Why kevlar is so strong

Before then, scientists knew that chemical bonds between atoms were very strong, but researchers were unable to arrange these molecules into large structures relative to the size of a molecule to capitalize on this strength. Using organic polymers based on "light elements"--such as carbon, nitrogen, hydrogen and oxygen--rather than "heavy elements" such as iron, gives the advantage of low-weight structures.

For example, Kevlar fiber has a density of 1. To achieve both the strength and stiffness of Kevlar, the molecular chains within the organic fiber needed to be fully extended and perfectly aligned to make them strong, stiff and tough. Such a high degree of alignment was not easy to achieve. Kevlar fibers are based on poly-paraphenylene terephthalamide, a rigid molecule that makes it easier to realize a fully extended, or straight, chain configuration.

Also, these rigid molecules will even arrange in solutions. Such solutions are called liquid crystalline, which underscores their good organization. Poly-paraphenylene terephthalamide molecules behave like uncooked spaghetti, whereas other, less rigid molecules behave more like cooked strands of spaghetti. Thus, the nature of the molecule makes it easier to achieve the desired aligned structure. In addition, poly-paraphenylene terephthalamide strongly resists high temperatures and flames.

Offering strength under heat, Kevlar protects against thermal hazards up to degrees Farenheit. This combination of unusual properties makes Kevlar useful for a broad range of applications, such as ballistic vests, cut-resistant gloves and blast and flame barriers.

Kevlar has also boosted sports gear performance. Applications in that vein include bicycle tires that are virtually flat-free and puncture-resistant; running shoes that maximize the energy output of runners; boats that are lighter and more damage-tolerant; and durable lightweight sails that tolerate high winds and saltwater.

Originally published on September 30, Sign up for our email newsletter. Already a subscriber? The following table shows the strengths of all three types.

Tensile Modulus GPa. Tensile Strength GPa. The strength of Kevlar comes from its unusually regular internal structure; this has implications for the Hydrogen bonding which occurs between the electron dense oxygen atom and the electron deficient hydrogen.

The all trans configuration, giving long straight chains, means that the hydrogen bonding can occur very regularly to form a very strong lattice, similar to those formed in crystals. The fibres consequently have very few flaws and so are very difficult to break up.