Effects of compatibilizer and testing speed on the mechanical and morphology behaviors of co-continuous amorphous copolyester-polyoxymethylene blends

Abstract

Co-continuous amorphous copolyester (PETG)/polyoxymethylene (POM) (50/50 wt%/wt%) blends were prepared using a twin screw extruder followed compression molding. Two types of thermoplastic polyurethane (TPU) (i.e., polyester-based and polyether-based) were used to compatibilize the blends system. The thermal properties were characterized by using differential scanning calorimetry (DSC). The mechanical properties of the co-continuous PETG/POM blends were studies through flexural and single-edge notch tensile test (SEN-T). The SEN-T test was performed at three different testing speeds; 1, 100, and 500 mm/min. Scanning electron microscope (SEM) was used to access the fracture surface morphology. The flexural strength of the PETG/POM blends was decreased in the presence of TPU. This was attributed to the elastomeric nature of the TPU. The compatibilizing effects of TPU on the PETG/POM blends were proven by moderate improvement in the fracture toughness and confirmed by the SEM observation. The SEN-T fractured surface of the compatibilized blends showed gross matrix shear yielding as compared to the uncompatibilized system. The Kc values of the PETG/POM blends decreased as the testing speed increased. The optimum toughening effect was observed in PETG/POM blends compatibilized with polyether-based TPU at testing speed of 100 mm/min. The polyether-based TPU is a more efficient compatibilizer, because the amount required is one-half that of the polyester-based counterpart to achieve the same Kc value. This was attributed to the elastomeric nature of the polyether-based TPU. The softer nature of polyether-based TPU could provide better toughening effect than the polyester-based TPU, which is relatively harder in nature. POLYM. ENG. SCI., 45:710–719, 2005. © 2005 Society of Plastics Engineers