Kevlar is the registered
trademarkfor a light, strong para-aramid synthetic fiber, related to other aramids such as Nomexand Technora.
DuPontin 1965 by Stephanie Kwolekand Roberto Berendt,cite web
title=What is Kevlar
accessdate=2007-03-28] it was first commercially used in the early 1970s as a replacement for steel in racing tires. Typically it is spun into ropes or
fabricsheets that can be used as such or as an ingredient in composite materialcomponents.
Currently, Kevlar has many applications, ranging from bicycle
tiresand racing sails to body armor because of its high strength-to-weight ratio—famously: "...5 times stronger than steel on an equal weight basis..."
A similar fiber called
Twaronwith roughly the same chemical structure was introduced by Akzoin 1978, and now manufactured by Teijin.
In the 1970s, one of its most significant achievements in the development of body armor was the invention of DuPont's Kevlar ballistic fabric. The fabric was originally intended to replace steel belting in vehicle
tires. ...The development of Kevlar body armor by the National Institute of Justicewas a four-phase effort that took place over several years. The first phase involved testing Kevlar fabric to determine whether it could stop a lead bullet. The second phase involved determining the number of layers of material necessary to prevent penetration by bullets of varying speeds and calibers and developinga prototype vest that would protect officers against the most common threats: .38 Specialand .22 Long Riflebullets. By 1973, researchers at the Army's Edgewood Arsenal responsible for the bullet proof vest design had developed a garment made of seven layers of Kevlar fabric for use in field trials. It was determined that the penetration resistance of Kevlar was degraded when wet. The bullet resistant properties of the fabric also diminished upon exposure to ultraviolet light, including sunlight.
Dry cleaning agents and
bleachalso had a negative effect on the antiballistic properties of the fabric, as did repeated washing. To protect against these problems, the vest was designed with waterproofing, as well as with fabric coverings to prevent exposure to sunlight and other degrading agents.
When Kevlar is spun, the resulting fiber has great
tensile strength(ca. 3 000 MPa), and a relative densityof 1.44. When used as a woven material, it is suitable for mooring lines and other underwater application objects....
There are three grades of Kevlar: (i) Kevlar, (ii) Kevlar 29, and (iii) Kevlar 49. Typically, Kevlar is used as reinforcement in tires and rubber mechanical goods. Kevlar 29's industrial applications are as cables, in
asbestosreplacement, brake linings, and body armor. Kevlar 49 has the greatest tensile strength of all the aramids, and is used in plastic reinforcement for boat hulls, airplanes, and bicycles. The ultraviolet lightcomponent of sunlight degrades and decomposes Kevlar, a problem known as UV degradation, and so it is rarely used outdoors without protection against sunlight.
synthesisedin solution from the monomers 1,4- phenylene-di amine("para"-phenylenediamine) and terephthaloyl chloridein a condensation reaction yielding hydrochloric acidas a byproduct. The result has liquid-crystalline behaviour, and mechanical drawing orients the polymer chains in the fiber's direction. Hexamethylphosphoramide(HMPA) was the polymerization solvent first used, but toxicology tests demonstrated it provoked tumors in the noses of rats, so DuPont replaced it by a "N"-methyl-pyrrolidone and calcium chloride as the solvent. As this process was patented by Akzo (see above) in the production of Twaron, a patent war ensued....
Kevlar (poly paraphenylene terephthalamide) production is expensive because of the difficulties arising from using concentrated
sulfuric acid, needed to keep the water-insoluble polymer in solution during its synthesis and spinning.
Fibers of Kevlar consist of long molecular chains produced from PPTA (poly-paraphenylene terephthalamide). There are many inter-chain bonds making the material extremely strong. Kevlar derives part of its high strength from inter-molecular
hydrogen bondsformed between the carbonyl groups and protons on neighboring polymer chains and the partial pi stacking of the benzenoid aromatic stacking interactions between stacked strands. These interactions have a greater influence on Kevlar than the van der Waals interactions and chain length that typically influence the properties of other synthetic polymers and fibers such as Dyneema. The presence of salts and certain other impurities, especially calcium, could interfere with the strand interactions and caution is used to avoid inclusion in its production. Kevlar's structure consists of relatively rigid molecules which tend to form mostly planar sheet-like structures rather like silkprotein.
For a polymer, Kevlar has very good resistance to high temperatures, and maintains its strength and resilience down to cryogenic temperatures (-196°C); indeed, it is slightly stronger at low temperatures.
At higher temperatures the tensile strength is immediately reduced by about 10-20%, and after some hours the strength progressively reduces further. For example at 160°C about 10% reduction in strength occurs after 500 hours. At 260°C 50% reduction occurs after 70 hours. [ [http://www2.dupont.com/Kevlar/en_US/assets/downloads/KEVLAR_Technical_Guide.pdf KEVLAR Technical Guide] ]
At 450°C Kevlar sublimates.
Kevlar is well-known as a component of some
bulletproof vests and bulletproof facemasks. The PASGT helmet and vest used by USmilitary forces since the early 1980s both have Kevlar as a key component, as do their replacements. Other military uses include bulletproof facemasks used by sentries. Civilian applications include Kevlar reinforced clothing for motorcycle riders to protect against abrasion injuries and also Emergency Service's protection gear if it involves high heat (e.g., tackling a fire), and Kevlar body armor such as vests for police officers, security, and SWAT.
Rope and cable
The fiber is used in woven rope and in cable, where the fibers are kept parallel within a
polyethylenesleeve. Known as "Parafil", the cables have been used in small suspension bridges such as the bridge at Aberfeldyin Scotland. They have also been used to stabilise cracking concrete cooling towers by circumferential application followed by tensioning to close the cracks.
It is used as an inner lining for some
bicycle tires to prevent punctures, and due to its excellent heat resistance, is used for fire poiwicks. It is used for motorcycle safety clothing, especially in the areas featuring padding such as shoulders and elbows. It was also used as speed control patches for certain Soap Shoesmodels.In Kyudoor Japanese archery, it may be used as an alternative to more expensive hempfor bow strings. It is one of the main materials used for paraglidersuspension lines.
It has also been found to have useful acoustic properties for loudspeaker cones, specifically for bass and midrange drive units [ [http://www.audioholics.com/reviews/speakers/bookshelf/bw-cm1/cm1-design-and-construction Audio speaker use] ] .
Kevlar was used by scientists at
Georgia Institute of Technologyas a base textile for an experiment in electricity-producing clothing. This was done by weaving zinc oxide nanowires into the fabric. If successful, the new fabric would generate about 80 milliwatts per square meter. [ [http://www.sciam.com/podcast/episode.cfm?id=3E0E600F-F7B2-4F1F-DA377027B8FDC443&sc=rss Scientific American: Fabric Produces Electricity As You Wear It] ]
Kevlar is sometimes used as a material in high tension drum heads usually used on marching snare drums. It supposedly gives a higher pitched sound and allows for an extremely high amount of tension. There is usually some sort of resin poured onto the kevlar to prevent the air inside the drum from escaping through the head. This is one of the primary types of marching snare drum heads.
Remo's falam slam patch is made with kevlar and is stuck to bass drum heads where the beater strikes to strengthen the head so it doesn't wear down as quickly.
Kevlar is used in the woodwind reeds of Fibracell. The material of these reeds is a composite of aerospace materials designed to duplicate the way nature constructs cane reed. Very stiff but sound absorbing Kevlar fibers are suspended in a lightweight resin formulation.
Fiber Optic Cable
Kevlar is widely used as a protective outer sheath for
fiber optic cable, as its strength protects the cable from damage and kinking.
A retractable roof of over 60,000 square feet (5,575 square metres) of Kevlar was a key part of the design of Montreal's Olympic stadium for the
1976 Summer Olympics. It was spectacularly unsuccessful, as it was completed ten years late and replaced just ten years later in May 1998 after a series of problems. [Structurae|id=s0000742|title=Roof of the Montreal Olympic Stadium] [ [http://www.andrewclem.com/Baseball/OlympicStadium.html Clem's Baseball ~ Olympic Stadium ] ]
The chopped fiber has been used as a replacement for
asbestosin brake pads. Dust produced from asbestos brakes is toxic, while aramids are a benign substitute.
Expansion joints and hoses
Kevlar can be found as a reinforcing layer in
rubber bellows expansion jointsand rubber hoses, for use in high temperature applications, and for its high strength. It is also found as a braid layer used on the outside of hose assemblies, to add protection against sharp objects.
Aramid fibers are widely used for reinforcing
composite materials, often in combination with carbon fiberand glass fiber. The matrix for high performance composites is usually epoxy resin. Typical applications include monocoquebodies for F1 racing cars, helicopterrotor blades, tennis, table tennis, badmintonand squash rackets, kayaks, cricketbats, and field hockey, ice hockeyand lacrossesticks. [Kadolph, Sara J. Anna L. Langford. Textiles, Ninth Edition. Pearson Education, Inc 2002. Upper Saddle River, NJ] [cite journal
author = D. Tanner, J. A. Fitzgerald, B. R. Phillips
year = 1989
title = The Kevlar Story - an Advanced Materials Case Study
Angewandte Chemie International Edition in English
volume = 28
issue = 5
pages = 649–654
doi = 10.1002/anie.198906491 ] [cite journal
author = E. E. Magat
year = 1980
title = Fibers from Extended Chain Aromatic Polyamides, New Fibers and Their Composites
journal = Philosophical Transactions of the Royal Society of London Series A
volume = 294
issue = 1411
pages = 463–472
url = http://links.jstor.org/sici?sici=0080-4614%2819800121%29294%3A1411%3C463%3AFFECAP%3E2.0.CO%3B2-P ] [Ronald V. Joven. Manufacturing Kevlar panels by thermo-curing process. Los Andes University, 2007. Bogotá, Colombia.]
DuPont(Company that invented and manufactures Kevlar)
Interceptor body armor
Personnel Armor System for Ground Troops
Ultra high molecular weight polyethylene
* [http://www.kevlar.com/ Kevlar Home Page]
* [http://www.pslc.ws/macrog/aramid.htm Aramids]
* [http://www.designdictionary.co.uk/en/kevlar.htm Kevlar - Design Dictionary. Illustrated article about Kevlar]
* [http://www.matweb.com/search/SpecificMaterial.asp?bassnum=PDUKEV29 Matweb material properties of Kevlar]
* [http://www.lbl.gov/MicroWorlds/Kevlar/index.html Kevlar]
* [http://web.umr.edu/~wlf/Synthesis/kevlar.html Synthesis of Kevlar]
* [http://www.ngcc.org.uk/DesktopModules/ViewDocument.aspx?DocumentID=1003 Aberfeldy Footbridge over the River Tay]
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Look at other dictionaries:
kevlar — [ kɛvlar ] n. m. • 1972; nom déposé ♦ Technol. Résine aramide utilisée sous forme de fibre dans certains matériaux composites. Gilet pare balles, voile en kevlar. ● Kevlar nom masculin (nom déposé) Fibre aramide, caractérisée par son grand module … Encyclopédie Universelle
Kevlar — Kevlar® [ kef ], Handelsname für eine Aramidfaser (Aramide) mit hoher Zugfestigkeit und Biegsamkeit; dient als Verstärkermaterial bei der Reifenherstellung sowie in der Luft und Raumfahrtindustrie … Universal-Lexikon
kevlar — KEVLÁR s.n. Material compozit foarte uşor, foarte rezistent la şoc şi la coroziune, neinflamabil, care nu permite propagarea fisurilor şi amortizează vibraţiile, folosit în aeronautică. – Denumire comercială. Trimis de catalin caba, 15.07.2004.… … Dicționar Român
Kevlar — registered trademark (DuPont) for a synthetic fiber developed there c.1965 … Etymology dictionary
kevlar — kèvlār m <G kevlára> DEFINICIJA umjetno sintetičko vlakno izuzetne čvrstoće; upotrebljava se u zrakoplovima, svemirskim brodovima ETIMOLOGIJA tvorničko ime proizvoda© … Hrvatski jezični portal
Kevlar — [kev′lär΄] [arbitrary coinage] trademark for an aramid fiber used in making bulletproof vests, boat hulls, airplane parts, etc … English World dictionary
Kevlar® — /kevˈlär/ noun A lightweight synthetic fibre of exceptionally high strength and heat resistance, used in aerospace, firefighting equipment, etc … Useful english dictionary
Kevlar — Estructura química Kevlar. Resaltado: unidad monomérica. Punteado: Puentes de hidrógeno. El Kevlar® o poliparafenileno tereftalamida es una poliamida sintetizada por primera vez en 1965 por la química Stephanie Kwolek, quien trabajaba para DuPont … Wikipedia Español
Kevlar — Le poly(p phénylènetéréphtalamide) (PPD T) est un polymère thermoplastique constitué de noyaux aromatiques séparés par des groupes amide. Il appartient à la famille des fibres d aramides. Le poly para phénylène téréphtalamide a été découvert et… … Wikipédia en Français
KEVLAR® — The brand name of a DuPont™ synthetic fabric that is clothlike in feel and is used in cold outdoor activities (e.g., by bicyclists and motorcyclists). In racing, the material of choice for NASCAR Winston Cup cars. KEVLAR® was chosen by NASCAR… … Dictionary of automotive terms