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Measurement of the equibiaxial elongational viscosity of polystyrene using lubricated squeezing
Author(s) -
Hsu T. C.,
Harrison I. R.
Publication year - 1991
Publication title -
polymer engineering and science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.503
H-Index - 111
eISSN - 1548-2634
pISSN - 0032-3888
DOI - 10.1002/pen.760310404
Subject(s) - materials science , viscosity , polystyrene , shear rate , composite material , newtonian fluid , superposition principle , strain rate , shear thinning , apparent viscosity , steady state (chemistry) , rheology , lubrication , time–temperature superposition , thermodynamics , viscoelasticity , polymer , chemistry , physics , quantum mechanics
The equibiaxial elongational viscosity of polystyrene was determined using a lubricated squeezing technique. Constant strain rates up to Hencky strains of 4.5 could be maintained by a newly constructed instrument. Test results from controlled stress and controlled strain rate measurement were consistent and yielded well‐defined steady‐state viscosities. Measurements appeared to be unaffected by sample geometry, although proper lubrication is important in achieving steady state. The measured biaxial viscosity appeared to be strain rate thinning above a biaxial strain rate of ≈ 0.01 s −1 at 160°C. As anticipated in the Newtonian region, biaxial elongational viscosity was approximately six times the shear viscosity. Thinning indices of both shear and biaxial elongational viscosities were 0.75. Data obtained at various temperatures were shifted following the timetemperature superposition principle. The resulting master curve could be fitted by a Carreau model with n ≈ 0.3 and a time constant of 110 s.