Hallo Tushar

During the heating you observe (1) the glass transition with the related heat capacity change (ca. 50-58°C), the exothermic crystallization (ca. 95-140°C) and the endothermic melting (ca. 125-160°C).

During cooling only the glass transition heat capacity change is indicated (around 50-60°C) because you seem to have no secondary nucleators in your PLA melt and consequently you supercooled the melt without crystallization. You may have also cooled quite rapidly which has lead to a fast viscosity increase and thus slowing down the primary nucleation/crystallization kinetics largely.

Kind regards

Erich Windhab

@ Erich Windhab,

Thank you for your reply,

1. If I would have cooled the PLA by fast cooling say 100°C/min, then I would have understand the statement you made but in this case the heating and cooling rate are same 10°C/min also I had tried cooling with 2°C/min and did not observe Tc.

2. agreed that there is no secondary nucleators in the PLA but still I am getting double melting peak which could be due to presence of two crystalline populations (need explanation).

*PLA grade: Naturworks PLA 3051D

What cooling rate did you use?

@peter farrington

Heating and cooling rate is 10°C/min.

Tushar Sheshrao Ambone The two melting peaks you are observing are of melting of Primary and secondary crystals of homopolymer. Where you can observe a primary crystal as Tcc but not able to see sec crystals as Tc which may be in very very small quantity. This is the reason that these tiny crystals melted completely in first heating hence you could not observe the two melting peaks in second heating.

Tushar Sheshrao Ambone

Dear Tushar Sheshrao Ambone,

Greetings.

Surprisingly, in my case (DSC curves of PET), I observed the undetermined peak exactly before Tm of PET. My results show same trend in comparison with your DSC profile.

In my case: First, I prepared PET filament by melt spinning method and then I measured its DSC analyses for first heating with heating rate of 10 oC min-1 . You can see the DSC profile in attached image.

I would like ask you tell me know if you have any suggestion about these trends in DSC measurement?

Best regards,

I have a similar question, I observed in some of my DSC two peaks for the melting temperature, somebody explains me it could be due to different kind of crystals in my polymer or different crystal's size too.

Do you have some other explanations?

Thank a lot!

@ Bolley Anaëlle

Hello

My question is a bout undetermined peak exactly before Tm of PET. I don't know what causes this event .