Most of the researchers do report the results of second heat cycle of polymer nanocomposites. Why the reheating is needed? is there a significant difference in properties of the sample (Tg, Tm, Tc etc,) compared to the first heat cycle?
Well, the first heating scan in DSC is mostly used for removal of residual solvents, and erase the thermal history of the polymer. However, there is some exception especially for biopolymers like starch and proteins where the major transitions are obtained in the first run as starch gelatinization or protein denaturation occurred in the first run.
For polymers, the Tg is very distinct in 2nd run whereas Tm and Tc show insignificant difference in their respective values between two runs.
First heating is done to eliminate any thermal history that the polymer may have gone through during its synthesis and post processing steps. Yes, you can see a change in Tm and Tc after first heating
Well, the first heating scan in DSC is mostly used for removal of residual solvents, and erase the thermal history of the polymer. However, there is some exception especially for biopolymers like starch and proteins where the major transitions are obtained in the first run as starch gelatinization or protein denaturation occurred in the first run.
For polymers, the Tg is very distinct in 2nd run whereas Tm and Tc show insignificant difference in their respective values between two runs.
Thank you, Aishwarya Madam and Ahmed Sir. Can you plz also explain if there is any effect of rate of cooling after the first heat cycle?
Dear Chetan,
The first heating in DSC can permit to erase the history of thermoplastic based nanocomposite that they undergo during the sythesis. The Tg and Tm can be different in first and 2nd heat as well as the crystallinity.This means that you can change the microstructure of polymer after first heating.
Chetan: Sure cooling and heating rate has significant effect on thermal properties. For example: if you do your scanning at 5C/min and 20C/min then you can see the difference in Tg due to faster and slower heating ramp.
You can consult our book on Glass Transition of Biopolymers (Wiley).
DSC heat flow differences are dependent on heating rate, sample heat capacity (which is sample mass dependent) and heat flow at an absolute temperature. A typical DSC curve plots heat flow versus temperature. The latent heats of fusion and freezing can then be calculated by integrating the areas under the curves for the respective transitions.
removal of residual solvents, and erase the thermal history of the polymer
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