The crystallization rate and morphological structure of poly(ethylene/trimethylene terephthlate) copolyesters under isothermal melt-crystallization and cold-crystallization

The crystallization behavior and morphological structure of isothermally melt-crystallized and cold-crystallized poly(ethylene/trimethylene terephthalate) (ET) copolyesters were investigated by differential scanning calorimetry, wide-angle X-ray diffraction, and small-angle X-ray scattering. At a given crystallization temperature, the rate of cold crystallization was found to be faster than that of melt crystallization. The Avrami analysis revealed that the nuclei formed rapidly during the cooling process. This suggests that the nuclei formed during rapid cooling and that the athermal nucleation mechanism contributes to the cold-crystallization process of ET copolyesters. The crystal thickness ( l c ), amorphous layer thickness ( l a ), and long period ( L ) of ET53 and ET82 between the isothermal melt-crystallization and cold-crystallization had no significant difference. The values of the linear crystallinity ( ϕ c lin ) for PET, PTT, and ET copolyesters under isothermal melt-crystallization and cold-crystallization conditions were similar. This means that the random distribution of the constitutional repeating unit in the molecular chain of ET copolyesters was not exclusively in the lamella formation.