Plastics. Determination of the transient extensional viscosity of polymer melts

2005 ◽  
Keyword(s):  
Polymer Melts ◽  
Extensional Viscosity

Local versus integral measurements of the extensional viscosity of polymer melts

2009 ◽  
Vol 53 (6) ◽  
pp. 1363-1377 ◽  
Author(s):  
Teodor I. Burghelea ◽  
Zdeněk Starý ◽  
Helmut Münstedt
Keyword(s):  
Polymer Melts ◽  
Extensional Viscosity

scholarly journals Recoverable Extensional Flow of Polymer Melts and Its Relevance for Processing

Polymers ◽  
2020 ◽  
Vol 12 (7) ◽  
pp. 1512
Author(s):  
Helmut Münstedt
Keyword(s):  
Polymer Melts ◽  
Extensional Flow ◽  
Elongational Flow ◽  
Fused Deposition Modelling ◽  
Extrudate Swell ◽  
Fused Deposition ◽  
Rigid Particles ◽  
Experimental Parameters ◽  
Slit Die

While the uniaxial elongational viscosity is widely investigated, and its relevance for processing is described in the literature, much less has been published on the recoverable extensional flow of polymer melts. This paper presents a short overview of the dependencies of the recoverable elongation on the molecular structure of a polymer, and on some experimental parameters. Its main focus lies on the discussion of processing operations and applications that are largely affected by the elastic components of elongational flow. The recoverable portions of stretched films are considered, and the exploitation of the shrinkage of films, due to the recovery of frozen recoverable deformations, and its role for applications are addressed. The analysis of measurements of velocity fields in the entry region of a slit die and results on the determination of the recoverable elongation from uniaxial experiments, according to the literature, lead to the conclusion of dominant elastic extensions. Considering these facts, the assumptions for Cogswell’s widely used method of determining elongational viscosities under processing conditions from entrance flow are not realistic. As examples of a direct application of extrudate swell from short dies for processing, pelletizing and fused deposition modelling within additive manufacturing are addressed. The special features of extrudate swell from short dies, and uniaxial recoverable elongation for a polymer filled with rigid particles in comparison to an immiscible polymer blend, are presented and discussed.

Measurement technique and data analysis of extensional viscosity for polymer melts by Sentmanat extensional rheometer (SER)

2010 ◽  
Vol 49 (4) ◽  
pp. 359-370 ◽  
Author(s):  
Johanna Aho ◽  
Víctor H. Rolón-Garrido ◽  
Seppo Syrjälä ◽  
Manfred H. Wagner
Keyword(s):  
Data Analysis ◽  
Measurement Technique ◽  
Polymer Melts ◽  
Extensional Viscosity

Molecular Drag-Strain Coupling in Branched Polymer Melts

2000 ◽  
Vol 629 ◽  
Author(s):  
Richard J. Blackwell ◽  
Tom C. B. McLeish ◽  
Oliver G. Harlen
Keyword(s):  
Branch Point ◽  
Polymer Melts ◽  
Uniaxial Extension ◽  
Extensional Viscosity ◽  
Low Density Polyethylene ◽  
Model Parameters ◽  
Low Density ◽  
Branch Points ◽  
Nonlinear Rheology ◽  
Branched Polymer

ABSTRACTThe “pom-pom” model of McLeish and Larson (J. Rheol. 42, 81, 1998) provides a simple molecular theory for the nonlinear rheology of long chain branched polymer melts. The Edwards-de Gennes tube concept is used to derive a constitutive equation for a simple branched molecule composed of two star polymers linked by a single backbone chain. A feature of this model is that the backbone section of tube can stretch up to maximum length given by the maximum entropic drag-force from the arms, after which the star arms are withdrawn into the backbone tube. This produces a sharp transition in the extensional viscosity at this maximum stretch. This unphysical feature results from an over-simplification of the behaviour near the branch points.In this paper we introduce a simple treatment of the coupling between relaxed and unrelaxed polymer segments at branch-points. This allows for localised displacements of branch-point within a quadratic potential before maximum extension is reached. Displacing the branch-point reduces the length of arm outside the tube and so reduces in the drag on the star arms. This smoothes out the sharp transitions in extensional viscosity in the original “pom-pom” model at the cost of introducing an extra unknown parameter.This modification improves the prediction of the nonlinear rheology of H-polymers whose molecular structure is known. Alternatively, for polymers of unknown structure such as commercial Low Density Polyethylene, the model parameters may be fitted from linear viscoelastic and uniaxial extension data, to provide predictions for the behaviour in transient nonlinear shear and planar extension. By including local branch-point displacement we find improved agreement with the data for Low-Density Polyethylene.

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