Thermal Behavior, Aggregation Structure And Rheological Properties In Poly (Trimethylene Terephthalate) And Poly (Trimethylene Terephthalate)/ Poly (Butylene Terephthalate) Blends

Poly(trimethylene terephthalate) (PTT) is newly commercialized aromatic polyester by Shell Chemical Company. PTT has properties in between those of poly(ethylene terephthalate) (PET) and poly(buthyene terephthalate) (PBT), with an unusual combination of the physical properties of PET and processing characteristics of PBT. These make PTT highly suitable for uses in fiber, carpet, textile, film and engineering thermoplastic applications. PBT exhibits good chemical stability, fast crystallization rate and excellent processing property. If PTT is blended with PBT, the addition of PBT will influence melt viscosity. On the other hand, the introduction of PBT into PTT will certainly affect thermal behavior and phase morphology of the latter. Therefore, it is of interest to study the thermal behavior, morphology structure and rheological behavior of PTT and PTT/PBT blends for academic studies and practical applications.The effects of self-seeding nucleation on crystallization behavior and morphology of PTT are studied. DSC results indicated that the crystallization temperature of PTT increased obviously after the process of self-seeding nucleation. The decrease of crystallization active energy and chain folding work indicates that the self-nucleation can greatly promote the overall crystallization of PTT. The density of crystal nucleus can increase obviously and the spherulite size can decrease markedly after self-seeding nucleation process is applied.At different film forming temperatures, phase morphologies of PTT solution-cast film are related to the presence of residual solvent or not. Transmission electron microscope (TEM), selected area electron diffraction (SAED) and tilting experiment along the crystal a-axis are applied and two completely different phase compositions and structure are found in the light and dark regions of the ring-banded spherulites. The light region is mainly amorphous phase, but the dark region is mainly crystalline phase. The spherulite radial direction can be determined to be the crystal a-axis. The development of the ring-banded spherulites in PTT solution-cast film is a rhythmic growth process, and thus it is consistent with the structural discontinuity model.Thermal behavior of PTT/PBT blends are studied. The results suggest that the presence of the less crystallizable PBT (or PTT) molecules in the PTT-rich (or PBT-rich) blends decreases the crystallizability and crystalline (peak) temperature of the blends. The complicated phase morphology of the PTT/PBT blends is strongly dependent on the compositions of the blends. PTT-rich blends (Wpbt≤30%) isothermally crystallize toform ring-banded spherulite. The spacing of ring-bands decreases with increasing crystallization temperature. The increase of PBT content in PTT-rich blends (Wpbt≤ 30%) result in decrease of initiative crystallization temperature that formed ring-banded spherulite.The flow behavior of PTT/PBT blends is nearly related to composition of the blends, compatibility of two phase and phase inversion. A variation of complex viscosity of PTT/PBT blends with composition shows positive-negative deviations from the log-additivity rule and the viscosity-composition curves reveal an S shape. The minimum and maximum complex viscosity are found when PBT content is 10% and 90% weight fraction, respectively. Complex viscosity shows negative deviation at a PBT content between 0 and 0.6 weight fraction, whereas positive deviation occurs for PBT content much than a 0.6 weight fraction. The point of transition shows that phase inversion takes place at composition with a 0.6 weight fraction of PBT in the blend. Further, a plateau region can be observed in the figure at intermediate compositions, which can be related to their cocontinuous morphology. Variation of the storage modulus (G') or loss modulus (G") with composition shows a trend similar to that observed for complex viscosity. Steady shear viscosities for PTT/PBT blends decrease slightly with increasing shear rate, suggesting a slight shear-thinning behavior.