Effect of the radial flow on the volume defect in polydimethylsiloxane extrusion using piv the technique

Abstract

The present work aims to investigate the influence of flow geometry on volume instability associated to a linear polydimethylsiloxane (PDMS). To do so, a convergent radial flow is created at the die entrance. Particle Image Velocimetry (PIV) recordings performed under unstable flow regime, in the capillary rheometer, characterized with the new entrance zone, show a new pattern of streamlines above the die: elongational stresses are less pronounced; furthermore elongational stresses, as well as shear stresses, tend to concentrate near the lip of the capillary die. Photographs of extrudate strands obtained at the die exit, depict a new morphology of defect which appears with a well-established radial flow. These results lead to the agreement the correlation between the gross melt fracture and the flow instability at the entrance zone, as well as the importance of elongational and shear components linked to the upstream flow in the appearance and the development of volume distortion.