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[[uk:Кевлар]]
[[uk:Кевлар]]
[[zh:克維拉]]
[[zh:克維拉]]
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Kevlar
Ball-and-stick model of a single layer of the crystal structure
Identifiers
ChemSpider
Properties
[-CO-C6H4-CO-NH-C6H4-NH-]n
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Kevlar is the registered trademark for a para-aramid synthetic fiber, related to other aramids such as Nomex and Technora. Developed at DuPont in 1965,[1][2][3] 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 fabric sheets that can be used as such or as an ingredient in composite material components.

Currently, Kevlar has many applications, ranging from bicycle tires and racing sails to body armor because of its high tensile strength-to-weight ratio; by this measure it is 5 times stronger than steel on an equal weight basis.[2] When used as a woven material, it is suitable for mooring lines and other underwater applications.

A similar fiber called Twaron with roughly the same chemical structure was developed by Akzo in the 1970s; commercial production started in 1986, and Twaron is now manufactured by Teijin.[4][5]

History

Poly-paraphenylene terephthalamide - branded Kevlar - was invented by Stephanie Kwolek while working for DuPont.[6] 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.[6] The polymers she had been working with at the time, poly-p-Phenylene-terephthalate and polybenzamide,[7] formed liquid crystal while in solution, something unique to those polymers at the time.[6]

The solution was "cloudy, opalescent 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.[6] However, Kwolek was not very involved in developing the applications of Kevlar.[8]

Production

Kevlar is synthesized in solution from the monomers 1,4-phenylene-diamine (para-phenylenediamine) and terephthaloyl chloride 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 was patented by Akzo (see above) in the production of Twaron, a patent war ensued.[9]

The reaction of 1,4-phenylene-diamine (para-phenylenediamine) with terephthaloyl chloride yielding kevlar.

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

Several grades of Kevlar are available:

  1. Kevlar K-29 – in industrial applications, such as cables, asbestos replacement, brake linings, and body/vehicle armor.
  2. Kevlar K49 – high modulus used in cable and rope products.
  3. Kevlar K100 – colored version of Kevlar
  4. Kevlar K119 – higher-elongation, flexible and more fatigue resistant.
  5. Kevlar K129 – higher tenacity for ballistic applications.
  6. Kevlar AP – has 15% higher tensile strength than K-29.[10]
  7. Kevlar XP – lighter weight resin and KM2 plus fiber combination.[11]
  8. Kevlar KM2 – enhanced ballistic resistance for armor applications[12]

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.[citation needed]

Structure and properties

Molecular structure of Kevlar: bold represents a monomer unit, dashed lines indicate hydrogen bonds.

When Kevlar is spun, the resulting fiber has a tensile strength of about 3,620 MPa,[13] and a relative density of 1.44. The polymer owes its high strength to the many inter-chain bonds. These inter-molecular hydrogen bonds form between the carbonyl groups and NH 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 Dyneema. The presence of salts and certain other impurities, especially calcium, could interfere with the strand interactions and caution is used 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.[14]

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 at 160 °C (320 °F) about 10% reduction in strength occurs after 500 hours. At 260 °C (500 °F) 50% strength reduction occurs after 70 hours.[15]

Applications

Protection

Armor

pieces of Kevlar helmet used to help absorb the blast of a grenade

Kevlar is a well-known component of personal armor such as combat helmets, ballistic face masks, and ballistic vests. The PASGT helmet and vest used by United States military forces from the 1980s into 2005 both have Kevlar as a key component, as do their replacements. Other military uses include bulletproof facemasks used by sentries and spall liners used to protect the crews of armoured fighting vehicles. Even Nimitz-class aircraft carriers include Kevlar armor around vital spaces. Related civilian applications include Emergency Service's protection gear if it involves high heat (e.g., tackling a fire), and Kevlar body armor such as vests for police officers, security, and SWAT.[16]

Personal protection

Kevlar is used to manufacture gloves, sleeves, jackets, chaps and other articles of clothing[17] 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.[16]

Sports equipment

Kevlar is a very popular material for racing canoes.

It is used as an inner lining for some bicycle tires to prevent punctures, and due to its excellent heat resistance, is used for fire poi wicks. In table tennis, plies of Kevlar are added to custom ply blades, or paddles, in order to increase bounce and reduce weight. It is used for motorcycle safety clothing, especially in the areas featuring padding such as shoulders and elbows. It was also used as speed control patches for certain Soap Shoes models.[citation needed]

In Kyudo or Japanese archery, it may be used as an alternative to more expensive hemp for bow strings. It is one of the main materials used for paraglider suspension lines.[18]

In Fencing it is used in the protective jackets, breeches, plastrons and the bib of the masks.

It is also used in the laces for the adidas F50 adiZero Prime football boot.

It is even used in sails for high performance racing boats.

It is increasingly being used in the "peto", the padded covering which protects the picadors' horses in the bullring.

Music

Audio equipment

Kevlar has also been found to have useful acoustic properties for loudspeaker cones, specifically for bass and midrange drive units.[19] Additionally, Kevlar has been used as a strength member in fiber optic cables such as the ones used for audio data transmissions.[20]

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. Remo's "Falam Slam" Patch is made with Kevlar and is used to reinforce bass drum heads where the beater strikes.[citation needed]

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.[21]

Other uses

Frying pans

Kevlar is sometimes used as a substitute for Teflon in some non-stick frying pans.[22]

Rope, cable, sheath

Kevlar mooring line

The fiber is used in woven rope and in cable, where the fibers are kept parallel within a polyethylene sleeve. The cables have been used in suspension bridges such as the bridge at Aberfeldy in 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.[citation needed]

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 zinc oxide nanowires into the fabric. If successful, the new fabric would generate about 80 milliwatts per square meter.[23]

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 ten years late and replaced just ten years later in May 1998 after a series of problems.[24][25]

Brakes

The chopped fiber has been used as a replacement for asbestos in brake pads. Dust produced from asbestos brakes is toxic, while aramids are a benign substitute.[citation needed]

Expansion joints and hoses

Kevlar can be found as a reinforcing layer in rubber bellows expansion joints 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.[citation needed]

Particle physics experiment

A thin Kevlar window has been used by the NA48 experiment at CERN 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 radiation length).[citation needed]

Smartphones

The Motorola Droid RAZR has a kevlar backplate, chosen over other materials such as carbon fiber due to its resilience and lack of interference with signal transmission.[26]

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. Typical applications include monocoque bodies for F1 racing cars, helicopter rotor blades, tennis, table tennis, badminton and squash rackets, kayaks, cricket bats, and field hockey, ice hockey and lacrosse sticks.[27][28][29][30]

See also

References

  1. ^ Stephanie Kwolek, Hiroshi Mera and Tadahiko Takata “High-Performance Fibers” in Ullmann's Encyclopedia of Industrial Chemistry 2002, Wiley-VCH, Weinheim. doi:10.1002/14356007.a13_001
  2. ^ a b "What is Kevlar". DuPont. Retrieved 2007-03-28.
  3. ^ Wholly Aromatic Carbocyclic Polycarbonamide Fiber Original Kevlar patent awarded in 1974 to Stephanie Kwolek
  4. ^ Tatsuya Hongū, Glyn O. Phillips, New Fibers, Ellis Horwood, 1990, p. 22
  5. ^ J. K. Fink, Handbook of Engineering and Specialty Thermoplastics: Polyolefins and Styrenics, Scrivener Publishing, 2010, p. 35
  6. ^ a b c d "Inventing Modern America: Insight — Stephanie Kwolek:". Lemelson-MIT program. Archived from the original on May 24, 2009. Retrieved May 24, 2009.
  7. ^ "Stephanie Louise Kwolek Biography". Bookrags. Archived from the original on May 24, 2009. Retrieved May 24, 2009. {{cite web}}: Unknown parameter |unused_data= ignored (help)
  8. ^ Quinn, Jim. "I was able to be Creative and work as hard as I wanted". American Heritage Publishing. Archived from the original on May 24, 2009. Retrieved May 24, 2009.
  9. ^ http://www.explainthatstuff.com/kevlar.html
  10. ^ Kevlar K-29 AP Technical Data Sheet - Dupont
  11. ^ Kevlar XP - Dupont
  12. ^ Kevlar KM2 Technical Description
  13. ^ Quintanilla, J. (1990). "Microstructure and properties of random heterogeneous materials : a review of theoretical results". Polymer engineering and science. 39: 559–585.
  14. ^ Michael C. Petty, Molecular electronics: from principles to practice, John Wiley & Sons, 2007, p. 310
  15. ^ KEVLAR Technical Guide
  16. ^ a b Body Armor Made with Kevlar. (2005, June 04). DuPont the Miracles of Science. Retrieved November 4, 2011, from http://www2.dupont.com/Kevlar/en_US/uses_apps/body_armor/index.html
  17. ^ Kevlar - DuPont Personal Protection
  18. ^ Pagen, Dennis (1990), Paragliding Flight: Walking on Air, Pagen Books, p. 9, ISBN 0-936310-09-X {{citation}}: External link in |publisher= (help)
  19. ^ Audio speaker use
  20. ^ Welcome to Kevlar. (2005, June 04). DuPont the Miracles of Science. Retrieved November 4, 2011, from http://www2.dupont.com/Kevlar/en_US/index.html
  21. ^ "FibraCell Website".
  22. ^ M.Rubinstein, R.H.Colby, Polymer Physics, Oxford University Press, p337
  23. ^ Scientific American: Fabric Produces Electricity As You Wear It
  24. ^ Roof of the Montreal Olympic Stadium at Structurae
  25. ^ Clem's Baseball ~ Olympic Stadium
  26. ^ Droid RAZR by Motorola. (2011, October 11). Motorola Mobility. Retrieved November 4, 2011, from http://www.motorola.com/Consumers/US-EN/Consumer-Product-and-Services/Mobile-Phones/DROID-RAZR-BY-MOTOROLA-US-EN
  27. ^ Kadolph, Sara J. Anna L. Langford. Textiles, Ninth Edition. Pearson Education, Inc 2002. Upper Saddle River, NJ
  28. ^ D. Tanner, J. A. Fitzgerald, B. R. Phillips (1989). "The Kevlar Story - an Advanced Materials Case Study". Angewandte Chemie International Edition in English. 28 (5): 649–654. doi:10.1002/anie.198906491.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  29. ^ E. E. Magat (1980). "Fibers from Extended Chain Aromatic Polyamides, New Fibers and Their Composites". Philosophical Transactions of the Royal Society of London Series A. 294 (1411): 463–472. doi:10.1098/rsta.1980.0055. JSTOR 36370.
  30. ^ Ronald V. Joven. Manufacturing Kevlar panels by thermo-curing process. Los Andes University, 2007. Bogotá, Colombia.
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