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Extrudate swell during the melt spinning of fibers—influence of rheological properties and take‐up force
Author(s) -
White James L.,
Roman Joseph F.
Publication year - 1976
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.1976.070200413
Subject(s) - die swell , swell , materials science , rheology , composite material , capillary action , polypropylene , shear rate , viscosity , silicone oil , shear stress , extrusion , mechanics , thermodynamics , physics
A theoretical and experimental study has been carried out on extrudate swell B , especially the influence of rheological properties and applied take‐up force on the emerging melt. The problem is analyzed in terms of (1) dimensional analysis, (2) force–momentum balances, (3) partially constrained elastic recovery. Analyses in terms of force–momentum balances are only able to give extrudate swell B in the asymptote of high Reynolds numbers. For low Reynolds numbers, they simply relate the take‐up force to the pressure field in the spinneret. Increasing the take‐up force predicts a decrease in the exit pressure. The partially constrained elastic recovery theory yields an expression for B as a decreasing function of applied take‐up force. Specifically, this is\documentclass{article}\pagestyle{empty}\begin{document}$ {\rm B}^{\rm 6} = [B(0)]^6 - (4/\pi \lambda _{eff} /\mu D^2 )F $\end{document}where B (0) is the extrudate swell in the absence of applied forces, λ eff is the effective relaxation time, μ is viscosity (both evaluated at the capillary wall), and D is the spinneret capillary diameter. An experimental study of extrudate swell of several rheologically characterized melts (high density polyethylene, low‐density polyethylene, polypropylene, polystyrene) has been carried out at 180°C by four different methods (frozen, annealed in hot silicone oil, photographed emerging into air, photographed emerging through 180°C silicone oil) in the absence of applied take‐up forces. Extrudate swell for a melt emerging from dies with differing diameters correlates with capillary‐wall shear rate. A comparison of extrudate swell with normal stress–shear stress ratio shows the best agreement for frozen extrudates and photographs of melts emerging into air. The data is compared to the Tanner theory of extrudate swell. B has been determined during melt spinning and shown to be a function of take‐up force for both a high‐density polyethylene and polypropylene melt. B decreases rapidly with applied take‐up stresses. The results are compared to the predictions of the partially constrained elastic recovery theory.