Volume 31, Issue 5 (September 2003)
Influence of the Geometry of the Extrusion Die on the Melt Strength of Polymers
In the past some studies have been carried out to investigate the melt strength of polymers with the purpose of comparing the results obtained with different materials and at different temperatures. In those experimental activities, once that the testing instrument had been chosen, the polymers were considered the object of the investigation and the attention was rarely focused on the testing geometry. The present work, instead, intends to analyze the influence that the geometry of the extrusion die has on the melt strength of polymers. In particular, attention is focused on the analysis of the differences produced on the melt strength of a material, when the extruded filament is subjected, via the use of two different dies specifically designed, to two distinct temperature profiles along the stretching axis. This investigation highlights that the testing geometry chosen for an experimental activity based on melt tension tests, via haul-off measurements, plays a fundamental role in the correct interpretation of the results. In fact it is demonstrated that the correct choice of the extrusion die allows one to obtain results much more similar to the real processing type that, using melt tension tests, has to be analyzed.