Aramid fiber and ordinary nylon belong to amide fiber, and the main chain of macromolecule contains amide bond. The difference is that the amide bond of nylon is connected with fatty group, while the amide bond of aramid is connected with benzene ring.
Types of aramid fiber
Aramid fiber mainly includes two kinds of full-aromatic polyamide fiber and heterocyclic aromatic polyamide fiber, which can be divided into ortho-aramid fiber, para-aramid fiber (PPTA) and meta-aramid fiber (PMTA). Among them, products realizing industrialization mainly include meta-aramid fiber and para-aramid fiber. The main difference between these two kinds of aramid fibers is that the connection position of the amide bond and the C atom on the benzene ring is different.
Paraaramid
Para-aramid fiber, namely PPTA, is a linear polymer with more than 85% of the amide bonds in the molecular chain directly bonded to the aromatic ring. It is the first fiber made from polymer liquid crystal spinning solution in the world, and it has created a new era of high-performance synthetic fiber.
Metaaramid
Meta-aramid fiber, namely polyisophthalyl-phenylenediamine (PMTA), is also called aramid 1313 in China. Meta-aramid fiber is the fastest growing crystal seed among organic high-temperature resistant fibers. The fiber molecule is composed of amide groups connected with meta-phenyl, and the molecular chain is linear serrated. Due to the strong hydrogen bonding between molecules, the fiber has excellent flame retardancy, thermal stability, radiation resistance and other properties.
Excellent properties of aramid fiber
It has excellent properties such as ultra-high strength, high modulus, high temperature resistance, acid and alkali resistance, light weight, insulation, anti-aging, long life cycle, stable chemical structure, no droplet during combustion, and no toxic gas.
The temperature resistance of para-aramid fiber is higher than that of meta-aramid fiber. The continuous use temperature range is - 196~204 ℃, and does not decompose and melt at 560 ℃. The most remarkable characteristics of para aramid fiber are super high strength, high modulus, high temperature resistance, acid and alkali resistance, light weight and other excellent properties. Its strength is more than 25 g/denier, which is 5~6 times of high-quality steel, 3 times of glass fiber, and 2 times of high-strength nylon industrial fiber; The modulus is 2-3 times of high-quality steel or glass fiber, and 10 times of high-strength nylon industrial fiber; Its toughness is twice that of steel wire, and its weight is only about 1/5 of that of steel wire. It has good insulation and anti-aging properties, and has a long life cycle.
Good mechanical properties of aramid fiber
Meta-aramid fiber is a flexible polymer, with higher breaking strength than ordinary polyester, cotton, nylon, etc., higher elongation, soft feel, good spinnability, and can be produced into short fibers and filaments of different sizes and lengths. It can be woven into fabrics and non-woven fabrics of different yarn counts in general textile machinery. After finishing, it can meet the requirements of protective clothing in different fields.
Excellent flame retardancy and heat resistance of aramid fiber
The limiting oxygen index (LOI) of meta-aramid fiber is greater than 28, so it will not continue to burn when it leaves the flame. The flame retardancy of meta-aramid fiber is determined by its chemical structure, so it is a permanent flame retardant fiber, which will not reduce or lose flame retardancy due to use time and washing times. Meta-aramid fiber has good thermal stability, can be used continuously at 205 ℃, and can still maintain high strength at higher temperature than 205 ℃. The meta-aramid fiber has a high decomposition temperature, and will not melt and melt under high temperature conditions. It will start carbonization when the temperature is greater than 370 ℃.
Stable chemical properties of aramid fiber
Meta-aramid fiber has excellent resistance to most chemical substances, most high concentrations of inorganic acids, and good alkali resistance at room temperature.
Radiation resistance of aramid fiber
Meta-aramid fiber has excellent radiation resistance. For example, in 1.2 × 10-2 w/in2 UV and 1.72 × 108rads γ The intensity of the radiation remains unchanged under long-term irradiation.
Durability of aramid fiber
The meta-aramid fiber has excellent friction resistance and chemical resistance. After 100 times of washing, it can be used in Nuesta ® The tear strength of the fabric processed by intermediate aramid fiber can still reach more than 85% of the original strength.
Aviation
Aramid fiber has low density, high strength, and good corrosion resistance. It can be used to manufacture the rocket engine shell of missiles, as well as the wide-band wave-transparent materials of aircraft, spacecraft fuselage, main wing, tail wing, and other structural components that can withstand the impact force. The multilayer honeycomb structure plate made of aramid prepreg impregnated with epoxy resin and bonded directly with honeycomb or foam structure has outstanding characteristics such as impact resistance and electromagnetic wave transmission. The super-mixed composite laminates formed by hot-pressing aramid fiber with thin aluminum plate and epoxy weftless cloth have extremely high specific modulus and specific strength, and the fatigue life is 100~1000 times that of aluminum alloy plate, which can be used in aircraft fuselage and other parts. The application of resin matrix reinforced composites made of aramid fiber in aircraft objects can greatly reduce the total weight of aircraft.
Military field
With the development of new military weapons such as chemical and nuclear weapons, there are more new requirements for the performance of military protective clothing: durability, portability, bulletproof, flame retardant, good environmental adaptability and camouflage. The bulletproof vest and helmet made of aramid fiber can replace the old nylon vest and tank helmet. Adding appropriate amount of aramid fiber into the bulletproof vest and helmet can not only make it small and light, but also improve its bulletproof efficiency by 40%. The soft bulletproof vest made of high-grade bulletproof aramid weftless cloth and high-performance polyethylene film has better bulletproof performance and heat resistance than UHMWPE fiber. Aramid fiber can also be compounded with other materials (such as metal, ceramics, etc.) to make various high-strength and impact-resistant explosion-proof tanks, bullet-proof shields, bullet-proof armor plates, etc. In addition, the aramid fiber fabric is bonded to the inner wall of the structure, which can effectively absorb the explosion wave and prevent the injury of shrapnel to human body.
Construction field
The ductility of aramid fiber fabric is better than that of carbon fiber. The material is light in weight and flexible in degree of freedom. It is an ideal reinforcement material for building engineering. Especially when reinforcing irregularly shaped components, due to its good flexibility, there is no need to chamfer when reinforcing edges and corners. The aramid fiber woven into reinforcement can be used as the cement reinforced skeleton of large buildings. In addition to the advantages of high strength and light weight, it can also be corrosion resistant and can also play a good role in shear resistance.
Transportation
Due to its low density, high and low temperature resistance and good adhesion to rubber, aramid fiber can be used as tire cord for automobile or aircraft. The tire made of aramid fiber has the advantages of light weight, thin tire, low rolling resistance, high bearing capacity, good wear resistance, cutting resistance and puncture resistance. In addition, the center of gravity of the ground pressure is small, the steering performance is good, the heat is easy to disperse, and it is not easy to change shape, which improves the ride comfort of the car, extends the service life of the tire, and can meet the requirements of modern supersonic aircraft for the use of the tire.
Electronic and electrical field
Aramid fiber has high strength and modulus, low dielectric coefficient, and good electromagnetic wave transmission. Under the same stiffness condition, the thickness of radar antenna protective cover made of aramid composite can be reduced by 30% compared with glass fiber composite, and the electromagnetic wave transmission can be increased by 10%; Laminated substrates made of aramid and epoxy, phenolic, polyimide and other resins have a high matching coefficient of linear expansion with ceramics, which will not cause cracking under the effect of thermal expansion and contraction. They can be used to make special printed circuit boards in surface mounting technology, which is conducive to miniaturization and lightweight of electronic equipment.
Utilizing aramid fiber's high strength, high temperature resistance and other characteristics, it can be used as a "tension component" in optical fiber, which can protect the small and fragile optical fiber from elongation and deformation under the action of tension, and will not affect the transmission of light. The composite product of aramid fiber and carbon fiber has good processability and semiconductivity, and can withstand high temperature. It is mostly used to make materials for reducing electric field in high voltage devices. Aramid paper has good insulation after being impregnated with insulating paint, and is used as insulating material for heat-resistant motors in combination with natural mica sheet.
Other fields
The aramid fiber molecule contains a large number of benzene rings, with good chemical stability, corrosion resistance, high specific strength, light and strong, and can be used to manufacture marine and oil deep well cables. The aramid fiber can be used to produce high-quality rackets, fishing rods, sleds, snowboards, ski poles, bows and arrows, rowing, golf clubs, etc., and can also be used to produce mountaineering shoes and boots, boxing gloves, racing helmets, racing car bodies, etc. with harsh sports conditions. As asbestos has serious harm to human respiratory tract, aramid fiber can be used to replace asbestos to make reinforced rubber sealing plates and other seals for the gaskets and linings of automobile brakes.
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