Innovatives Inline‐Rheometer zur Bestimmung des Stärkeabbaus im Extruder

Abstract

In der Lebensmitteltechnik werden Cerealien oft durch Extrusion von Stärkeschmelzen hergestellt. Zur Charakterisierung der rheologischen Eigenschaften der Stärkeschmelze im Prozess wurde ein neues Inline‐Rheometer entwickelt, das eine im Betrieb verstellbare Messgeometrie besitzt und dessen einstellbarer Druckverlust Rückwirkungen des Rheometers auf die Beanspruchung der Stärke im Extruder auszuschließen vermag. Mithilfe dieses Inline‐Rheometers konnte gezeigt werden, dass aus der inline ermittelten Viskositätsfunktion Rückschlüsse auf die Molmassenverteilung der Stärke möglich sind.

In‐process rheological monitoring of extrusion‐based polymer processes

“…In order to keep constant extrusion conditions, the device must be coupled to extruders operating in starve-fed mode. Hochstein et al 53 combined some of the above solutions: the lower half of a multiple-step slit die is mounted on a wedge that can slide horizontally, allowing the gap to be varied; a flow valve near to the die exit is used to control the total pressure drop. In the twin-slit designed by Springer et al 54 and revisited by Vergnes et al 44 (Fig.…”

“…Figure 3 shows in-process and off-line measurements of (complex and steady) viscosity and normal stress differences for a polystyrene (PS). 51 Robin et al 60 fitted the twin-slit design with adjustable gap by means of the sliding solution developed by Hochstein et al, 53 but the flow valves were located close to the die exit, which may preclude the development of a viscometric flow, as discussed above.…”

“…Robin et al 60 . fitted the twin‐slit design with adjustable gap by means of the sliding solution developed by Hochstein et al ., 53 but the flow valves were located close to the die exit, which may preclude the development of a viscometric flow, as discussed above.…”

In‐process Measurements for Reactive Extrusion Monitoring and Control

“…A few constructive solutions were proposed to vary the shear rate in the measuring section, or generate different shear rates in a single measurement, under constant extrusion operating conditions. They involve the utilization of tapered slit geometries [83], of multiple-step slits with different heights but uniform width [84], and of variable gap constructions [85][86][87], as well as the use of flow regulators (flow valves or gear pumps) [88,89]. In most cases, the shear rate ranges made available remain narrow.…”

“…The shear rate at the measuring slit can be altered by adjusting the respective valve and rotating the other valve in the opposite direction, so that the total pressure drop remains constant and so does the thermomechanical environment of the polymer in the extruder. The concept was revisited by Vergnes et al [93] and was recently adopted in a modified form [87,94]. On-line capillary rheometry measurements along the extruder are much scarcer.…”