Abstract
Summary: Due to its unique combination of properties, PTT is a promising material for textile fibre and engineering thermoplastic applications, both as neat polymer and in formulated products. To bring down the cost yet keeping some of its advantageous properties it seems interesting to apply PTT in blends and particularly with PET. We consider here the effect of composition and reaction time on co‐precipitated mixtures PTT/PET, in terms of melting and crystallization behaviour, solution properties and morphology. Blends of various compositions were prepared from mixed solutions, kept in the DSC at 280 °C for different times (0–120 min) and analysed during a successive cooling‐heating cycle. A single T~g~ was detected for each composition, indicative of miscibility in the glassy state. Melting temperatures, at fixed composition, decrease with increasing treatment time. Mixtures rich in one component show a single T~m~, whereas two distinct peaks were observed for the 50/50 blend; on increasing the treatment time some transesterification takes place, evidenced by the melting peak broadening and merging together. The overall crystallinity developed when transesterification plays a role strongly depends on composition: it is inhibited for the 50/50 mixture on cooling, though it can be induced to some extent by reheating or holding during cooling, whereas in one component‐rich blends the main effect is a reduction of the crystallization temperature. Isothermal crystallizations were also carried out as a function of the composition and of the residence time in the molten state; crystallization rate decreases with increasing holding time in the melt. Morphology of PTT and PTT‐rich mixtures under the adopted crystallization conditions exhibits typical banded spherulites, whose growth rate and band spacing vary with melt holding time; moreover, less regular concentric circles develop on increasing residence time at 280 °C.
Spherulitic texture developed at 198 °C after 60 min storage at 280 °C by a PTT/PET 90/10 mixture.
magnified imageSpherulitic texture developed at 198 °C after 60 min storage at 280 °C by a PTT/PET 90/10 mixture.