Kevlar

Kevlar was invented by American chemist Stephanie Kwolek while working for DuPont in anticipation of a gasoline shortage. In 1964, her group began looking for a new lightweight and strong fiber for light but strong tires. 

Kevlar is not like cotton: not everyone can make it with the right raw materials. It is a proprietary material manufactured solely by the DuPont chemical company and comes in two main grades called Kevlar 29 and Kevlar 49 (other grades are made for special uses)

Kevlar was introduced in 1971 after it was discovered in the early 1960s by American chemist Stephanie Kwolek (1923-2014) who, along with Paul Morgan, received US Patent 3,287,323 for her invention in 1966. Originally developed as a lightweight replacement for steel reinforcements, vehicle tires, probably best known today for use in things like bulletproof vests; By the time Kwolek died in 2014, she had sold a million Kevlar vests and countless lives had been saved.

Properties:

The tensile strength and modulus of aramid fiber are significantly higher than previous organic fibers and the elongation of the fiber is lower. Aramid fibers are easier to weave on looms than brittle fibers such as glass, carbon, or ceramic. They also have an inherent resistance to organic solvents, fuels, lubricants, and exposure to flames.

 

It is strong but relatively light. The specific tensile strength (tensile strength or tensile strength) of both Kevlar 29 and Kevlar 49 is more than eight times that of steel wire. Unlike most plastics, it does not melt - it can withstand temperatures to some degree and only breaks down at around 450 ° C (850 ° F).

Very low temperatures have no effect on Kevlar: DuPont found no "embrittlement or decomposition" down to -196 ° C (-320 ° F). As with other plastics, prolonged exposure to ultraviolet light (such as sunlight) causes discoloration and some degradation of Kevlar fibers. Kevlar can resist attack by many different chemicals, although prolonged exposure to strong acids or bases will degrade it over time.

Production:

Kevlar is synthesized in a solution from the monomers 1,4-phenylenediamine (paraphenylenediamine) and terephthaloyl chloride in a condensation reaction, producing hydrochloric acid as a by-product. The result shows a liquid-crystalline behavior and the polymer chains are oriented in the direction of the fibers by mechanical traction. 

 

You probably know that natural materials like wool and cotton need to be spun into fibers before they can be made into useful textiles, just like man-made fibers like nylon, kevlar, and Nomex.

The basic aramid is turned into fibers by a process called wet spinning, which involves forcing a hot, concentrated, and very viscous solution of poly-para-phenylene terephthalamide through a spinneret (a metal former a bit like a sieve) to make long, thin, strong, and stiff fibers that are wound onto drums. The fibers are then cut to length and woven into a tough mat to make the super-strong, super-stiff finished material we know as Kevlar.

Types: 

Kevlar fibers and filaments are available in a variety of types, each with its own unique properties and performance characteristics for different protection needs.

 

 

 1) Kevlar K29 -    in industrial applications such as cables, asbestos substitutes, brake pads, and body/vehicle armor. 

 2) Kevlar K49    -     High modulus for cable and rope products. 

 3) Kevlar K100  -     Colored version of Kevlar 

 4) Kevlar K119  -     Higher elongation, more flexible, and more resistant to fatigue. 

 5) Kevlar K129  -     Higher toughness for ballistic applications. 

 6) Kevlar AP      -     Has 15% higher tensile strength than K29. 

 7) Kevlar XP      -     Lighter resin and KM2 plus fiber combination. 

 8) Kevlar KM2   -    Increased ballistic resistance for armor applications.

Applications: 

Kevlar is a type of aramid fiber. It is woven in textile materials and is extremely strong and lightweight, resistant to corrosion and heat. It is used in extensive applications such as aerospace engineering (such as the body of the airplane), bulletproof vests, car, and boat brakes.

Automotives:

Kevlar cellulose brake pads are better equipped for friction abrasion with their increased thermal stability and inherent resistance to abrasion; Kevlar-reinforced brake pads are designed for long life and safe, quiet braking. 

Kevlar is also effective in clutches subject to high friction. Tests have shown that Kevlar clutch linings do not need to be repaired or replaced as often as standard clutch linings.

Formula 1 racing cars are known to crash at high speeds and catch fire. This was mainly due to the gas tank being punctured and the fuel caught on fire / exploded. Some drivers were seriously injured and died. Modern Formula 1 cars have Kevlar reinforced fuel tanks. These types of tanks are very difficult to pierce and are flexible enough that such a tank will fit into a narrow space of unusual shape. Safety has been improved due to the level of protection provided by Kevlar. 

 Kevlar fibers help improve the safety, performance, and durability of automotive components for a wide variety of vehicles, from cars and trucks to professional racing cars. Kevlar auxiliaries provide internal and external strength to automotive components. 

DuPont Kevlar fiber helps improve the safety, performance, and durability of automotive components such as automotive hoses and belts for a wide variety of vehicles, from cars and trucks to professional race cars

Armors:

The armor systems made of Kevlar-Aramid fiber are designed to protect human life and vital equipment against ballistic threats, the ballistic resistance of Kevlar-Aramid is due to its excellent thermal properties, its high crystallinity, its highly oriented fine structure, and its high strength properties. . The high glass transition temperature and thermal stability of Kevlar fiber ensure the integrity of the ballistic structure at a relatively high temperature in a ballistic event. 

Kevlar fiber is a very important component of military assets. By incorporating its inherent protection technology into military helmets, it has helped save thousands of lives.

Kevlar is an excellent anti-ballistic material (resistant to bullets and knives) because it takes a lot of energy to get through a knife or bullet. Tightly entangled fibers of highly oriented (aligned) polymer molecules are extremely difficult to separate - it takes energy to separate them. Energy is "stolen" from a bullet (or a knife hit hard by an attacker) as it tries to breakthrough. If it manages to penetrate the material, it will slow down considerably and cause much less damage. 

Kevlar provides a lightweight and effective armor solution that helps protect against ballistic attacks and allows cars and trucks to retain most of their original drivability while stopped for multiple laps. Law enforcement agencies, cash security companies, and people who live or work in harsh environments rely on Kevlar armor to increase safety in vehicles where weight is a critical factor.

Cables:

Kevlar ropes and cables help deliver performance and value to customers in the fine rope industry by providing excellent strength, fatigue resistance, shrinkage, and durability. Find out how branded Kevlar fibers strengthen ropes and cables to withstand extreme temperatures and harsh environments. Due to its chemical and thermal stability, Kevlar reinforcement helps make seals strong and durable.

 

 

Kevlar is used as a reinforcement in fiber optics. Kevlar, which is normally placed on the edge of the cable, provides the necessary protection. Kevlar also offers additional functionality that meets the dielectric, weight, diameter, flexibility and handling requirements of a fiber optic cable.

Sports:

It is used as the inner lining of some bicycle tires to avoid punctures. In table tennis, Kevlar layers are added to custom layer blades or paddles to increase bounce and reduce weight. It is used for motorcycle safety clothing, especially in padded areas such as the shoulders and elbows.

 

In kyudo or Japanese archery, it can be used as an alternative to more expensive hemp for bowstrings. It is one of the most important materials for paragliding suspension lines. In fencing, it is used in protective jackets, breeches, plastrons, and the front of the masks. Tennis rackets are usually covered with Kevlar. It is even used in sails for high-performance racing boats.

Space:

Kevlar is a material widely used in the design and manufacture of the shields that protect the manned elements of the International Space Station (ISS) from the threat of meteorites and space debris that are increasingly polluting the Earth's orbits. Kevlar was also selected for extensive use in the fabrication of innovative flexible structures that are under development for future manned exploration missions.

 

Kevlar was originally chosen for its excellent ballistic properties to protect debris, but its compatibility with the space environment had to be carefully evaluated. In parallel with the high-speed impact tests, a significant amount of analysis, testing, and simulations were carried out to quantify its capabilities in reducing the lethality of space debris to understand and characterize the behavior of Kevlar under space conditions. 

Kevlar's ability to protect human crews from the powerful mixture of high-energy charged particles destined for long-term missions has been studied.

Reference:

1) https://en.wikipedia.org/wiki/Kevlar

2) https://materials-today.com/kevlar-uses-properties-and-processing/

3) https://sites.google.com/site/sailclothscience/sailcloths/composite/kevlar/synthesis

4) https://www.dupont.com/products/dupont-kevlar-fiber.html

5) https://kevlarweb.wordpress.com/applications/

6) https://textilelearner.net/kevlar-fiber-types-properties-manufacturing/