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 °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.