I'm currently working on a project on the glass temperature transition (Tg). I'm working with polymer such as thermosets, thermoplastics or epoxy resin and I know the value of their Tg. My question is : For a given material, how close can we get to Tg ? For example is there any statement or standards that recommand to use a polymer at 20°C above Tg ? Or 5°C ?
Thank you in advance for your answer.
Hi Antoine Wachspress ,
Many people use polymers above and below their Tg - it really depends on the application. For instance a CD case is below it's Tg at room temperature and so is brittle when flexed, whereas a wash bottle is above it's Tg and can be squeezed without a problem. If you want to keep some flexibility in your epoxy resin, it could be possible to mix it with something with a lower Tg, but that is technically immiscible. This creates domains in the sample that allow flexibility, but wont cause the material to fracture so easily. This is known as tailor blending polymers to give desired moduli at desired temperatures.
Dear Antoine Wachspress, none of such standards or recommandations exist. Tg is just a temperature that marks the transition state to a rubberylike state. It defines a partial localized rotational mouvements of segments of the chains. Generally speaking, polyolefins and rubbers are used far above their Tg's. On the other hand, polyacrylates ans polystyrene are used below their Tg's, of course with respect to room temperature.
There exists a stability temperature which should be respected for the safe use of polymers. My Regards
Dear Antoine Wachspress,
They are right; there is no straight-forward recommendation on how far should the service temperature of the polymers be. (http://qepp.matweb.com/search/DataSheet.aspx?Bassnum=P1SM50, http://qepp.matweb.com/search/DataSheet.aspx?Bassnum=P1SM10B)
You may see that the gaps from the service temperatures and glass transition temperatures are not fixed.
It is dependent on the Factor of Safety applicable for the intended application design, and destructive mechanical tests may be carried out at the selected gaps to check if the material performance is acceptable for the intended applications.
Hope this helps.
From the internet:
The values of Tgand Tm relative to room temperature can be used to classify polymers:
•Elastomers are polymers with crosslinks, whose Tg is such that Tg+75°C< Troom
•Glassy polymers are amorphous substances whose Tg > Troom+75°C
•Semicrystallinepolymers are substances of 50-90% crystallinity whose Tgis much below Troom and Tm is much above Troom
•Fibers are highly crystalline polymers with a Tm such that Tm>Troom+150°C
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