Isothermal crystallization kinetics of poly(vinylidene fluoride) in the alpha-phase in the scope of the Avrami equation

Isothermal melt crystallization of poly(vinylidene fluoride) (PVDF) at different crystallization temperatures was studied by differential scanning calorimetry. Analysis by the two different approaches of the Avrami equation was performed: first the classical double logarithmic approximation was used, but a non-linear least squares search showed to clearly improve the fit of the model to the experimental isotherms. The differences found by both methods in the Avrami parameters are discussed. The limitation of the Avrami equation in this polymer has to do not only with the fitting procedure to determine the parameters but also with the lack of a consistent physical interpretation of their temperature evolution. The melting behavior of the samples was analyzed and an equilibrium melting temperature of 190.9 A degrees C was obtained by the Hoffmann-Weeks extrapolation. The samples crystallize in a spherulitic structure, as observed by optical microscopy with polarized light (OMPL). Lauritzen-Hoffmann theory was applied to analyze the crystallization kinetics and the Regime III was found for the crystallization of alpha-PVDF.