Rheology testing is measuring the deformation of matter under the influence of imposed stress, by analysing the internal response of materials to forces. Polymer flow characteristics are critical in all the conversion and production processes: the material is forced to flow and the rheological characteristics determine the processability.
Why is Rheology Testing Important?
Firstly, flow is involved in the processing and fabrication of such materials in order to make useful objects. Thus, fluid rheology is relevant to polymer processing and determines stress levels in operations such as extrusion, calendaring, fibre spinning, and film blowing. Similarly, rheology influences residual stresses, cycle times, and void content in composite processing operations such as blow moulding, compression moulding, and injection moulding.
Secondly, in the use of polymers the mechanical properties are very important, and the mechanical behaviour is also influenced by rheology. Then, rheological measurements are also employed for product characterisation and quality control purposes. Such measurements are often used for examining and understanding the interaction of the different constituents of a multi-component or multiphase mixture and their influence on the flow and other properties of such materials.
Different Types of Rheological Behavior
All the rheological properties of complex fluids, like polymer melts, depend upon the rate of deformation (shear rate), the molecular weight and the structure, the concentration of various additives and fillers, as well as the temperature. In addition, even at a constant rate of deformation, stresses are found to depend on time.