Viscous and elastic properties of a linear polypropylene (PP) and a long-chain branched low-density polyethylene (LDPE) have been investigated by creep and creep–recovery experiments in shear and elongation. The data obtained verify the ratios between the linear values of the viscosities and the steady-state elastic compliances in shear and elongation predicted by the theory of linear viscoelasticity. In the nonlinear range, no simple correlation between the viscous behaviour in shear and elongation exists. The elongational viscosity of the PP decreases with increasing stress analogously to the shear thinning observed; the linear range extends to higher stresses in elongation than in shear, however. The LDPE shows thinning in shear and strain hardening in elongational flow. For the LDPE, a linear steady-state elastic tensile compliance corresponding to one third of the linear steady-state elastic compliance in shear was determined. For the PP, this theoretically predicted value is approximately reached. Analogous to the viscous behaviour, the linear range extends to higher stresses in elongation than in shear. For both materials, the steady-state elastic compliances in the nonlinear range decrease with increasing stress in shear as well as in elongation. However, the decrease in elongation is more pronounced.
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Auhl D, Stange J, Münstedt H, Krause B, Voigt D, Lederer A, Lappan U, Lunkwitz K (2004) Long-chain branched polypropylenes by electron beam irradiation and their rheological properties. Macromolecules 37:9465–9472CrossRefADSGoogle Scholar
Ferry JD (1970) Viscoelastic properties of polymers. Wiley, New YorkGoogle Scholar
Kurzbeck S (1999) Dehnrheologische Eigenschaften von Polyolefinschmelzen und Korrelation mit ihrem Verarbeitungsverhalten beim Folienblasen und Thermoformen. Dissertation, Universität Erlangen-NürnbergGoogle Scholar
Laun HM, Münstedt H (1978) Elongational behaviour of a low density polyethylene melt. I. Strain rate dependence of viscosity and recoverable strain in the steady state. Comparison with shear data. Influence of interfacial tension. Rheol Acta 17:415–425CrossRefGoogle Scholar
Meissner J (1972) Development of a universal extensional rheometer for the uniaxial extension of polymer melts. Trans Soc Rheol 16:405–420CrossRefGoogle Scholar
Münstedt H (1975) Viscoelasticity of polystyrene melts in tensile creep experiments. Rheol Acta 14:1077–1088CrossRefGoogle Scholar
Münstedt H (1979) New universal extensional rheometer for polymer melts—measurements on a polystyrene sample. J Rheol 23:421–436CrossRefADSGoogle Scholar
Münstedt H, Laun HM (1979) Elongational behaviour of a low density polyethylene melt. II. Transient behaviour in constant stretching rate and tensile creep experiments. Comparison with shear data. Temperature dependence of the elongational properties. Rheol Acta 18:492–504CrossRefGoogle Scholar
Münstedt H, Laun HM (1981) Elongational properties and molecular structure of polyethylene melts. Rheol Acta 20:211–221CrossRefGoogle Scholar
Münstedt H, Kurzbeck S, Egersdörfer L (1998) Influence of molecular structure on rheological properties of polyethylenes. Part II. Elongational behavior. Rheol Acta 37:21–29CrossRefGoogle Scholar
Münstedt H, Steffl T, Malmberg A (2005) Correlation between rheological behaviour in uniaxial elongation and film blowing properties of various polyethylenes. Rheol Acta 45:14–22CrossRefGoogle Scholar
Patham B, Jayaraman K (2005) Creep recovery of random ethylene-octene copolymer melts with varying comonomer content. J Rheol 49:989–999CrossRefADSGoogle Scholar