Kevlar is a man-made fiber most commonly associated with the material used in bulletproof vests for soldiers and police officers. Kevlar is also used to make cables, radial tires, boat hulls, fire-resistant clothes and certain types of sports equipment such as lightweight bikes and golf club shafts.
Kevlar was first manufactured at Dupont by a team of scientists including Stephanie Kwolek in 1965. Production began in 1971 for use as a substitute for steel in radial tires, but Kevlar was later manufactured for many more uses, including in bulletproof vests and sports equipment.
Kevlar is categorized as a carbon aramid, which is a manufactured fiber similar to the nylon family in its chemical composition. Despite being chemically similar, however, Kevlar produces very different properties to nylon. Kevlar contains closely packed polymer chains which make the material resilient to bullets and fire.
The aramid ring provides Kevlar with thermal stability and resilience, which are not present in most common nylons. The polymer used in the production of Kevlar is spun from a heated concentration of sulphuric acid. Kevlar is available in three different grade types: 29, 49 and 149, each with greater strength and stability than the previous one.
The filaments of Kevlar are produced by squeezing the material’s precursor via the use of a spinneret. The aramids in Kevlar exist in a rod-like structure, which produce a liquid crystalline solution. This accounts for the ultrahigh strength and stiffness of the finished Kevlar product, containing five times the strength of steel per weight.
Kevlar is not manufactured as extensively as more common materials such as nylon and polyester. However, as it yields a high unit price per item, the production and selling of Kevlar is a large and profitable business. Kevlar has few domestic uses, but is increasingly used in industrial circles in the design and manufacturing of new products.
Despite its strength and resilience, Kevlar also has some disadvantages which limits its efficiency. Kevlar fibers quickly absorb moisture, meaning it is more sensitive to its environment than other materials. Although Kevlar is strong and tensile, its ability to cope with compression is fairly poor and it can be difficult to cut. Specially made scissors are usually required to sever dry fabric and cured laminates can only be pierced by specially made drill bits.