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Homework Help: Kevlar heat resistivity

  1. Dec 10, 2005 #1
    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 doesnt 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.
     
  2. jcsd
  3. Dec 10, 2005 #2

    cronxeh

    User Avatar
    Gold Member

    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
     
  4. Dec 11, 2005 #3
    Ah great thanks. I also saw that kevlar has a "self extinguishing" property, could you tell me how this would work?
     
  5. Dec 13, 2005 #4
    How could I calculate the ammount 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.
     
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