What Makes Kevlar So Strong?

   
 
  • CLUE #1: KEVLAR is a long chain-like molecule known as a polymer, which consists of repeating units called monomers.

  • CLUE #2: A Kevlar fiber is an array of molecules oriented parallel to each other like a package of uncooked spaghetti. This orderly, untangled arrangement of molecules is described as a crystalline structure. Crystallinity is obtained by a manufacturing process known as spinning, which involves extruding the molten polymer solution through small holes. The crystallinity of the Kevlar polymer strands contributes significantly to Kevlar's unique strength and rigidity.

  • CLUE #3: Kevlar is a polyaromatic amide. That is, it contains aromatic and amide groups. Other polymers with a high breaking strength often contain one or both of these molecular groups.

  • CLUE #4: The individual polymer strands of Kevlar are held together by hydrogen bonds that form between the polar amide groups on adjacent chains.



  • CLUE #5: The aromatic components of Kevlar polymers have a radial (spoke-like) orientation, which gives a high degree of symmetry and regularity to the internal structure of the fibers. This crystalline-like regularity is the largest contributing factor in the strength of Kevlar. Only with bright synchrotron radiation could the secret strength of Kevlar be revealed.

As you have discovered, there are many components that contribute to the strength of Kevlar, including the fact that Kevlar is a polymer containing aromatic and amide molecular groups. 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. The most recent XANES images confirm that the aromatic components of Kevlar have a radial (spoke-like) orientation, which allows for a high degree of symmetry and order.

Kevlar Introduction

Clue #1

Clue #2

Clue #3

Clue #4

Clue #5

   
 

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