Physical properties of poly(butylene terephthalate)/poly(ester-carbonate) blends

Poly(butylene terephthalate)/poly(ester-carbonate) copolymer (PBT/PEC) blends were prepared by both compression molding with prior kneading and direct injection molding. They were characterized by differential scanning calorimetry (DSC), dynamic mechanical thermal analysis (DMTA), Vicat softening temperature, density, and mechanical properties, which were determined by tensile tests. Unlike the compression-molded blends, the directly injected blends showed, by DMTA, at most compositions very wide T g's, which indicated both partial miscibility and a biphasic nature. The mechanical property changes are discussed on the basis of the solid-state structure characteristics, namely, miscibility level, possible interchange reactions, processing-induced orientation, crystalline content, and free volume content.