Rheology-morphology relationship in polystyrene/poly(methyl methacrylate) blends

Abstract

The relationship between rheological properties and morphology of immiscible polystyrene(PS)/poly(methyl methacrylate)(PMMA) blends was studied. The blends were prepared using a twin screw extruder. A single screw extruder equipped with a slit die was used to perform shear flow measurements of PS/PMMA blends. Morphological examinations were conducted on the cryogenically fractured and extracted samples by scanning electron microscopy. The results show that the melt viscosity of PS/PMMA blend decreases with increasing shear stress, which is attributed to not only the disentanglement of macromolecules but also the reduction in the domain size and the resultant increase of the interfacial area. The power-law index of the blend melt is lower than any of its component melt, suggesting that deformation and breakup of the dispersed phase increase the dependence of the melt viscosity on the shear stress. The blend whose domain size decreases at a faster rate with increasing shear stress, exhibits a strong shear rate dependence on the melt viscosity. The comparison of the morphologies of samples before and after the slit section of the die indicates that the morphology of the blend has a quick response to shear flow, the coalescence of the dispersed drops is predominant for blends at low shear rates.

Keywords

polystyrene / polylmethyl methacrylate / blend / rheological properties

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