Study On Solid State Polycondensation And Crystallization Behavior Of Poly (Ethylene Terephthalate)

Solid State Polycondensation (SSP) is preparing Poly (ethylene terephthalate) (PET) with high molecular generally preferred. It is important to examine the mechanism of SSP process in order to put up the productivity of PET. The crystallization behavior during SSP has a great influence upon molecular weight of PET. So it is interesting to study the mechanism of SSP and crystallization.In this paper, SSP of PET was carried out in the special reactor to study the infoulences of operating conditions. The influence of the SSP on the crystallization behavior and structure were investigated by the combination of differential scanning calorimetric (DSC and MDSC) and Nikon E600 polarizing microscope with heating and freezing stage.The investigation reflected that temperature had greater effects than time on SSP. And the results of SSP in gas phase showed that the intrinsic viscosity of PET chips was increased with the reaction temperature and time, the optimizing temperature was higher than 220°C;as the temperature higher than 230°C, the chips tended to agglomerate into lumps. While SSP in liquid phase did not agglomerate, so the reaction ould be put up higher than 230°C;and more porous prepolymers were got in liquid phase SSP.The fractional crystallinity increased as the increasing of the SSP time and temperature. The crystallization temperature of the peak was higher and the enthalpy was smaller as the DSC heating rate increased. The results indicated that the melting-recrystallization-remelting process existed for PET at low DSC heating rates. The imperfect crystallites formed at lower SSP reaction temperature. The appearance of crystallizing and fusing peak were due to the "dynamic unbalance" of the crystallization vs fusion. The crystallization structure was observed by Nikon E600 polarizing microscope with heating and freezing stage.Crystallization behavior of PET changed with SSP. The isothermal crystallization of PET with SSP was investigated using differential scanning calorimetry (DSC) polarizing microscope (with heating and freezing stage). The isothermal crystallization of PET suits Avrami equation. There were different morphologies with different isothermal crystallization temperature. As intrinsicviscosity (average molecular weight) of PET increased, crystallization rate constant K and spherulite growing rate decreased, Avrami constant n increased, and more complex morphology was formed corresponding.