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The development of the velocity field in polymer melts in a reservoir approaching a capillary die
Author(s) -
Ballenger Timothy F.,
White James L.
Publication year - 1971
Publication title -
journal of applied polymer science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.575
H-Index - 166
eISSN - 1097-4628
pISSN - 0021-8995
DOI - 10.1002/app.1971.070150813
Subject(s) - capillary action , extrusion , materials science , polystyrene , laminar flow , composite material , polyethylene , weissenberg number , polypropylene , shear rate , flow (mathematics) , polymer , mechanics , rheology , physics
Color motion pictures have been made of the flow of low‐density polyethylene, polystyrene, and isotactic polypropylene at 180°C in the reservoir approach to a capillary extrusion rheometer. Detailed observations of the variation of flow patterns with extrusion rate were made. At low flow rates, essentially radial flow into the capillary entrance was observed in all polymers. With increasing flow rate, the included entrance angle α for the polyethylene and polystyrene decreased from 180°C and a “wine glass” structured velocity field was observed with stagnant circulating regions in the corners and the melt channeling in through the wine glass to the capillary entrance. The angle α was related to entrance pressure drop Δ p e and capillary wall shear stress σ w data through the semilogarithmic equation\documentclass{article}\pagestyle{empty}\begin{document}$$ \alpha = 178.5\left( {0.9644} \right)^{{{\Delta p_e } \mathord{\left/ {\vphantom {{\Delta p_e } {\sigma _w }}} \right. \kern-\nulldelimiterspace} {\sigma _w }}} $$\end{document} where α is in degrees; Δ p e /σ w is interpreted as a Weissenberg number. The breakdown of stable laminar flow of the melts in the reservoir and the distortion of extrudates was observed. These phenomena seemed to be initiated by the formation of a spiralling motion in the reservoir.