HDPE (CM1) optical birefringence pattern in cross-slot flow, piston speed 2.2mm/s, 175C
The optical birefringence pattern obtained from lightly branched high density polyethyene (HDPE - produced by metallocene catalysis polymerisation) flowing in a cross-slot multi-pass rheometer cell. Experiment carried out on the Cambridge Multi Pass Rheometer (MPR4) at a piston speed of 2.2 mm/s at 175C. The geometry generates a flow field with an extensional component at the centreline. If the no slip condition at a solid surface is satisfied, the side walls are high shear rate regions. The experiments were carried out to evaluate the material behaviour in extensional flow. At low extensional rates, an almost Newtonian stress profile is exhibited.
Conditions: Material = HDPE CM1, Mw=104kg/mol, Mn=50.2kg/mol, Polydipersity=2.07, Temperature = 175 degrees celsius, Piston speed = 2.2mm/s, Width of flow channels = 1.5mm, depth of sample = 10mm (hence 2D flow approximation is possible), Back pressure in the side arms = 5bar. For further details see:Hassell DG, Auhl D, McLeish TCB and Mackley MR, The effect of viscoelasticity on stress fields within polyethylene melt flow for a cross-slot contraction-expansion slit geometry, Rheologica Acta, 47, 821-834 (2008)