Kevlar canoe algonquin.JPG
   HOME

TheInfoList



OR:

Kevlar (para-aramid) is a strong, heat-resistant
synthetic fiber Synthetic fibers or synthetic fibres (in British English; see spelling differences) are fibers made by humans through chemical synthesis, as opposed to natural fibers that are directly derived from living organisms, such as plants (like cotton) ...
, related to other aramids such as Nomex and Technora. Developed by
Stephanie Kwolek Stephanie Louise Kwolek (; July 31, 1923 – June 18, 2014) was a Polish-American chemist who is known for inventing Kevlar. Her career at the DuPont company spanned more than 40 years. She discovered the first of a family of synthetic fibers of ...
at
DuPont DuPont de Nemours, Inc., commonly shortened to DuPont, is an American multinational chemical company first formed in 1802 by French-American chemist and industrialist Éleuthère Irénée du Pont de Nemours. The company played a major role in ...
in 1965, the high-strength material was first used commercially in the early 1970s as a replacement for steel in racing tires. It is typically spun into ropes or fabric sheets that can be used as such, or as an ingredient in composite material components. Kevlar has many applications, ranging from bicycle tires and racing sails to
bulletproof vest A bulletproof vest, also known as a ballistic vest or a bullet-resistant vest, is an item of body armor that helps absorb the impact and reduce or stop penetration to the torso from firearm-fired projectiles and fragmentation from explosions. T ...
s, all due to 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 drumheads that withstand high impact; and for mooring lines and other underwater applications. A similar fiber called Twaron with the same chemical structure was developed by Akzo in the 1970s; commercial production started in 1986, and Twaron is now manufactured by Teijin.


History

Poly-paraphenylene terephthalamide (K29) – branded Kevlar – was invented by the American chemist
Stephanie Kwolek Stephanie Louise Kwolek (; July 31, 1923 – June 18, 2014) was a Polish-American chemist who is known for inventing Kevlar. Her career at the DuPont company spanned more than 40 years. She discovered the first of a family of synthetic fibers of ...
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
liquid crystal Liquid crystal (LC) is a state of matter whose properties are between those of conventional liquids and those of solid crystals. For example, a liquid crystal may flow like a liquid, but its molecules may be oriented in a crystal-like way. T ...
s while in solution, something unique to those polymers at the time. The solution was "cloudy,
opalescent Opalescence refers to the optical phenomena displayed by the mineraloid gemstone opalopalescent. 2019. In Noah Webster's 1828 American Dictionary of the English Language. Retrieved January 7, 2019, from https://1828.mshaffer.com/d/word/opale ...
upon being stirred, and of low viscosity" 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 nylon. Her supervisor and her laboratory director understood the significance of her 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. Kevlar 149 was invented by Dr.
Jacob Lahijani Jacob (; ; ar, يَعْقُوب, Yaʿqūb; gr, Ἰακώβ, Iakṓb), later given the name Israel, is regarded as a patriarch of the Israelites and is an important figure in Abrahamic religions, such as Judaism, Christianity, and Islam. Jac ...
of Dupont in the 1980s.


Production

The reaction of 1,4-phenylene-diamine (''para''-phenylenediamine) with terephthaloyl chloride yielding Kevlar Kevlar is synthesized in solution from the monomers 1,4-
phenylene In organic chemistry, the phenylene group () is based on a di-substituted benzene ring ( arylene). For example, poly(''p''-phenylene) is a polymer A polymer (; Greek '' poly-'', "many" + ''-mer'', "part") is a substance or material cons ...
-di amine ( ''para''-phenylenediamine) and
terephthaloyl chloride Terephthaloyl chloride (TCL, 1,4-benzenedicarbonyl chloride) is the acyl chloride of terephthalic acid. It is a white solid. It is one of two precursors used to make Kevlar(R), the other being ''p''-phenylenediamine. TCL is used as a key compone ...
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. Hexamethylphosphoramide (HMPA) was the solvent initially used for the polymerization, 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 Twaron, a
patent war A patent war is a "battle" between corporations or individuals to secure patents for litigation, whether offensively or defensively. There are ongoing patent wars between the world's largest technology and software corporations. Contemporary pate ...
ensued. Kevlar production is expensive because of the difficulties arising from using concentrated
sulfuric acid Sulfuric acid (American spelling and the preferred IUPAC name) or sulphuric acid ( Commonwealth spelling), known in antiquity as oil of vitriol, is a mineral acid composed of the elements sulfur, oxygen and hydrogen, with the molecular formu ...
, needed to keep the water-insoluble polymer in solution during its synthesis and
spinning Spin or spinning most often refers to: * Spinning (textiles), the creation of yarn or thread by twisting fibers together, traditionally by hand spinning * Spin, the rotation of an object around a central axis * Spin (propaganda), an intentionally b ...
. Several grades of Kevlar are available: * ''Kevlar K-29'' – in industrial applications, such as cables,
asbestos Asbestos () is a naturally occurring fibrous silicate mineral. There are six types, all of which are composed of long and thin fibrous crystals, each fibre being composed of many microscopic "fibrils" that can be released into the atmosphere b ...
replacement, tires, and brake linings. * ''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 K149'' – highest tenacity for ballistic, armor, and aerospace applications * ''Kevlar AP'' – 15% higher tensile strength than K-29 * ''Kevlar XP'' – lighter weight resin and KM2 plus fiber combination * ''
Kevlar KM2 Kevlar KM2 is a synthetic para-aramid fibre produced by DuPont. The fiber is an evolution of the original Kevlar fibre. The following quotes summarise Kevlar KM2's properties. "DuPont created Kevlar KM2 to achieve the performance goals defined by ...
'' – enhanced ballistic resistance for armor applications The ultraviolet component of sunlight degrades and decomposes Kevlar, a problem known as '' UV degradation'', and so it is rarely used outdoors without protection against sunlight.


Structure and properties

When Kevlar is spun, the resulting fiber has a tensile strength of about , and a
relative density Relative density, or specific gravity, is the ratio of the density (mass of a unit volume) of a substance to the density of a given reference material. Specific gravity for liquids is nearly always measured with respect to water at its densest ...
of 1.44 (0.052 lb/in3). The polymer owes its high strength to the many inter-chain bonds. These inter-molecular
hydrogen bonds In chemistry, a hydrogen bond (or H-bond) is a primarily electrostatic force of attraction between a hydrogen (H) atom which is covalently bound to a more electronegative "donor" atom or group (Dn), and another electronegative atom bearing a ...
form between the carbonyl groups and N''H'' centers. Additional strength is derived from
aromatic stacking interaction In chemistry, pi stacking (also called π–π stacking) refers to the presumptive attractive, noncovalent pi interactions ( orbital overlap) between the pi bonds of aromatic rings. However this is a misleading description of the phenomena sinc ...
s 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
ultra-high-molecular-weight polyethylene Ultra-high-molecular-weight polyethylene (UHMWPE, UHMW) is a subset of the thermoplastic polyethylene. Also known as high-modulus polyethylene, (HMPE), it has extremely long chains, with a molecular mass usually between 3.5 and 7.5 million amu. T ...
. The presence of salts and certain other impurities, especially calcium, 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 silk protein.


Thermal properties

Kevlar maintains its strength and resilience down to cryogenic temperatures (): 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 for 500 hours, its strength is reduced by about 10%; and enduring for 70 hours, its strength is reduced by about 50%.


Applications


Science

Kevlar is often used in the field of cryogenics for its low thermal conductivity and high strength relative to other materials for suspension purposes. It is most often used to suspend a paramagnetic salt enclosure from a
superconducting magnet A superconducting magnet is an electromagnet made from coils of superconducting wire. They must be cooled to cryogenic temperatures during operation. In its superconducting state the wire has no electrical resistance and therefore can conduct mu ...
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. A thin Kevlar window has been used by the
NA48 experiment The NA48 experiment was a series of particle physics experiments in the field of kaon physics being carried out at the North Area of the Super Proton Synchrotron at CERN. The collaboration involved over 100 physicists mostly from Western Europe ...
at
CERN The European Organization for Nuclear Research, known as CERN (; ; ), is an intergovernmental organization that operates the largest particle physics laboratory in the world. Established in 1954, it is based in a northwestern suburb of Gene ...
to separate a vacuum vessel from a vessel at nearly atmospheric pressure, both in diameter. The window has provided vacuum tightness combined with reasonably small amount of material (only 0.3% to 0.4% of radiation length).


Protection

Kevlar is a well-known component of personal armor such as
combat helmet A combat helmet or battle helmet is a type of helmet. It is a piece of personal armor designed specifically to protect the head during combat. Modern combat helmets are mainly designed to protect from shrapnel and fragments, offer some protec ...
s,
ballistic face mask A ballistic face mask, also known as facial armor, is a type of personal armor designed to protect the wearer's face from ballistic threats. Ballistic face masks are usually made of Kevlar or other bullet resistant materials and the inside of the m ...
s, and ballistic vests. The PASGT helmet and vest used by United States military forces, use Kevlar as a key component in their construction. Other military uses include bulletproof face masks and
spall liner Military vehicles are commonly armoured (or armored; American and British English spelling differences#-our, -or, see spelling differences) to withstand the impact of Fragmentation (weaponry), shrapnel, bullets, Shell (projectile), shells, Rocke ...
s 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
SWAT In the United States, a SWAT team (special weapons and tactics, originally special weapons assault team) is a police tactical unit that uses specialized or military equipment and tactics. Although they were first created in the 1960s to ...
.Body Armor Made with Kevlar
. (2005-0604). DuPont the Miracles of Science. Retrieved November 4, 2011
Kevlar is used to manufacture gloves, sleeves, jackets,
chaps Chaps ( or ) are sturdy coverings for the legs consisting of leggings and a belt. They are buckled on over trousers with the chaps' integrated belt, but unlike trousers, they have no seat (the term "assless chaps" is a tautology) and are not jo ...
and other articles of clothing 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. It is used for
motorcycle safety clothing To improve motorcycle safety many countries mandate the wearing of personal protective equipment such as protective clothing and helmets. Protective clothing may include certain types of jackets, gloves, boots, and pants. Jackets meant for motor ...
, especially in the areas featuring padding such as the shoulders and elbows. In the sport of fencing 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 picadors' horses in the bullring. Speed skaters also frequently wear an under-layer of Kevlar fabric to prevent potential wounds from skates in the event of a fall or collision.


Sport

In '' kyudo'', or Japanese
archery Archery is the sport, practice, or skill of using a bow to shoot arrows.Paterson ''Encyclopaedia of Archery'' p. 17 The word comes from the Latin ''arcus'', meaning bow. Historically, archery has been used for hunting and combat. In m ...
, it may be used for bow strings, as an alternative to the more expensive
hemp Hemp, or industrial hemp, is a botanical class of ''Cannabis sativa'' cultivars grown specifically for industrial or medicinal use. It can be used to make a wide range of products. Along with bamboo, hemp is among the fastest growing plants o ...
. It is one of the main materials used for paraglider suspension lines. It is used as an inner lining for some bicycle tires to prevent punctures. In table tennis, plies of Kevlar are added to custom ply blades, or paddles, in order to increase bounce and reduce weight.
Tennis racquets A racket, or racquet, is a sports implement used for striking a ball or shuttlecock in games such as squash, tennis, racquetball, badminton and padel. In the strictest sense a racket consists of a handled frame with an open hoop across which a ...
are sometimes strung with Kevlar. It is used in sails for high performance racing boats. 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 basketball shoes by using Kevlar in the
anterior Standard anatomical terms of location are used to unambiguously describe the anatomy of animals, including humans. The terms, typically derived from Latin or Greek roots, describe something in its standard anatomical position. This position prov ...
as well as the
shoe lace Shoelaces, also called shoestrings (US English) or bootlaces (UK English), are a system commonly used to secure shoes, boots, and other footwear. They typically consist of a pair of strings or cords, one for each shoe, finished off at both e ...
s. This was done to decrease the elasticity of the tip of the shoe in contrast to the nylon conventionally used, 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
Adidas Adidas AG (; stylized as adidas since 1949) is a German multinational corporation, founded and headquartered in Herzogenaurach, Bavaria, that designs and manufactures shoes, clothing and accessories. It is the largest sportswear manufactur ...
F50 adiZero Prime football boot. Several companies, including
Continental AG Continental AG, commonly known as Continental or colloquially as Conti, is a German multinational automotive parts manufacturing company specializing in tires, brake systems, interior electronics, automotive safety, powertrain and chassis compo ...
, manufacture cycle tires with Kevlar to protect against punctures. Folding-bead bicycle tires, introduced to cycling by
Tom Ritchey Tom Ritchey (born 1956) is an American bicycle frame builder, Category 1 racer, fabricator, designer, and founder of Ritchey Design. Ritchey is a US pioneer in modern frame building and the first production mountain bike builder/manufacturer i ...
in 1984, 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

Kevlar has also been found to have useful acoustic properties for loudspeaker cones, specifically for bass and mid range drive units. Additionally, Kevlar has been used as a
strength member Strength may refer to: Physical strength *Physical strength, as in people or animals *Hysterical strength, extreme strength occurring when people are in life-and-death situations *Superhuman strength, great physical strength far above human ca ...
in fiber optic cables such as the ones used for audio data transmissions. Kevlar can be used as an acoustic core on bows for
string instruments String instruments, stringed instruments, or chordophones are musical instruments that produce sound from vibrating strings when a performer plays or sounds the strings in some manner. Musicians play some string instruments by plucking the Str ...
. 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 CodaBow. Kevlar is also presently used as a material for tailcords (a.k.a. tailpiece adjusters), which connect the tailpiece to the
endpin The endpin is the component of a cello or double bass that makes contact with the floor to support the instrument's weight. It is made of metal, carbon fiber, or, occasionally, wood, and is typically extensible from the bottom of the instrument, s ...
of bowed string instruments. 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. Remo's Falam Slam patch is made with Kevlar and is used to reinforce bass drum heads where the beater strikes. 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

Kevlar is sometimes used in structural components of cars, especially high-value performance cars such as the
Ferrari F40 The Ferrari F40 (''tipo'' F120) is a mid-engine, rear-wheel drive sports car engineered by Nicola Materazzi with styling by Pininfarina. It was built from 1987 until 1992, with the LM and GTE race car versions continuing production until 1994 ...
. The chopped fiber has been used as a replacement for asbestos in brake pads. Aramids such as Kevlar release less airborne fibres than
asbestos Asbestos () is a naturally occurring fibrous silicate mineral. There are six types, all of which are composed of long and thin fibrous crystals, each fibre being composed of many microscopic "fibrils" that can be released into the atmosphere b ...
brakes and do not have the carcinogenic properties associated with asbestos.


Other uses

Fire poi on a beach in San Francisco Kevlar mooring line Wicks for fire dancing 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 fiberglass or cotton. Kevlar's high heat resistance allows the wicks to be reused many times. Kevlar is sometimes used as a substitute for Teflon in some non-stick frying pans. Kevlar fiber is used in rope and in cable, where the fibers are kept parallel within a polyethylene sleeve. The cables have been used in
suspension bridge A suspension bridge is a type of bridge in which the deck (bridge), deck is hung below suspension wire rope, cables on vertical suspenders. The first modern examples of this type of bridge were built in the early 1800s. Simple suspension bridg ...
s such as the bridge at Aberfeldy, Scotland. 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. Kevlar was used by scientists at
Georgia Institute of Technology The Georgia Institute of Technology, commonly referred to as Georgia Tech or, in the state of Georgia, as Tech or The Institute, is a public research university and institute of technology in Atlanta, Georgia. Established in 1885, it is part of ...
as a base textile for an experiment in electricity-producing clothing. This was done by weaving zinc oxide nanowires into the fabric. If successful, the new fabric will generate about 80 milliwatts per square meter. A retractable roof of over of Kevlar was a key part of the design of the
Olympic Stadium, Montreal Olympic Stadium (french: Stade olympique) is a multi-purpose stadium in Montreal, Canada, located at Olympic Park in the Hochelaga-Maisonneuve district of the city. Built in the mid-1970s as the main venue for the 1976 Summer Olympics, it is n ...
for the
1976 Summer Olympics Events January * January 3 – The International Covenant on Economic, Social and Cultural Rights enters into force. * January 5 – The Pol Pot regime proclaims a new constitution for Democratic Kampuchea. * January 11 – The 1976 Phi ...
. 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. Kevlar can be found as a reinforcing layer in rubber bellows
expansion joints An expansion joint, or movement joint, is an assembly designed to hold parts together while safely absorbing temperature-induced expansion and contraction of building materials, and vibration, or to allow movement due to ground settlement or seis ...
and rubber
hose A hose is a flexible hollow tube designed to carry fluids from one location to another. Hoses are also sometimes called ''pipes'' (the word ''pipe'' usually refers to a rigid tube, whereas a hose is usually a flexible one), or more generally '' ...
s, 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. Some cellphones (including the Motorola RAZR Family, the Motorola Droid Maxx, OnePlus 2 and
Pocophone F1 The Xiaomi Pocophone F1 (Xiaomi POCO F1 in India) is a smartphone developed by Xiaomi Inc, a Chinese electronics company based in Beijing. It was announced on 22 August 2018 in New Delhi, India. Though part of Xiaomi's line of mid-range devices, ...
) have a Kevlar backplate, chosen over other materials such as carbon fiber due to its resilience and lack of interference with signal transmission. 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 carbon fiber and glass fiber. The matrix for high performance composites is usually
epoxy resin Epoxy is the family of basic components or cured end products of epoxy resins. Epoxy resins, also known as polyepoxides, are a class of reactive prepolymers and polymers which contain epoxide groups. The epoxide functional group is also coll ...
. Typical applications include monocoque bodies for F1
racing car Auto racing (also known as car racing, motor racing, or automobile racing) is a motorsport involving the racing of automobiles for competition. Auto racing has existed since the invention of the automobile. Races of various sorts were organise ...
s, helicopter rotor blades, tennis, table tennis, badminton and squash
racket Racket may refer to: * Racket (crime), a systematised element of organized crime ** Protection racket, a scheme whereby a group provides protection to businesses or other groups through violence outside the sanction of the law * Racket (sports equ ...
s,
kayak A kayak is a small, narrow watercraft which is typically propelled by means of a double-bladed paddle. The word kayak originates from the Greenlandic word ''qajaq'' (). The traditional kayak has a covered deck and one or more cockpits, each se ...
s,
cricket bat A cricket bat is a specialised piece of equipment used by batters in the sport of cricket to hit the ball, typically consisting of a cane handle attached to a flat-fronted willow-wood blade. It may also be used by a batter who is making ground ...
s, and field hockey, ice hockey and lacrosse sticks. Kevlar 149, the strongest fiber and most crystalline in structure, is an alternative in certain parts of aircraft construction. The wing leading edge is one application, Kevlar being less prone than carbon or glass fiber to break in bird collisions.


See also

*
Innegra S Innegra S is the brandname of Innegra Technologies LLC for a polyolefin (highly oriented; 90+% polypropylene). History Work on Innegra began in 2004. A pilot production line was opened in Greer, SC in June 2006 On July 11, 2006 the US Patent O ...
*
Ultra-high-molecular-weight polyethylene Ultra-high-molecular-weight polyethylene (UHMWPE, UHMW) is a subset of the thermoplastic polyethylene. Also known as high-modulus polyethylene, (HMPE), it has extremely long chains, with a molecular mass usually between 3.5 and 7.5 million amu. T ...
* Twaron * Vectran


References


External links

*
Aramids

Matweb material properties of Kevlar
*


Kevlar in body armor



Aberfeldy Footbridge over the River Tay

Kevlar
at Plastics Wiki {{Fibers Organic polymers Body armor DuPont products Synthetic fibers Technical fabrics Brand name materials Products introduced in 1965 American inventions