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A k de environmental chemistry pdf plus#
Kevlar XP – lighter weight resin and KM2 plus fiber combination.Kevlar AP – 15% higher tensile strength than K-29.Kevlar K149 – highest tenacity for ballistic, armor, and aerospace applications.Kevlar K129 – higher tenacity for ballistic applications.Kevlar K119 – higher-elongation, flexible and more fatigue resistant.Kevlar K100 – colored version of Kevlar.Kevlar K49 – high modulus used in cable and rope products.Kevlar K-29 – in industrial applications, such as cables, asbestos replacement, tires, and brake linings.
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Kevlar 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. As this process had been patented by Akzo (see above) in the production of Twaron, a patent war ensued. Hexamethylphosphoramide (HMPA) was the solvent initially used for the polymerization, but for safety reasons, DuPont replaced it by a solution of N-methyl-pyrrolidone and calcium chloride. The result has liquid-crystalline behavior, and mechanical drawing orients the polymer chains in the fiber's direction. Kevlar is synthesized in solution from the monomers 1,4- phenylene-di amine ( para-phenylenediamine) and terephthaloyl chloride in a condensation reaction yielding hydrochloric acid as a byproduct. The reaction of 1,4-phenylene-diamine ( para-phenylenediamine) with terephthaloyl chloride yielding Kevlar
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However, Kwolek was not very involved in developing the applications of Kevlar. Her supervisor and her laboratory director understood the significance of her discovery and a new field of polymer chemistry quickly arose. However, Kwolek persuaded the technician, Charles Smullen, who ran the spinneret, to test her solution, and was amazed to find that the fiber did not break, unlike nylon. The solution was "cloudy, opalescent upon being stirred, and of low viscosity" and usually was thrown away. The polymers she had been working with at the time, poly-p-phenylene-terephthalate and polybenzamide, formed liquid crystals while in solution, something unique to those polymers at the time. In 1964, her group began searching for a new lightweight strong fiber to use for light, but strong, tires. Poly-paraphenylene terephthalamide (K29) – branded Kevlar – was invented by the American chemist Stephanie Kwolek while working for DuPont, in anticipation of a gasoline shortage. Inventor of Kevlar, Stephanie Kwolek, an American chemist