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Kevlar
Kevlar (para-aramid) is a strong, heat-resistant synthetic fiber, related to other aramids such as Nomex and Technora. Developed by Stephanie Kwolek at DuPont in 1965, the high-strength material was first used commercially in the early 1970s as a replacement for steel in racing tires. It is typically spun into ropes or fabric sheets that can be used as such, or as an ingredient in composite material components.
Kevlar has many applications, ranging from bicycle tires and racing sails to bulletproof vests, due to its high tensile strength-to-weight ratio; by this measure it is five times stronger than steel. It is also used to make modern marching drumheads that withstand high impact, and for mooring lines and other underwater applications.
A similar fiber, Twaron, with the same chemical structure was developed by Akzo in the 1970s. Commercial production started in 1986, and Twaron is manufactured by Teijin Aramid.
Poly-paraphenylene terephthalamide (K29) – branded Kevlar – was invented by the American chemist Stephanie Kwolek while working for DuPont, in anticipation of a gasoline shortage. In 1964, her group began searching for a new lightweight strong fiber to use for light, but strong, tires. The polymers she had been working with, poly-p-phenylene-terephthalate and polybenzamide, formed liquid crystals in solution, something unique to polymers at the time.
The solution was "cloudy, opalescent upon being stirred, and of low viscosity" and usually was thrown away. 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. Her supervisor and her laboratory director understood the significance of her discovery and a new field of polymer chemistry quickly arose. By 1971, modern Kevlar was introduced. However, Kwolek was not very involved in developing the applications of Kevlar.
In 1971, Lester Shubin, who was then the director of Science and Technology for the National Institute for Law Enforcement and Criminal Justice, suggested using Kevlar to replace nylon in bullet-proof vests. Prior to the introduction of Kevlar, flak jackets made of nylon had provided much more limited protection to users. Shubin later recalled how the idea developed: "We folded it over a couple of times and shot at it. The bullets didn't go through." In tests, they strapped Kevlar onto anesthetized goats and shot at their hearts, spinal cords, livers and lungs. They monitored the goats' heart rate and blood gas levels to check for lung injuries. After 24 hours, one goat died and the others had wounds that were not life threatening.[verification needed] Shubin received a $5 million grant to research the use of the fabric in bullet-proof vests.
Kevlar 149 was invented by Jacob Lahijani of Dupont in the 1980s.
Kevlar is synthesized in solution from the monomers 1,4-phenylene-diamine (para-phenylenediamine) and terephthaloyl chloride in a condensation reaction yielding hydrochloric acid as a byproduct. The result has liquid-crystalline behavior, and mechanical drawing orients the polymer chains in the fiber's direction. 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. As this process had been patented by Akzo (see above) in the production of Twaron, a patent war ensued.
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Kevlar
Kevlar (para-aramid) is a strong, heat-resistant synthetic fiber, related to other aramids such as Nomex and Technora. Developed by Stephanie Kwolek at DuPont in 1965, the high-strength material was first used commercially in the early 1970s as a replacement for steel in racing tires. It is typically spun into ropes or fabric sheets that can be used as such, or as an ingredient in composite material components.
Kevlar has many applications, ranging from bicycle tires and racing sails to bulletproof vests, due to its high tensile strength-to-weight ratio; by this measure it is five times stronger than steel. It is also used to make modern marching drumheads that withstand high impact, and for mooring lines and other underwater applications.
A similar fiber, Twaron, with the same chemical structure was developed by Akzo in the 1970s. Commercial production started in 1986, and Twaron is manufactured by Teijin Aramid.
Poly-paraphenylene terephthalamide (K29) – branded Kevlar – was invented by the American chemist Stephanie Kwolek while working for DuPont, in anticipation of a gasoline shortage. In 1964, her group began searching for a new lightweight strong fiber to use for light, but strong, tires. The polymers she had been working with, poly-p-phenylene-terephthalate and polybenzamide, formed liquid crystals in solution, something unique to polymers at the time.
The solution was "cloudy, opalescent upon being stirred, and of low viscosity" and usually was thrown away. 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. Her supervisor and her laboratory director understood the significance of her discovery and a new field of polymer chemistry quickly arose. By 1971, modern Kevlar was introduced. However, Kwolek was not very involved in developing the applications of Kevlar.
In 1971, Lester Shubin, who was then the director of Science and Technology for the National Institute for Law Enforcement and Criminal Justice, suggested using Kevlar to replace nylon in bullet-proof vests. Prior to the introduction of Kevlar, flak jackets made of nylon had provided much more limited protection to users. Shubin later recalled how the idea developed: "We folded it over a couple of times and shot at it. The bullets didn't go through." In tests, they strapped Kevlar onto anesthetized goats and shot at their hearts, spinal cords, livers and lungs. They monitored the goats' heart rate and blood gas levels to check for lung injuries. After 24 hours, one goat died and the others had wounds that were not life threatening.[verification needed] Shubin received a $5 million grant to research the use of the fabric in bullet-proof vests.
Kevlar 149 was invented by Jacob Lahijani of Dupont in the 1980s.
Kevlar is synthesized in solution from the monomers 1,4-phenylene-diamine (para-phenylenediamine) and terephthaloyl chloride in a condensation reaction yielding hydrochloric acid as a byproduct. The result has liquid-crystalline behavior, and mechanical drawing orients the polymer chains in the fiber's direction. 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. As this process had been patented by Akzo (see above) in the production of Twaron, a patent war ensued.
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