The melting of polymers — a three-phase approach

Abstract

Information on the morphology of semi-crystalline polymers can be obtained from their melting behaviour. Due to the lamellae thickness distribution, a very broad melting region is observed. From a comparison of the glass transition intensity and the crystallinity, e.g. from X-ray diffractometry, it is known that there are rigid amorphous regions inside semi-crystalline polymers with no contribution to the glass transition or to the melting. Both the broad melting region and the deviation from the normally used two-phases model often result in incorrect crystallinities and other morphological parameters. Therefore, the analysis of the melting behaviour, taking into account the broad melting region and the rigid amorphous fraction, should result in a better, more detailed description of the morphology. A procedure to do this on the basis of a separation of the measured heat flux into the baseline specific heat capacity and the excess portion is suggested here. Using this procedure, it should be possible to obtain the temperature dependence of the crystalline, rigid amorphous, and liquid amorphous fractions, as well as the lamellae thickness distribution, the thickness of the interfaces of the lamellae, and the specific inner surface of the crystalline fraction.