IN
LINE MEASUREMENT OF THE POLYMER MELTING BEHAVIOR IN SINGLE SCREW EXTRUDERS
María
del Pilar Noriega*,
Tim A. Osswald and Nicola Ferrier
Polymer
Engineering Center (PEC)
Department of
Mechanical Engineering
1513
University Avenue
University of
Wisconsin-Madison
Madison,
Wisconsin 53706, USA
* ICIPC-
Plastics and Rubber Institute
Carrera 49 No. 5 Sur – 190
Medellín, Colombia, South America
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.