Fabric made of synthetic fiber with a crystalline structure is called Kevlar. The incredible strength of the fabric is given by the benzene ring, which lies in the cross section of the crystal. According to its characteristics, the material is stronger and more durable than metal, while it is very thin and light.
Kevlar fiber
Everyone gets to know Kevlar differently, and everyone learns what it is from certain life situations. Modern youth are familiar with the material thanks to the game Rast, in which characters are invited to purchase armor and ammunition from it. Older generations associate the fiber with protective clothing and sports equipment.
Types of Kevlar fiber
Briefly about the origin
Back in 1975, a material called Kevlar was first introduced to the market and immediately began to enjoy enormous demand, which is only increasing every day. This unique polymer was obtained in the laboratories of the world famous DuPont concern. Officially, chemist Stephanie Kwolek is considered its creator.
In those days it was used for tires as a reinforcing material. It subsequently found application in a variety of composite materials, sports equipment, and cable products. Kevlar fabric began to be used to produce personal protective equipment.
Kevlar thread
Kevlar concrete - characteristics, materials, production
Kevlar concrete is an innovative building material produced using vibratory casting technology.
In terms of its composition, it is the same traditional heavy concrete on granite chips, but with a different appearance and different performance characteristics. Ultraconcrete, granite, pelletized concrete - these are all names of one material that has high strength, many times greater than the strength of classical concrete.
Content
Initially, the material was developed for reinforcing car tires, and is still used in this capacity today. In addition, Kevlar is used as a reinforcing fiber in composite materials, which are strong and lightweight.
Kevlar is used to reinforce copper and fiber optic cables (a thread along the entire length of the cable that prevents stretching and breaking of the cable), in speaker cones, and in the prosthetic and orthopedic industry to increase the wear resistance of parts of carbon fiber feet.
Kevlar fiber is also used as a reinforcing component in mixed fabrics, giving products made from them resistance to abrasive and cutting influences; in particular, protective gloves and protective inserts in sportswear (for motorsports, snowboarding, etc.) are made from such fabrics .). It is also used in the shoe industry to make anti-puncture insoles.
Personal armor protection
The mechanical properties of the material make it suitable for the manufacture of personal armor protection (PB) - body armor and body armor. Research in the second half of the 1970s showed that Kevlar-29 fiber and its subsequent modifications, when used in the form of multilayer fabric and plastic (fabric-polymer) barriers, show the best combination of energy absorption rate and duration of interaction with the striker, thereby providing relatively high, given the mass of the obstacle, indicators of bulletproof and anti-fragmentation resistance [1]. This is one of the most famous uses of Kevlar.
In the 1970s, one of the most significant advances in the development of body armor was the use of Kevlar fiber reinforcement. Development of Kevlar body armor by the National Institute of
) occurred over several years in four stages. In the first stage, the fiber was tested to determine whether it could stop a bullet. The second step was to determine the number of layers of material needed to prevent penetration by bullets of different calibers and traveling at different speeds, and to develop a prototype vest that could protect employees from the most common threats: .38 Special and .22 Long Rifle caliber bullets. By 1973, a seven-layer Kevlar fiber vest was developed for field testing. It was found that when wet, the protective properties of Kevlar deteriorated. The ability to protect against bullets also decreased after exposure to ultraviolet light, including sunlight. Dry cleaning and bleaches also negatively affected the protective properties of the fabric, as did repeated washing. To overcome these problems, a waterproof vest has been developed that has a fabric coating to prevent exposure to sunlight and other harmful factors.
Shipbuilding
In the last decade, Kevlar has become widespread in shipbuilding. Due to the technological difficulties and price of Kevlar, it is used selectively. For example, only in the keel part or at the seams. Many manufacturers (such as the shipyards BAIA Yachts, Blue water, Danish yacht, Zeelander Yachts), making not a very large number of yachts per year, are systematically switching to using Kevlar.
Who invented Kevlar
We have described the production of Kevlar, and now you are probably wondering who came up with this complex process? One of the most durable fabrics on earth was invented by a lady - Stephanie Kwolek, who at that time (1964) collaborated with the famous American chemical concern DuPont.
Working to improve the production of polyaramids, Stephanie was the first to abandon the melt method and create an unusual solution that, when passed through high-strength molds, turned into aramid fibers - Kevlar.
Kevlar production
You probably know that natural materials such as wool and cotton must be spun into fibers before they can be turned into useful textiles. The same is true for man-made fibers such as nylon, Kevlar and Nomex.
There are two main stages in making Kevlar. The first is directly related to chemistry - first the base plastic from which Kevlar is made (a chemical called poly-para-phenylene terephthalamide) must be produced. The direct transformation of a chemical product into a more useful, practical and durable material occurs during the second and final stage of production.
Currently, more than 80% of the world's Kevlar is produced at Chesterfield's Spruance plant. The synthetic fiber is wound onto spools, as shown here, and then transformed into other products.
Through a complex process, a hot and viscous solution of poly-p-phenylene terephthalamide is forced through a die (a metal molder a bit like a sieve). The result is long, thin, strong and stiff fibers that are wound on drums. The fibers are then cut to length and woven into the tough mat we know as Kevlar.
Kevlar release forms
Kevlar fiber is an intermediate product. It is very thin and transparent. Its thickness is only 1 micron. The fiber is used to make:
- Coarse cords for ropes and cables.
- Spinning threads.
- Rogovina.
- Fabrics.
Kevlar fibers are very short. However, for some applications they can be additionally crushed. Thus, the material for the production of felt and non-woven products has a length of only 6 mm. To reinforce resins, fibers can be crushed to 1 mm.
Threads and yarn are practically never found on the open market, as they are intermediate raw materials for the manufacture of various products. A private buyer can purchase Kevlar in the form of finished fabric. It is used for sewing various protective clothing.
The high strength of the fabric is explained not only by the characteristics of the fibers it consists of, but also by the special weaving method. Due to this, it holds up well to blows and is resistant to cuts. The minimum density of Kevlar fabric is only 36 g/m². In this design, its thickness is only 0.08 mm. It is very light and can even be used for sewing light summer clothes, which are many times stronger than any other materials, even denser ones. The most durable fabric is with a density of 460 g/m². Its thickness is 0.6 mm. It is less flexible, but has the maximum strength available for Kevlar.
The strength characteristics of Kevlar are high, but not as high as people think about it. Even the densest fabric in one layer is not capable of stopping a bullet or a strong stab blow from a knife.
Why is this rare now?
To purchase a carpet in the USSR, you had to save money from your salary for a year. And if such a gift was presented by one of the guests at the wedding, then the joy of the newlyweds knew no bounds. Naturally, such an expensive item was hung in the most visible place, each time remembering the donor with warmth.
Only in the mid-90s did carpets go on sale for free, and the excitement somehow immediately died down. It was no longer possible to show off a carpet, and the fashion of hanging it on the wall gradually faded away.
Today, textiles on the wall can only be seen in the home of some 90-year-old grandmother, who is still nostalgic for the USSR, or rather, for her youth that is gone forever.
History of the invention of Kevlar
This unique polymer, like many other synthetic fibers, was obtained in the laboratories of the world famous DuPont concern. Its official creator is chemist Stephanie Kwolek, head of a group working on the problem of synthesizing durable polymer fibers for tire reinforcement. In 1964, Kwolek proposed a new method for producing polyaramid threads - not from a melt, as for most polymers, but from a solution. Polycondensed para-aramid is dissolved in acid, and then opaque crystalline fibers of varying densities, having a yellowish-golden color, are grown from the solution; on average their thickness is approximately 11 microns. The crystal structure of such a fiber is a rod, in the cross section of which lies a benzene ring, which gives the structure very high strength . When testing the tensile strength of the first laboratory samples of polyaramid fibers, the researchers even decided that the equipment was faulty, since the resulting strength (up to 260 cn/Tex) turned out to be several times higher than that of steel, and moreover, the new polymers turned out to be flexible and lightweight. For further use, the fibers are twisted into a thread; their number in one thread may vary. Kevlar fabric is produced from threads with up to 1000 fibers; thicker threads (up to 10 thousand fibers) are used for technical purposes, for reinforcing various materials and for the production of ropes.
In 1975, a new ultra-strong polymer went on sale under the brand name Kevlar. It was, as expected, used as a reinforcing material for tires. In addition, it has found application for various composite materials, for the production of cable products, prosthetics, sports equipment, etc. The largest share of manufactured products is occupied by Kevlar fabric, which is used mainly for the production of personal protective equipment. Regardless of the form of release, polyaramid fibers and threads made from them have the following characteristics:
- high tensile and tear strength (cut);
- low density (30-60 g/sq.m);
- increased strength when the temperature drops down to -200 degrees;
- high elasticity;
- chemical resistance;
- low electrical conductivity;
- resistance to burning and melting;
- no corrosion;
- non-toxic.
However, Kevlar fibers also have their disadvantages.
Their strength decreases with increasing temperature, and at 450 degrees the process of thermal decomposition occurs. They are not resistant to UV radiation and lose strength when abraded and wet. However, Kevlar fabric is quite soft and has the ability to exchange air, which allows it to be used for clothing and shoes for special purposes. Kevlar is a synthetic fabric with a crystalline structure. This material is durable due to the benzene ring located in the cross section of the crystal. Kevlar is stronger than metal in its properties.
This material is produced in America at the DuPont chemical plant. Kevlar production begins only when low temperatures are reached.
Calcium chloride and methylpyrrolidone are mixed, then reagents are added. All these substances enter into a chemical reaction, and a polymer is obtained that has the properties of liquid crystals.
The resulting polymer looks like a gel or fine crumbs. It is thoroughly washed, then dried and then dissolved in sulfuric acid. The resulting solution is passed through dies. The result is fibers. By twisting them, threads are created and fabric is obtained from them.
Main types of Kevlar
Polyaramid threads can have different thicknesses, strength and elasticity. Today, the main types of Kevlar on the market are:
- K-29. It has standard characteristics: density from 280 kg per mm², yellowish color, thickness 1 mm. It is used for the manufacture of sports equipment, protective inserts in suits, orthopedic prostheses, threads for fishing, strings for musical instruments.
- K-49. Has increased resistance to corrosion. It is used for the manufacture of automotive cables, hoses and tires, and plastic reinforcement.
- K2-100. The marking indicates that the thread is dyed. Typically Kevlar K2-100 is used to make fiber optic braid.
- K-119. Elongated threads with increased flexibility. As a rule, they are used for reinforcing car tires and other rubber products.
- KM2 and KM2+. Fabric with increased strength, protection from moisture and ultraviolet radiation. Used in the manufacture of armor for law enforcement agencies.
Chopped fibers are also commercially available. For example, Kevlar staple consists of cut threads up to 6 mm long. They are not as durable as K-29, but they are used to make fabric that has increased thermal insulation and vibration insulation properties.
Flock Kevlar is cut fibers up to 1 mm long. They are intended for reinforcing resins.
The usual fiber diameter is 1 micron, opaque.
- The main characteristic of the material is its high mechanical strength. The density and, accordingly, the mass are quite low.
- Kevlar has tensile strength.
- Does not burn or melt, has the ability to self-extinguish. Begins to decompose at temperatures above 430 °C. When exposed to high temperatures, it begins to lose strength only over time, not immediately.
- It is resistant to organic solvents.
- Has a high elastic modulus.
- Resistant to corrosion.
- Under the influence of very low temperatures (cryogenic) it not only does not deteriorate, but also becomes even stronger.
- Has low electrical conductivity.
- Cut resistant.
Technical characteristics and properties
The technical characteristics and properties of Kevlar are truly unique. The main feature is considered to be high mechanical strength. At the same time, the mass and density are relatively low.
Kevlar is a material with unique tensile strength and self-extinguishing ability. However, it does not burn or melt. Only at temperatures above 430 degrees does it begin to decompose. As a result of exposure to high temperatures, not immediately, but after a certain time, it begins to lose its strength.
It is resistant to organic solvents and corrosion and has a high elastic modulus. Under the influence of low temperatures, not only does it not deteriorate, but on the contrary, it becomes stronger. Resistant to cuts and has low electrical conductivity.
Waterproof Kevlar fabric
Applications of Kevlar
As mentioned above, the goal of the developers was to create a lightweight but at the same time durable material that could replace heavy steel in the production of tires.
Later, thanks to the excellent properties of Kevlar, they began to use it in sewing clothes, overalls, military uniforms, etc.
Armor
Kevlar is a well-known component for the production of personal armor and protection products.
Combat helmets, ballistic face masks and body armor are made using Kevlar. The armed forces of various countries use Kevlar to create bulletproof masks and balaclavas for armored vehicle crews.
Kevlar is so strong that it is used as armor for Nimitz-class aircraft carriers.
In the civilian sphere, the properties of Kevlar are used to create equipment to protect emergency response workers. The body armor of police officers, private security companies and special forces soldiers is also made of Kevlar.
Sport equipment
Kevlar is used to line bicycle cleats, which increases their puncture resistance.
Kevlar fibers are also used to increase the rebound of tennis rackets and reduce their weight. In motorsports, Kevlar is used to produce safe clothing for motorcycle athletes and to strengthen elements in the shoulder and elbow areas.
The properties of Kevlar have been successfully used in other sports - creating jackets, trousers, elements of masks in fencing, in the Japanese art of archery Kyudo to strengthen the bowstring, to improve performance in sails for racing boats, etc.
Musical instruments
Kevlar has excellent acoustic properties, which are used in the creation of acoustic speaker cones for transmitting low and mid frequencies.
Kevlar is used as a base material in strings for stringed instruments. Kevlar strings become stronger, more flexible and more resistant to temperature changes.
Other Applications
Due to its physical properties, Kevlar is used as a reinforcing fiber, allowing parts to be made lighter and stronger.
Kevlar fiber is used to strengthen cables, which protects the wires from stretching and breaking. The ability to combine Kevlar with other polymers through a chemical reaction allows the creation of more advanced materials used in specific areas.
As an example, carbon-Kevlar, which is characterized by high heat resistance and lightness, is used for the construction of high-speed boat hulls.
Kevlar: what is it?
Durable Kevlar fibers have long been woven into the structure of developments in the automotive, construction, and military industries, partially displacing less durable and practical steel. The material “woven” from organic threads has become simply irreplaceable due to its unique characteristics. So, now let’s take a closer look at the question of what Kevlar is, and find out the history of its appearance.
Compound
It's time to find out what Kevlar is made of - such a durable material that cannot be replaced by anything else. It is a para-aramid fiber with a yellowish tint. It is a polymer, so the resulting threads are synthetic. They are added to the composition of fabrics from which durable workwear and equipment (for example, gloves) are sewn.
Kevlar is also used as a composite (tires), but here, in addition to it, carbon fiber and fiberglass are added, although Kevlar is many times stronger than them. If it is the main material, then the item made from it will be too expensive.
Strength averages 360 kg per 1 mm2, but in some species it can reach up to 550 kg. In terms of structure and properties, they tried to bring Kevlar as close as possible to a durable, natural material - spider web. Compared to steel, for which this figure only reaches 150 kg, Kevlar is much stronger. It also has a low density (about 1500 kg per cubic meter), which is slightly more than water (1000 kg/m3).
Kevlar as an anti-ballistic material
A firearm bullet moves at high speeds and is endowed with a significant amount of kinetic energy. In fact, there are no things that are completely bulletproof. But things like bulletproof glass are quite effective at protecting against bullets by absorbing and dissipating kinetic energy.
Bulletproof vests are used not only to protect military personnel directly. Protective clothing made of Kevlar fiber often protects working dogs. In this regard, Kevlar is a successful anti-ballistic material, since it takes a lot of energy for a knife or bullet to pass through the material. Tightly woven fibers of highly oriented polymer molecules are extremely difficult to pull apart (separate). Separation requires a significant amount of energy.
A projectile (or a pushed knife blade) that is charged with a high level of energy will lose a significant portion of that energy as it penetrates the material. Even if the bullet manages to penetrate the Kevlar, the speed is significantly slowed down and does not cause serious damage.
Kevlar's structure is stronger than steel, but the material is about 5.5 times less dense (about 1.44 g/cm3) compared to steel, which has a density of about 7.8–8 g/cm3. That is, a certain volume of Kevlar weighs 5–6 times less by mass than the same volume of steel.
Therefore, Kevlar armor provides the same protection as steel, but is lighter and more flexible in terms of comfort. Increased protection efficiency is achieved by increasing the thickness of the Kevlar plates.
