The compatible nature of a new polyester blend, polybutylene-terephthalate (PBT) and a copolyester of bisphenol-A-neopentyl glycol-terephthalate (CP-350), has been inferred from the single Tg by DSC and dynamic mechanical studies. Compatibility is further confirmed from the progressive melting point depression of PBT, and the increasingly coarse and open spherulitic morphology of the blends as the weight percent of CP-350 increases. At and above 40 weight percent of CP-350, crystallization of PBT is impeded by the presence of high concentrations of CP-350 which results in a low degree of PBT crystallinity (0-8 percent) in such blends. The melt viscosity as a function of blend composition shows a good fit to the Hayashida model. 相似文献
Summary: Poly(ethylene 2,6‐naphthalate) (PEN) can crystallize either from the glassy state or from the melt state. When crystallized from the glassy state, the sample was quenched from the melt in liquid nitrogen and then annealed at certain crystallization temperatures. When crystallized from the melt state, the sample was cooled to a preset temperature from the melt and then annealed for a certain time. The crystal modifications, morphologies and melting behaviors of PEN were investigated by means of wide‐angle X‐ray diffraction (WAXD), polarized optical microscopy (POM), small‐angle light scattering (SALS) and differential scanning calorimetry (DSC). The results show that an α crystal modification of PEN was obtained when PEN crystallized from the glassy state, whilst a β crystal modification was obtained when PEN crystallized from the melt state at a higher temperature. An hedritic morphology of PEN crystal was obtained with only one melting peak observed in DSC curves when PEN was crystallized at a higher temperature from either the glassy state or the melt state. The α crystal modification could also be obtained when PEN was crystallized at a lower temperature from the melt. Spherulitic or banded spherulitic morphologies of PEN crystals, exhibiting multiple melting peaks in DSC curves, were observed when PEN was crystallized at a lower temperature. The multiple melting behaviors of PEN crystals may be associated with spherulitic structures composed of lamellae of varying thickness.
WAXD patterns of PEN isothermally crystallized from different states. 相似文献
Summary A detailed morphological analysis of the melting process of poly(butylene terephthalate) (PBT) is presented. Investigations were conducted by polarizing optical microscopy, coupling the measurement of depolarized light intensity with examination of morphology of PBT spherulites during their fusion. These analyses allowed to prove that the spherulitic superstructure of PBT developed upon isothermal crystallization from the melt does not vary with temperature until complete melting takes place, despite the large reorganization involved in the fusion process. It is thus shown that the double melting behavior commonly observed in PBT does not arise from the presence of various spherulitic morphologies with different thermal stabilities, and the structural changes caused by the reorganization processes do not involve variations in the spherulitic morphology. The recrystallization of PBT above the apparent melting point was also analyzed, and the role of memory effects of crystalline precursors remaining in the melt was discussed. 相似文献
