Kevlar®

by Chris Woodford . Last updated: July 8, 2021.

N ature has given us some amazing materials. There’s wood: a material so strong and versatile you can use it for everything from making paper to building houses. There’s also wool, with insulation so effective it lets sheep stand outside in the snow all winter. Or how about skin: a material that will repair itself automatically and often completely invisibly in only a matter of days? Truly incredible though these materials are, they’re far from perfect for every application, especially in the modern world where the challenges we face are ones nature could never have anticipated. 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. [2] Let’s take a closer look at how it’s made and what makes it so tough!

Photo: Super-strong Kevlar is best known for its use in body armor—and this photo shows you why: it’s a piece of Kevlar after being hit by a projectile. You can see a dent (coming up toward the camera)—but you can’t see a hole. You might be bruised by this impact (or suffer what’s called a “blunt trauma” injury), but you wouldn’t die. Picture courtesy of US Army.

Contents

  1. What exactly is Kevlar?
  2. What’s so good about Kevlar?
  3. How is Kevlar made?
  4. What’s Kevlar used for?
  5. What makes Kevlar such a good antiballistic material?
  6. Find out more

What exactly is Kevlar?

Kevlar is one of those magic modern materials people talk about all the time without ever really explaining any further. “It’s made of Kevlar”, they say, with a knowing nod, as though that were all the explanation you needed.

Kevlar is simply a super-strong plastic. If that sounds unimpressive, remember that there are plastics—and there are plastics . There are literally hundreds of synthetic plastics made by polymerization (joining together long chain molecules) and they have widely different properties. Kevlar’s amazing properties are partly due to its internal structure (how its molecules are naturally arranged in regular, parallel lines) and partly due to the way it’s made into fibers that are knitted tightly together. [3]

Photo: Kevlar textiles get their properties partly from the inherent strength of the polymer from which the fibers are made and partly from the way the fibers are knitted tightly together, as shown here in a NASA ballistics test. Picture courtesy of NASA Glenn Research Center (NASA-GRC).

Kevlar is not like cotton—it’s not something anyone can make from the right raw materials. It’s a proprietary material made only by the DuPont™ chemical company and it comes in two main varieties called Kevlar 29 and Kevlar 49 (other varieties are made for special applications). [4] In its chemical structure, it’s very similar to another versatile protective material called Nomex. Kevlar and Nomex are examples of chemicals called synthetic ar omatic poly amid e s or aramids for short. Calling Kevlar a synthetic aromatic polyamide polymer makes it sound unnecessarily complex. Things start to make more sense if you consider that description one word at a time:

  • Synthetic materials are made in a chemical laboratory (unlike natural textiles such as cotton, which grows on plants, and wool, which comes from animals).
  • Aromatic means Kevlar’s molecules have a strong, ring-like structure like that of benzene.
  • Polyamide means the ring-like aromatic molecules connect together to form long chains. These run inside (and parallel to) the fibers of Kevlar a bit like the steel bars (“rebar”) in reinforced concrete.
  • Polymer means that Kevlar is made from many identical molecules bonded together (each one of which is called a monomer). Plastics are the most familiar polymers in our world. As we’ve seen, the monomers in Kevlar are based on a modified, benzene-like ring structure.

Like Nomex, Kevlar is a distant relative of nylon, the first commercially successful “superpolyamide”, developed by DuPont in the 1930s. Kevlar was introduced in 1971, having been discovered in the early 1960s by US chemist Stephanie Kwolek (1923–2014), who earned US Patent 3,287,323 for her invention, with Paul Morgan, in 1966. Originally developed as a lightweight replacement for steel bracing in vehicle tires, it’s probably best-known today for its use in things like body armor; by the time of Kwolek’s death in 2014, one million Kevlar body vests had been sold—and countless lives saved. [5]

What’s so good about Kevlar?

Photo: Braided Kevlar can be used to make super-strong rope. Compared on a strength-to-weight ratio, Kevlar is about 5–6 times stronger than steel wire and twice as strong as ordinary nylon fiber. Picture by Casey H. Kyhl courtesy of US Navy.

These are some of Kevlar’s properties:

  • It’s strong but relatively light. The specific tensile strength (stretching or pulling strength) of both Kevlar 29 and Kevlar 49 is over eight times greater than that of steel wire. [6]
  • Unlike most plastics it does not melt: it’s reasonably good at withstanding temperatures and decomposes only at about 450°C (850°F).
  • Unlike its sister material, Nomex, Kevlar can be ignited but burning usually stops when the heat source is removed.
  • Very low temperatures have no effect on Kevlar: DuPont found “no embrittlement or degradation” down to −196°C (−320°F).
  • Like other plastics, long exposure to ultraviolet light (in sunlight, for example) causes discoloration and some degradation of the fibers in Kevlar.
  • Kevlar can resist attacks from many different chemicals, though long exposure to strong acids or bases will degrade it over time.
  • In DuPont’s tests, Kevlar remained “virtually unchanged” after exposure to hot water for more than 200 days and its super-strong properties are “virtually unaffected” by moisture.

And what’s bad?

It’s worth noting that Kevlar also has its drawbacks. In particular, although it has very high tensile (pulling) strength, it has very poor compressive strength (resistance to squashing or squeezing). That’s why Kevlar isn’t used instead of steel as a primary building material in things like buildings, bridges, and other structures where compressive forces are common.

How is Kevlar made?

There are two main stages involved in making Kevlar. First you have to produce the basic plastic from which Kevlar is made (a chemical called poly-para-phenylene terephthalamide —no wonder they call it Kevlar). Second, you have to turn it into strong fibers. So the first step is all about chemistry; the second one is about turning your chemical product into a more useful, practical material.

Polyamides like Kevlar are polymers (huge molecules made of many identical parts joined together in long chains) made by repeating amides over and over again. Amides are simply chemical compounds in which part of an organic (carbon-based) acid replaces one of the hydrogen atoms in ammonia (NH3). So the basic way of making a polyamide is to take an ammonia-like chemical and react it with an organic acid. This is an example of what chemists call a condensation reaction because two substances fuse together into one. [7]

Artwork: Kevlar’s monomer: C=carbon, H=hydrogen, O=oyxgen, N=nitrogen, — is a single chemical bond, and = is a double bond. This basic building block is repeated over and over again in the very long chains that make up the Kevlar polymer. Source: “US Patent: 3287323: Process for the production of a highly orientable, crystallizable, filament” by Stephanie Kwolek et al.

Kevlar’s chemical structure naturally makes it form in tiny straight rods that pack closely together, like lots of stiff new pencils stuffed tightly into a box (only without the box). These rods form extra bonds between one another (known as hydrogen bonds) giving extra strength—as though you’d glued the pencils together as well. This bonded rod structure is essentially what gives Kevlar its amazing properties. (More technically speaking, we can say the Kevlar rods are showing what’s called nematic behavior (lining up in the same direction), which is also what happens in the liquid crystals used in LCDs (liquid crystal displays).)

You probably know that natural materials such as wool and cotton have to be spun into fibers before they can turned into useful textile products—and the same is true of artificial fibers such as 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. [8]

Artwork: How Kevlar is made. 1) The rodlike Kevlar molecules start off in dilute solution. 2) Increasing the concentration increases the number of molecules but doesn’t make them align. At this stage, the molecules are still tangled up and not extended into straight, parallel chains. 3) The wet-spinning process causes the rods to straighten out fully and align so they’re all oriented in the same direction—forming what’s called a nematic structure—and this is what gives Kevlar its exceptionally high strength. Image based on an original artwork from DuPont’s Kevlar Technical Guide (see references below).

What’s Kevlar used for?

Kevlar can be used by itself or as part of a composite material (one material combined with others) to give added strength. It’s probably best known for its use in bulletproof vests and knifeproof body armor, but it has dozens of other applications as well. It’s used as reinforcement in car tires, in car brakes, in the strings of archery bows, and in car, boat, and even aircraft bodies. It’s even used in buildings and structures, although not (because of its relatively low compressive strength) as the primary structural material. [9]

What makes Kevlar such a good antiballistic material?

Photo: Think of Kevlar as a lightweight modern alternative to heavy, cumbersome, medieval suits of armor! Photo by Staff Sgt. Nate Hauser courtesy of US Marine Corps.

If you’ve read our article on bullets, you’ll know that they damage things—and people—because they travel at high speeds with huge amounts of kinetic energy. Although there’s no such thing as completely “bulletproof,” materials like bulletproof glass do a good job at protecting us by absorbing (soaking up) and dissipating (spreading out) the energy of a bullet.

Kevlar is an excellent antiballistic (bullet- and knife-resistant) material because it takes a great deal of energy to make a knife or a bullet pass through it. The tightly woven fibers of highly oriented (lined-up) polymer molecules are extremely hard to move apart: it takes energy to separate them. A bullet (or a knife pushed hard by an attacker) has its energy “stolen” from it as it tries to fight its way through. If it does manage to penetrate the material, it’s considerably slowed down and does far less damage.

Although Kevlar is stronger than steel, it’s about 5.5 times less dense (the density of Kevlar is about 1.44 grams per cubic centimeter, compared to steel, which is round about 7.8–8 grams per cubic centimeter). That means a certain volume of Kevlar will weigh 5–6 times less than the same volume of steel. Think back to medieval knights with their cumbersome suits of armor: in theory, modern Kevlar gives just as much protection—but it’s light and flexible enough to wear for much longer periods.

More layers = more protection

If you think of Kevlar “soaking up” the energy of a bullet, it’s fairly obvious that a greater thickness of Kevlar—more layers of the material bonded together—will give more protection.

How much Kevlar do you need to stop a bullet? It depends on the Kevlar and it depends on the weight, type, and speed of the bullet. Kevlar comes in different weights—and bullets also come in different types and weights and travel at very different speeds, with different amounts of energy. The bigger the bullet and the faster it’s travelling, the more kinetic energy it has, the further it will penetrate, and the more damage it will do. You need more layers of Kevlar to stop bigger, faster bullets than smaller, slower ones. Typically, bulletproof vests have at least 8–16 layers of Kevlar and often 32–48 layers or even more. Some vests combine Kevlar with other materials, while others use different materials instead of Kevlar, such as Spectra®. [10]

Chart: You need a greater thickness of Kevlar body armor to stop higher-speed (velocity) bullets. In theory, the thicker the Kevlar, the shorter the distance a bullet should be able to pass through (the shorter the penetration depth); in practice, it’s a little bit more complicated than that.

Generally speaking, the more layers of heavier Kevlar you have, the more protective your “bulletproof” armor, but the heavier, bulkier, and hotter it will be to wear, and the more it will restrict your movement. You could cover yourself with a million layers of Kevlar, which might stop most everyday bullets, but it’s hardly going to be practical. So there’s a tradeoff to be made between protection and usability. And, where Kevlar’s concerned, it’s not always a matter of “thicker equals better”: there’s another qualification too. Bullets travel fast—a rifle bullet can be going 10 times faster than a race car—and they’re designed to deform when they hit things so they do more damage. According to some recent ballistics research, the Kevlar in a bulletproof vest will affect this process, sometimes making a bullet travel further into a target than if no (or less) Kevlar were used. That’s why you need a lot of Kevlar in effective bulletproof vests, both to allow for how it might alter the bullet and to soak up all the bullet’s energy.

Kevlar isn’t always enough

If you want to protect soldiers against high-velocity rifle bullets, you’re going to need much thicker armor than if you simply want to protect police officers against handgun bullets, which have lower velocity and less kinetic energy. It’s important to remember that no material is 100 percent bulletproof—and sometimes even Kevlar isn’t enough.

You can see this clearly in the official US National Institute of Justice Body Armor Classification, which ranks bulletproof vests and other body protection (made of Kevlar and other materials) on a scale from I to IV for its ability to protect against bullets fired from weapons of different power. At the low end of the scale, type IIA armor has to protect against smaller handgun bullets (typically 9mm full metal jacketed bullets weighing 8.0g or 0.3 oz and fired at about 373 m/s or 834 mph); you need at least 16 layers of Kevlar for that. Higher up the scale, type IIIA armor has to resist more powerful handheld bullets (such as .44 Magnum bullets weighing 15.6 g or 0.6 oz and fired at 436 m/s or 975 mph); that needs twice as much Kelvar—at least 30 layers. It’s important to note that even Kevlar has its limits. For protection against rifle bullets (ordinary ones or armor-piercing ones), which travel much faster (850–900 m/s or 1900–2000 mph) with considerably higher kinetic energy, Kevlar isn’t enough: you need body armor made from steel or ceramic plates (classified as type III and IV).

6 Amazing Uses for Kevlar Webbing

Kevlar webbing is a great choice for high stress applications and is used in body armor. Find out more about its uses here.

Have you ever had to move a piece of furniture? If so, odds are good that you put it in the back of a pickup truck and strapped it down. Odds are also good that you didn’t think much about the straps you were using.

As a result, you might not have realized that your cargo straps were made of Kevlar webbing. So, what is Kevlar webbing?

When people hear the term Kevlar, they usually think of bulletproof vests used by police officers and military personnel. The truth is, Kevlar has many different uses. Webbing is a form of Kevlar that many industries use.

Keep reading to learn about six of the most common uses of Kevlar webbing.

1. Cargo Straps

You might be wondering, “Is Kevlar webbing different than the Kevlar in body armor? How is Kevlar made, anyway?” To answer the first question: the molecular structure is the same, but the actual construction is different.

Kevlar webbing is often woven into ropes, cables, and straps; Kevlar is often used in cargo straps because its high load capacity is great for holding heavy objects in place during travel.

2. Harnesses

A little bit of Kevlar webbing goes a long way; a simple Kevlar harness can safely support and protect people working in high-heat environments. You can find great examples of Kevlar harnesses at Osnf.com.

3. Protective Gloves

Do you have a pair of heavy-duty, heat-resistant gloves? If so, you may have been using Kevlar webbing without realizing it! Protective gloves are another common use for Kevlar webbing.

Kevlar is highly resistant to heat and chemicals, so it’s excellent at protecting people who work with dangerous substances.

4. Belts

Belts are used in a variety of equipment; lawnmowers, wood chippers, and other machines all rely on belts to function. These belts need to be made of tough material–otherwise, you’d have to replace the belt constantly.

Few materials are tougher than Kevlar webbing, making it an ideal candidate for belt construction.

5. Furnace Roller Lining

How does Kevlar work? That’s a complicated question, but part of the answer lies in its crystal structure. This structure makes it remarkably resistant to high temperatures.

People often use Kevlar webbing to line rollers and other moving parts in furnaces.

6. Drag Rescue Devices

Firefighting is a dangerous job; the people who carry out this work need every advantage they can get. That’s where drag rescue devices come in: they allow unconscious firefighters to be pulled to safety.

Kevlar webbing is a perfect choice for drag rescue devices because it’s strong enough to support a person’s weight and heat-resistant enough to function in a burning building.

The Many Uses of Kevlar Webbing

Kevlar webbing is a strong, versatile material that you’ve probably used without even realizing it. Whether you’ve got Kevlar straps for your truck or special gloves for work, you’re familiar with a few Kevlar uses.

Kevlar straps are a must if you’re planning on moving soon! If that’s the case, check out our real estate and household blog for advice on finding the perfect home, investing in property, and more!

What Exactly is Kevlar?

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Heard of super strength Kevlar but unsure about what it is? Yeah, so were we. In today’s article we piece together all things Kevlar.

police-wearing-kevlar

Though most people are aware of Kevlar’s durable properties, many of us don’t know specifically what Kevlar is made of, nor the reason that it has such incredible toughness. So, you may be surprised to know that Kevlar is not a metal; in fact, it’s constructed from highly durable plastics. It’s also one of the strongest known materials on the face of the Earth, even more so than steel, and we continue to find new uses for it to this day.

Some of the links below are affiliate links, meaning, at no additional cost to you, we may make a commission if you click through and make a purchase.

When was Kevlar discovered?

Stephanie_Kwolek

Stephanie Kwolek, the scientist that discovered Kevlar

The specific plastic that was ultimately branded as Kevlar was first discovered in the 1960s by a Polish-American chemist named Stephanie Kwolek. Working for a chemical company named DuPont, Kwolek was searching for a stronger fiber to use in the creation of automobile tires, during a gasoline shortage. The end result was the discovery of the plastic used in the creation of Kevlar.

Kevlar is actually the registered trademark for the synthetic fiber that Kwolek developed. Similar chemical structures exist with different names. Twaron is another material that is very similar to Kevlar.

How is Kevlar made?

Kevlar gets its high strength from the numerous inter-chain bonds that make up its chemical composition while gaining additional strength from aromatic stacking interactions. The process of creating this polymer can be broken down into 2 main processes. Firstly, you must produce the base plastic that forms the building blocks of Kevlar; this plastic is called poly-para-phenylene terephthalamide, a name that is far less consumer-friendly than ‘Kevlar.’

Kevlar in raw form

Kevlar (aramid fiber)

Next, you must convert this plastic into a network of strong fibers to create the durable polyamide that we know as Kevlar. An amide is created by replacing a hydrogen atom from ammonia with part of an organic acid, which is then repeated over and over until you end up with a polyamide.

The chemical makeup of Kevlar naturally falls into small, straight rods that closely knit together and form hydrogen bonds with one another for additional strength. It is this structure that gives Kevlar such highly durable properties and makes it difficult to break apart.

It’s also impressive to note that Kevlar can maintain its chemical properties and resilience down to temperatures as low as minus 196°C, without any impact on its tensile strength. At higher temperatures, the material does not fare so well, losing approximately 10-20% of its tensile strength after a prolonged period of exposure.

How does Kevlar work?

Though Kevlar has a range of different uses, one of the best-known properties that it has is for absorbing the high-impact energy of a variety of weapons, and preventing the wearer from being injured, for example, protecting against bullets or stabbing and slashing weapons. Although this doesn’t necessarily make Kevlar products completely bulletproof, they are highly effective in protecting against fast-moving projectiles such as bullets, owing to the way that they absorb and dissipate energy.

What makes Kevlar such a good anti-ballistic material is the fact that it takes an incredibly large volume of energy to enable a bullet or knife to penetrate the fibers, as they are so tightly woven together and extremely difficult to separate without a very high volume of energy being applied. As a projectile makes contact with the Kevlar material, its energy is transferred into the Kevlar and dissipated across the surface of the polymer. Even if an object was moving quickly enough and had high enough energy to penetrate the material, it would be significantly slowed and have less potential for damage.

Though Kevlar material is stronger overall than steel, it is also approximately 5.5 times less dense, meaning that an amount of steel will weigh 5.5 times more than the same amount of Kevlar. Not only does this make a material that offers better protection against ballistic injury than steel, but also one that is far easier to incorporate into personal protective wear, as the wearer will not become over-encumbered so easily.

Recommended Next: Ever heard of tactical pens? Check out our guide next.

Popular uses of Kevlar

bulletproof vest

Now you know how to make Kevlar, as well as some of the antiballistic properties of the material, you may be interested to know that there are a variety of other applications for this extremely tough material.

So, aside from in military and law enforcement armor, what else do we use Kevlar for? On an everyday basis, there are products as small as bicycle tires and cell phone cases incorporating Kevlar into their designs.

The lining on a bike’s tire helps to guard against punctures from the road, while an insulated phone case protects a delicate cellphone from impacts when dropped. Similarly, many pairs of work gloves contain Kevlar lining, as well as chef’s gloves that are slash and stab resistant for working with sharp knives.

Here are a few other popular uses of Kevlar:

Kevlar is used in the construction of many items of motorcycle clothing, as well as for other sportswear, such as fencing outfits, horse riding equipment, and protective equipment worn by skaters.

In addition to being used in the creation of sportswear, Kevlar is also used to create some sporting equipment. For example, ping pong paddles often use Kevlar for the surface of the paddle, which can create a better rebound effect than rubber.

Kevlar has been used in the creation of loudspeaker cones, as well as within the design of some fiber optic cabling, and has even been included as part of the design for some snare drums due to its high tension.

Kevlar has been known to be used in the design of some non-stick frying pans, as a replacement for the more commonly used Teflon.

Certain brands, such as Motorola and OnePlus, have used Kevlar in the design of some of their smartphone backplates, due to their durability and the low likelihood of interfering with cell phone signals.

We hope you enjoyed learning about Kevlar in today’s post. There will be lots more like this coming over the coming weeks and months

Interested in sporting optics? We’ve got a couple of awesome guides on spotting scopes and monoculars that you don’t want to miss out on!

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Source https://www.explainthatstuff.com/kevlar.html

Source https://jumpmanjump.com/6-amazing-uses-for-kevlar-webbing/

Source https://stealthyninjas.com/what-is-kevlar/

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