Crystal Morphology and Melting Behavior of the Isothermally Crystallized Poly(Trimethylene Terephthalate)

The crystal morphology and melting behavior of the poly (trimethylene terephthalate)(PTT) formed in limited space at specific temperatures were studied by the polarized optical microscopy,optical microscopy,atomic force microscopy (AFM),respectively. The results show that crystal morphology of PTT depends strongly on the temperature. When the isothermal crystallization temperature increases from 190 ℃ to 225 ℃,the spherulites continuously change in the following order:non-banded → regular banded → zigzag banded → non-banded spherulites. Furthermore,the band spacing increases with crystallization temperature. The forming of banded spherulites is due to the fold surface stress. When heating the samples,the initial banded spherulite will melt and the bandings will change its morphology in a certain range of temperatures:clear→faint→clear→melt,which is proposed to result from the melting→recrystallization→remelting of the lamellaes.