IN LINE MEASUREMENT OF THE POLYMER MELTING BEHAVIOR IN SINGLE SCREW EXTRUDERS

Abstract

Existing experimental techniques designed to study melting behavior of polymers inside the screw extruder suffer from limited functions or tedious procedures. All the techniques developed in the past three decades are invasive, time consuming, difficult to implement and expensive. Their invasive nature affect friction characteristics and heat transfer, significantly influencing the outcome of measured parameters. This paper presents an in-line, non-invasive measuring technique that can accurately capture experimental data and images from inside the extruder through a small quartz window and a rigid boroscope at short response times using a highly instrumented 45 mm single screw extruder with built-in sensors. By sensing the difference in optical properties between the melt and the solid phase, the melting behavior of high density polyethylene was visualized and measured with this non-invasive technique. Using the system developed during this project we were able to observe and fully describe the mechanisms of melting in the plasticating zone of the single screw extruder. Through our experiments we were able to actually see and verify Tadmor and Pearson's melting mechanisms. In addition, we were able to see, for the first time, a melt pool formation delay due to a solid bed saturation process. Besides presenting a new optical measurement system for polymer processing, a significant contribution of this research is the better understanding of polymer melting inside extruders and plastication zone of injection molding and blow molding machines.