Hello,
I have annealed a HDPE powder near its melting temperature for different durations. What I have observed in their DSC analysis is the appearance of a secondary endotherm with a lower melting temperature during the melting cycle. What strikes me is the shift in the lamellar thickness of the secondary crystals(DSC curves are in the attached PDF). Can anyone help me understand what may the possible explanation be for this observation and what following tests can clarify the morphological evolution?
Thanks.
First of all i would evaluate the peak areas to get the information whether crystallinity is increasing with annealing or not.
Then you should evaluate whether the content of big crystalls (melting temperature appears to be the same for all samples) is stable or reducing.
An explanation could be that by annealing at i guess 125°C (what was the used temperature?) you allow the formation of additional nuclei which grow slowly. As the freedom of motion is limited and the chains coiled they can not form as big crystalls as the already crystallized chains.
If you would perform several isothermal annealing processes in decreasing temperature order you would possibly create several additional peaks.
Additional analysis could also include scattering methods for studying the formed crystalls.
I hope this helps
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