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Donald G. Baird, J. Huang
Elongational Viscosity Measurements Using A Semi-Hyperbolic Die
Appl. Rheol. 16:6 (2006) 312-320
►
The lubricated semi-hyperbolic die has been proposed as a technique for generating uni-axial extensional flow
and, hence, as a device for measuring elongational viscosity. Two methods for extracting extensional viscosity
data for polymer melts in laminar flow from this device have been proposed and are evaluated here. Following
the approach proposed by Collier and coworkers, values of the transient extensional viscosity,
ηc+, obtained from
a non-lubricated semi-hyperbolic (SHPB) die for several polyethylene (PE) melts were found to be considerably
higher than values obtained by means of the Münstedt type device. Furthermore, the values of
ηc+
obtained from
the SHPB die were considerably higher than the strain averaged values of
ηc+
which Everage and Ballman proposed
would be obtained from a lubricated SHPB. The pressure drop across a SHPB die was estimated assuming
resistance was all due to wall shear (using the lubrication approximation) for two PE resins. In the case of low
density PE (LDPE) the values agreed to within 20% of the measured values suggesting that shear effects at the
die wall were dominating the pressure drop and not extensional stresses. An analysis was carried out which
showed that in the presence of lubrication the conditions for which the values of
ηc+
obtained from the SHPB
would be relatively accurate (Hencky strains > 5.0).
► Cite this publication as follows:
Baird DG, Huang J: Elongational Viscosity Measurements Using A Semi-Hyperbolic Die, Appl. Rheol. 16 (2006) 312.
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