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Elastic and Viscous Properties of Polyolefin Melts with Different Molecular Structures Investigated in Shear and Elongation

In this thesis, rheological measurements in shear and elongational were performed in order to investigate the viscous and elastic properties of polyolefin melts with different molecular architectures in the linear and nonlinear stress regime.

Polyethylenes (mLLDPE, LCB-mLLDPE and LDPE) and polypropylenes (linear iPP and LCB-PP) were selected and thoroughly characterized usingDSC, FT-IR-spectroscopy, SEC-MALLS, and dynamic-mechanical experiments. The molecular characterization is of great importance as viscosity is highly influenced by molar mass and long-chain branching and elasticity is mainly determined by polydispersity and long-chain branching.

About the influence of molar mass Mw, molar mass distribution (MMD), and long-chain branching (LCB) on viscosity extensive knowledge is available. For the elastic properties the literature is scarce and particularly systematic studies are missing. Also the comparison of viscous and elastic properties in shear and elongation is of interest, though, little is know from the literature. Therefore, creep-recovery measurements in shear, which allow the determination of the viscosity η and the elasticity, in terms of the steady-state elastic compliance Je, were applied to well characterized polyethylenes and polypropylenes. By these means, correlations of the molecular structure with the linear rheological quantities, zero shear-rate viscosity η0 and linear steady-state elastic compliance Je0, as well as with the stress dependence of viscosity and elasticity could be found.

The creep-recovery measurements in shear were performed at different measuring temperatures in order to investigate the temperature dependence of viscosity and elasticity, too.

Additionally, for some materials the stress dependence of steady-state tensile viscosities µs and steady-state elastic tensile compliances De was determined using creep-recovery experiments in elongation. The results from shear and elongational rheology were analyzed with respect to the molecular structure of the polyolefins.

Lesen Sie die deutsche Zusammenfassung auf Kunststoffe.de
Author
 Julia Resch

Julia Resch
Lehrstuhl für Polymerwerkstoffe
Universität Erlangen-Nürnberg

Information

Free keywords: Rheology, Poyethylene, Polypropylene, Elasticity, Viscosity, molecular structure, GPC-MALLS
Institute / chair: Technische Fakultät der Universität Erlangen-Nürnberg
Language: German
Technical consultant for expert services: Prof. Dr. Helmut Münstedt (Betreuer), Prof. Dr. Alois Schausberger
Publication year: 2010
Provider: Wissenschaftlicher Arbeitskreis Kunststofftechnik (WAK) / Kunststoffe.de

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