Hello,
to get an exact result for crystallinity of polymers I want to use the total enthalpy method suggested by Kong and Hay.
For doing so one has to calculate the enthalpy of fusion of the 100% crystalline polymer at your starting temperature. I am using PA6, which has a enthalpy of fusion of 230 J/g at the metling point. In the article (The measurement of crystallinity of polymers by DSC, Polymer, 43 (2002)) it is stated that you can calculate this shift by subtracting the enthalpy of 100% crystalline material (integrated from starting temperature to end temperature) from the amorphous value. How do I get that value of 100% crystalline material in my temperature range?
Best regards
Tobias
The enthalpy of fusion is equal to the difference of the enthalpies of total amorphous and total crystalline material. Both are temperature dependent functions (got by integration of respective cp-curves) and the difference as well. We recommend the thermodynamical founded method (explained in our book) to avoid uncertainties concerning the "right" baseline. I hope I could explain in more detail and avoid any misunderstanding. Attached you find an article (in German language) about the problem.
The gold standard in ascertaining crystallinity is by using XRD, why not try out this method to be sure that your polymer is 100% crystalline?
Dear Adeyinka,
I do not look for a 100% crystalline polymer but for the value of heat capacity of 100% crystalline PA-6 - this is needed to correct the baseline of DSC. The value is more of theoretical nature.
XRD could help me, of course. Yet I have difficulties to get access to this measurement technique unfortunately.
The heat capacity (and/or enthalpy) of 100% crystalline polymers should be published in literature. We used the ATHAS databank created by Prof Wunderlich to get the respective data. The respective values of PA6 should be published there or otherwise in literature. If the respective values are not known the method you mentioned will not work. Details of the method are explained in our book "Calorimetry" in chapter 9.3.1 (see attached flyer)
Regards Günther Höhne.
Sorry for not being clear. The problem is not that there is no literature value for the enthalpy of fusion of PA-6 material. In literature the enthalpy of fusion is determined at the melting point only. Phase transition enthalpy (in my case fusion enthalpy) is temperature dependent. This is the reason I need the temperature dependancy of fusion enthalpy. It is a somewhat theoretical value because the process of melting usually happens at the melting point. (I can imagine supercooled liquids will also show a different phase transition enthalpy when phase transition happens substantially below the melting point.)
I am a bit surprised the baseline correction is not more common. To get the most accurate results for fusion enthalpy of polymers by the method of DSC the baseline should not be drawn arbitrarily.
The enthalpy of fusion is equal to the difference of the enthalpies of total amorphous and total crystalline material. Both are temperature dependent functions (got by integration of respective cp-curves) and the difference as well. We recommend the thermodynamical founded method (explained in our book) to avoid uncertainties concerning the "right" baseline. I hope I could explain in more detail and avoid any misunderstanding. Attached you find an article (in German language) about the problem.
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