Comparison of rheological behavior of LDPE in linear and nonlinear viscoelastic flow and using Multimode Pom-Pom model for prediction of uniaxial elongational flow

Khoshbakhti, Ehsan; Golshan Ebrahimi, Nadereh

Comparison of rheological behavior of LDPE in linear and nonlinear viscoelastic flow and using Multimode Pom-Pom model for prediction of uniaxial elongational flow

Document Type : Original Research

Authors

E. khoshbakhti ¹

N. Golshan Ebrahimi ²

¹ Student

² science Committee

Abstract

Research Subject:

Polymer melts show complex response under the act of deformation. This response has direct relation to their molecular structure. The purpose of this study was to investigate the rheological behavior of branched polymers and the effect of branching on linear and nonlinear viscoelastic flow for usage in various industrial applications.

Research Approach:

For this purpose, the tests such as frequency sweep and extensional for two polyethylene (LDPE) with long branches have been used. From these tests we obtained storage and loss moduli, complex viscosity and extensional viscosity. Molecular models in nonlinear regions can also be used in this regard.

Main Results:

Linear tests can partly show the presence of branch in LDPE, while nonlinear tests show strain hardening behavior for branched sample. One of the models for branched polymers is the Multimode Pom-Pom (MPP) model which can be used to predict the strain hardening phenomenon in extensional flows. In this study, the average number of lateral branches was also calculated using this model.

Keywords

Rheology

Linear and nonlinear viscoelatic

Extentional viscosity

Strain hardening

Multimode Pom-Pom model

Subjects

Processing

1- Münstedt, H., S. Kurzbeck, and J. Stange, Importance of Elongational Properties of Polymer Melts for Film Blowing and Thermoforming. Polymer Engineering & Science, 2006. 46(9): p. 1190-1195.
2- Doi, M. and S.F. Edwards, Dynamics of Concentrated Polymer Systems. Part 2.-Molecular Motion Under Flow. Journal of the Chemical Society, Faraday Transactions 2: Molecular and Chemical Physics, 1978. 74: p. 1802-1817.
3- Doi, M. and S.F. Edwards, Dynamics of Concentrated Polymer Systems. Part 3.-The Constitutive Equation. Journal of the Chemical Society, Faraday Transactions 2: Molecular and Chemical Physics, 1978. 74: p. 1818-1832.
4- Doi, M. and S.F. Edwards, Dynamics of Concentrated Polymer Systems. Part 1.-Brownian Motion in the Equilibrium State. Journal of the Chemical Society, Faraday Transactions 2: Molecular and Chemical Physics, 1978. 74: p. 1789-1801.
5- John, D. and L. Ronald, Structure and Rheology of Molten Polymers From Structure to Flow Behavior and Back Again. 2006, Munich: Hanser Gardner Publications.
6- Benham, E. and M. McDaniel, Ethylene Polymers, HDPE. Encyclopedia of Polymer Science and Technology, 2002. 2.
7- Shroff, R.N. and H. Mavridis, Long-Chain-Branching Index for Essentially Linear Polyethylenes. Macromolecules, 1999. 32(25): p. 8454-8464.
8- Chen, X., C. Costeux, and R.G. Larson, Characterization and Prediction of Llong-Chain Branching in Commercial Polyethylenes by a Combination of Rheology and Modeling Methods. Journal of Rheology, 2010. 54(6): p. 1185-1205.
9- Inkson, N.J., et al., Predicting Low Density Polyethylene Melt Rheology in Elongational and Shear Flows with ``Pom-Pom'' Constitutive Equations. Journal of Rheology, 1999. 43(4): p. 873-896.
10- McLeish, T.C.B., Long Chain Branching. Chemical Engineering Research and Design, 2000. 78(1): p. 12-32.
11- Graham, R.S., T.C.B. McLeish, and O.G. Harlen, Using the Pom-Pom Equations to Analyze Polymer Melts in Exponential Shear. Journal of Rheology, 2001. 45(1): p. 275-290.
12- McLeish, T.C.B., Tube Theory of Entangled Polymer Dynamics. Advances in Physics, 2002. 51(6): p. 1379-1527.
13- McLeish, T. and R. Larson, Molecular Constitutive Equations for a Class of Branched Polymers: The Pom-Pom Polymer. Journal of Rheology, 1998. 42(1): p. 81-110.