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Determination of steady‐state elongational viscosity for rubber compounds using bell‐mouthed dies
Author(s) -
Clarke J.,
Petera J.
Publication year - 1997
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/(sici)1097-4628(19971107)66:6<1139::aid-app14>3.0.co;2-x
Subject(s) - pressure drop , die (integrated circuit) , natural rubber , composite material , materials science , drop (telecommunication) , viscosity , elongation , rheometer , rheology , thermodynamics , ultimate tensile strength , mechanical engineering , physics , engineering , nanotechnology
A bell‐mouthed die geometry was designed to cause convergent flow at a constant, uniform, elongational strain rate. An equation was derived, which showed that steady‐state elongational viscosity could be calculated from a plot of pressure drop due to elongation against a simple function of die length. To obtain values of pressure drop due to elongation, it was necessary to correct the total pressure drop measured across the bell‐mouthed dies for the contribution from shear occurring near the die wall. For this purpose, a simplified shape for the bell‐mouthed dies was assumed, comprising several parallel sided segments. Applying a formula to pressure drop data measured across straight dies corresponding to these segments gave an estimate of the pressure drop due to shear across the bell‐mouthed dies. Pressure drops due to elongation were determined by subtracting the pressure drop due to shear from the total pressure drop measured across the bell‐mouthed dies. Measurements were also carried out with lubrication to validate the shear correction method. The results indicate that for the compound used in this study, a combination of bell‐mouthed and straightsided dies can be used in a conventional capillary rheometer to determine steady‐state elongational viscosity. An elongational viscosity of 190 kPa s at 90°C and at a strain rate of 10 s −1 was determined for a simple styrene‐butadiene rubber compound. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 1139–1150, 1997