Kevlar

I have chosen to write of Kevlar because it's a flexible, light material that's 5x stronger than steel. It is quite interesting as it is extremely resistant to damage yet yielding and able to form fibers. It is however, not impervious to damage, as I could punch through Kevlar sheets without any trouble.
-Master Seeya
History

           Poly-paraphenylene terephthalamide, also known as Kevlar, was invented by a Polish-American chemist named Stephanie Kwolek in 1964. Kwolek was working with a research group called DuPont to find a successor to popular products like nylon, when she accidentally discovered a polymer that was five times stronger than steel, yet very lightweight. Kwolek was trying to dissolve two polymers, poly-p-Phenylene-terephthalate and polybenzamide, and found the resultants to be liquid, while forming crystal structures in the solution. The solution itself was cloudy, with low viscosity, and was usually ignored. Kwolek, however, persuaded a technician, Charles Smullen, to test the solution for its properties. The results showed the compound to be much stronger than nylon, and this discovery triggered the rise of polymer chemistry. 

Structure and Properties
Kevlar polymers are comprised of several parts: a Benzene (C6H6) ring, Nitrogen, Oxygen and Hydrogen. Between each Benzene ring, a Nitrogen atom is bound with a Hydrogen and a Carbon, which is in turn bound to the  next Benzene ring and a double bonded Oxygen atom. The bonds between each "level" or chain of Kevlar monomers are Hydrogen Bonds, between the slightly positive Hydrogen atoms and slightly negative Oxygens, which form the staircase-like structure of the weave. The orientation of the Oxygen and Hydrogen switch with each Benzene ring, making a "lock and key" like fit with the chains above and below. This powerful set of bonds between each row and symmetrical sequence result in the powerful tensile strength that makes Kevlar such an important asset in protective technologies.

[-CO-C6H4-CO-NH-C6H4-NH-]

Production     

             Kevlar is created in solution by using two monomers, 1,4-phenylene-diamine (para-phenylenediamine) and terephthaloyl chloride, resulting in poly-paraphenylene terephthalamide (Kevlar) and a by-product of hydrochloric acid. Production of Kevlar is very expensive due to the level of concentration of sulfuric acid that must be used in the synthesis. This makes the process extremely dangerous, and safety precautions must be put in place and sophisticated storage units must be used and constantly replaced, as the sulfuric acid pre-reaction, and the hydrochloric acid post-reaction pose a threat to worker safety. The actual joining of Kevlar monomers together is simply a condensation reaction, with the Hydroxyl arm and Hydrogen arm of each adjacent monomer forming a water molecule and the two monomers joining to form a polymer.

Use

           The main use of Kevlar today is in military and protective applications. Kevlar is made into garments and fabric by winding threads into a weave. Utilizing the enormous tensile strength of Kevlar wound fibers, kinetic weapons can have their impact spread out and the damage lessened. Small arms and shrapnel can be rendered harmless and larger projectile rounds can have their wound-inflicting abilities lowered. Anti-knife gear is also produced using Kevlar, as the tensile strength is also useful against slashing injuries that would otherwise kill victims and would stop most knives from making an effect. Kevlar fibers are also extremely heat resistant, and much of the gear firefighters use contain Kevlar covers and sheets to protect from roaring flames. Today, there are three different grades of Kevlar with different properties and uses.

Kevlar 29 :  Mostly used in the for reinforcement in tires and rubber in machines.
(Density : 1.44g/cm^3)(Tensile Modulus: 83GPa)(Tensile Strength: 3.6GPa)(Tensile Elongation: 4.0%)
Kevlar 49 : Industrial applications such as cables, brake linings, and body armour.
(Density : 1.44g/cm^3)(Tensile Modulus: 131GPa)(Tensile Strength: 3.6-4.1GPa)(Tensile Elongation: 2.8%)
Kevlar 149 : Strongest of the 3 grades, typically used in plastic reinforcement in boat hulls, airplanes, bicycles.
(Density : 1.47g/cm^3)(Tensile Modulus: 186GPa)(Tensile Strength: 3.4GPa)(Tensile Elongation: 2.0%)

Sources
http://en.wikipedia.org/wiki/Kevlar
Yang, H. H. Kevlar Amarid Fiber. New York: John Wiley & Sons, 1993. Print.
Ikenson, Ben. Ingenious Inventions; How They Work and How They Came to Be. New York: Black Dog and Leventhal Publishers, 2004. 126-27. Print.
Kevlar Brand Aramid Fiber. N.p., n.d. Web. 26 May 2011. <http://www2.dupont.com/Kevlar/en_US/index.html>.
History of Kevlar. N.p., n.d. Web. 26 May 2011. <http://inventors.about.com/library/inventors/blkevlar.htm>.
Ball, Philip. Stories of the Invisible: A Guided Tour of Molecules. Oxford, New York: Oxford University Press, n.d. Print. 


Warning: Kevlar is not impervious to damage. The only thing that is invincible to damage is Captain America's Shield, which is currently used as a nuclear deterrent against America's enemies. As of now Captain America lives in Vancouver, British Columbia and teaches Chemistry to highschool students, training the next generation of peacekeepers and superheroes.  Ridiculous. Complete nonsense.