Articles

    Kevlar: The Millennium Molecule

    Kids, last month we learned about teflon and this month we'll learn about another amazing polymer (which is actually a really, really big molecule) called Kevlar. Kevlar is also called the "fabric of steel" because of its outstanding strength. Underwater, it is 20 times stronger than steel! Since its introduction in 1971 it has been used in bulletproof vests and helmets, aircraft, sports equipment, gloves, boats, flight jackets, brake linings, windsurfing sails, cables, even as part of the Orbiter 3 balloon that circled the globe last March.

    Last month we learned about polymers in general. Here you'll learn that the secret to the strength of Kevlar lies in something called hydrogen bonding. The long chains of kevlar polymer molecules are stacked like uncooked spaghetti in a box. But the attraction between hydrogen and oxygen atoms on chains next to each other (this is hydrogen bonding) is very strong, and it holds the chains solidly together. Imagine if you moistened the box of spaghetti just enough to make the strands stick together like glue. It is also a bit like the attractive force in static electricity where (a) electrons are relatively easy to remove from atoms and (b) some materials (or atoms) attract electrons better than others. 

    Please note:  All chemicals and experiments can entail an element of risk, and no experiments should be performed without proper adult supervision.

    Here is an activity to mimic this bonding: tear off a strip of scotch tape (which is a plastic or polymer, by the way) about the length of your finger and fold a little bit of one end down so that it sticks to itself. Press it down on a desk top. Tear off another piece of tape, fold a tab as before, and press it down on top of the first piece with the little folded parts together. Rub the top piece several times so that they are well stuck together. Now peel them off together, grab the folded parts and quickly rip them apart. Bring the two pieces slowly near each other, without touching. What happens? The pieces of tape should be attracted to each other because electrons moved toward one side of each tape, leaving the other sides deficient, and the opposite charges attracted.

    Dr. Stephanie Kwolek was the chemist at DuPont who discovered the precise chemical concoction needed to prepare Kevlar into useful fibers for making things. At the time, DuPont was looking for a material to replace steel in radial tires (why do you think they would want to do this?). Dr. Kwolek's most satisfying reward for her work has been recognition by the Kevlar Survivors Club. These 2,300 members are police officers whose lives have been saved by wearing Kevlar armored vests. For lots more info about Kevlar please look at the references below.

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    Kathleen Carrado Gregar, PhD, Argonne National Labs 
    [email protected]
    January 2000

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    References: "ChemMatters" 10/99, p. 7 by Peter Banks; American Chemical Society, Washington, DC; www.lbl.gov/MicroWorlds/Kevlar; or, look up "aramids" on www.psrc.usm.edu/macrog/index.htm