Development of extrudate distortions in poly(dimethyl siloxane) and its suspensions with rigid particles

Abstract

The developments of flow instabilities and the associated surface and bulk irregularities during the extrusion of a poly(dimethyl siloxane), PDMS, melt and its suspensions with spherical hollow glass particles (10% to 40% by volume) were investigated using both capillary and rectangular slit flows. Flow instabilities were pronounced in the extrusion of unfilled PDMS as manifested by surface and bulk distortions of extrudates over a wide range of shear rates. The range of apparent shear rates, in which such flow instabilities and the associated surface/bulk distortions of the extrudates were observed, decreased upon the incorporation of rigid particles, especially as the concentration of the particles increased. Flow instabilities and the distortions of the extrudates could largely be eliminated upon the incorporation of particles at 40% by volume to the PDMS melt. The geometry of the entry region from the reservoir into the die (taper angles of 15, 45, and 75°) did not generate any differences in the flow instability behavior.