Remarks regarding the determination of the initial crystallinity by temperature modulated DSC

Abstract

The determination of the crystallinity of polymer samples is a typical use of the DSC and it is evaluated from the heat flow curves by various methods A received polymer sample will have an initial crystalline content, which could be zero if the sample was totally amorphous or which is smaller than unity for semicrystalline polymers. The problem with assessing the initial level of crystallinity, is that crystallization may occur during heating, so that the total measured melting enthalpy is the sum of the original amount plus that formed by cold crystallization, for example. Several claims in the literature recommend that the determination of crystallinity can be improved by using temperature modulated DSC (TMDSC). In this contribution we analyze the TMDSC method to determine the initial crystallinity of polymers proposed by Sauerbrunn and Thomas. The conclusion from this result shows that the apparent advantage of the TMDSC technique only arises when a poor baseline selection is made for the evaluation of the DSC curve. It is shown that the method for determination of the initial crystallinity by TMDSC results from incorrect conclusions. The occasionally discussed advantages of this technique are not real. Different techniques for evaluation of conventional DSC curves are referred.