Introduction to Aramid

Introduction to Aramid 

1, a brief introduction to Kevlar, the original English name is KEVLAR, also translated as Kevlar. It is the brand name of an aramid fiber material product developed by DuPont in the United States. The original name of the material is "poly-p-phenylene terephthalamide". The repeating unit of the chemical formula is -[-CO-C6H4-CONH- C6H4-NH-]-The amine group attached to the benzene ring has a para-position structure (the meta-position structure is another product with the brand name Nomex, commonly known as fireproof fiber). In the 1960s, DuPont of the United States developed a 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. Models are divided into K29, K49, K49AP, etc. Due to the low density, high strength, good toughness, high temperature resistance, easy processing and forming of this new material, its strength is 5 times that of steel of the same quality, but its density is only one-fifth of steel (Kevlar density is 1.44 per cubic centimeter) Gram, the density of steel is 7.859 grams per cubic centimeter), and is valued by people. Because the materials of Kevlar brand products are tough and wear-resistant, rigid and flexible, they have the special ability of invulnerability. Known as "Armored Guards " in the military.

2, the emergence of anti-tank weapons has prompted people to improve the armor performance of tanks and armored vehicles. Generally, to improve the protective performance of tanks and armored vehicles, it is necessary to increase the thickness of the metal armor, which will inevitably affect its flexibility and maneuverability. The emergence of "Kevlar" materials has solved this problem, and the protective performance of tanks and armored vehicles has been improved to a new stage. Compared with FRP, under the same protection situation, the weight can be reduced by half when using "Kevlar" material, and the toughness of "Kevlar" laminated sheet is three times that of steel, and it can withstand repeated impacts. The combination of "Kevlar" sheet and steel armor is extremely powerful. If the "Gangzao Aramid Zaogang" type of composite armor is used, it can resist anti-tank missiles with a thickness of 700 mm and can also resist neutron bombs. At present, the composite armor of "Kevlar" laminated sheet and steel and aluminum plates has been widely used not only in tanks and armored vehicles, but also in nuclear-powered aircraft carriers and guided missile destroyers, greatly improving the protective performance and maneuverability of the above weapons. . The composite material of "Kevlar" and ceramics such as boron carbide is an ideal material for the cockpit and cockpit of a helicopter. According to tests, its ability to withstand armor-piercing bullets is much better than fiberglass and steel armor. In order to improve the survivability of battlefield personnel, people are paying more and more attention to the development of bullet avoidance vests. "Kevlar" material is also an ideal material for making bullet-proof vests. According to reports, the use of "Kevlar" material instead of nylon and glass fiber,

Under the same circumstances, its protective ability can be at least doubled, and it has good flexibility and comfortable wearing. The body armor made of this material weighs only 2 to 3 kilograms and is easy to wear and move, 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 import Kevlar brand products into China, and then slowly loosened import restrictions.     The fiber used for transmission nowadays also uses Kevlar to form a protective film. The Kevlar layer has good flexibility and protects the 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. 

3. Performance parameters  

Mechanical properties: strength: 3.6 GPa  elongation modulus: 131 GPa  elongation at break: 2.8 %  thermal performance:   long-term use temperature: 180℃  axial thermal expansion coefficient: -2 × 10 ^ (-6) / K  Thermal conductivity:  0.048 W(m·K)  Fourth, Kevlar fiber properties  1, permanent heat and flame resistance, limiting oxygen index Loi greater than 28. 2. Permanent antistatic property. 3. Permanent resistance to acid, alkali and organic solvents. 4. High strength, high wear resistance, high tear resistance. 5. No droplets will be produced in case of fire, and no toxic gas will be produced. 6. When the cloth surface is fired, the cloth surface will be thicker, which will enhance the sealing performance and prevent cracking.