Simultaneous measurements of pressure, electric charge and transmitted light intensity during the extrusion of polymer melts

The simultaneous measurement and record of pressure, as well as the electric charge and transmitted light intensity in an extrudate allows one to study the flow instabilities occurring in the extrusion of linear polymer melts. An experimental procedure to carry out measurements of these variables during the continuous extrusion of polymer melts was developed. A board with conditioning circuits to handle the analog signals coming from the transducers was built for this purpose. The voltages generated by these circuits are sent to a data acquisition board in order to measure and record the variables of interest by means of a personal computer. A program was written in the graphical programming language G of LabVIEW™ which permits the visualization and plotting of the physical variables in real time. The program is also able to store the measured data and presents options to filter the signals and to obtain their frequency spectrum. The system was successfully tested in the study of the unstable flow of linear polyethylene melts.