I am not sure if I may be doing something wrong but my R-squared for primary crystallization (Xt of 3% to 20%) is about 0.9998. I am also looking to compare my data/results. Working with PLA at the moment.
If Avrami coefficient is 4 it means crystal growth is taking place in 3 dimensions and is dependent on time (growth is not instantaneous)
1. Have you done the temperature jump using the DSC instrument ? If so, what are the cooling rates to Tc and what is the Tc window for the isothermal crystallization ?
2. Have you tried to reproduce the experimental data with what ever 'n' and 'k' you obtained based on Avrami calculations?
3. During the Avrami calculation, I think you have considered induction time. You should do the Avrami fitting from where actual crystallization starts ? If you do that, you can do back calculations to reproduce the experimental data and you won't get 'n' > 4.
Article Isotope Effect on the Melt–Isothermal Crystallization of Pol...
This is very abnormal. PLA is not fast crystallization polymers, so it should be not good for Avarami Fitting, because spherulite is harder to be form than polymers, like PE and PP. Anyway, Avarami eqn can only describe crystallization at low supercooling state (high Tc), n has physical meaning, but sometimes values are stranger in case that polymer cannot form perfect crystal. For your case, did u make sure you really melt the sample to amorphous and there was not crystal formed during cooling to isothermal temperature.
You should also check the onset crystallization time during the isothermal crystallization process. When you are doing the avrami fitting, the induction time for crystallization should not be included.
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