My setting is a 2 cycle process where it heats up to its dwelling point. cools down and finally heats up to 250 DegC
In my opinion more information is needed here. What kind of material? (crosslinking thermoset most likely) How high is the dwelling temperature? Are we talking here about a production process or DSC measurements?
Are you performing isothermal curing and afterwards characterization of the actual glass transition temperature?
Please provide more specific information.
Sorry about that Mr Matthias.
I am using CFRP carbon fibre reinforced polymer. (Thermoset)
My dwelling temperature is at 160 DegC.
My enquiry will be on Dsc measurements.
Yeap I am performing an isothermal curing and characterization of the actual TG.
Thank you
Dear Mr. Kumar,
the i would expect that your intention is to characterize the crollsinking process with your Tg. In dependence of your dwelling/curing time the glass transition temperature will increase (c.f. DiBenedetto equation) and can be used to describe the degree of conversion. This in comparison to enthalpy avaluation can can give better information when high degrees of cure are reached.
In principle Tg increase can go up to the theoretical possible Tg but you are limited if your dwelling temperature is to low as the resin will vitrify when the actual Tg becomes bigger as the dwelling temperature and this will strongly hinder additional curing reaction as the reaction partners have restricted mobility.
So due to vitrification your possible Tg can be limited by your dwelling temperature and time. If the dwelling temperature is sufficiently high (close to Tg max) you Tg is only dependent on the dwelling time (assumed that no degradation takes place).
regards
Matthias Jaunich
I would suggest that Glass transition temperature for a thermoset material is meaningless if you regard the GTT as a second order phase change i.e the temperature at which the medium is fluid enough to allow segmental motion. It also is dependent on the method of measurement.Are you sure that the GTT is what you are really after? For Thermosets the normal thermal tests are heat distortion temp (See BS2782)
It is still not clear if you describing the manufacturing process or a DSC experiment. I am guessing the latter, as it would make no sense to cure at 160 deg C, cool down, only to reheat.
If you material is epoxy (??) then you might expect Tg of about 170-180 deg C, but the indication on the DSC curve will depend on heat up rate and whether or not the polymer is undergoing significant post cure.
The importance of DSC can be explained as:
1. For structural application the material must be well below Tg. Once it crosses Tg to rubbery phase there may be sagging of structure ans strength reducec drastically. For coating application, it should be above Tg to avoid brittleness and failure of coating on small impact. Further example, Tg of shoe sole in Antartica should be below 70 degreeC. If it goes below Tg it looses rubbery nature and will crack due to stepping impact.
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