1、 Main characteristics and application status of aramid fiber
Aramid fiber, a new type of high-tech synthetic fiber, has excellent properties such as ultra-high strength, high modulus, high temperature resistance, acid and alkali resistance, light weight, etc. its strength is 5-6 times of that of steel wire, modulus is 2-3 times of that of steel wire or glass fiber, toughness is 2 times of that of steel wire, and weight is only about 1 / 5 of that of steel wire. It does not decompose or melt at 560 ℃. It has good insulation and anti-aging properties, and has a long life cycle. It is a high-temperature and flame-retardant fiber with high strength, high modulus, low density and good wear resistance. It has high technical content, high added value, excellent mechanical and chemical stability and mechanical properties. It can not only be used as a variety of structural materials and functional materials, but also be used in combination with other materials. In addition, it has good resilience and sealing performance, no harm to human health and environment. It can be used for sealing of water, oil, hydrocarbon and medium strength acid and alkali medium. The gasket has excellent sealing performance and creep relaxation resistance. It can be used as an alternative to asbestos for friction sealing materials, high-performance heat-resistant insulating paper and reinforced composite materials.
1. Main varieties of aramid fiber
Commercial aramid fiber mainly includes meta aramid fiber and para aramid fiber, and meta aramid fiber mainly includes Nomex of DuPont, conex of emperor, etc.; para aramid fiber mainly includes Kevlar, technora, Twaron, etc.
2. Research and application of aramid functional textiles
The unique physical and chemical properties of aramid fiber make it widely used in high temperature resistant, flame retardant, wear-resistant and high-strength functional textiles. All over the world, the research on it is also in the ascendant, new functional textiles emerge in endlessly, and the application field is constantly expanding.
Aramid fiber is an important national defense and military material. In order to meet the needs of modern war, at present, the bulletproof vests of the United States, Britain and other developed countries are all made of aramid. The lightweight of aramid bulletproof vests and helmets effectively improves the quick response ability and lethality of the military. In the Gulf War, aramid composite materials were widely used in American and French aircraft. In addition to military applications, it has been widely used as a high-tech fiber material in aerospace, mechanical and electrical, construction, automobile, sporting goods and other aspects of the national economy. In aviation and aerospace, aramid fiber is light in weight and high in strength, which saves a lot of power fuel. According to foreign data, in the process of launching the spacecraft, every kilogram of weight reduced means a cost reduction of 1 million US dollars. In addition, the rapid development of science and technology is opening up more new civil space for aramid fiber. According to reports, at present, aramid products are used in bulletproof clothing, helmets, etc. about 7-8%, aerospace materials, sports materials about 40%; tire framework materials, conveyor belt materials, etc. about 20%, and high-strength ropes, etc. about 13%.
2.1 aramid flame retardant series textiles
Although aramid fiber has good heat resistance and flame retardancy, it is expensive. Secondly, it is difficult to dye because of high crystallinity and strong intermolecular adhesion. The high price and the difficulty in dyeing restrain the development of its yield and variety to some extent. Therefore, a variety of flame-retardant aramid blended fabrics have been developed to improve the dyeing effect and reduce the product price.
(1) Aramid and wool blended flame-retardant fabric wool is a natural fiber with certain flame-retardant properties. Aramid staple fiber is first formed into a strip, then mixed with wool into a yarn, and then woven. When the blending ratio of aramid fiber is more than 30%, the ultimate oxygen index is more than 28. Without flame retardant finishing, the fabric can achieve good and lasting flame retardant performance, and reduce the cost without affecting the appearance and comfort of the fabric. The blending proportion can be adjusted according to the use to realize multi-function.
(2) In order to reduce the cost and realize the multi-functional demand, the flame-retardant fabric is made by blending aramid fiber and cotton fiber in a certain proportion. In the study of aramid and cotton fiber blending, the blending ratio of aramid and cotton is usually 80 / 20, 50 / 50 and 20 / 80. The survival time, smoldering time and damage length of these three kinds of blended fabrics meet the requirements of gb8965-88 grade II and above before and after washing, and the LOI value of ultimate oxygen index is also greater than the 28 standard with flame retardant requirements. With the increase of aramid content, LOI increased. Among them, 80 / 20 fabric has excellent heat resistance and flame retardancy, which can meet the requirements of national flame retardant clothing without flame retardant finishing; 50 / 50 and 20 / 80 blended fabric can meet the requirements of flame retardant standard only after being flame retardant treated by proban.
(3) Flame retardant viscose is a kind of toxic fiber containing silicate. Its physical and mechanical properties are similar to those of ordinary viscose fiber, and it can be processed into various textiles. Aramid and flame-retardant viscose blended fabric has soft hand feel, good fluffy, drapability, moisture absorption and permeability, high strength and wear resistance, good cloth surface finish, color fastness and non melting drop in case of fire carbonization, which can meet the quality requirements of high and medium grade flame-retardant clothing and decorative fabric.
(4) Aramid / Ramie core spun yarn was obtained by covering ramie fiber around aramid / Ramie flame retardant fabric with friction spinning technology. In addition, ramie yarn and aramid filament treated by alkali are combined to get composite yarn without twisting. After being woven into fabric and treated with proper flame retardant treatment, certain flame retardant requirements can be achieved.
2.2 aramid antistatic functional textiles
Ordinary textile fibers, especially chemical fibers, are prone to generate and accumulate a large amount of static electricity. In flammable and explosive environment, electrostatic discharge sparks as ignition sources often cause fire and explosion accidents. At the same time, the vast majority of textile fibers belong to combustible or flammable materials. The limiting oxygen index is generally between 17 and 25, far lower than the minimum value of 27 that can be self extinguished in the air. Once the fabric meets the ignition source, it will burn rapidly. In order to ensure the safety of operators in fire, petrochemical, military, mining and many other areas involving fire and explosion hazards, it is necessary to replace the ordinary inflammable and static prone fabrics with fabrics with flame-retardant and antistatic properties.
When aramid and conductive fibers are blended and interwoven to form a new type of fabric, due to the compatibility and complementarity of the flame retardancy and electricity dissipation properties of the fabric, the fabric has a long-term protection function of flame retardancy and anti-static. The latest aramid product developed by DuPont company, aracon, uses magnetron sputtering technology to sputter metal on the surface of aramid fiber to form a very thin film, which not only has antistatic effect, but also can shield high-frequency radiation and signal.
2.3 development of aramid fiber impregnated fabric
Kevlar fiber impregnated fabric is a new high-grade insulating material used in large motors. The impregnation process of Kevlar fiber fabric is two impregnation and two rolling. First, after the fabric is dipped in glue, some glue is rolled out to make the glue dip into the gap of the fabric, and then rolled to make the glue dip into all the hairiness inside the fiber; then the second dip is carried out, this time mainly to be coated, so that the surface of the fabric is covered with a certain amount of glue, and the second press is to make the glue cover evenly, and then dried in the oven.
Because of its excellent performance, using aramid fiber as insulation material for motor can make the heat-resistant grade up to above 180 ℃; if mica can withstand the high temperature of 180 ℃, but because of its large ratio, it can increase the weight of motor, and the cloud parent material is brittle, and the source is not abundant. Compared with the same power motor made of mica insulating material, each motor made of aramid fiber can save 28% copper, 15% steel and 10% silicon steel. The composite made of aramid fiber is 30% lighter and twice harder than the glass fiber composite made by the same method.
2.4 application of para aramid in bulletproof clothing
The para aramid fiber fabric has the highest expansion strength, high elastic modulus and low specific density, which can absorb and disperse the energy of bullet impact to other fibers of the fabric, avoiding "blunt injury", so the protective effect is significant. At the same time, the lightweight of aramid bulletproof clothing and helmet effectively improves the quick response ability and protection ability of the army.
Study on 2.5 aramid / carbon fiber hybrid woven fabric reinforced concrete
Through the theoretical analysis and practical test of aramid / carbon fiber fabric reinforced concrete, it can be seen that the function of fiber fabric reinforced concrete is very obvious, especially using these two kinds of high-performance fibers as the reinforcement material of bearing structure, which can replace the role of reinforcement, and the weight is 41.8% less than that of reinforced concrete, which is conducive to improving the seismic performance of buildings and the structure base Foundation treatment, so as to obtain higher economic and bearing benefits. However, how to use the fiber fabric to facilitate the construction and at the same time, it is easy to be mastered by ordinary construction workers, so more in-depth research is still needed.
2.6 aramid tire textiles
Because of the excellent properties of aramid, the mechanical properties of the tire cord are not affected by the temperature at high temperature. Under the action of alternating stress, the internal consumption is low, the heat output is small and the service life is long. Aramid can reduce the volume and mass of tire reinforcement material, and reduce the material and energy consumption to the maximum extent, and improve some limit indexes to a new height. In addition, aramid fiber does not have rust problem, and can replace all the metals (including bead wire) in the tire, save rubber materials, so that the tire performance can achieve light weight, rolling resistance reduction, fuel saving and dimensional stability, good uniformity, and no flat spots, high-speed performance, traction and braking performance is the best, wear resistance, puncture resistance is good, waste tires are easy to handle, etc Characteristic.
2.7 aramid weftless functional textiles
It is also used for bullet proof, puncture weftless cloth and plain cloth with better bullet resistance. In the manufacturing process of weftless fabric, aramid fiber material has been fully developed, fixed by adhesive, and there is no cross point between the fibers. When impacted by projectile, it is conducive to energy dispersion, more fibers can participate in it, and energy can be absorbed in a larger area, so its elastic resistance is better.
The surface density of aramid weft free fabric and the mass fraction of matrix resin are both important factors affecting the elastic resistance of its laminate. When weftless cloth has a smaller surface density and a lower mass fraction of matrix resin, its elastic resistance will be better.
2.8 aramid / carbon fiber non-woven fabric
The aramid / carbon fiber non-woven fabric was made by puncture process. The LOI of the fabric is 38-42 and the fire temperature is 700 ℃. It is mainly used for fireproof and heat insulation lining, high temperature dust filtering, decorative lining, fire splash covering cloth, etc.
2.9 aramid / armor steel composite plate
The aramid fiber reinforced resin matrix composite has the characteristics of light weight, high strength, good elastic resistance and excellent explosion-proof effect. Adding aramid fiber composite plate to armored steel can improve its anti knock performance, and the structure of the material will affect the shock wave attenuation effect of the material. When the materials are arranged in the order of decreasing wave impedance, the shock wave can be attenuated more effectively. The attenuation effect of the material with multilayer structure is better than that of the material with double-layer structure.
2、 Development direction of aramid fiber
In accordance with the 12th Five Year Plan, during this period, China's production technology of 1000 tons of para aramid fiber will achieve a breakthrough and enter a rapid growth period, so as to drive related industries