Kevlar Who?, Where?, Why?, What?
Where did it all begin?
Since the beginning of time, man has harnessed the materials of mother nature and used them to his advantage to carry us through the ages. Wood, stone, metals and animal elements being our primary resources for shelter and tools in pretty much every application. Taking in mind the great pyramids of Giza were built wayyyyy before synthetic materials were developed! So why not just keep using them? This was until the turn of the 19th century (1930’s to be exact) when an American researcher called Wallace Carothers at the chemical firm DuPont, created the first fully synthetic fiber called Nylon. Which soon made its debut in the United States as a replacement for silk, just in time for the introduction of rationing during World War II. Synthetic fabrics, such as nylon and polyester, are produced entirely from chemicals. Natural fabrics, such as cotton, silk, and wool are made of fibres from plants and animals. Synthetic fabrics are useful because they have very different or enhanced (improved) properties in comparison to natural materials.
Back to the fact of the matter, why is Kevlar so important in today's world?
Why are synthetic materials such as Kevlar® used so vastly compared to natural materials that we have used since the beginning of time?
Hopefully this blog will shed some light on the pros and cons of such a great synthetic material.
What exactly is Kevlar?
In it’s essence Kevlar is a super-strong plastic that has been rigorously tested and proven to help protect against heat, fire, electric, chemicals and cut hazards.
If that is not enough to raise your eyebrows then remember both Kevlar 29 and Kevlar 49 is over eight times greater than that of steel wire based on an equal weight basis.
There are hundreds of synthetic plastics made by polymerization (joining together long chain molecules) but they have any different properties. Kevlar's incredible strength mainly lies in its internal structure (the way its molecules are arranged - parallel lines) not forgetting the way it's fibers are knitted tightly together.
Kevlar is not like most natural fabricated materials as it cannot be made right from 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). In its chemical structure, it's very similar to another versatile protective material called Nomex. Kevlar and Nomex are examples of chemicals called synthetic aromatic polyamides or aramids for short. 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 chemist Stephanie Kwolek, who earned US Patent 3,287,323 for her invention, with Paul Morgan, in 1966.
What exactly makes Kevlar so special?
“Light in Weight, High in Performance — Kevlar® Fiber”
The number of applications for Kevlar is limitless but DuPont™ Kevlar® fibers are mainly used in a variety of clothing, accessories, and equipment to help make them safer and more durable. With five times the strength of steel based on an equal weight basis, it’s the go-to fiber for protective apparel and accessories. Kevlar® fiber and filament come in a variety of types, each with its own unique set of properties and performance characteristics for different protection needs.
Kevlar® 29 (K29) & Kevlar® 49 (K49) being the two most common fibres used.
Kevlar® 29 (K29) - The original family of product types of Kevlar®, having similar tensile properties with many decitex and finishes. These yarns are used in ballistic applications, ropes and cables, protective apparel such as cut-resistant gloves, in life protection uses such as helmets, vehicular armouring, and plates, and as rubber reinforcement in tires and automotive hoses.
Kevlar® 49 (K49) - High-modulus type used primarily in fiber optic cable, textile processing, plastic reinforcement, ropes, cables, and composites for marine sporting goods and aerospace applications.
Several grades of Kevlar are available:
Kevlar K100 – coloured version of Kevlar
Kevlar K119 – higher-elongation, flexible and more fatigue resistant
Kevlar K129 – higher tenacity for ballistic applications
Kevlar AP – 15% higher tensile strength than K-29
Kevlar XP – lighter weight resin and KM2 plus fiber combination
Kevlar KM2 – enhanced ballistic resistance for armour applications
These are some of Kevlar's properties:
- Negative co-efficient of thermal expansion
- Abrasion resistance
- Withstands temperatures up to 450C when most plastics would melt and as low as -196C
- 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.
- Kevlar can withstand long exposure to many different chemicals & strong acids but will degrade it over time.
- Unlike most plastics it does not melt and can withstanding temperatures up to about 450°C (850°F).
- Its not effected by low temperatures: DuPont study found "no embrittlement or degradation" down to −196°C (−320°F).
- DuPont test studies found Kevlar’s super-strong properties remained "virtually unchanged" after exposure to hot water for more than 200 days.
- Kevlar can be ignited but burning usually stops when the heat source is removed.
- Long exposure to ultraviolet light (e.g. sunlight,) causes discolouration and some degradation of the fibres.
And what's bad?
Like everything Kevlar does have its drawbacks, surprisingly not many. Due to its very high pulling strength (tensile), it has very poor resistance to squashing or squeezing strength (compressive strength). For this reason Kevlar is not used instead of steel throughout building and bridges where compressive forces are common.
How is Kevlar made?
Summarised: The chemical obtained is turned into fibres by a process called wet spinning, which involves forcing a hot, concentrated, and very viscous solution of poly-paraphenylene terephthalamide through a spinneret (a metal former a bit like a sieve) to make long, thin, strong, and stiff fibres that are wound onto drums. The fibres are then cut to length and woven into a tough mat to make the super-strong, super-stiff finished material we know as Kevlar. Later, this fibre is woven into sheets.
In depth: 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). Secondly you have to turn it into strong fibres. 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.
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 behaviour (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
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 has many applications ranging from bicycle tires, car tires, racing sails, car brakes, in the strings of an archery bows and boat. Yet Kevlar is most famously known for its military use in bulletproof vests and knifeproof body armour.
The PASGT helmet and vest used by United States military forces, use Kevlar as a key component in their construction. Kevlar is used to manufacture gloves, sleeves, jackets, chaps and other articles of clothing designed to protect users from cuts, abrasions and heat.
It's high tensile strength-to-weight ratio measures it five times stronger than steel. It is also used to make modern marching drumheads that withstand high impact. When used as a woven material, it is suitable for mooring lines and other underwater applications.
Kevlar-based protective gear is often considerably lighter and thinner than equivalent gear made of more traditional materials. Which is why civilian applications include: high heat resistance uniforms worn by firefighters, body armour worn by police officers, security, body guards and police tactical teams such as SWAT.
Comparison between steel and Kevlar
Impact of bullet on steel
HOW IT WORKS?
When a bullet strikes body armour, it is caught in a “web” of very strong fibers. These fibers absorb and disperse the impact energy that is transmitted to the bullet proof vest from the bullet, causing the bullet to deform or “mushroom.”
What makes Kevlar such a good antiballistic material?
Kevlar is an excellent antiballistic material because it takes a great deal of energy for 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 centimetre, compared to steel, which is round about 7.8–8 grams per cubic centimetre). 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 armour: in theory, modern Kevlar gives just as much protection—but it's light and flexible enough to wear for much longer periods.
Computer Predicted and Experimental Impact Crater – Steel Only
Verses Impact on Kevlar® Panel
Experimental Impact Crater – Kevlar®
Comparison of Computer Predicted
More layers = More protection
Chart: You need a greater thickness of Kevlar body armour to stop higher-speed bullets. If you fire a bullet faster than the penetration speed, it will pierce through the armour but exit with less speed than it entered, because the armour will absorb some of its kinetic energy. Please note that this chart is simply a very rough illustration; it's not based on any particular bullet type.
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. As you can see from this chart, the more layers you have, the faster you need to fire a bullet to get it to penetrate through Kevlar armour. In other words, if you want to protect soldiers against high-velocity rifle bullets, you're going to need much thicker armour than if you simply want to protect police officers against handgun bullets, which have lower velocity and less kinetic energy.
You can see this clearly in the official US National Institute of Justice Body Armour 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 armour 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 armour 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 Kevlar—at least 30 layers. It's important to note that even Kevlar has its limits. For protection against rifle bullets (ordinary ones or armour-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 armour made from steel or ceramic plates (classified as type III and IV).
General uses of Dupont Kevlar for everyday protection
25 most common uses of Dupont Kevlar in todays world.Adhesives, Sealants, & Coatings
In adhesive, sealant, coating, and fiber reinforced plastic applications, DuPont™ Kevlar® helps provide better viscosity control and lower costs. Learn how the inherent strength and heat resistance of Kevlar® provides performance that cannot be worn or aged away.
DuPont™ Kevlar® and DuPont™ Nomex® helps manufacturers in aerospace, marine, and rail industries to build aircraft, ships, and rail carriages. Learn how the remarkable performance characteristics of Kevlar® and Nomex® can help to increase fuel efficiency – and decrease operating and maintenance costs.
Kevlar® and Nomex® brand fibers help improve the safety, performance, and durability of automotive components for a wide variety of vehicles, from passenger cars and light trucks to professional race cars. Learn how Kevlar® and Nomex® help provide inherent strength in automotive components, inside and out.
DuPont™ Kevlar® brand fiber helps improve the safety, performance, and durability of automotive components such as automotive hoses and automotive belts for a wide variety of vehicles, from passenger cars and trucks to professional race cars.
DuPont™ Kevlar® helps make a wide variety of Consumer Products light weight and Strong. Kevlar® is a product unique to DuPont invented by DuPont and is a brand and trademark owned by DuPont. Check here to be sure the products with Kevlar® you are purchasing are authentic.
DuPont™ Kevlar® helps create cost saving solutions for conveyor belts in the mining industry
Kevlar® provides high tensile strength, helping to safeguard fiber optic cables against mechanical stresses to ensure optimal performance. Learn how the inherent dielectric properties, light weight, small diameter, and flexibility of Kevlar® meet requirements for a wide variety of fiber optic cable applications.
Manufacturers use DuPont™ Kevlar® thread for seams and tape edges to help keep out flames. Learn more about the properties of this material.
For a trusted source of protection, firefighters look for turnout gear made of Nomex® and Kevlar® fibers.
The excellent strength-to-weight ratio of DuPont™ Nomex® and DuPont™ Kevlar® brings performance and value to industries such as mass transportation, construction, and marine shipping.
Our scientists and technicians have created and rigorously tested our leading brands used in industrial protective clothing, including Nomex®, Tychem®, Tyvek® and Kevlar®. Learn more about their roles in industrial safety and worker protection.
DuPont™ Kevlar® helps provide strength, endurance, and stability to enhance automotive power train and body components such as brake pads, clutches and gaskets.
Kevlar® reinforcement helps reduce weight without compromising strength in marine, energy, and maritime vessel composites.
For 40 years, Americans serving in every branch of the Armed Forces have depended upon body armour and flak jackets made with Kevlar® fiber to help protect them from combat hazards.
Kevlar® fiber is a very important part of the military’s assets. By incorporating its inherent protective technology into military helmets, it has helped to save thousands of lives.
Manufacturers of personal electronics, such as cellular phones, handheld devices, notebook computers, are turning to DuPont™ Kevlar® to help make their products more portable and durable.
Reebok has partnered with DuPont to develop a line of apparel with emphasis on the specific needs of the CrossFit® athlete
Kevlar® ropes and cables help deliver performance and value to customers in the fine gauge cable industry by helping to provide excellent robustness, fatigue resistance, shrinkage, and durability. From land to sea to space, learn how Kevlar® brand fiber has helped strengthen ropes and cables to stand up to temperature extremes and harsh environments.
In protective motorcycle apparel, DuPont™ Kevlar® fibers reinforce gloves, jackets and pants to help improve tear and abrasion resistance
Protecting people and the environment is a top priority for DuPont. DuPont collaborates with U.S. government agencies to help them develop materials, products and solutions for safety and protection.
The quest for lighter, stronger, and safer sporting goods has made Kevlar® a popular choice for both equipment manufacturers and consumers. Learn how the same properties and performance attributes that have proven so effective in industrial and life-protection applications also appeal to athletes, outdoors enthusiasts and anyone else looking for better performance in sports products.
Learn how DuPont™ Kevlar® has continued to help innovate in strength-members for the oil and gas industry.
Tactical Vests — essential equipment officers can live with because police officers never know what type of weapons or perpetrators they may come up against, wearing the right tactical vest can mean the difference between walking away from a criminal assault and facing a potentially fatal or disabling injury
DuPont™ Kevlar® Engineered Elastomer helps provide enhanced strength, resistance, and traction to tires and other goods.
MRAP vehicles made using Kevlar® fibers help protect soldiers who are involved in IED and RPG attacks
We would like to acknowledge and thank the follow site for contributing information.
1 - https://www.dupont.com/
2 - https://www.explainthatstuff.com/
3 - https://www.nij.gov/
4 - https://en.wikipedia.org/
5 - https://www.factmonster.com/