What Makes Kevlar Highly Heat Resistant?

[wais]

Hey,

I'm doing a presentation on Kevlar, and was asked to state its properties and why it has those. I came across the fact that kevlar has a low flamability due to the high carbon:hydrogen ratio, I'm assuming that carbon doesn't burn whereas hydrogen does. Am i correct? Sorry it may be a bit of a silly question but I just wanted to confirm it.

Thanks.

 

[cronxeh]

The flammability or burning has to do with stability of the molecule - e.g. the forces that hold the bonds together. In this case there are a lot of hydrogen-hydrogen bonds, which make the Kevlar and other amide polymers have a high tensile strength as well as their melting point (MP of Kevlar is 500 deg C). There are other factors that affect flammability but basically because carbon is unsaturated in Kevlar it is more stable, and therefore harder to "oxygenate" (burn), or react chemically so it broke apart the bonds and released heat in exothermic reaction.


From wikipedia I pulled up the following table of approximate intermolecular forces and their strenght comparisons:

Ionic bonds
1000
Hydrogen bonds
100
Dipole-dipole
10
London Forces
1

 

[wais]

Ah great thanks. I also saw that kevlar has a "self extinguishing" property, could you tell me how this would work?

 

[wais]

How could I calculate the amount of heat needed to apply to make kevlar react? I know its 500c but I just want to add into my presentation the calculation used.

Thanks.