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Research Papers

Chain Entanglements and Mechanical Behavior of High Density Polyethylene

[+] Author and Article Information
Joy J. Cheng

Department of Chemical Engineering, Institute for Polymer Research, University of Waterloo, Waterloo, ON, N2L 3G1, Canada

José A. Alvarado-Contreras

Machine Design and Modeling Group, Facultad de Ingeniería, Escuela de Ingeniería Mecánica, Núcleo La Hechicera, Universidad de Los Andes, Mérida, Estado Mérida 5101, Venezuela

Maria A. Polak

Department of Civil and Environmental Engineering, University of Waterloo, Waterloo, ON, N2L 3G1, Canada

Alexander Penlidis1

Department of Chemical Engineering, Institute for Polymer Research, University of Waterloo, Waterloo, ON, N2L 3G1, Canada

1

Corresponding author.

J. Eng. Mater. Technol 132(1), 011016 (Dec 01, 2009) (7 pages) doi:10.1115/1.4000220 History: Received December 09, 2008; Revised August 05, 2009; Published December 01, 2009; Online December 01, 2009

It has long been suspected that physical chain entanglements in the amorphous phase affect the strain hardening behavior of polyethylene. The precise number of chain entanglements in solid polyethylene cannot be measured using any current techniques. Since entanglements in the melt state are known to be preserved in the polymer upon solidification, determination of the molecular weight between entanglements (Me) is used as a measure of chain entanglements for polyethylene. A decrease in molecular weight between entanglements means an increase in the number of entanglements in the polymer. As the Me value decreases, increasing tensile strain hardening of polyethylene is observed. In addition to experimental work, parallel micromechanical modeling was carried out to study the entanglement effect in uniaxial tensile deformation. The model was able to shed more light over the earlier empirical speculations. By combining experimental observations and modeling results, the presence of physical chain entanglements in the amorphous phase was demonstrated to be the controlling factor in strain hardening behavior of polyethylene.

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References

Figures

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Figure 1

Dogbone dimensions for tensile tests

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Figure 2

Relationship between Me, Mw, and PDI of resins

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Figure 3

Tensile elongation curves at 0.5 mm/min constant deformation rate

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Figure 11

Influence of the number of rigid links on stress-strain response for semicrystalline polyethylene

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Figure 10

Influence of the number of rigid links on the stress-strain response of the amorphous phase

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Figure 9

Influence of the number of rigid links on the stress-strain response of the crystalline phase

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Figure 8

Schematic illustration of the eight chain network model for the amorphous phase, Ref. 4

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Figure 7

Schematic representation of polyethylene crystal and slip system, Ref. 4

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Figure 6

Simulation results of semicrystalline polyethylene (4): equivalent stress versus equivalent strain behavior under uniaxial tension

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Figure 5

Relationship between hardening stiffness and Me of resins (the line is only a visual guide to the eye)

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Figure 4

Shifted load-displacement curves of the strain hardening stage and corresponding Me of resins; deformation rate 0.5 mm/min

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