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.
- 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.