End Corrections in the Capillary Flow of Polyethylene

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  • E. B. Bagley
    Central Research Laboratory, Canadian Industries Limited, McMasterville, Quebec, Canada

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Abstract

<jats:p>End corrections n for the capillary flow of some polyethylenes have been determined as a function of shear rate Gn. The end correction term increases slowly at first with log Gn, but as the shear rate approaches the critical value at which the extruded filament becomes rough, both n and dn/d log Gn increase very rapidly. At the critical shear rate there is an abrupt decrease in dn/d log Gn, and at higher shear rates n increases very slowly with log Gn, with the slope dn/d log Gn being practically constant. All flow curves for a given polyethylene, obtained using capillaries of length to radius ratio ranging from zero to thirty, could be reduced to one single master curve by calculating effective shear stresses using the appropriate values of the end correction term n, with no apparent decrease in viscosity even for short capillaries in which the transit time of the polymer is very short.</jats:p>

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