based on earlier research by Monsanto Company and Bayer, a fiber – para-aramid –

with much higher tenacity and elastic modulus was also developed in the 1960s–1970s

by DuPont and Akzo Nobel, both profiting from their knowledge

of rayon,polyester and nylon processing.

Much work was done by Stephanie Kwolek in 1961 while working at DuPont, and that

company was the first to introduce a para-aramid called Kevlar in 1973. A similar fiber

called Twaron with roughly the same chemical structure was introduced by Akzo in

Page 2: Aramid Fiber

1978. Due to earlier patents on the production process, Akzo and DuPont engaged in a

patent dispute in the 1980s. Twaron is currently owned by the Teijin company (see

Production).

Para-aramids are used in many high-tech applications, such as aerospace and military

applications, for "bullet-proof" body armor fabric.

The Federal Trade Commission definition for aramid fiber is:

A manufactured fiber in which the fiber-forming substance is a long-chain synthetic

polyamide in which at least 85% of the amide linkages, (-CO-NH-) are attached directly

to two aromatic rings.

[edit]Health

During the 1990s, an in vitro test of Aramid fibers showed they exhibited "many of the

same effects on epithelial cells as did asbestos, including

increased radiolabeled nucleotide incorporation into DNA and induction of ODC

(ornithine decarboxylase) enzyme activity", raising the possibility

of carcinogenic implications.[2]

[edit]Production

World capacity of para-aramid production is estimated at about 41,000 tonnes/year in

2002 and increases each year by 5–10%.[3] In 2007 this means a total production

capacity of around 55,000 tonnes/year.

[edit]Polymer preparation

Aramids are generally prepared by the reaction between an amine group and a

carboxylic acid halide group. Simple AB homopolymers may look like:

nNH2-Ar-COCl → -(NH-Ar-CO)n- + nHCl

The most well-known aramids (Kevlar, Twaron, Nomex, New Star and Teijinconex)

are AABB polymers. Nomex, Teijinconex and New Star contain predominantly the

meta-linkage and are poly-metaphenylene isophtalamides (MPIA). Kevlar and

Twaron are both p-phenylene terephtalamides (PPTA), the simplest form of the

AABB para-polyaramide. PPTA is a product of p-phenylene diamine (PPD)

and terephtaloyl dichloride (TDC or TCl). Production of PPTA relies on a co-solvent

with an ioniccomponent (calcium chloride (CaCl2)) to occupy the hydrogen bonds of

the amide groups, and an organic component (N-methyl pyrrolidone (NMP)) to

dissolve the aromatic polymer. Prior to the invention of this process by Leo

Vollbracht, who worked at the Dutch chemical firm Akzo, no practical means of

Page 3: Aramid Fiber

dissolving the polymer was known. The use of this system led to an extended patent

dispute between Akzo and DuPont.

[edit]Spinning

After production of the polymer, the aramid fiber is produced by spinning the solved

polymer to a solid fiber from a liquid chemical blend. Polymer solvent for spinning

PPTA is generally 100% anhydrous sulfuric acid (H2SO4).

[edit]Appearances

� Fiber

� Chopped fiber

� Powder

� Pulp

[edit]Other types of aramids

Besides meta-aramids like Nomex, other variations belong to the aramid fiber range.

These are mainly of the copolyamide type, best known under the brand

name Technora, as developed by Teijin and introduced in 1976. The manufacturing

process of Technora reacts PPD and 3,4'-diaminodiphenylether (3,4'-ODA)

with terephtaloyl chloride (TCl).[4] This relatively simple process uses only one amide

solvent and therefore spinning can be done directly after the polymer production.

[edit]Aramid fiber characteristics

Aramids share a high degree of orientation with other fibers such as ultra high

molecular weight polyethylene, a characteristic which dominates their properties.

[edit]General

� good resistance to abrasion

� good resistance to organic solvents

� nonconductive

� no melting point, degradation starts from 500°C

� low flammability

� good fabric integrity at elevated temperatures

� sensitive to acids and salts

� sensitive to ultraviolet radiation

� prone to static build-up unless finished[5]

Page 4: Aramid Fiber

[edit]Para-aramids

� para-aramid fibers such as Kevlar and Twaron, provide outstanding strength-to-

weight properties

� high Young's modulus

� high tenacity

� low creep

� low elongation at break (~3.5%)

� difficult to dye – usually solution dyed [5]

[edit]Major industrial uses

� flame-resistant clothing

� heat protective clothing and helmets

� body armor,[6] competing with PE based fiber products such

as Dyneema and Spectra

� composite materials

� asbestos replacement (e.g. brake linings)

� hot air filtration fabrics

� tires, newly as Sulfron (sulfur modified Twaron)

� mechanical rubber goods reinforcement

� ropes and cables

� wicks for fire dancing

� optical fiber cable systems

� sail cloth (not necessarily racing boat sails)

� sporting goods

� drumheads

� wind instrument reeds, such as the Fibracell brand

� loudspeaker diaphragms

� boathull material

� fiber reinforced concrete

� reinforced thermoplastic pipes

� tennis strings (e.g. by Ashaway and Prince tennis companies)

� hockey sticks (normally in composition with such materials as wood and carbon)

� snowboards

� jet engine enclosures

Page 5: Aramid Fiber

[edit]See also

Para-aramid

� Kevlar

� Technora

� Twaron

� Heracron

Meta-aramid

� Nomex

Others

� Innegra S

� Nylon

� Textile

� Ultra high molecular weight polyethylene

� Vectran

[edit]Notes and references

1. ^ a b James A. Kent, ed. (2006). Handbook of Industrial Chemistry and Biotechnology. Springer.

p. 483. ISBN 0-387-27842-7.

2. ^ Marsh, J. P.; Mossman, B. T., Driscoll, K. E., Schins, R. F., Borm, P. J. A. (1 January

1994). "Effects of Aramid, a high Strength Synthetic Fiber, on Respiratory Cells in Vitro". Drug and

Chemical Toxicology (Informa Healthcare) 17 (2): 75–92.DOI:10.3109/01480549409014303.

Retrieved 15 August 2011.

3. ^ Committee on High-Performance Structural Fibers for Advanced Polymer Matrix Composites,

National Research Council (2005). High-Performance Structural Fibers for Advanced Polymer

Matrix Composites. The National Academies Press. p. 34. ISBN 0-309-09614-6.

4. ^ Ozawa S (1987). "A New Approach to High Modulus, High Tenacity Fibers". Polym. J. Japan 19:

199. DOI:10.1295/polymj.19.119.

5. ^ a b Kadolph, Sara J. Anna L. Langford (2002). Textiles.

6. ^ Reisch, Marc S (2005). "High-performance fiber makers respond to demand from military and

security users". Chemical and Engineering News 83 (31): 18–22. DOI:10.1021/cen-

v083n050.p018.