Jun 17, 2019 | Updated: 11:54 AM EDT

Kevlar: A Revolutionary Plastic

Mar 18, 2019 08:02 AM EDT


Contrary to popular belief, Kevlar has not been around for very long. Stephanie Kwolek who worked for DuPont made Kevlar. Kwolek did a lot of testing and was attempting to develop a stronger tire for DuPont to manufacture and sell during a gas shortage. Instead of revolutionizing the tire world, Kevlar revolutionized the entire world.

Kevlar is a heat-resistant and strong synthetic fiber and is one of the world's strongest materials. Woven together it becomes five times stronger than steel at equal weight. The use of Kevlar can be found in various products--from bulletproof vests and ballistic helmets to gloves and even sporting equipment such as boats or tennis rackets. It's worth noting that Kevlar also has its drawbacks. In particular, although it has very high tensile strength, it has very poor compressive strength. That's why Kevlar isn't used instead of steel as a primary building material in things like buildings, bridges, and other structures where compressive forces are common.

But what is the science behind Kevlar? Kevlar is synthesized from para-phenylenediamine and terephthaloyl chloride and yields hydrochloric acid as a byproduct. Kevlar's chemical name is Poly Paraphenylene Terephtalamide and its strength comes from hydrogen bonds formed between the carbonyl groups and protons on the neighboring monomers. When the molten Kevlar is spun into fibers, the polymers have a crystalline arrangement, with the polymer chains oriented parallel to the fiber's axis. The amide groups are able to form hydrogen bonds between the polymer chains, which act like glue holding the separate polymer chains together. Although Kevlar is technically a plastic, it does not melt but decomposes at high temperatures.

When used in body armor applications, Kevlar has a relatively short lifespan of five years. However, that is in regards to Kevlar's effectiveness versus projectiles. Kevlar infused boats have been known to stay in good condition for up to 30 years. The significant difference in the lifespans of these two products is mainly caused by wear and tear and exposure to elements. For example, a bulletproof vest, normally worn by law enforcement or members of the military, would need to be placed inside a fabric shell that is usually made from a polyester/cotton blend or nylon. And of course worn close to the body, which generates heat, over several years can, as we know, start to decompose or weaken the Kevlar. However, Kevlar-infused boats are of course used in water, which helps to keep the fibers cool and essentially prolong their lifespan. When not in use, most boats are stored in cool, dry areas, such as garages, this too can prolong the life of Kevlar products.

Although there are several imitations or similar products available, DuPont's Kevlar has securely positioned itself as the unbreakable king of super strength plastics.

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