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Kevlar is a heat-resistant and strong , related to other such as and . Developed by at in 1965,

(2019). 9783527306732
this high-strength material was first commercially used in the early 1970s as a replacement for steel in racing tires. Typically it is spun into ropes or sheets that can be used as such or as an ingredient in composite material components.

Kevlar has many applications, ranging from bicycle and racing sails to , because of its high tensile strength-to-weight ratio; by this measure it is five times stronger than steel. It is also used to make modern marching that withstand high impact. When used as a woven material, it is suitable for mooring lines and other underwater applications.

A similar fiber called with the same chemical structure was developed by in the 1970s; commercial production started in 1986, and Twaron is now manufactured by .Tatsuya Hongū, Glyn O. Phillips, New Fibers, Ellis Horwood, 1990, p. 22J. K. Fink, Handbook of Engineering and Specialty Thermoplastics: Polyolefins and Styrenics, Scrivener Publishing, 2010, p. 35


History
Poly-paraphenylene terephthalamide – branded Kevlar – was invented by Polish-American chemist while working for DuPont, in anticipation of a gasoline shortage. In 1964, her group began searching for a new lightweight strong fiber to use for light but strong tires. The polymers she had been working with at the time, poly-p-phenylene-terephthalate and polybenzamide, formed while in solution, something unique to those polymers at the time.

The solution was "cloudy, upon being stirred, and of low " and usually was thrown away. However, Kwolek persuaded the technician, Charles Smullen, who ran the spinneret, to test her solution, and was amazed to find that the fiber did not break, unlike . Her supervisor and her laboratory director understood the significance of her accidental discovery and a new field of polymer chemistry quickly arose. By 1971, modern Kevlar was introduced. However, Kwolek was not very involved in developing the applications of Kevlar.


Production
Kevlar is synthesized in solution from the monomers 1,4--di ( para-phenylenediamine) and terephthaloyl chloride in a condensation reaction yielding hydrochloric acid as a byproduct. The result has behavior, and mechanical drawing orients the polymer chains in the fiber's direction. Hexamethylphosphoramide (HMPA) was the solvent initially used for the , but for safety reasons, DuPont replaced it by a solution of N-methyl-pyrrolidone and calcium chloride. As this process had been patented by Akzo (see above) in the production of , a ensued. How Kevlar® works: a simple introduction. Explainthatstuff.com (2009-12-07). Retrieved on 2012-05-26.

Kevlar (poly paraphenylene terephthalamide) production is expensive because of the difficulties arising from using concentrated , needed to keep the water-insoluble polymer in solution during its synthesis and spinning.

Several grades of Kevlar are available:

Kevlar K-29 – in industrial applications, such as cables, replacement, brake linings, and body/vehicle armor.
Kevlar K49 – high modulus used in cable and rope products.
Kevlar K100 – colored 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 K-29 AP Technical Data Sheet – Dupont
Kevlar XP – lighter weight resin and KM2 plus fiber combination Kevlar XP – Dupont
Kevlar KM2 – enhanced ballistic resistance for armor applications Kevlar KM2 Technical Description. dupont.com. Retrieved on 2012-05-26.

The ultraviolet component of sunlight degrades and decomposes Kevlar, a problem known as , and so it is rarely used outdoors without protection against sunlight.


Structure and properties
When Kevlar is spun, the resulting fiber has a of about 3,620 MPa, and a of 1.44. The polymer owes its high strength to the many inter-chain bonds. These inter-molecular form between the carbonyl groups and N H centers. Additional strength is derived from aromatic stacking interactions between adjacent strands. These interactions have a greater influence on Kevlar than the van der Waals interactions and chain length that typically influence the properties of other synthetic polymers and fibers such as . The presence of salts and certain other impurities, especially , could interfere with the strand interactions and care is taken to avoid inclusion in its production. Kevlar's structure consists of relatively rigid molecules which tend to form mostly planar sheet-like structures rather like protein.Michael C. Petty, Molecular electronics: from principles to practice, John Wiley & Sons, 2007, p. 310


Thermal properties
Kevlar maintains its strength and resilience down to cryogenic temperatures (−196 °C); in fact, it is slightly stronger at low temperatures. At higher temperatures the tensile strength is immediately reduced by about 10–20%, and after some hours the strength progressively reduces further. For example: enduring 160 °C (320 °F) for 500 hours, reduces strength by about 10%; and enduring 260 °C (500 °F) for 70 hours, reduces strength by about 50%. KEVLAR Technical Guide. dupont.com. Retrieved on 2012-05-26.


Applications

Protection

Cryogenics
Kevlar is often used in the field of for its low thermal conductivity and high strength relative to other materials for purposes. It is most often used to suspend a salt enclosure from a superconducting magnet mandrel in order to minimize any heat leaks to the paramagnetic material. It is also used as a thermal standoff or structural support where low heat leaks are desired.


Armor
Kevlar is a well-known component of such as , ballistic face masks, and . The PASGT helmet and vest used by military forces, use Kevlar as a key component in their construction. Other military uses include bulletproof face masks and spall liners used to protect the crews of armoured fighting vehicles. Nimitz-class aircraft carriers use Kevlar reinforcement in vital areas. Civilian applications include: high heat resistance uniforms worn by firefighters, body armour worn by police officers, security, and police tactical teams such as . Body Armor Made with Kevlar. (2005-0604). DuPont the Miracles of Science. Retrieved November 4, 2011


Personal protection
Kevlar is used to manufacture gloves, sleeves, jackets, and other articles of clothing Kevlar – DuPont Personal Protection. .dupont.com. Retrieved on 2012-05-26. designed to protect users from cuts, abrasions and heat. Kevlar-based protective gear is often considerably lighter and thinner than equivalent gear made of more traditional materials.


Sports

Personal protection
It is used for motorcycle safety clothing, especially in the areas featuring padding such as shoulders and elbows. In it is used in the protective jackets, breeches, plastrons and the bib of the masks. It is increasingly being used in the peto, the padded covering which protects the ' horses in the bullring. also frequently wear an under-layer of Kevlar fabric to prevent potential wounds from skates in the event of a fall or collision.


Equipment
In , or Japanese , it may be used as an alternative to more expensive for . It is one of the main materials used for suspension lines. It is used as an inner lining for some to prevent punctures. In , plies of Kevlar are added to custom ply blades, or paddles, in order to increase bounce and reduce weight. are sometimes strung with Kevlar. It is used in sails for high performance racing boats.


Shoes
In 2013, with advancements in technology, Nike used Kevlar in shoes for the first time. It launched the Elite II Series, with enhancements to its earlier version of by using Kevlar in the anterior as well as the . This was done to decrease the elasticity of the tip of the shoe in contrast to nylon used conventionally as Kevlar expanded by about 1% against nylon which expanded by about 30%. Shoes in this range included LeBron, HyperDunk and Zoom Kobe VII. However these shoes were launched at a price range much higher than average cost of basketball shoes. It was also used in the laces for the F50 adiZero Prime football boot.


Cycle tires
Several companies, including , manufacture cycle tires with Kevlar to protect against punctures.

Folding-bead bicycle tires, introduced to cycling by /ref> use Kevlar as a bead in place of steel for weight reduction and strength. A side effect of the folding bead is a reduction in shelf and floor space needed to display cycle tires in a retail environment, as they are folded and placed in small boxes.


Music

Audio equipment
Kevlar has also been found to have useful acoustic properties for cones, specifically for bass and mid range drive units. Audio speaker use. Audioholics.com (2009-07-23). Retrieved on 2012-05-26. Additionally, Kevlar has been used as a in fiber optic cables such as the ones used for audio data transmissions. Welcome to Kevlar. (2005-06-04). DuPont the Miracles of Science. Retrieved November 4, 2011


Bowed string instruments
Kevlar can be used as an acoustic core on bows for string instruments. carbon fiber bows for violin, viola, cello and bass . CodaBow. Retrieved on 2012-05-26. Kevlar's physical properties provide strength, flexibility, and stability for the bow's user. To date, the only manufacturer of this type of bow is . carbon fiber bows for violin, viola, cello and bass . CodaBow. Retrieved on 2012-05-26.

Kevlar is also presently used as a material for tailcords (a.k.a. tailpiece adjusters), which connect the to the of bowed string instruments. Tailpieces and Tailcords Aitchison Mnatzaganian cello makers, restorers and dealers. Retrieved on 2012-12-17.


Drumheads
Kevlar is sometimes used as a material on marching snare drums. It allows for an extremely high amount of tension, resulting in a cleaner sound. There is usually a resin poured onto the Kevlar to make the head airtight, and a nylon top layer to provide a flat striking surface. This is one of the primary types of marching snare drum heads. 's Falam Slam patch is made with Kevlar and is used to reinforce bass drum heads where the beater strikes.


Woodwind reeds
Kevlar is used in the woodwind reeds of Fibracell. The material of these reeds is a composite of aerospace materials designed to duplicate the way nature constructs cane reed. Very stiff but sound absorbing Kevlar fibers are suspended in a lightweight resin formulation.


Motor vehicles

Chassis and bodywork
Https://www.topgear.com/car-news/classic/story-ferrari-f40-its-creators< /ref>


Brakes
The chopped fiber has been used as a replacement for asbestos in . Dust produced from asbestos brakes is toxic, while aramids are a benign substitute.


Other uses

Fire dancing
Wicks for props are made of composite materials with Kevlar in them. Kevlar by itself does not absorb fuel very well, so it is blended with other materials such as or . Kevlar's high heat resistance allows the wicks to be reused many times.


Frying pans
Kevlar is sometimes used as a substitute for in some non-stick frying pans.M.Rubinstein, R.H.Colby, Polymer Physics, Oxford University Press, p337


Rope, cable, sheath
The fiber is used in woven rope and in cable, where the fibers are kept parallel within a sleeve. The cables have been used in suspension bridges such as the bridge at Aberfeldy in . They have also 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. When used in this application it is commonly known by the trademarked name Parafil.


Electricity generation
Kevlar was used by scientists at Georgia Institute of Technology as a base textile for an experiment in electricity-producing clothing. This was done by weaving into the fabric. If successful, the new fabric will generate about 80 milliwatts per square meter. Fabric Produces Electricity As You Wear It. Scientific American (2008-02-22). Retrieved on 2012-05-26.


Building construction
A retractable roof of over 60,000 square feet (5,575 square metres) of Kevlar was a key part of the design of Montreal's Olympic stadium for the 1976 Summer Olympics. It was spectacularly unsuccessful, as it was completed 10 years late and replaced just 10 years later in May 1998 after a series of problems. Clem's Baseball ~ Olympic Stadium. Andrewclem.com. Retrieved on 2012-05-26.


Expansion joints and hoses
Kevlar can be found as a reinforcing layer in and rubber hoses, for use in high temperature applications, and for its high strength. It is also found as a braid layer used on the outside of hose assemblies, to add protection against sharp objects.
(2019). 9781845697570, Woodhead Publishing. .


Particle physics
A thin Kevlar window has been used by the NA48 experiment at to separate a vacuum vessel from a vessel at nearly atmospheric pressure, both 192 cm in diameter. The window has provided vacuum tightness combined with reasonably small amount of material (only 0.3% to 0.4% of ).


Smartphones
The , the , and the OnePlus 2 have a Kevlar backplate, chosen over other materials such as carbon fiber due to its resilience and lack of interference with signal transmission. Droid RAZR. (2011-10-11). Motorola Mobility. Retrieved November 4, 2011


Marine current turbines and wind turbines
The Kevlar fiber/epoxy matrix composite materials can be used in marine current turbines (MCT) or wind turbines due to their high specific strength and light weight compared to other fibers.


Composite materials
Aramid fibers are widely used for reinforcing composite materials, often in combination with and glass fiber. The matrix for high performance composites is usually . Typical applications include bodies for F1 , rotor blades, , , and squash , , bats, and , and sticks.Kadolph, Sara J. Anna L. Langford. Textiles, Ninth Edition. Pearson Education, Inc 2002. Upper Saddle River, NJRonald V. Joven. Manufacturing Kevlar panels by thermo-curing process. Los Andes University, 2007. Bogotá, Colombia.

Kevlar is an alternative in certain parts of light aircraft construction. The wing leading edge is one application, Kevlar being less prone than carbon or glass fiber to break in bird collision.


See also


External links

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