Exceptional
Strength
Kevlar is an exceptionally strong material, it is currently produced in three grades and even the weakest is much stronger than steel and also only half as dense. It is used for many applications where strength and low weight is paramount, such a bulletproof vests. The following table shows the strengths of all three types.
|
Grade |
Density |
Tensile |
Tensile |
Tensile |
|
29 |
1.44 |
83 |
3.6 |
4.0 |
|
49 |
1.44 |
131 |
3.6--4.1 |
2.8 |
|
149 |
1.47 |
186 |
3.4 |
2.0 |
Reasons For strength
The
strength of Kevlar comes from its unusually regular internal structure; this
has implications for the Hydrogen bonding which occurs between the electron
dense oxygen atom and the electron deficient hydrogen. The all trans
configuration, giving long straight chains, means that the hydrogen bonding can
occur very regularly to form a very strong lattice, similar to those formed in
crystals.
The fibres consequently have very few flaws and so are very difficult to break up.
This
diagram shows an x-ray microscopy of the cut end of a Kevlar fibre, as can be seen it has a very
symmetrical orientation.
Introduction History of Kevlar The future