DSC/SAXS analysis of the thickness of lamellae of semicrystalline polymers-restrictions in the case of materials with swollen amorphous phase

Abstract

Due to the simplicity and speed of the analysis, calorimetric (DSC measurements and Gibbs-Thomson method) or x-ray methods (SAXS measurements and Bragg's law or correlation function method) are the most frequently used in determining the thickness of crystals. This paper revealed that the direct application of the above mentioned methods in order to analyze the lamellar structure of semicrystalline polymers, the amorphous phase of which was swollen, may lead to incorrect results. Swelling of the amorphous phase (without changing the thickness of crystals) leads to a shift of the observed melting temperature towards lower values, what in turn will result in underestimated values of thickness of crystals, in the case of calorimetric method. At the same time, an increase of the value of long period is observed, what in turn will result in overestimated values of thickness of crystals, in the case of classical x-ray method (with the use of value of long period estimated according to the Bragg's law and crystalline volume fraction). We have observed that only the analysis of x-ray data with the use of the correlation function method enables to obtain actual values of the thickness of lamellar crystals of the polymeric materials with swollen amorphous phase. The means for correct analysis are pointed out. The above effects have been presented on the example of model, miscible, non-cocrystallizing semicrystalline polymer/low molecular weight modifier systems.