Kevlar, a trademark of para-aramid synthetic fiber, is related to other aramids such as Nomex and Technora. DuPont developed Kevlar in 1965 and was first commercially used in the 1970s as a replacement for steel in racing tires. Its normal form is as a rope or a sheet of fabric that can be used as an ingredient in composite material components.
Kevlar is used in bicycle tires, racing sails, and body armor due to its high tensile strength-to-weight ratio. Twaron, produced in 1978, is a similar fiber with a similar chemical structure.
Kevlar is created in a synthesized solution from the monomers 1,4-phenylene-diamine and terephthaloyl chloride in a condensation reaction yielding hydrochloric acid as a byproduct. A patent war was ensued when Akzo used the process in the creation of Twaron.
Due to the use of sulfuric acid needed to keep the water-insoluble polymer in solution during its synthesis and spinning, Kevlar production is expensive. Ultraviolet light can degrade and decompose Kevlar, known as UV degradation, and is therefore rarely used outside.
Once Kevlar is spun it has a tensile strength of about 3,620 MPa. The strength comes from the many inter-chain bonds while additional strength comes from aromatic stacking interactions between adjacent strands. Salts and other impurities can interfere with strand interactions and caution must be taken in order to keep it out of production. The structure is a lot like silk protein in that it is a relatively rigid set of molecules that tend to form mostly planar sheet-like structures.
The lower the temperature the stronger the Kevlar is while at a higher temperature the tensile strength is immediately reduced by about 10-20%. Kevlar is used in combat helmets, ballistic face masks, and Ballistic vests. It is also used in bulletproof facemasks, emergency service’s protection gear if it involves high heat, and in Kevlar body armor such as vest for police officers, security, and SWAT. It is used to manufacture gloves, sleeves, jackets, chaps, and other clothing articles designed to protect users from cuts, abrasions, and heat.
Many times it is used as an inner lining in bicycle tires to prevent punctures and also for fire poi wicks due to its excellent heat resistance. It is used in paraglider suspension lines and as a replacement to more expensive hemp bow strings.