Pressure / temperature realtionship in polymers

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Discussion Overview

The discussion revolves around the relationship between pressure and temperature in polymers, particularly in the context of injection molding and the behavior of materials under pressure. Participants explore whether the gas laws applicable to gases can be extended to polymers in a liquid state.

Discussion Character

  • Debate/contested
  • Technical explanation

Main Points Raised

  • One participant questions whether the gas law relationship (P1*V1)/T1 = (P2*V2)/T2 applies to polymers in a liquid state during injection molding.
  • Another participant asserts that solid and semi-solid materials do not obey gas laws but acknowledges that increasing pressure can lead to an increase in temperature when the material is confined.
  • A participant provides an example of rocks under great depth and pressure to illustrate the behavior of materials under similar conditions.
  • Safety comments emphasize the importance of keeping plastics dry during heating and compression molding, noting that water vapor behaves according to gas laws and can lead to foamed plastics.

Areas of Agreement / Disagreement

Participants express disagreement regarding the applicability of gas laws to polymers, with some asserting that no simple relationship exists between temperature and pressure for these materials. The discussion remains unresolved regarding the specific nature of the pressure-temperature relationship in polymers.

Contextual Notes

Participants highlight the limitations of applying gas laws to solid and semi-solid materials, indicating that assumptions about material behavior under pressure may vary significantly from gases.

Colnago
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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?

Thanks.
 
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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.
 
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.
 
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

Worthwhile comment.
 

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