Regime crystallization and banded spherulite of poly(trimethylene terephthalate)

An optical microscope equipped with a video photography system was used to monitor the spherulite growth of poly(trimethylene terephthalate) (PTT). Linear growth rates of crystallization were measured in the temperature range of 165-215degreesC for melt-pressed film. Kinetic analysis indicated that PTT exhibits a regime II --> III transition at 193 +/- 1degreesC, and is clearly present irrespective of the drastic changes in the values of T-m(o), U* and T-infinity. This transition is expected to shift to a higher temperature for solvent-cast films. The PTT thin films with thickness in the range of micrometers for polarized light microscopy (PLM) and of 10 nm for transmission electron microscopy were prepared by solvent casting. Both reflected and transmitted modes of PLM were used to obtain optical images. A clear change in morphology was detected for solvent-cast films after melt crystallization. Regular spherulites were exhibited for films crystallized at temperature (T-c) between 180 and 200degreesC. Banded spherulites were observed between T-c = 205 and 225degreesC. The results indicated that the distance between these concentric rings decreased with the reduction in sample thickness and crystallization temperature.