Hi all, please, its is also possible, that cold crystallization occurs AFTER melting point?
E.g. by PE at about 220 °C (melting at 112 °C) and by PP at about 235 °C (melting at 150 °C) .
I think it will be difficult to cold crystallize after melting temperature. Because chain mobility after Tm will be hard.
Could you please define whether your question is based on an analytical observation or just a theoretical concern? Regarding your question, I think, a cold crystallization-like phenomenon is almost impossible at quiescent conditions above Tm. But (!), polyolefins and olefinic copolymers may exhibit "unusual" rheological behavior at higher temperatures than their Tm. These phenomena sometimes are misattributed to weird issues. High shear deformations and specific structural modifications might induce such phenomena. A few papers have been reported on these issues. I will share some of these papers with you...
Arun,
I have never seen/heard/read about a crystallization peak above/after melting to form new crystalline structures for polyolefins. We are discussing about polymers, "thermoplastics" not ceramics, metals and/or alloys.
Please check your knowledge or prove your argument scientifically.
Thanks, actually, I got the answer from elsewhere =) .
But I really observed this phenomenon while running a DSC analysis of 2–3 mg of PE and PP powder with 10 °C/min heating in a hermeticaly sealed Al pan from room temperature to about 280 °C, so UNDER degradation onset - in the first DSC run, so basically while "erasing the thermal history of the sample". See the picture, up PE, down PP, EXOTHERM IS UP. No such phenomena have been observed during a second run.
It should be actually crosslinking, which is by such temperatures possible also by PE and PP. By polymer moulding and forming in the plastic industry it is called "degradation in the machine".
Dear all, I wonder if PE and PP you used are virgin, I think they may contain some inorganic matter. The following attached paper talk about another polymer filled with TiO2 and shows this phenomenon. My Regards
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