Thermal, crystallization, and rheological characteristics of poly (trimethylene terephthalate)/poly(butylene terephthalate) blends

Blends of poly(trimethylene terephthalate) (PTT) and poly(butylene terephthalate) (PBT) were miscible in all of the blend compositions studied, as evidenced by an observed single and composition-dependent glass transition temperature for each blend composition. The variation of the glass transition temperature with the blend composition was well predicted by the Gordon-Taylor equation, with fitting parameter being ca. 6.9. The cold crystallization (peak) temperature was found to increase, while the melt crystallization (peak) temperature was found to decrease, with increasing PTT content. The subsequent melting behavior for these blends (after cold crystallization) showed the melting point depression behavior, in that the melting (peak) temperature for each component was lowered with increasing content of the other component. During crystallization, the pure components crystallized simultaneously to form their own crystals. The blend having 60 percent by weight of PTT showed the lowest apparent degree of crystallinity. The steady shear viscosities for the pure components and the blends showed slight decrease with increasing shear rate (within the shear rate range of 0.25-25 s(-1)), with those of the blends lying in between those of the pure components. (C) 2003 Elsevier Ltd. All rights reserved.