A9.2 Kevlar
Kevlar ® was developed in 1965 and its name is a registered Trademark – here the Dupont Chemical Company
It is a polyamide with a very strong and ordered structure (spot the amide link)
Figure 9.5 How Kevlar is formed
It is exceptionally strong because of the extensive hydrogen bonds between the O and N atoms of adjoining polymer chains. Its high tensile strength-to-weight ratio makes it five times stronger than steel. The cross-links between the polymer chains are broken in concentrated sulphuric acid. The NH group becomes an amine
$\textsf{NH}_\textsf2$
and the C=O becomes a carboxylic acid group
$\textsf{COOH}$
, and the polymer becomes soluble.
Figure 9.6 Kevlar structure
Some of this material’s many uses include: body armour, crash helmets and protective clothing, sports equipment, tyres, shoes, bows for string players and drum heads.