FLOW BEHAVIOR OF POLYPROPYLENE MELT NEAR THE MELTING TEMPERATURE

Abstract

In the case of the extrusion of polypropylene near the melting temperature, an anomalous increase in extruding pressure was observed. Bagley plots of extruding pressure in this region deviated from the linear relationship. To explain this anomalous increase, an additional pressure drop was adopted, which was separated from the extruding pressure by use of the reduced time-temperature superposition, that is, the extruding pressure was described as a sum of the pressure drop due to the viscous flow in a capillary, the drop due to the entrance effect and the additional drop mentioned above.
Part of the additional pressure drop was explained based on the reduction of free volume in terms of the Doolittle free volume theory and the Tait equation, and the other part of the pressure drop was suggested to be due to hindrance by some crystallites produced in the polymer melt.