Dresden 2011 – wissenschaftliches Programm

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 26: Polymer Dynamics

CPP 26.5: Vortrag

Mittwoch, 16. März 2011, 11:30–11:45, ZEU 160

Polymer dynamics under uniaxial mechanical stress — Ute Böhme and •Ulrich Scheler — Leibniz-Institut für Polymerforschung Dresden e.V., Hohe Str. 6, 01069 Dresden

The influence of uniaxial mechanical stress on the dynamics in semicrystalline polymers has been studied using low-field NMR. While in elastomers a monotonic change of the polymer dynamics, a time-dependent behaviour is found for semicrystalline materials. Under mechanical stress there is creep of the polymer chains, which results in a rearrangement of the crystallites. Though not change in the degree of crystallinity has been found, DSC shows better quality of the crystallites, which is a clear indication of rearrangement of the polymer chains. Low-field NMR using permanent magnets in a Halbach arrangement permit in-situ NMR experiments during stretching. The example of poly(propylene) shows an initial shortening of the transverse relaxation time, which is followed by a prolongation. In a stress-relaxation experiment the stress required to keep a constant elongation decreases exponentially. The transverse relaxation time returns to its initial value with a comparable time constant.