Equibiaxial Extension of Two Polymer Melts: Polystyrene and Low Density Polyethylene

1985 ◽  
Vol 29 (5) ◽  
pp. 493-517 ◽  
Author(s):  
Paul R. Soskey ◽  
H. Henning Winter
Keyword(s):  
Polymer Melts ◽  
Low Density Polyethylene ◽  
Low Density

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can stretch up to maximum length given by the maximum entropic drag-force from the arms, after which the star arms are withdrawn into the backbone tube.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.

On the Use of a Kolsky Torsion Bar to Study the Transient Large-Strain Response of Polymer Melts at High Shear Rates

2004 ◽  
Vol 71 (4) ◽  
pp. 441-449 ◽  
Author(s):  
Y. Hu ◽  
R. Feng
Keyword(s):  
Polymer Melts ◽  
Large Strain ◽  
High Rate ◽  
Low Density Polyethylene ◽  
Large Strains ◽  
Low Density ◽  
Strain Response ◽  
High Shear ◽  
Instantaneous Rate ◽  
Torsion Bar

A Kolsky torsion bar is utilized successfully in a novel rheometric experiment for measuring the transient large-strain response of polymer melts under high shear-rate loading. A molten low-density polyethylene is studied with the new technique. The results show that the high-rate shear response of the material has an instantaneous rate dependence that may not be discernible at low rates and a strain-dependent hardening that saturates at large strains instead of fading. The usefulness of the technique and the significance of the findings are discussed in comparison with a modified rubberlike liquid theory and high-rate capillary measurements for low-density polyethylene melts.

Dynamics, heat transfer and structure development in tubular film extrusion of polymer melts: a mathematical model and predictions

1985 ◽  
Vol 5 (2) ◽  
pp. 135-158 ◽  
Author(s):  
Toshitaka Kanai ◽  
James L. White
Keyword(s):  
Heat Transfer ◽  
Polymer Melts ◽  
Flow Behavior ◽  
Low Density Polyethylene ◽  
Experimental Investigations ◽  
Low Density ◽  
Temperature Dependent ◽  
Temperature Dependent Viscosity ◽  
Film Extrusion ◽  
Dependent Viscosity

Abstract A theoretical model of the dynamics, heat transfer and crystallization processes in tubular film extrusion is presented. It is presumed that the polymer melts flow behavior is dominated by the temperature dependence of its rheological properties, as opposed to the specific rheological model used to represent it. Specifically we presume the melt is a Newtonian fluid with a temperature dependent viscosity, characterized by an activation energy of viscous flow E. The shape of the bubble and radius and film thickness profiles are primarily influenced by E. Crystallization makes a second order correction. Detailed comparisons are made to experimental investigations for low density polyethylene, linear low density polyethylene and high density polyethylene and generally good agreement is found.

Biodegradation of low density polyethylene/starch films exposed to soil burial

2009 ◽  
Vol 34 (1) ◽  
pp. 41-48 ◽  
Author(s):  
Souad Djellalia ◽  
Nassima Benmahmoud ◽  
Tahar Sadoun
Keyword(s):  
Low Density Polyethylene ◽  
Low Density ◽  
Soil Burial ◽  
Starch Films
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