Berlin 2008 – scientific programme

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 2: DRG-DPG SYMPOSIUM Rheology II

CPP 2.3: Talk

Monday, February 25, 2008, 14:45–15:00, C 130

Thermorheological behaviour of polyethylene in dependence on molecular structure — •Ute Keßner, Joachim Kaschta, and Helmut Münstedt — Lehrstuhl für Polymerwerkstoffe, Universität Erlangen-Nürnberg, Martensstrasse 7, D-91058 Erlangen

The thermorheological behaviour of polyethylenes is strongly influenced by their molecular structure. In the literature, they are reported to be thermorheologically simple or complex. A clear distinction is not made, however, between the behaviour in the linear and nonlinear ranges of deformation. This paper systematically addresses this topic by presenting the activation energies of various polyethylenes determined in the linear and nonlinear range. Thermorheological simplicity was found for the linear ethylene homopolymers (HDPE) under all applied conditions. The LDPE investigated showed a thermorheologically simple behaviour in the linear range, but a thermorheologically complex behaviour in the nonlinear regime. The activation energy decreases with increasing stresses and approaches the value of the HDPE. Long-chain branched polyethylenes polymerised with metallocene catalysts do exhibit a thermorheological complexity in the linear and nonlinear range of deformation.

Various branching topographies lead to distinct differences in the thermorheological behaviour and result in different flow activation energies. Using these results it will be shown in which way the thermorheological behaviour of different polyethylenes can be used to get an insight into their branching architecture.