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.
Several grades of Kevlar are available:
- Kevlar K-29 – in industrial applications, such as cables, asbestos 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 XP – lighter weight resin and KM2 plus fiber combination
- Kevlar KM2 – enhanced ballistic resistance for armor applications
Structure and properties
When Kevlar is spun, the resulting fiber has a tensile strength of about 3,620 MPa, 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 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.
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.
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 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.
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 since the 1980s 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.
Kevlar is used to manufacture gloves, sleeves, jackets, chaps 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 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. It is used for motorcycle safety clothing, especially in the areas featuring padding such as shoulders and elbows.
In fencing it is used in the protective jackets, breeches, plastrons and the bib of the masks.
Tennis racquets are often strung with Kevlar.
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.
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 as well as the shoe laces. 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.
Kevlar has also been found to have useful acoustic properties for loudspeaker cones, specifically for bass and midrange drive units. Additionally, Kevlar has been used as a strength member in fiber optic cables such as the ones used for audio data transmissions.
Bowed string instruments
Kevlar can be used as an acoustic core on bows for string instruments. 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 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.
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.
Rope, cable, sheath
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.
Kevlar was used by scientists at zinc oxide nanowires into the fabric. If successful, the new fabric would generate about 80 milliwatts per square meter.
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.
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.
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.
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).
The Motorola RAZR Family and the Motorola Droid Maxx have a kevlar backplate, chosen over other materials such as carbon fiber due to its resilience and lack of interference with signal transmission.
Marine Current Turbine and Wind turbine
The Kevlar fiber/epoxy matrix composite materials can be used in marine current turbine (MCT) or wind turbine due to their high specific strength and light weight compared to other fibers.
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.
- 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
- Wholly Aromatic Carbocyclic Polycarbonamide Fiber Original Kevlar patent awarded in 1974 to Stephanie Kwolek
- Tatsuya Hongū, Glyn O. Phillips, New Fibers, Ellis Horwood, 1990, p. 22
- J. K. Fink, Handbook of Engineering and Specialty Thermoplastics: Polyolefins and Styrenics, Scrivener Publishing, 2010, p. 35
- "Inventing Modern America: Insight — Stephanie Kwolek:". Lemelson-
- "Stephanie Louise Kwolek Biography". Bookrags. Archived from the original on May 24, 2009. Retrieved May 24, 2009.
- 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.
- How Kevlar® works: a simple introduction. Explainthatstuff.com (2009-12-07). Retrieved on 2012-05-26.
- Kevlar K-29 AP Technical Data Sheet – Dupont
- Kevlar XP – Dupont
- Kevlar KM2 Technical Description. dupont.com. Retrieved on 2012-05-26.
- Quintanilla, J. (1990). "Microstructure and properties of random heterogeneous materials : a review of theoretical results". Polymer engineering and science 39: 559–585.
- Michael C. Petty, Molecular electronics: from principles to practice, John Wiley & Sons, 2007, p. 310
- KEVLAR Technical Guide. dupont.com. Retrieved on 2012-05-26.
- Body Armor Made with Kevlar. (2005-0604). DuPont the Miracles of Science. Retrieved November 4, 2011
- Kevlar – DuPont Personal Protection. .dupont.com. Retrieved on 2012-05-26.
- Pagen, Dennis (1990), Paragliding Flight: Walking on Air, Pagen Books, p. 9,
- Audio speaker use. Audioholics.com (2009-07-23). Retrieved on 2012-05-26.
- Welcome to Kevlar. (2005-06-04). DuPont the Miracles of Science. Retrieved November 4, 2011
- carbon fiber bows for violin, viola, cello and bass. CodaBow. Retrieved on 2012-05-26.
- carbon fiber bows for violin, viola, cello and bass. CodaBow. Retrieved on 2012-05-26.
- Tailpieces and Tailcords Aitchison Mnatzaganian cello makers, restorers and dealers. Retrieved on 2012-12-17.
- "FibraCell Website".
- M.Rubinstein, R.H.Colby, Polymer Physics, Oxford University Press, p337
- Fabric Produces Electricity As You Wear It. Scientific American (2008-02-22). Retrieved on 2012-05-26.
- Roof of the Montreal Olympic Stadium at Structurae
- Clem's Baseball ~ Olympic Stadium. Andrewclem.com. Retrieved on 2012-05-26.
- Droid RAZR. (2011-10-11). Motorola Mobility. Retrieved November 4, 2011
- Wang, Jifeng; Norbert Müller (December 2011). "Numerical investigation on composite material marine current turbine using CFD". Central European Journal of Engineering 1 (4): 334–340. Retrieved 26 December 2012.
- Kadolph, Sara J. Anna L. Langford. Textiles, Ninth Edition. Pearson Education, Inc 2002. Upper Saddle River, NJ
- D. Tanner, J. A. Fitzgerald, B. R. Phillips (1989). "The Kevlar Story – an Advanced Materials Case Study".
- E. E. Magat (1980). "Fibers from Extended Chain Aromatic Polyamides, New Fibers and Their Composites".
- Ronald V. Joven. Manufacturing Kevlar panels by thermo-curing process. Los Andes University, 2007. Bogotá, Colombia.
- Kevlar Home Page
- Kevlar – Design Dictionary. Illustrated article about Kevlar
- Matweb material properties of Kevlar
- U.S. Patent 5,565,264
- Kevlar in body armor
- Synthesis of Kevlar
- Aberfeldy Footbridge over the River Tay
- Kevlar at Plastics Wiki