Abstract
By generalizing the Doi-Edwards model to the Molecular Stress Function theory of Wagner and Schaeffer, the extensional viscosities of polyolefin melts in uniaxial, equibiaxial and planar constant strain-rate experiments starting from the isotropic state can be described quantitatively. While the strain hardening of four linear polymer melts (two high-density polyethylenes, a polystyrene and a polypropylene) can be accounted for by a tube diameter that decreases affinely with the average stretch, the two long-chain-branched polymer melts considered (a low-density polyethylene and a long-chain branched polypropylene) show enhanced strain hardening in extensional flows due to the presence of long-chain branches. This can be quantified by a molecular stress function, the square of which is quadratic in the average stretch and which follows from the junction fluctuation theory of Flory. The ultimate magnitude of the strain-hardening effect is governed by a maximum value of the molecular stress, which is specific to the polymer melt considered and which is the only free non-linear parameter of the theory.
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Received: 1 June 1999/Accepted: 24 November 1999
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Wagner, M., Bastian, H., Hachmann, P. et al. The strain-hardening behaviour of linear and long-chain-branched polyolefin melts in extensional flows. Rheol. Acta 39, 97–109 (2000). https://doi.org/10.1007/s003970050010
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DOI: https://doi.org/10.1007/s003970050010