Rheology of rubber‐modified polymer melts

Abstract

The influence of rubber particles on rheological properties of styrene‐acrylonitrile, and poly(vinyl chloride) was investigated. The temperature dependence of the viscosity functions was found to be independent of the kind of rubber and its concentration. The extrudate swell becomes smaller with increasing particle concentration, the entrance pressure loss remaining nearly unaffected. The strong viscosity increase at small shear rates is more pronounced the higher the concentration and the smaller the size of the particles. It can be interpreted by the assumption of a yield stress caused by the fillers. This yield stress is independent of temperature within the accuracy of the measurements and comes out distinctly higher in elongation than in shear. An analytical expression of the dependence of the viscosity on particle concentration cannot be given. It is demonstrated how sensitively an agglomeration of particles is reflected in elongation and recoverable strain. Based on the morphology shown by electron micrographs of acrylonitrile‐butadiene‐styrene and acrylonitrile‐styreneacrylic ester copolymers, two different models for the occurrence of a yield stress are discussed qualitatively.