Measuring the rheological properties of polymer melts with on-line rotational rheometry

Since the rheological response of a polymer system to an imposed stress is sensitive to composition, morphology, degree of mixing or temperature, on-line rheometry carried out along the length of the processing or compounding equipment - and able to follow the evolution of physical-chemical processes - is of great technical and scientific significance. This work presents and validates a computer controlled on-line rotational rheometer capable of quickly collecting material samples from within an extruder at different axial locations and performing the usual measurements of typical bench top commercial instruments. Validation of the prototype is made by direct comparison of its measurements with those carried out conventionally, including off-line measurements at room and high temperatures and on-line measurements. In order to illustrate its usefulness, the instrument is then used to monitor the evolution of the rheological behavior of three different materials along the axis of a twin screw extruder.