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Pressure / temperature realtionship in polymers

  1. Aug 21, 2012 #1
    Hi, these is possibly a dumb question but...

    I know that with regards to gases: (P1*V1)/T1 = (P2*V2)/T2

    However does this still apply to polymers in liquid state?

    In an injection moulding machine if I increase the pressure will you get an increase in temperature if the volume of material is constant?

  2. jcsd
  3. Aug 21, 2012 #2
    No it's not a dumb question
    No solid and semi solid materials do not obey the gas laws
    but yes they will increase in temperature if you pressurise them whilst at the same time confining them.

    The ultimate example of this is what happens to rocks at great depth (and pressure) in the earth.

    There is I'm sorry to tell you, no simple relationship between temperature and pressure for these materials.
  4. Aug 21, 2012 #3
    Safety comment, Plastics need to be VERY dry when heated and used in compression
    molding or extrusion. The water vapor does obey the gas law, and will at best create
    foamed plastics.
  5. Aug 21, 2012 #4
    Worthwhile comment.
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