Thermal properties and phase morphology of melt-mixed poly(trimethylene terephthalate)/polycarbonate blends-Mixing time effect

This work examined the mixing time effect on the thermal properties and phase morphology of melt-mixed blends of poly(trimethylene terephthalate) (PTT) with polycarbonate (PC). Differential scanning calorimetry (DSC) results indicated that the short time-mixed blends are miscible to a limited extent, with the PTT/PC-75/25 blend exhibiting the most miscibility. With increasing mixing time, the miscibility of the blends was enhanced, owing mostly to the occurrence of a transesterification reaction. The crystallization ability of PTT was hindered in the blends, and was further depressed with the increase in the mixing time. The PTT/PC-50/50 blend was inferred to possess the highest extent of transesterification after extended mixing. As revealed from thermogravimetry (TGA) analyses, the thermal stability of the blends declined as the mixing time increased; the blend with a higher PC content showed a higher degradation temperature. The original two-phased morphology was observed by scanning electron microscopy (SEM) to evolve to one homogeneous phase with increasing the mixing time for PTT/PC-75/25 and PTT/PC-50/50 blends. The PTT/PC-25/75 blend showed a higher resistance to developing the homogeneous phase morphology with mixing time, indicating less vulnerability to the transesterification reaction. The polarized light microscopy (PLM) results showed that the PTT spherulites became smaller or disappeared in the blends with increase in the mixing time.