Berlin 2001 – wissenschaftliches Programm

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CPP: Chemische Physik und Polymerphysik

CPP 16: Poster: Dynamics of Molecular Systems, Polymer Dynamics, Glass Transition, Crystallization, Electronic Properties of Polymers

CPP 16.10: Poster

Montag, 2. April 2001, 12:30–15:00, AT1

A Molecular Weight Dependent Transition in the Yield properties of Linear Polyethylene — •Yongfeng Men and Gert Strobl — Fakultät für Physik, der Universität Freiburg, Hermann-Herder-Str. 3, 79104 Freiburg

It was found that true stress-strain curves measured during uniaxial tensile deformation of polyethylene and its copolymers generally show four characteristic points(A, B, C, D) where the differential compliance and recovery properties change[1,2]. The strains at A, B, and C are the same ones for all samples with different crystallinity, testing temperatures and strain rates whereas the stresses vary greatly.These critical points can be associated with the onset of isolated inter- and intralamellar slip processes(A), a change into a collective activity of slips (B), the beginning of crystallite fragmentation (C), and chain disentanglement (D). In this study, we paid particular interest on the molecular weight dependence of these critical strains. A series of linear PEs with different molecular weight were investigated. There is no influence of the molecular weight on the critical strains A and B. On the other side, as pointed out first by R.K. Bayer[3], C and D are found to depend on the molecular weight; there is a critical molecular weight at which the critical strains change abruptly. The behavior must have its physical origin in the state of the network built up by both the entanglements and crystals, the details, however, are under discussion.

[1] Hiss, R.; Hobeika, S.; Lynn, C.; Strobl, G. Macromolecules 1999, 32, 4390.

[2] Hobeika, S.; Men, Y.; Strobl, G. Macromolecules 2000, 33, 1827.

[3] Bayer, R.K. Plaste und Kautschuk 1993 40.