Fast-scan and temperature-modulated calorimetry of recrystallization of poly(ethylene terephthalate)

Abstract

The recrystallization behavior of poly(ethylene terephthalate), PET, in the melting region was examined by Fast-Scan and Temperature-Modulated Calorimetry. In addition to the prior results of Fast-Scan Calorimetry, FSC, evidence that recrystallization caused double PET melting peaks was obtained. An exothermic recrystallization peak was directly observed in the second heating run of FSC after the lower-temperature melting peak was eliminated through rapid heating and cooling. FSC was then performed with a temperature protocol of a periodic step-wise jump in temperature, a mode of temperature modulated FSC, T-M FSC. A broad and large peak of the effective dynamic heat capacity of complex quantity was observed in the melting region during T-M FSC analysis, which proved that melting occurred in the temperature range between the double melting peaks. A broad negative peak in the phase angle of the dynamic heat capacity was observed in the melting region at a low underlying heating rate with long modulation periods, which indicated that recrystallization and melting occurred simultaneously.