Abstract
According to the 3-phase model, semi-crystalline thermoplastics consist of a mobile amorphous fraction (MAF), a rigid amorphous fraction (RAF), and a crystalline fraction (CF). For the two polyesters Polybutylene Terephthalate (PBT) and Polyethylene Terephthalate (PET), the composition of these phases was investigated using the largest possible variation in the isothermal and non-isothermal boundary conditions. This was performed by combining the conventional Differential Scanning Calorimetry (DSC) with the Fast Scanning Calorimetry (FSC). From the results it can be deduced that the structural composition of both polymers is characterised by a large fraction of the rigid amorphous phase. This is mainly formed either during the primary crystallization in the low temperature range or during the subsequent secondary crystallization that follows primary crystallization in the high temperature range. Depending on the thermal history, the fraction of the mobile amorphous phase of both polymers approaches a minimum, which does not appear to be undercut.
Highlights
Despite the enormous variety of today’s polymer applications, the nature and effects of the structural characteristics of polymers are still not understood in detail
The mobile amorphous fraction (MAF) is to be equated with the conventional amorphous phase of the 2-phase model, whereas the rigid amorphous fraction (RAF) is characterised as an intermediate phase that can arise on the surface of crystallites if macromolecules do not refold properly
If the phase composition is analysed in regard to the 2-phase model, this would result in a decreasing cumulative amorphous phase for both polymers
Summary
Despite the enormous variety of today’s polymer applications, the nature and effects of the structural characteristics of polymers are still not understood in detail. The so-called 3-phase model was introduced, which was first verified experimentally by Menczel and Wunderlich [1] in 1981 According to this model, the amorphous phase is further divided into a rigid and a mobile amorphous fraction (RAF, MAF). The MAF is to be equated with the conventional amorphous phase of the 2-phase model, whereas the RAF is characterised as an intermediate phase that can arise on the surface of crystallites if macromolecules do not refold properly. They are partly both inside and outside the crystallite.
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