Flow induced crystallisation of HDPE (DOW 96001) in cross-slot flow
Bright-field optical observation of supercooled high density polyethylene (HDPE) flowing in a cross-slot multi-pass rheometer (MPR) cell. 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 appearence of dark regions in the flow denotes the formation of crystals. Flow induced crystallisation occurs during flow at the centreline and near the walls.
Conditions: Material = HDPE DOW 96001, Mw=215kg/mol, Mn=38.2kg/mol: Temperature = 133.5 degrees celsius (corresponding to 6 degrees celsius of supercooling): Piston speed = 0.4mm/s (corresponding to an extension rate of 1.5s-1 at the centreline and a shear rate of 3.7s-1 at the side walls): Width of flow channels = 1.5mm Depth of sample = 10mm (hence 2D flow approximation is possible): Back pressure in the side arms = 5bar