The transitions and melting behavior of thermally crystallized poly(ethylene terephthalate) and their correlations with ftir and density measurements

The transitions and melting behavior of thermally crystallized poly(ethylene terephthalate) (PET) are studied using a computerized differential scanning calorimeter (DSC). A transition occurs from a structural stage characterized by a strong glass transition and an exothermic crystallization peak to a stage with a barely perceptible glass transition and an endothermic low melting (LM) peak in the DSC thermograms. This transition corresponds to the change from the primary to secondary crystallization process of PET. The exothermic crystallization peak is only observed within the primary crystallization stage. The maximum temperature of the LM peak is a function of annealing temperature and time, and depends on the microstructure of the imperfectly formed crystallites. The high melting peak is the melting of crystallites of higher perfection and is influenced by the recrystallization process of the sample during the scan.