Viscosity and density measurement methods for polymer melts

In this article review of density and viscosity measurement methods is presented, including ultrasonic pulse echo methods, which are capable to measure these properties of polymer melts. The methods are presented according to measurement principles, methodology, accuracy and possibility to measure density and viscosity of polymer melts on-line during extrusion process. Such measurements are very important for process automation, process monitoring and control. The ultrasonic pulse echo methods are separated from other methods, because very often they are superior to other techniques. The advantage of this technique is that at the same time sound velocity and attenuation in a plastic melt may be measured, what gives more information. For this purpose polarized shear waves as well as longitudinal, torsional and other types of waves in a wide frequency range may be employed.