Crystallization and molecular relaxation of poly(ethylene terephthalate) annealed in Supercritical carbon dioxide

Poly(ethylene terephthalate) was annealed at different temperature and pressure of supercritical carbon dioxide (CO2) using samples quenched from the melt. Crystallization and molecular relaxation behavior due to CO2-annealing of samples were investigated using differential scanning calorimetric and dynamic mechanical measurements. The glass transition and crystallization temperatures significantly decreased with increasing temperature and pressure of CO2. The dynamic mechanical measurement of samples annealed at 150 degrees C in supercritical CO2 showed three relaxation peaks, corresponding to existence of different amorphous regimes such as rigid, intermediate, and mobile domains. As a result, the mobile chains were likely to facilitate crystallization in supercritical state. It also led to the decreased modulus of CO2-annealed samples with increasing pressure.