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Dispersive Mixing

Dispersive mixing means breaking down and then dispersing particles. In order to break down a particle, its surface must first be wetted to enable forces that split the particles to be transferred. The dispersing of particles/drops in a simple shear flow is possible up to a certain ratio of the viscosity of drop/matrix. In most compounding processes of polymer alloys this is the limiting factor regarding dispersion quality which can be achieved.

It is possible to show that elongation flows are better suited to this than shear flows. Everything is made more difficult if the particles have elastic properties, e.g. in the case of rubber-type materials.

The RingExtruder is good at generating the required forms of flow due to its basic design. Elongational flow is generated in the apex of a co-rotating screw system. In a FEM-simulation its shown that in the apex a high axial velocity is generated(red color). This high axial velocity is caused by the compression of the melt volume which results in high normal forces applied to the melt. High normal forces cause a high elongational flow and therefore an excellent dispersion.
The large volume of its intermeshing section in particular forms the basis for excellent dispersion capabilities.