The modern world brings challenges that nature never anticipated. Constant development has naturally increased the demand for the production of strong and durable synthetic materials. One such material is kevlar – a revolutionary synthetic fiber that has been pushing the boundaries of what is possible since 1968. What kevlar is, what properties it has, where it is used and why it holds such an important place in human life, you will learn in this article.
What is kevlar and what properties does it have?
Kevlar is an extremely versatile and strong type of synthetic material with a number of interesting properties and wide practical use. It belongs to para-aramid fibers and is characterized by high tensile strength at low specific weight, comparable only to carbon fibers. It is characterized by excellent thermal resistance and excellent stiffness, which alone predetermines it for a wide range of practical applications.
Thanks to very strong bonds and the parallel alignment of its molecules, which are interconnected by hydrogen bonds, kevlar is bulletproof and provides a strong protective barrier against abrasion, puncture and cutting. Kevlar fibers are fire-resistant and protect against thermal risks. Kevlar is corrosion-resistant, non-conductive and resistant to most chemicals except very strong acids and bases. It is also ultra-light and five times stronger than steel. However, it has poor resistance to ultraviolet radiation and moisture.
Its molecular formula is [-CO-C6H4-CO-NH-C6H4-NH-]n.
The relative density is 1.44 g/cm3, the tensile strength of the fibers reaches 20-21 cN/dtex (modulus of strength 3.6-4.1 GPa), at 160 °C the strength decreases by 10 %, at 450 °C it sublimates.
An invention that changed the world
It could be said that this revolutionary material was created, in a way, thanks to chance. The inventor of this unique fiber is American scientist Stephanie Kwolek. She worked as a chemist at DuPont - one of the largest companies in the field of polymer processing, which became famous just before World War II for its nylon patent.
In 1964, Stephanie began working on improving the production of rod-structured polymer substances with the aim of replacing the relatively heavy steel reinforcements in car tires with a more suitable and lighter polymer. After a long research process, she created an unusually looking solution for that time in the form of the first aramid fibers, which she patented in 1968. The fiber itself, under the trademark kevlar, was launched on the market by DuPont in 1971.
Since its discovery, kevlar has undergone development, and since 1988 its second generation has been available. The original group of products bears the designations K29 and K49. Kevlar is currently available in several versions:
- K29 – multi-purpose yarn
- K49 – high-modulus type of yarn
- K100 – manufacturer-dyed kevlar
- K119 – kevlar yarns with higher elongation and flexibility
- K129 – light, high-performance type of yarns
- Kevlar AP - a new generation fiber that offers advanced performance, value and increased design flexibility in many applications
- Kevlar KM2 - a fabric that meets the performance requirements for helmets and vests for military forces
Kevlar retains its properties even after repeated stress. This can be partly attributed to its internal structure (how its molecules are naturally arranged in regular and parallel lines) and partly to the way its fibers are manufactured.
Manufacturing method
Kevlar fiber is produced by spinning a melt of para-phenylenediamine and terephthaloyl chloride (PPD-T), which passes at a constant speed and under high pressure through a spinning nozzle, where it then solidifies into fiber form in a stream of cold air. The spinning assembly then twists the individual fibers into a continuously spun yarn. This is wound onto spools and further processed for practical use.
Kevlar is produced in several modifications and is supplied in the form of fiber, chopped strands, flakes or fabric.
Most common uses of Kevlar
The unique properties of Kevlar allow it to be used in countless fields, and it could be said that new applications for its use appear almost daily.
Its extreme strength and heat resistance make it suitable, for example, for use in the automotive, marine or aerospace industries, especially in the production of car bodies, aircraft components, brake linings, ship hulls or racing tires.
Kevlar also finds application in the mining industry, where it is used to manufacture conveyor belts for transporting ore, significantly improving performance and cost efficiency.
This material is also known to athletes, as it is part of numerous pieces of sports equipment (tennis rackets, protectors, hockey sticks, skis, nets, trekking tent flysheets and the like).
When discussing Kevlar, motorcyclists cannot be left out either, as they too are accompanied by Kevlar on the road, this time in the form of Kevlar fabric. Their favorite items are Kevlar jeans, Kevlar suits, gloves or helmets. The advantage of Kevlar pants shows up especially in a fall and subsequent sliding, where contact surfaces heat up to more than 200 degrees. In such a situation, resistant and strong Kevlar is a true blessing.
Kevlar fabric is also widely applied in the manufacture of protective equipment and clothing. Typical examples include work and firefighter uniforms, police uniforms or complete military gear. This material, capable of withstanding even the most demanding conditions, is now commonly used to make fire-resistant boots, Kevlar gloves, protective face masks, vests, helmets, protectors or entire suits. Interestingly, Kevlar gloves have up to 5 times higher cut resistance compared to leather ones.
Kevlar bulletproof vest
Clearly the most significant and most useful application of Kevlar has been in the production of the Kevlar vest. Kevlar is indeed one of the few materials that literally save human lives, and many a member of the army, security personnel or police force has already experienced this firsthand.
The current generation of modern bulletproof Kevlar vests can now offer their wearers not only protection against high-velocity bullets but also relatively high wearing comfort.
The principle of bulletproof vests works, in simplified terms, something like this:
The vest is sewn from several layers of Kevlar, which are firmly bonded together. Kevlar fibers absorb the kinetic energy of bullets, which reduces the bullet's ability to penetrate the body. Without sufficient penetrating force, the bullets subsequently become harmless.
The moment a bullet or any other high-speed projectile hits the Kevlar, the fibers literally catch the projectile, dispersing its kinetic energy, which they then absorb into themselves. The bullet thus finds itself in a web of strong fibers, whose task is to absorb and disperse the impact energy. Additional energy is absorbed by each subsequent layer of material in the vest, until the bullet is completely stopped. This process is also facilitated by the relatively large surface area of the garment, which has proven effective in eliminating so-called blunt trauma (injury to internal organs from the force of impact, not from a penetrating bullet).
And what to add in conclusion? The ways of using this almost miraculous invention seem to be endless, and we can't wait to see what else this discovery will bring us.
