What is Kevlar?
Kevlar is well known as the material from which bullet-proof vests and body-armour is made. But it can be used in many more applications, such as bicycle tyres, yacht sails, ropes, and brakepads. It can do this because, despite it being a fibre, it has an extremely high stength-to-weight ratio, often qiuoted as being 5 times stronger than an equal weight of steel. It is actually a trademark of the chemical company DuPont, who first synthesised it in 1965.
Who invented it?
A chemist called Stephanie Kwolek invented Kevlar while working for DuPont in their Wilmington labs. In anticipation of a gas shortage, in 1964 the DuPont research group led by Kwolek began searching for a new lightweight but strong fibre to use for tyres. One day in 1965, while trying to dissolve one of her polymers, something strange happened. She reported:
"Ordinarily a polymer solution sort of reminds you of molasses, although it may not be as thick. And its generally transparent. This polymer solution poured almost like water, and it was cloudy. I thought, Theres something different about this. This may be very useful.'"
Normally such a "cloudy, opalescent, and low viscosity" solution would just be thrown away. However the technician, Charles Smullen, who ran the "spinneret" persuaded Kwolek to test her solution. When spun into a fibre, they were amazed to find that, unlike the other well-known fibre of the time, nylon, this new fibre did not break. Both her supervisor and laboratory director understood the significance of her discovery and a new field of aramid polymer chemistry was born. It then took six years to produce Kevlar commercially, finally reaching the market in 1971.
What actually is it?
Kevlar is a type of fibre called an aramid, short for 'aromatic polyamide', in which the molecules form long, highly-oriented chains. The fibres can be spun or woven into mats or fabrics to exploit these exceptional properties.
Kevlar is made by a condensation reaction of an amine (1,4-phenylene-diamine) and and acid chloride (terephthaloyl chloride).
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A section of an individual kevlar chain looks like:
The kevlar chains are relatively rigid and tend to form mostly planar sheets, similar to those of silk. This is due to the para-orientation of the benzene rings. When kevlar is spun the chains lock together via H-bonds to form a sheet that has a very high tensile strength. The sheets also stack radially, like the spokes on a wheel, allowing additional interactions between the face-to-face aromatic groups on neighbouring sheets to help to increase the strength of the overall fibre.
Why is Kevlar so special?
Kevlar has some superb properties:
- It's strong but relatively light.
- Unlike most plastics it does not melt: it's reasonably good at withstanding temperatures and decomposes only at ~450°C (850°F).
- Kevlar can be ignited but burning usually stops when the heat source is removed.
- Very low temperatures have no effect on Kevlar. There is no appreciable embrittlement or degradation down to -196°C (-320°F), which makes it excellent for Arctic conditions.
- Like other plastics, long exposure to ultraviolet light (in sunlight, for example) causes discoloration and some degradation of the fibers.
- Kevlar can resist attacks from many different chemicals, though long exposure to strong acids or bases will degrade it over time.
- Kevlar remains virtually unchanged after exposure to hot water for more than 200 days and its properties are virtually unaffected by moisture.
Can it be used for other things?
As mentioned above, the most well-known application for kevlar is in personal armour, such as bulletproof vests, combat helmets, face-masks, etc. But Kevlar can also be used in sports equipment, such as inner linings for bicycle tyres, tabletennis bats, bow strings for archery, paraglider suspension lines, and motorcycle safety clothing. It can also be used in snare drums, since it can be pulled very taut leading to a cleaner sound. Kevlar fibres can be woven into ropes or cables, which have been used to support suspension bridges. It is also used as a protective outer sheath for optical fibres. Kevlar has been used as a replacement for the asbestos in automobile brake pads, and in some rubber hose joints. Kevlar is often used in conjunction with glass fibre and carbon fibres as reinforcing agents in composite materials. Such composites find uses in aerospace, racing cars (like the kevlar Corvette in the photo, right), helicopter rotor-blades, and many specialised pieces of sports equipment.
References
- Kevlar at DuPont
- Kevlar Technical Guide
- Wikipedia - kevlar
- D. Tanner, J. A. Fitzgerald, B. R. Phillips, "The Kevlar Story - an Advanced Materials Case Study". Angew. Chemie Int. Ed. Eng. 28 (1989) 649.
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FAQs
One of these market-leading materials is Kevlar® - a material that could cushion, trap, and prevent a bullet from penetrating through to the body.
What is the molecule of Kevlar? ›
Kevlar is synthesized in solution from the monomers 1,4-phenylene-diamine (para-phenylenediamine) and terephthaloyl chloride in a condensation reaction yielding hydrochloric acid as a byproduct. The result has liquid-crystalline behavior, and mechanical drawing orients the polymer chains in the fiber's direction.
Was Kevlar discovered on accident? ›
The creation of Kevlar came about completely by accident in 1965. While analyzing molecule chains at low temperatures, Kwolek found a specific formation of molecule chains that was exceptionally strong and stiff. The solution was strange – it was cloudy and thin, unlike nylon polymers, that are clear and thick.
What problems does Kevlar solve? ›
Kevlar is a type of aramid fiber. It is woven into textile materials and is extremely strong and lightweight, with resistance toward corrosion and heat. It is used in vast applications such as aerospace engineering (such as the body of the aircraft), body armor, bulletproof vests, car brakes, and boats.
Can a bulletproof vest stop an AK 47? ›
Level III Body Armour
They consist of a carry vest with or without soft body armour into which the plates are inserted (ceramic, steel, etc.). Level III body armour vests must be able to withstand up to six shots from 7.62×51 NATO rounds. These vests are capable of stopping AK-47 rounds.
Can Kevlar block a knife? ›
Kevlar is a synthetic fiber commonly used in body armor manufacturing due to its strength and durability. It can provide great protection against knife threats as the tightly woven fibers are difficult to puncture and can deflect slashing attacks as well.
Is Kevlar stronger than steel? ›
The chemical structure of Kevlar® is comprised of several repeating inter-chain bonds. These chains are cross-linked with hydrogen bonds, providing a tensile strength 10X greater than steel on an equal weight basis.
How strong is Kevlar? ›
Kevlar has a measured tensile strength of about 3,620 megapascals, whereas nylon has a tensile strength of about 75 megapascals (depending on the types of nylon and Kevlar).
Is Kevlar safe? ›
INGESTION: Based on animal studies, KEVLAR® is nontoxic when eaten. INHALATION: KEVLAR® fiber is too big to inhale into the lungs, but fiber dust and fly from processing may be breathed into the nose and throat. Working unprotected in dusty conditions may cause upper respiratory irritation and cold-like symptoms.
Is Kevlar expensive? ›
Kevlar armor, for instance, is a popular material used in soft armor, as it's known for being highly durable and effective against stopping bullets. But, Kevlar can be more expensive than other materials due to the higher quality.
In 1965 Stephanie Kwolek created the first of a family of synthetic fibers of exceptional strength and stiffness. The best-known member is Kevlar, a material used in protective vests as well as in boats, airplanes, ropes, cables, and much more—in total about 200 applications.
How many lives has Kevlar saved? ›
According to the International Association of Chiefs of Police, more than 3,100 law enforcement officershave been saved because they were wearing body armor.
What are 3 facts about Kevlar? ›
It is actually five times stronger than steel when based on its weight. Kevlar is very easy to clean: as long as bleach is not used, it will not deteriorate or shrink. Kevlar will deteriorate somewhat if left in sunlight or exposed to other sources of UV. It will discolor and experience some degradation.
What is stronger than Kevlar? ›
Darwin's bark spider, however, takes tensile strength an entirely new level. Its dragline silk – the type that forms the energy-absorbing primary spokes of the orb-web – is twice as strong as that of any other silk thus far tested, and an astonishing 10 times stronger than Kevlar.
What is Kevlar used for today? ›
That's why we now rely on synthetic materials such as Kevlar®. It's a plastic strong enough to stop bullets and knives—often described as being "five times stronger than steel on an equal weight basis." [1] It has many other uses too, from making boats and bowstrings to reinforcing tires and brake pads.
What thickness of Kevlar will stop a bullet? ›
A bullet-resistant panel just 1/4-inch thick can stop at least three 9mm bullets fired dead on from just a few feet away. Need to stop a larger bullet? Just laminate together more layers of Kevlar® and resin during the production process, or layer up finished panels during installation.
What caliber bullet can Kevlar stop? ›
357 Sig, and a . 44 Magnum. Generally, Level 3A body armor is a soft insert made from Kevlar or similar material. The most important thing to remember about a Level 3A soft armor insert is that it will stop handgun bullets, but will not stop any rifle caliber bullet, including a 5.56mm (M193) or 7.62x39mm.
What happens when a bullet hits Kevlar? ›
This material is usually made from a combination of different materials, such as layers of fabric, metal, and ceramic plates. When a bullet hits a bulletproof vest, the vest will absorb the energy from the bullet. This energy will spread the force of the impact over a larger area.
What grade of Kevlar stops bullets? ›
Ballistic Protection
Bulletproof vests at Levels I-IIIa use soft materials like Kevlar®, which are incredibly strong and can trap and slow bullets to a complete stop. A bulletproof vest at Level IIIa can stop the vast majority of ammunition used in handguns and is the strongest soft body armor available.
Who invented it?
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