Journal ArticleDOI
Determination of elongational viscosity of polymer melts by RME and Rheotens experiments
TLDR
In this article, a new process model is introduced which assumes that the elongational viscosity in the RME Rheometrics test is a function of the draw ratio only.Abstract:
Several linear (LLDPE, HDPE, PS) and long-chain-branched (LDPE, PP) polymer melts were investigated by an elongational rheometer (RME Rheometrics) and by Rheotens (Gottfert). The Molecular Stress Function (MSF) theory is briefly reviewed and used to extrapolate the steady-state elongational viscosity. To evaluate Rheotens experiments, a new process model is introduced which assumes that the elongational viscosity in the Rheotens test is a function of the draw ratio only. The apparent elongational viscosities extracted from Rheotens curves are found to lie in between the steady-state elongational viscosity and three times the shear viscosity.read more
Citations
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Journal ArticleDOI
Strain hardening in polypropylenes and its role in extrusion foaming
TL;DR: In this article, the extensional viscosity of several polypropylene polymers and their blends was measured and the foam processing of these blends using carbon dioxide blowing agent was studied.
Journal ArticleDOI
Quantitative assessment of strain hardening of low-density polyethylene melts by the molecular stress function model
Abstract: The elongational viscosity of three tubular and five autoclave low-density polyethylene (LDPE) melts is analyzed, and quantitative comparison of the strain-hardening characteristics is made by using the molecular stress function model. This is based on a new strain-energy function, which assumes that the total strain energy of a branched section of a macromolecule is given by the addition of the strain energies of the individual chain segments contained in this section. The model employs only two nonlinear material parameters: one parameter describes the average number of crosslinked chain segments, which occupy the same tube section, and determines the slope of the elongational viscosity after inception of strain hardening. The second parameter indicates the maximum relative stretch of the chain segments and determines the steady-state (plateau) value of the elongational viscosity. Both parameters depend on the complex branching topology of LDPE melts. While quantitative relationships between branching structure and the two nonlinear parameters are not yet available, the results of this comparison seem to indicate that the more tree-like structure of autoclave LDPE leads to a higher density of crosslinked chain segments in the same tube section than in the case of LDPE polymerized in tubular reactors.
Journal ArticleDOI
Quantitative analysis of melt elongational behavior of LLDPE/LDPE blends
TL;DR: In this paper, the authors analyzed the shear and elongational data of linear (LLDPE) and branched (LDPE)-polyethylene polyethylene blends and showed that the strain hardening behavior of LLDPE/LDPEs is completely determined by the LDPE component.
Journal ArticleDOI
Relating rheology and molecular structure of model branched polystyrene melts by molecular stress function theory
Abstract: A quantitative analysis of the experimentally observed strain-hardening characteristics of comb-shaped polystyrene melts with different numbers and lengths of grafted sidechains is made using the molecular stress function (MSF) model. This is based on a specific strain energy function, which assumes that the backbone of the grafted molecule is stretched by deformation, while the side chains are compressed. It is demonstrated that the experimentally observed slope of the elongational viscosity after inception of strain-hardening depends on the ratio β of total molar mass to backbone molar mass as predicted by the model. The steady-state (plateau) value of the elongational viscosity depends on the maximum relative stretch, fMAX2, which can be supported by chain segments. It is found that fMAX2 increases with the molar mass fraction of sidechains, and at the same molar mass fraction, more short sidechains lead to higher values of fMAX2 than a few long sidechains. Surprisingly, even sidechains which are short...
Journal ArticleDOI
The molecular stress function (MSF) model in rheology
TL;DR: The molecular stress function (MSF) model is an integral constitutive equation introduced more than two decades ago as discussed by the authors, which is based on the time-deformation separability principle.
References
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Journal ArticleDOI
A new elongational rheometer for polymer melts and other highly viscoelastic liquids
J. Meissner,J. Hostettler +1 more
TL;DR: In this paper, a rotary clamp-based rheometer for polymer melt elongational rheometry is presented, which can be extended by metal conveyor belts with a resolution better than 100 mgf (0.001 N).
Journal ArticleDOI
The molecular stress function model for polydisperse polymer melts with dissipative convective constraint release
TL;DR: In this article, a new dissipative constraint release model was proposed for tube deformation in polymer melts, which is based on a dissipative convective constraint release process and a strain-dependent evolution equation for the molecular stress.
Journal ArticleDOI
The strain-hardening behaviour of linear and long-chain-branched polyolefin melts in extensional flows
Manfred H. Wagner,Heike Bastian,Peter Hachmann,J. Meissner,Stefan Kurzbeck,Helmut Münstedt,F. Langouche +6 more
TL;DR: In this paper, the authors generalize the Doi-Edwards model to the molecular stress function theory of Wagner and Schaeffer and show that the extensional viscosities of polyolefin melts in uniaxial, equibiaxial and planar constant strain-rate experiments starting from the isotropic state can be described quantitatively.
Journal ArticleDOI
The rheology of the rheotens test
TL;DR: In this article, the tensile force needed for elongation of an extruded filament is measured as a function of the draw ratio, and the analysis of this complicated deformation history is simplified by the existence of Rheotens grandmaster curves.
Journal ArticleDOI
Rubbers and polymer melts: Universal aspects of nonlinear stress–strain relations
Manfred H. Wagner,J. Schaeffer +1 more
TL;DR: In this article, the authors analyzed the uniaxial elongation and compression data of linear and branched polymer melts as well as of crosslinked rubbers with respect to their nonlinear strain measure.
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