In-line ultrasonic measurement of velocity profiles of wall-slipping polymer melts during extrusion

To model the flow behavior of molten polymer during extrusion and to define an appropriate extrusion die, the flow profile of the melt under processing conditions must be known. Of particular interest is the presence or absence of wall slippage. Using Ultrasound Pulsed Wave Velocimetry, the velocity profile can be measured in transparent and opaque liquids as well. With a clamp-in waveguide built into the extrusion die, pulsed wave velocimetry can be used for in-line measurement of velocity profiles during extrusion. Results obtained during extrusion of wall-slipping polylactides (PLA) at different channel depths are shown.