Rheological characterization and modeling of linear and branched metallocene polypropylenes prepared by reactive processing

The aim of this contribution is to compare rheological behavior of three different samples of metallocene catalyzed polypropylene [virgin (linear) metallocene polypropylene (mPP), and (branched) mPPs prepared through reactive processing with (0.01 wt.%) and without peroxide]. For their theological description in different flow situations (shear and elongational) the extended Pom-Pom (XPP) and PTT-XPP models were used. A rotational rheometer (ARES 2000) with the SER Universal Testing Platform was used for the measurement of dynamic data (storage G' and loss G '' moduli) and uniaxial extensional viscosity. It was shown that both processed (branched) mPPs (with and without peroxide) exhibit distinct behavior in uniaxial extensional viscosity (appearance of strain hardening) in comparison to the virgin (linear) mPP. The XPP and PTT-XPP models proved their usefulness for a branching level quantification based on the measurements of steady shear and elongational viscosities. On the other hand, poorer models' predictions of the transient extensional viscosity indicate absence of an H branching for the processed mPPs. Based on the activation energy data it has been suggested that processed mPPs may have star-branched structure. (c) 2008 Elsevier B.V. All rights reserved.