Kevlar

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Kevlar is the DuPont Company's brand name for a particular light but very strong aramid fibre. It was created in DuPont's labs in 1965 by Stephanie Kwolek and Herbert Blades, and was first used commercially in the early 1970s. It can be spun into ropes or sheets of fabric that can either be used as-is, or used in the construction of composite components. It is now used in a wide range of applications - from bicycles to body armor - due to its high strength-to-weight ratio, five times greater than that of steel.

1 Properties
2 Production
3 Chemical properties
4 See also
5 References
6 External links

[edit] Properties

When Kevlar is spun in the same way that a spider spins a web, the resulting fibre has tremendous strength, and is heat- and cut-resistant. The fibres do not rust or corrode, and their strength is unaffected by water. When woven together, they form a good material for mooring lines and other underwater objects. However, unless specially waterproofed, Kevlar's ability to stop bullets and other projectiles is degraded when wet.

There are three common grades of Kevlar: Kevlar, Kevlar 29, and Kevlar 49. Kevlar is typically used as reinforcements in tires and other rubber mechanical goods. Kevlar 29 is used in industrial applications such as cables, asbestos replacement, brake lines, body armour (knife or bullet resistant). Kevlar 49 is considered to have the greatest tensile strength of all the aramids, and is used in applications such as plastic reinforcement for boat hulls, aeroplanes, and bikes.

Kevlar's main weaknesses are that it decomposes under alkaline conditions or when exposed to chlorine or UV light. While it can have a great tensile strength, sometimes in excess of 4.0 GPa, like all fibers it tends to buckle in compression.

[edit] Production

Kevlar is synthesized from the monomers 1,4-phenyl-diamine (para-phenylenediamine) and terephthaloyl chloride. The result is a liquid-crystalline behaviour and mechanical drawing causing the polymer chains to orientate in the direction of the fibre.

Kevlar has a high price, in part, due to the difficulties arising from the use of concentrated sulfuric acid in its manufacture. These harsh conditions are needed to keep the highly insoluble polymer in solution during synthesis and spinning.

[edit] Chemical properties

Image:Kevlar.JPG Fibers of Kevlar consist of long molecular chains produced from poly-paraphenylene terephthalamide. There are many inter-chain bonds making the material extremely strong. Kevlar derives a portion of its improved strength from inter-molecular hydrogen bonds formed 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 van der Waals interactions and chain length that typically influence the properties of other synthetic polymers and fibers like 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 that have similarities to silk protein.Image:Kevlar26.JPG

[edit] See also

[edit] References

[1] Kadolph, Sara J. Anna L. Langford. Textiles, Ninth Edition. Pearson Education, Inc 2002. Upper Sadddle River, NJ

[edit] External links

Link page to external chemical sources.

E.I. du Pont de Nemours and Company (DuPont)

Annual Revenue: $27.3 billion USD (Image:Green Arrow Up.svg1.3% FY 2004) | Employees: 60,000 | Stock Symbol: NYSE: DD | Website: www.dupont.com

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