Elastic and Viscous Properties of Polyolefin Melts with Different Molecular Structures Investigated in Shear and Elongation Elastische und viskose Eigenschaften von Polyolefinschmelzen mit verschiedenem molekularen Aufbau untersucht in Scherung und Dehnung
Year: 2010
Type: dissertation
Abstract: 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 using DSC, 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, molar mass distribution, and long-chain branching 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 and the elasticity, in terms of the steady-state elastic compliance, 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 and linear steady-state elastic compliance, 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 and steady-state elastic tensile compliances 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.
Author: Julia A. Resch
Language: German
Subfield: Fluid Flow and Transfer Processes
Field: Chemical Engineering
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W2181598853