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 as an asbestossubstitute. The name is a shortened form of " aromatic polyamide". They are fibers in which the chain molecules are highly oriented along the fiber axis, so the strength of the chemical bondcan be exploited.
Aromatic polyamides were first introduced in commercial applications in the early
1960s, with a meta-aramid fiber produced by DuPontunder the tradename Nomex. 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 for asbestos. Meta-aramid is also produced in the Netherlands and Japan by Teijinunder the tradename Teijinconex, in China by Yantai under the tradename New Starand a variant of meta-aramid in France by Kermel under the tradename Kermel.
Based on earlier research by
Monsantoand Bayer, a fiber - para-aramid - with much higher tenacity and elastic moduluswas 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 Kwolekin 1961 while working at DuPont, and that company was the first to introduce a "para-aramid" called Kevlarin 1973. A similar fiber called Twaronwith roughly the same chemical structure was introduced by Akzo in 1978. Due to earlier patents on the production process, Akzo and DuPont had a patent war 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.
Federal Trade Commissiondefinition 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.
World capacity of para-aramid production is estimated at about 41,000 tons/yr in 2002 and increases each year by 5-10% [http://books.nap.edu/openbook.php?record_id=11268&page=34 High-Performance Structural Fibers for Advanced Polymer Matrix Composites (2005)] ] . In 2007 this means a total production capacity of around 55,000 tons/yr.
Aramids are generally prepared by the reaction between an amine group and a carboxylic acid halide group. Simple AB homopolymers may look like::"n"NH2-Ar-COCl → -(NH-Ar-CO)n- + "n"HCl
The most well-known aramids (Nomex, Kevlar, Twaron and New Star) are AABB polymers. Nomex, New Star and Teijinconex contain predominantly the meta-linkage and are poly-"metaphenylene isophtalamide"s (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
ionic component ( 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 dissolving the polymer was known. The use of this system led to a patent war between Akzo and DuPont.
After production of the polymer, the aramid fiber is produced by spinning the solved polymer to a
solidfiber from a liquidchemical blend. Polymer solvent for spinning PPTA is generally 100% (water free) sulfuric acid(H2SO4).
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 Teijinand introduced in 1976. The manufacturing process of Technora reacts PPD and 3,4'-diaminodiphenylether (3,4'-ODA) with terephtaloyl chloride (TCl). [cite journal |author= Ozawa S| title= | journal= Polym. J. Japan | year= 1987| volume= 19 | issue= | pages= 199 | url= ] This relatively simple process uses only one amide solvent and therefore spinning can be done directly after the polymer production.
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.
* good resistance to abrasion
* good resistance to organic solvents
melting point, degradation starts from 500°C
* low flammability
* good fabric integrity at elevated
* sensitive to acids and salts
* sensitive to
* prone to static build-up unless finished
* para-aramid fibers such as Kevlar and Twaron, provide outstanding strength-to-weight properties
* high tenacity
* low creep
* low elongation at break (~3.5%)
* difficult to dye - usually solution dyed cite journal |author= Kadolph, Sara J. Anna L. Langford.| title= Textiles| journal= Pearson Education, Inc. Upper Saddle River, NJ| year= 2002| volume= | issue= | pages= | url= ]
Major industrial uses
* heat protective clothing and
* body armor cite journal |author= | title= High-performance fiber makers respond to demand from military and security users| journal= Battle Tested| year= | volume= | issue= | pages= | url= http://pubs.acs.org/email/cen/html080205142022.html ] , competing with PE based fiber products such as
asbestosreplacement (e.g. braking pads)
* hot air
tires, newly as Sulfron (sulfur modified Twaron)
ropes and cables
* wicks for
* optical fiber cable systems
sail cloth(not necessarily racing boatsails)
* wind instrument reeds, such as the Fibracell brand
* speaker woofers
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)
Ultra high molecular weight polyethylene
Notes and references
* [http://www.compositesworld.com/hpc/issues/2004/September/548 Aramid production increases]
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Look at other dictionaries:
aramid — ☆ aramid [ar′ə mid΄ ] n. [ar(omatic) (poly)amid(e)] any of a group of very strong, lightweight, synthetic fibers used in making radial tires, bulletproof vests, etc … English World dictionary
Aramid — Aramide ist die Bezeichnung für aromatische Polyamide. Diese polymeren Kunststoffe besitzen strukturelle Ähnlichkeit mit Proteinen. Inhaltsverzeichnis 1 Übersicht 2 Para Aramid Herstellungsprozess 3 Anwendungen … Deutsch Wikipedia
aramid — ˈarəmə̇d noun ( s) Etymology: aromatic polyamide : any of a group of lightweight but very strong heat resistant synthetic aromatic polyamide materials that are fashioned into fibers and used especially in textiles ; also : a fiber manufactured… … Useful english dictionary
aramid — noun Etymology: aromatic polyamide Date: 1972 any of a group of lightweight but very strong heat resistant synthetic aromatic polyamide materials that are fashioned into fibers, filaments, or sheets and used especially in textiles and plastics … New Collegiate Dictionary
aramid — /ar euh mid/, n. Chem. any of a class of synthetic aromatic long chain polyamides capable of extrusion into fibers having resistance to high temperatures and great strength. [prob. AR(OMATIC) + amid, resp. of AMIDE] * * * … Universalium
aramid — noun Any of a class of strong, heat resistant synthetic fibres, used in aerospace and military applications … Wiktionary
Aramid — Ar|a|mid [↑ Ar (2) u. ↑ Amid], das; s, e: temperaturbeständige, für technische Textilien brauchbare ↑ Polyamide aus aromatischen Diaminen u. Dicarbonsäuren … Universal-Lexikon
Aramid — A manufactured fiber in which the fiber forming substance is any long chain synthetic polyamide in which at least 85% of the amide linkage is attached directly to two aromatic rings … Forensic science glossary
aramid — n. strong fire resistant synthetic fiber derived from polymer chain; bullet proof protective armor fabric and an asbestos substitute … English contemporary dictionary
aramid — ar·a·mid … English syllables