In this study, poly(ethylene terephthalate) (PET), an important packaging material for carbonated beverages, was investigated on its glassy relaxations and melt crystallizations in CO2 in a high-pressure differential scanning calorimeter (PDSC) and a high-pressure thermostat chamber as a function of CO2 pressure, time, CO2 depressurization rate, and PET crystallinity. DSC measurements found a low glass transition temperature (T-gL) at near 50 degrees C in the wholly amorphous PET and a high glass transition temperature (T-gH) at near 70 degrees C in the PET sample with a fairly high crystallinity (X-c 50%). Both T-gL and T-gH decreased with increasing time in CO2, attributed to plasticization by CO2. PET sample with a moderate crystallinity (X-c 42%), however, exhibited both T-gL and T-gH corresponding to the relaxations of the dual amorphous phases as confirmed by dynamic mechanical analysis, with the T-gL. assigned to the free amorphous phase and the T-gH to the constrained amorphous phase. The T-gL is much farther apart from T-gH than those obtained in N-2. The T-gL and T-gH in PET with a moderate crystallinity unexpectedly appeared to be insignificantly varied with time in CO2: however, the magnitude of the T-gL signal increased but the T-gH signal decreased with increasing time in CO2, attributed to disentanglement of polymer chains by CO2. Dual melting peaks in PET were found after nonisothermal crystallization from the melt in CO2. Temperaturemodulated DSC (TMDSC) analysis indicated that melting-recrystallization model and double lamellar thickness model were both responsible for the appearance of the dual melting peaks. (C) 2010 Elsevier B.V. All rights reserved.