Flow-induced size distribution and anisotropy of the minor phase droplets in a polypropylene/poly (ethylene-octene) copolymer blend: Interplay between break-up and coalscence

The morphology of an immiscible blend of polypropylene and (ethylene-octene) copolymer has been studied for different flow conditions. Samples were taken and quenched at the exit of a slit die attached to an extruder. For a statistical analysis of the minor phase droplets, scanning electron images of cryo-fractured samples were used. The size distribution and anisotropy of the minority phase droplets were determined for different positions within the flow profile in the slit die. The distribution functions are discussed in terms of micro-structure of the droplets of the minority phase in the melt which develops due to the interplay of break-up and coalescence. The coexistence of two statistical ensembles for some flow conditions gives evidence for the existence of two regimes (or two length scales) of structure formation: break-up and coalescence. The deformed particles were found to be elongated in the flow direction, which results in a so-called skin/core morphology. From a quantitative analysis of the particle deformation, it was found that the deformability of particles is determined by their size rather than by the shear stress.