Morphology, Dynamic Mechanical, Thermal, and Crystallization Behaviors of Poly(trimethylene terephthalate)/Polycarbonate Blends

The phase morphology, dynamic mechanical, thermal, and crystallization behaviors of poly(trimethylene terephthalate) (PTT)/polycarbonate (PC) blends were studied. The phase morphology of the blends, investigated as a function of the composition, indicated a two-phase structure. Dynamic mechanical thermal analysis (DMTA) studies revealed that there is a shift in tan δmax toward each other especially in higher PTT contents. This is attributed to the small number of transesterification reactions most likely to occur under the reaction conditions that are more pronounced at higher PTT content. Thermogravimetric analysis revealed that PTT is more susceptible to thermal degradation than PC. The blends with a higher PC content showed a higher degradation temperature. However, the blends with a higher PTT content exhibited the lowest initial degradation temperature, which might be ascribed to its higher extent of transesterification reaction. The addition of PC to PTT increases the activation energy of the blends, which indicates an improvement in the thermal stability. The crystallization behavior of the blends was analyzed by differential scanning calorimetry (DSC) and wide-angle X-ray diffraction (WAXD). The DSC results showed that the crystallization behavior of PTT/PC blends was very much affected by the PC content. The onset and peak crystallization temperatures shifted to lower temperatures and the area of the crystallization exotherm decreased with an increase in the PC content. This suggests that the crystallization process of PTT was suppressed by the presence of PC. WAXD analysis revealed that that the intensity of the crystalline diffraction peaks of PTT decreased with an increase in the PC content in the blends. The amount of transesterification reactions occurring between PTT and PC is quantified by Fourier transform IR techniques; it is found that the amount of copolymer formed as a result of transesterification reactions is small, and hence this merely enhances the compatibility between the components.