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Kevlar Uses, Properties and Applications

All about KEVLAR – Process, Manufacturing and Applications

The world has seen some remarkable progress in technology over the years. From ceramics to steel, we are now able to make materials with incredible strength and durability. One of the most impressive advancements is the development of KEVLAR fiber, which has been proven to have the same strength as steel when both are equal in weight.

This material is used for a variety of applications, including body armor and high-performance specialty fabrics. KEVLAR fiber is even used in bulletproof vests and other protective gear, providing maximum protection to its wearer. It’s truly amazing to see such progress being made with technology!

Not only is this advancement in fiber beneficial for safety purposes, but it can also be used to make lighter and more durable fabrics for clothing. This means that consumers are able to enjoy high-end fashion items with the knowledge that they will remain in style for longer than normal fabric. KEVLAR fiber’s versatility is truly remarkable!

History Behind KEVLAR

The invention of KEVLAR fiber is credited to Stephanie Kwolek, an American chemist working for DuPont in the 1960s. In anticipation of a gasoline shortage, her team began searching for a new lightweight strong fiber to use for tires. The result was Poly-paraphenylene terephthalamide or K29 – branded Kevlar, which was found to have tensile strength five times more than steel.

What exactly is KEVLAR?

In scientific terms, KEVLAR is basically poly para-phenyleneterephthalamide (PPD-T) commonly known as para-aramid with a molecular structure of inter-chain bonds with properties like heat resistance, high strength and lightweight.

KEVLAR is synthetic and man made polymer

In simple terms, we can explicitly say, “Kevlar is the Super plastic“. Plastic is formed by polymerization of organic materials with widely different properties and KEVLAR is just an example of it, but specifically designed to replace steel in various applications.

KEVLAR Polymer is extraordinary because it has been specially crafted to replace steel in various applications. Unlike traditional polymers that are composed of natural materials like wool or cotton, KEVLAR is an entirely man-made product with unique properties and advantages.

The unique material that is KEVLAR has been patented by DuPont, and they are the only company who holds exclusive rights to produce various forms of this innovative product.

Reasons why KEVLAR is so Impressive

As we mentioned earlier, its a para aramid fiber with complex interconnected chains in KEVLAR structure, we are going to breakdown this term to make this definition more simpler:

  1. Synthetic material designed for specific application unlike wool or cotton.
  2. Aromatic chains within KEVLAR Chemical structure which is ring like carbon bonds giving us stable organic structure similar to Benzene.
  3. Polyamide or para-aramid fiber means ring like structure is connected in long chains that are interconnected to generate complex fiber giving strength equal to steel.
  4. Polymer means aromatic long chains interconnected with similar monomer.
Aromatic chains in KEVLAR Structure

Structure of KEVLAR

Structure of Kevlar is shown below;

Kevlar structure

Kevlar is a poly para-phenyleneterephthalamide (PPD-T) commonly known as para-aramid. The structure is composed of benzene rings responsible for high thermal stability along with para substitutions which result in high modulus and strength.

The filaments for fibers are extruded through the spinning of the precursor. The extruded rod-like para-aramid structure has high anisotropic KEVLAR properties. The strength and stiffness is higher in the axial direction and lowers in the transverse direction.

Grades of KEVLAR

KEVLAR is commercially available aramid fiber with excellent heat resistance and high stifness related to other aramid variants like Nomex. DuPoint, firstly, deveoped KEVLAR fiber in 1970 for their use in racing tires as a replacement of steel. It is commonly available in grades like K-29, K-49, K-100, K-119, and K-129.

Presently, KEVLAR Grades are available in following:

  • Kevlar K-29 – It is a high toughness grade used in industrial applications, such as cables, body/vehicle armor, brake linings.
  • Kevlar K49 – It has a high modulus used in rope and cable products.
  • K100 – The colored version of Kevlar
  • Kevlar K119 – It has higher-elongation, and more fatigue resistant
  • Kevlar K129 – It is a higher tenacity grade utilized in ballistic applications
  • Kevlar AP – It has 15% higher tensile strength than K-29.
Bullet Test on K29 Kevlar Grade

KEVLAR Manufacturing Process

Kevlar is made from a condensation reaction of 1,4- para-phenylenediamine and terephthalic acid. The presence of amine groups on aromatic ring results in a rod-like structure which has high glass transition temperature and low solubility.

The chains of polymer are connected to each other via Hydrogen bonding between adjacent polar amide groups explaining what is Kevlar. The fiber structure is consisting of orderly oriented molecules parallel to one another forming crystalline structure.  

Due to high glass transition temperature and poor solubility, These fibers are difficult to process via conventional drawing techniques hence melt spinning is used for their fabrication. 

During melt spinning, the PPD-T solution is extruded in a spinneret and drawn through an air gap resulting in the orientation of the liquid crystalline domains in the flow direction. The polymer chains also align in a fiber axis resulting in a high degree of anisotropy in this direction.

Manufacturing reaction of KEVLAR fiber

Melt Spinning Process

Fibers are manufactured by melt spinning of PPD-T solution extruded through a spinneret and then directly solidification upon cooling. The solution is heated to attain required viscosity in induction heated extruders.

This melt is passed at high pressure and constant rate from a spinneret and enters an air-cooled stream which solidifies it into a filament form. At the lower end of the spinning setup, a guided coverage converts these individual filaments to form a continuous spun yarn. This yarn is then wound onto bobbins or treated further for end-use applications.

Melt Spinning of KEVLAR

KEVLAR Mechanical Properties

Kevlar fibers have tensile strength twice than Nylon 6,6 ranging from about 2.6 to 4.1 GPa. The mechanical properties of different grades are given in the table below:

GradeDensity (g/cm3)Tensile Modulus (GPa)Tensile Strength (GPa)Elongation (%)
291.44833.64
491.441313.6-4.12.8
1491.471863.42.0

The structure of Kevlar has unique kinks bands responsible for the compression buckling of molecules and hence they behave elastically in tension. In compression, they yield at 0.3% to 0.5% strain and shows nonlinear, ductile behavior. The high thermal stability attributed to aromatic rings makes these fibers inherently flame resistant with a decomposition temperature of about 425°C. and are inherently flame resistant. The generic properties of these fibers are:

Other Properties of KEVLAR fiber

KEVLAR is not called super plastic only because of its strength. Reason for its excellent performance is combination of awesome properties making it ideal replacement of steel.

Cut & Puncture Resistance

Kevlar fibers have high cut and puncture resistance due to their alignment. The molecular chains are arranged in layers, thus providing a strong barrier against sharp edges.

High Tensile Strength

The presence of inter-chain hydrogen bonds between the adjacent molecules provides Kevlar with excellent tensile strength which is ten times greater than steel on equal weight basis.

Chemical Stability

Kevlar fibers are resistant to most organic solvents and have excellent chemical stability due to aromatic nature of the polymer chains. 

Lightweight & Durable

Despite having such strong properties, Kevlar is lightweight material making it suitable for applications such as body armor and ballistic protection. It is also durable and has low moisture absorption which makes it resistant to deterioration.

Thermal Stability

Kevlar fibers can withstand high temperatures up to around 425°C and have excellent flame-retardant properties. 

No Embrittlement

Kevlar exhibits no embrittlement or degradation even at temperatures down to -196°C.

Only Drawback is Poor Compression Strength

The only drawback of Kevlar is that it has poor compression strength which limits its application in the building and construction industry. That’s why usage of KEVLAR instead of steel as a primary building material in things like buildings. Despite this disadvantage, the material has found many useful applications, ranging from body armor to ropes and cables.

Stress-strain curve for tensile and compression test loading of Kevlar29_ Epoxy with Al 6061-T6 laminated plate
Stress-strain curve for tensile and compression test loading of Kevlar29_ Epoxy with Al 6061-T6 laminated plate

KEVLAR Applications

The exceptional and unique KEVLAR Characteristics enable them to apply in a variety of applications. These applications of KEVLAR range from premium sports goods and deep-sea umbilical lines and to high-performance structural composites in aircraft components, boat hulls, and high-performance cars.           

The high tenacity and thermally stable fibers are used for lightweight bulletproof body armor, and also due to weight-saving it can also replace heavier materials in airplanes, for fuel saving. The textile application was explored by Baxter, a textile engineering graduate of Clemson University, who fabricated a Draggin’ Jeans, using 100% Kevlar in denim jeans.

Kevlar function in Vehicle fuel tanks

Fuel tanks on contemporary race vehicles are strengthened with Kevlar. Kevlar’s great tensile strength makes it harder to pierce the fuel tanks in the event of an accident. 

This significantly reduced the possibility of fire in a crash. These tanks are also highly lightweight and flexible, which makes it simple for them to fit into small locations inside the vehicle.

Body Armour

KEVLAR Armor

Kevlar is quite effective at deflecting gunshots and knife slashes. It can absorb a significant amount of energy before giving way. It’s body Armour has the capacity to significantly slow down bullets that are moving quickly, giving protection upon impact. 

Steel plates were typically utilized as body Armour in the past. It has been used to make body Armour lighter and more flexible.

Tyres for off-road vehicles

Kevlar is utilized to give the side walls of the Tyre, which have an impact on handling and cornering, more rigidity. The Tyre becomes more resistant to punctures by adding Kevlar to it.  For off-road vehicles traversing tough terrain and jagged rocks, this is crucial.

KEVLAR Types

Protective sportswear for individuals:

Numerous motorcycle clothing pieces, as well as other sportswear including fencing outfits, horse riding gear, and protective gear worn by skaters, are made of Kevlar. 

Kevlar 29 is the specific grade of Kevlar fiber cloth used for protective applications. The military and law enforcement organizations are the main users of its fabric for protective applications such as bulletproof vests and helmets. 

Bulletproof vests made of Kevlar fabric have saved the lives of thousands of police officers and military personnel in the line of duty.

KEVLAR usese for Unbending Protective layer

  • Caps
  • Protected vehicles
  • Freight compartments
  • Military Humvees
  • Impact regulation
  • Protection plates and safeguards

Audio apparatus

Due to its high tension, Kevlar has even been included in the design of some snare drums. It has also been used to make loudspeaker cones, some fiber optic cabling, and some fiber optic cables.

Cookware

Kevlar has reportedly been utilized as an alternative to Teflon in the construction of some non-stick frying pans. The Kevlar provides a high temperature and heat resistance as well as a non-stick surface.

Mobile phones

Due to its durability and low risk of affecting mobile phone signals, some firms, like Motorola and OnePlus, have incorporated Kevlar in the design of some of their smartphone backplates.

Innovating kevlar usage include smart garments and charging cases. 

KEVLAR Strings

In tennis strings, high durability is considered a primary factor for consideration. KEVLAR Grade 16, 17, and 18 are primary grades which are used for making KEVLAR Strings. Polyester has slowly replaced KEVLAR strings due to better strength and durability.

Application in Ropes, Cables, and Suspension bridges

Kevlar in Suspension Bridges

Kevlar fiber is used in rope and in cable, where the fibers are kept parallel within a polyethylene sleeve. The cables have been used to stabilize cracking concrete cooling towers by circumferential application followed by tensioning to close the cracks. 

Kevlar is widely used as a protective outer sheath for optical fiber cable, as its strength protects the cable from damage and kinking. It is also extensively used in suspension bridges such as the bridge at Aberfeldy, Scotland. 

Kevlar Fabric Uses for Speed Skating

Kevlar is valued for its strong tensile strength, low weight and flexibility when used in protective clothing. It is often used for speed skaters’ team suits to reduce the possibility of cuts or abrasions from sharp skate blades. The low weight also helps with aerodynamic efficiency as the skater moves quickly across the ice. 

Kevlar fabric is also sometimes utilized as an under-layer of protection for speed skaters in the event of a fall or collision to protect against potential wounds from skates. The lightweight, flexible fabric helps to further minimize risk while maximizing both comfort and performance on the ice. 

Kevlar in Speed Skating

Conclusion

Kevlar is a strong, lightweight material that has many applications in a variety of industries. It is used for body armor, protective sports clothing, soundproofing and audio apparatus, cookware, mobile phones and cables and suspension bridges. 

Kevlar also provides protection to speed skaters from potential injuries due to falls or collisions. This material is an essential part of ensuring safety in the world today. It is clear why Kevlar has become a highly sought after material for its many valuable applications.