Morphology control of polyoxymethylene/thermoplastic polyurethane blends by adjusting their viscosity ratio

Polyoxymethylene (POM) is an important plastic with very good properties. However, its poor impactstrength limits its applications. Theoretical and experimental studies have confirmed that thermoplastic polyurethane (TPU) can effectively enhance the notched impact strength of POM. This paper reports that the notched impact strength of POM/TPU blends can be further improved when these blends are endowed with a fine morphology by changing the viscosity ratio of TPU to POM (P=eta(TPU)/eta(POM)) during processing. The experimental results show that the viscosity of TPU is more sensitive to temperature than that of POM, and that the viscosity ratio P decreases with increasing temperature; also for quite a wide range of shear rate, P is close to 1 when the processing temperature (T-p) is around 190 degrees C. Accordingly, the phase structure of POM/TPU blends changes with P. The dispersed phase of TPU shows ellipsoidal morphology when P>1 at T-p<190 degrees C, filamental morphology when P approximate to 1 at T-p approximate to 190 degrees C and spheroidal morphology when P<1 at T-p>190 degrees C. The results suggest that the filamental morphology endows POM/TPU (90/10) blends with the highest notched impact strength (similar to 14 kJ m(-2)). (C) 2006 Society of Chemical Industry.