Miscibility, Crystallization Behaviors and Toughening Mechanism of Poly(butylene terephthalate)/Thermoplastic Polyurethane Blends

Blends of poly(butylene terephthalate) (PBT)/thermoplastic polyurethane (TPU) were prepared by melt compounding. The miscibility, crystallization behaviors and toughening mechanism of the PBT/TPU blends were studied. Dynamic mechanical analysis results demonstrated that PBT was immiscible with TPU. Differential scanning calorimetry and wide angle X-ray diffraction results showed that the crystallinity of PBT decreased with increasing TPU content. Furthermore, blending with TPU did not modify the crystal structure of PBT. The small angle X-ray scattering results indicated that the crystal layer thickness decreased and the amorphous layer thickness increased with increasing TPU content, indicating that TPU mainly resided in the interlamellar region of PBT spherulites in the blends. An obvious improvement in toughness of PBT was achieved with addition of TPU. Neat PBT had elongation at break and impact strength of about 15 % and 2.9 kJ/m 2 , respectively. However, the elongation at break and impact strength of the 70/30 PBT/TPU blend reached 410 % and 62.9 kJ/m 2 , respectively. The morphology of the PBT/TPU blends after tensile and impact tests was investigated, and the corresponding toughening mechanism is discussed. It was found that the PBT showed obvious shear yielding in the blend during the tensile and impact tests, which induced dissipation of energy and, therefore, led to the improvement in toughness of the PBT/TPU blends.