Kevlar
Created | Updated Aug 15, 2002
OK, imagine this. You come to class, and a kid sits down next to you and puts his bag on the desk. He gets some books out of his bag, then he pulls out a handgun and fires two rounds into your chest. You may suffer several broken ribs, or maybe you just get some bad bruising. Either way, you survive.
You have just been saved by DuPont's Kevlar® brand fibres. (Kevlar is a registered trademark of DuPont.) Kevlar is the trade name for poly-para-phenylene terephthalamide.
The research leading to Kevlar was undertaken mainly by Stephanie Louise Kwolek of DuPont. Stephanie joined DuPont in 1946 with a chemistry degree from Carnegie Institute of Technology. She was especially interested in polymer chemistry, and in 1964, she began experimenting with poly-p-phenylene-terephthalate (PPD-T) and polybenzamide (PBA). Stephanie was a creative researcher, and was intent on breaking new ground in the then male-dominated world of chemical engineering.
She became the first to prepare pure monomers that could be used to synthesise PBA. She found a solvent and identified the low-temperature polymerisation conditions, and this produced an unusual polymer solution that was fluid and cloudy, rather than clear and viscous. She found that the tough fibres which formed had startling properties. They were stronger and stiffer than any previously-known synthetic fibre. Eventually, from these findings, in 1971, Kevlar was born.
Poly-para-phenylene terephthalamide is a polymer. It's a polymer that contains recurring amide groups (R-CO-NH-R') as integral parts of the main polymer chain. It's made by a condensation reaction between monomers, in which the molecules are linked through the formation of the amide groups. The most important amide polymers are the nylons, an versatile class of material that is an indispensable fibre and plastic.
Specifically, Kevlar is an aramid, an aromatic nylon. It's prepared by condensation of a diamine and terephthalic acid, which is a carboxylic acid that contains a hexagonal benzene ring in its molecules. The close packing of the aromatic polymer chains, along with the orientation of the molecules produces an exceptionally strong fibre.
The polymer used for Kevlar is wet-spun from a solution of concentrated sulfuric acid. Because of the rodlike structure of the aramids, a "liquid-crystalline" solution is obtained. This orients the molecules to a specific direction even before they are spun. This leads to fibres of ultrahigh strength and stiffness. Kevlar is lighter than nylon, has a tensile strength about five times that of steel, and is more resistant to abrasion than other high-strength fibres. It has no melting point but decomposes at temperatures above 400 degrees Celsius.
Kevlar is a versatile material which is strong, tough, stiff, high-melting, and well suited for uses such as in radial tyres, heat- or flame-resistant fabrics, and bullet-proof clothing. Other commercial applications include cables, aircraft panels and boat hulls, sports equipment such as golf club shafts and lightweight bicycles, and as asbestos replacements in clutches and brakes. It is available in such forms as yarns, unwoven mats, and chopped fibres. Because of its toughness, it requires special cutting and machine techniques to be worked.
Kevlar is revolutionary, and its design innovations make it one of the toughest commercial materials in existence today. One day, it could save your life, one way or the other. Thank you.
You have just been saved by DuPont's Kevlar® brand fibres. (Kevlar is a registered trademark of DuPont.) Kevlar is the trade name for poly-para-phenylene terephthalamide.
The research leading to Kevlar was undertaken mainly by Stephanie Louise Kwolek of DuPont. Stephanie joined DuPont in 1946 with a chemistry degree from Carnegie Institute of Technology. She was especially interested in polymer chemistry, and in 1964, she began experimenting with poly-p-phenylene-terephthalate (PPD-T) and polybenzamide (PBA). Stephanie was a creative researcher, and was intent on breaking new ground in the then male-dominated world of chemical engineering.
She became the first to prepare pure monomers that could be used to synthesise PBA. She found a solvent and identified the low-temperature polymerisation conditions, and this produced an unusual polymer solution that was fluid and cloudy, rather than clear and viscous. She found that the tough fibres which formed had startling properties. They were stronger and stiffer than any previously-known synthetic fibre. Eventually, from these findings, in 1971, Kevlar was born.
Poly-para-phenylene terephthalamide is a polymer. It's a polymer that contains recurring amide groups (R-CO-NH-R') as integral parts of the main polymer chain. It's made by a condensation reaction between monomers, in which the molecules are linked through the formation of the amide groups. The most important amide polymers are the nylons, an versatile class of material that is an indispensable fibre and plastic.
Specifically, Kevlar is an aramid, an aromatic nylon. It's prepared by condensation of a diamine and terephthalic acid, which is a carboxylic acid that contains a hexagonal benzene ring in its molecules. The close packing of the aromatic polymer chains, along with the orientation of the molecules produces an exceptionally strong fibre.
The polymer used for Kevlar is wet-spun from a solution of concentrated sulfuric acid. Because of the rodlike structure of the aramids, a "liquid-crystalline" solution is obtained. This orients the molecules to a specific direction even before they are spun. This leads to fibres of ultrahigh strength and stiffness. Kevlar is lighter than nylon, has a tensile strength about five times that of steel, and is more resistant to abrasion than other high-strength fibres. It has no melting point but decomposes at temperatures above 400 degrees Celsius.
Kevlar is a versatile material which is strong, tough, stiff, high-melting, and well suited for uses such as in radial tyres, heat- or flame-resistant fabrics, and bullet-proof clothing. Other commercial applications include cables, aircraft panels and boat hulls, sports equipment such as golf club shafts and lightweight bicycles, and as asbestos replacements in clutches and brakes. It is available in such forms as yarns, unwoven mats, and chopped fibres. Because of its toughness, it requires special cutting and machine techniques to be worked.
Kevlar is revolutionary, and its design innovations make it one of the toughest commercial materials in existence today. One day, it could save your life, one way or the other. Thank you.
