Amorphous Blends of Poly(Ethylene Terephthalate) and Poly(Butylene Terephthalate) through Ultraquenching

Abstract

Blends of poly(ethylene terephthalate) (PET) and poly(butylene terephthalate) (PBT) are obtained by means of an ultraquenching technique. The thermal behaviour, crystallization behaviour and mechanical properties are investigated by differential scanning calorimetry (DSC), wide angle X-ray scattering (WAXS) and mechanical testing. The results for as-quenched blends are compared with those for the same blends after three years of storage at -15°C. Both calorimetric and X-ray studies indicate that immediately after preparation, the blends are amorphous regardless of the composition. The stored blends are also amorphous. The thermal and mechanical properties of asquenched samples change significantly after a long time at low temperature relaxation. As-quenched blends exhibit two glass transition temperatures, while after the storage, at each composition, they are characterized by a single T g intermediate between those of the pure components. It is demonstrated that ultraquenched PET/PBT blends are miscible in an amorphous state. Both components crystallize simultaneously at all compositions. Each component forms its own crystal phase and the presence of the other one does not disturb but enhances the crystallization process. A well expressed positive synergistic effect is observed in the mechanical properties of PET/PBT blends. Better performance of the ultraquenched PET/PBT blends is explained by their initial amorphous structure and amorphous miscibility.