Improving the Characterisation of Samples Showing Edge Fracture
23 May 2017
Anton Paar has detailed the use of ts MCR 702 TwinDrive Rheometer to characterise the rheological properties of polymer melts and concentrated polymer solutions.
When characterising the rheological properties of a sample, a number of external influences need to be taken into consideration, such as temperature and pressure. Sample-specific properties must be considered when choosing a suitable measuring geometry and defining a measuring regime, in order to avoid any misinterpretation of the measuring results. For example wall-slip effects and shear banding but also turbulent flow may result in erroneous measuring results.
A main limitation for characterising polymer melts and concentrated polymer solutions at large deformation and/or high shear rates is known as edge fracture. This type of sample instability is characterised by a deformation of the sample's surface at the free edges between the upper and lower part of the geometry.
Measurements were conducted with an MCR 702 TwinDrive consisting of two EC motors. One motor is used as the upper drive and measuring unit, as known from a stress-controlled rheometer. The second motor is mounted in the lower port of the device and can be also used as drive and measuring unit. Because both motors can be separately used as drive units and torque transducers, it is possible to work not only in counter-rotation mode, but also in separate motor-transducer mode, where the lower motor is used as a drive unit and the upper motor is exclusively used as the measuring unit.