Kevlar
poly(p-phenyleneterephtalamide)
C14N2O2H10


General-

Kevlar is a synthetic polymer. Its scientific name is poly-paraphenylene terephthalamide, which is created from the joining of para-phenylenediamine and terephthaloyl chloride.

Trademarked name of poly-para-phenylene terephthalamide, a nylonlike polymer first produced by Du Pont in 1971. Kevlar can be made into strong, tough, stiff, high-melting fibres, five times stronger per weight than steel.


Diagram 1. A Kevlar molecular arrangement
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Diagram 2. Showing the synthesis of the two monomers to create Kevlar.

800px-Kevlar_chemical_synthesis.png

Kevlar (poly paraphenylene terephthalamide) production is expensive because of the difficulties arising from using corrosive concentrated sulfuric acid, needed to keep the water-insoluble polymer in solution during its synthesis and spinning.

Cross linkage does occur within this polymer, which has a great affect on it. It makes it strong and durable.

Kevlar can be used for many different things. It is used in the production of bullet proof vests, tires, racing sails, rope and cables, audio equipment, brakes, and many other things. The fact that is can absorb vibrations, is very strong, and bullet proof makes it very useful.

History- Stephanie Kwolek’s research with high performance chemical compounds for the DuPont Company led to the development of a synthetic material called Kevlar which is five times stronger than the same weight of steel. Kevlar, patented by Kwolek in 1966, does not rust nor corrode and is extremely lightweight. Many police officers owe their lives to Stephanie Kwolek, for Kevlar is the material used in bullet proof vests. Other applications of the compound include underwater cables, brake linings, space vehicles, boats, parachutes, skis, and building materials.

Chemical properties-

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 bonds formed between the carbonyl groups and protons on neighboring polymer chains and the partial pi stacking of the benzenoid aromatic stacking between stacked strands. 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 usually forms into silk planes because of its rigid crystallize.

Thermal properties-

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. Kevlar sublimates at 450°C.


Usage-
Kevlar has many uses in our world. It can be used to make tires, racing sails for boats, and probably most popularly, for bullet proof vests. Each year the United States military purchases many bullet proof vests, all made from Kevlar, that are able to save the lives of soldiers. Bullets cannot penetrate the tightly woven material. Down to the molecular structure, the way the material is constructed makes it simply to strong for a bullet to affect it.


In the video above, a US soldier is shot by a bullet in the chest. The bullet proof vest he is wearing, made of Kevlar, is what saves his life.



Recyclable?-
Kevlar could be used again, but it typically is not recycled. Military bases are known for their large quantities of Kevlar scrap laying around, but most of the time the bases will simply throw this material away. Recycle collection areas across the US do take the scrap pieces, however. It is considered a material on the 'global recycling' list. Fashion designers have also grown to like the material, and environmental friendly companies take the scrap pieces and integrate them into some of their newer lines. Items such as belts and headbands can be seen being made out of Kevlar.


‘Kevlar Belt’
‘Kevlar Belt’

The belt above is made of recycled Kevlar scrap. These types of belts run about 50 bucks, just because Kevlar is expensive to make. As stated before, sulfuric acid is needed to make it.



Citations:
Dictionary. The American Heritage® Dictionary of the English Language, Fourth Edition Copyright © 2007, 2000 by Houghton Mifflin Company. Updated in 2007. Published by Houghton Mifflin Company. All rights reserved.

US Military Dictionary. The Oxford Essential Dictionary of the U.S. Military. Copyright © 2001, 2002 by Oxford University Press, Inc. All rights reserved.

Britannica Concise Encyclopedia. Britannica Concise Encyclopedia. © 2006 Encyclopædia Britannica, Inc. All rights reserved.

Wikipedia. This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Kevlar".