The figure shows DSC cooling (blue) and 2nd heating (green) curves (step: 10 K/min) for a commercial sample supplied as Atactic Polypropylene (APP). The heating curve illustrates two major endotherms at 119.6 and 152.4 oC. However, in the cooling curve, there is only one crystallization peak located at Tc=105.8. How can the two melting peaks be merged in one crystallization peak in the cooling thermogram?
Another point is the two Tm values that as I searched the one at ca 150 corresponds to IPP but I could not identify a source for the one at 119.6. Can this also be related to PP?
I would be much grateful if you could help me with your expertise to get answers to these questions.
Dear Navid Mostofi Sarkari , the endotherm at 119.6ºC could be caused well by the presence of nucleating additives to promote crystallization or well it could be caused by some thermal annealing treatment given to the sample, as you can see on the following document:
https://www.hitachi-hightech.com/file/global/pdf/products/science/appli/ana/thermal/application_TA_086e.pdf
Presence of syndiotactic PP could also be the reason of such endotherm around 120ºC, as described in this article by Bourbigot et al. :
https://core.ac.uk/download/pdf/26803167.pdf
Hope it helps.
Dear Mina Karimi-Avargani ,
Thank you very much for your helpful comment and the attached article.
Dear Manuel Gómez ,
I appreciate your insightful answer and also thank you for the enclosed references.
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