Characterization of Phase Morphology of Polymer Melts (PP/PE Blends via Rhology

The melts of high impact polypropylene (impact PP) are heterophasic systems composed of isotactic polypropylene (i-PP), ethylene-propylene copolymer (ethylene-propylene-rubber: EPR) mainly. The phase morphology has a strong influence on the processing conditions and consequently on the product quality. Several studies have been done to establish the influence of the EPR-particles on mechanical properties like impact strength, scratch behaviour and tensile strength. The impact PPs are produced mainly by mixing linear PPs and EPRs or by sequential polymerisation process in a reactor cascade. In both cases i-PP forms the matrix. Mixing produces EPR inclusion of rather large diameters whereas the reactor product contains rather small EPR inclusions. And as is well known the diameter of the inclusions strongly influences the viscoelastic behaviour of the melt. As the optical density of molten i-PP and EPR is almost equal optical methods can not be used for the characterisation of the phase morphology. This report is to show that simple rheological tests are sufficient for an appropriate characterization of 2-phased systems.