The effect of viscosity ratio on the morphology of polypropylene/polycarbonate blends during processing

Abstract

The size of the minor phase in an immiscible polymer blend can have a significant effect on properties such as the impact strength. Few studies, however, have quantitatively considered the parameters controlling the size of the dispersed phase. In this paper, light and scanning electron microscopy have been used to examine the size of the minor phase in polypropylene/polycarbonate blends after melt processing. The size was examined as a function of both the viscosity ratio (p) and the torque ratio (TR). The viscosity ratio is studied in the regions of p > 1 and p < 1. p has a marked effect on the morphology of the dispersed phase with the phase size increasing by a factor of 3 to 4 times from p = 4.5 to p = 17.3. Reduction in the size of the minor phase was achieved below p = 1 with the minimum particle size occurring at p ≃ 0.15. The results for these systems indicate the presence of upper and lower limits of p beyond which deformation becomes difficult. This is shown to be similar in some respects to the behavior of Newtonian fluids in shear flow, although the upper limit extends beyond that observed in the Newtonian fluid studies.