KEVLAR is a brand name of an aramid fiber material product developed by DuPont of the United States. The original name of the material is "poly-terephthaloyl-p-phenylenediamine". The repeating unit of the chemical formula is- [-CO-C6H4-CONH -C6H4-NH-]- The amide group attached to the benzene ring is a para structure (the meta structure is another product named Nomex, commonly known as fire-resistant fiber).
In the 1960s, DuPont of the United States developed a new type of aramid fiber composite material-aramid 1414. This aramid composite material was officially commercialized in 1972 and the product was registered as Kevlar. The models are divided into K29, K49, K49AP and so on.
This new material has low density, high strength, good toughness, high temperature resistance, and is easy to process and form, its strength is five times that of steel of the same quality, but its density is only one fifth of that of steel (Kevlar density is 1.44 per cubic centimeter). The density of steel is 7.859 grams per cubic centimeter) and it is valued by people. Because the materials of Kevlar brand products are tough and wear-resistant, rigid and soft, they have the special ability of being invisible. It is called "armored guard" in the military.
1. Permanent heat resistance and flame retardancy, the limit oxygen index Loi is greater than 28.
2. Permanent antistatic.
3. Permanent resistance to acid and alkali and organic solvents.
4. High strength, high wear resistance, high tear resistance.
5. In case of fire, no molten droplets are generated and no toxic gas is generated.
6. When the cloth is burned, the cloth becomes thicker, which enhances the sealing performance and does not crack.
In the 21st century, the composite armor of "Kevlar" laminated sheet with steel and aluminum plates has been widely used not only in tanks, armored vehicles, and body armor, but also in nuclear-powered aircraft carriers and guided missile destroyers. Both are greatly improved. The composite material of "Kevlar" and ceramics such as boron carbide is an ideal material for the helicopter cockpit and cockpit. According to tests, it has much better resistance to armor-piercing bullets than FRP and steel armor. In order to improve the survivability of battlefield personnel, people have paid more and more attention to the development of bulletproof jackets. "Kevlar" material is also ideal for making body armor. According to reports, the use of "Kevlar" materials instead of nylon and fiberglass, under the same conditions, its protective ability can be at least doubled, and has good flexibility and comfortable wearing. The body armor made of this material weighs only 2-3 kg and is easy to wear, so it has been adopted by police and soldiers in many countries.
In the 1980s, when China imported DuPont products, the U.S. government did not allow DuPont to export Kevlar brand products to China, and then gradually released restrictions on exports. The optical fiber used for transmission today also uses Kevlar to form a protective film. The Kevlar layer has good flexibility to protect the optical fiber from damage. The Kevlar layer is generally called a buffer layer or a coating layer, which is outside the optical fiber and inside the outer skin.