Kevlar BY: Richmond Te Emilio Tan Mark Go Tomas Delos Reyes
History • Kevlar is the registered trademark for a para-aramid synthetic fiber, related to other aramidssuch as Nomex and Technora. Developed at DuPoint in 1965, this high strength material was first commercially used in the early 1970s as a replacement for steel in racing tires.
Structure • 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 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.
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.
Grades of Kelvar • 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 fatique resistant. • Kevlar K129 - higher tenacity for ballistic applications. • Kevlar AP - has 15% higher tenacity than K-29. • Kevlar XP - lighter weight resin and KM2 plus fiber combination.
Purposes • Protection • Armor- Kevlar is well-known component of personal armor such as combat helmets, Ballistic face masks, and Ballistic vests. • Personal Protection- Kevlar is used to manufacture gloves, sleeves, jackets, chaps and other articles of clothingdesigned to protect users from cuts, abrasions and heat.
Sport Equipment- 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.
Music • Audio equipment- Kevlar has also been found to have useful acoustic properties for loudspeaker cones, specifically for bass and midrange drive units • 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. • 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.
Other uses • Rope, cable, sheath • Electricity generation • Building construction • Brakes • Expansion joints and hoses • Particle physics experiment
Sources: • http://en.wikipedia.org/wiki/Kevlar#Structure_and_properties