How do I accurately determine the onset and end time of crystallization from DSC curves (heat flow versus time) when dealing with DSC crystallization kinetics of crystalline polymers? Also, how do I obtain the curves of relative crystallinity as a function of time?
The onset and and end time is very subjective as different people tend to set the region based on their judgement by looking at the DSC curves. Having said that if your DSC system have the capability of producing the derivative curves, you can use that as the guideline as it would sometime indicate the starting and ending point of the polymer behavior as being heated.
Following up the Ahmad Romli answer, try to integrate cristallization endotherm at 10 to 20°C before and after onsets. Compare regular and sigmoidal integrals, the best is the one which follows the signal smoothly, just as if the cristallization is not happening. Also keep in mind the heating rate when changing from temperature to time.
The best method is described by Mathot et al. based on the enthalpy of the sample. V.B.F. Mathot, M.F.J. Pijpers, Heat capacity, enthalpy and crystallinity for a linear polyethylene obtained by DSC, J. Therm. Anal. 28 (1983) 349-358. or
V.B.F. Mathot, Calorimetry and Thermal Analysis of Polymers, Hanser Publishers, München, 1994.
Thank you, Prof. Schick! It is great honor for me to have your reply. But presently, we only empirically estimate the onset and end time of non-isothermal crystallization when dealing with crystallization kinetics. The state-of-the art method is far from accuracy, can you give me some advice?
Choosing an arbitrary baseline is always dangerous. You need some objective criteria for the temperature range to define a meaningful baseline.
That is the problem. Therefore the method proposed by Mathot is preferable. It provides crystallinity as function of temperature (time) not much influenced by the operator.
Can you please teach, How to obtain the curves of relative crystallinity as a function of temperature when dealing with DSC crystallization kinetics of crystalline polymers?
- Badges
- Science topic
- Similar topics
- Physical Sciences
- Materials Science
- Materials Chemistry
- Polymer Chemistry