Dislocation Movement Induced by Molecular Relaxations in Isotactic Polypropylene

Autor(en)

Florian Spieckermann, Gerald Polt, Harald Wilhelm, Michael B. Kerber, Erhard Schafler, Marius Reinecker, Viktor Soprunyuk, Sigrid Bernstorff, Michael Zehetbauer

Abstrakt

The thermal stability of deformation-induced dislocations was investigated in polypropylene (PP) during annealing by means of in-situ X-ray diffraction using synchrotron radiation. The samples were cold rolled to high strains (ϵ = 1.2) in order to introduce a high number of dislocation lattice defects and immediately stored in liquid nitrogen afterard. Then, stepise annealing as applied from -180 °C up to above the melting temperature (165 °C) hile synchrotron X-ray diffraction patterns ere recorded at each step. The resulting lo noise, high angular resolution diffraction patterns ere evaluated using multireflection X-ray profile analysis (MXPA), revealing parameters such as the dislocation density and the thickness of the crystalline lamellae as a function of the annealing temperature. To significant decreases of the dislocation density ere found at annealing temperatures of about 10 and 85 °C. These distinct changes in the dislocation density could be identified as the mechanisms of β- and α-relaxation, respectively, by performing additional dynamic mechanical thermal analysis (DMTA). This behavior could be attributed to an increased intrinsic mobility of the macromolecules at these temperatures accompanied by thermal activation of dislocations, resulting in their mutual annihilation or their movement into the adjacent amorphous phase. The reduction of the dislocation density at the glass transition (β-relaxation) occurs because the stabilizing effect of backstresses originating from the amorphous phase is lost. At the α-relaxation the reduction in the dislocation density is attributed to defect propagations ithin the crystalline lamellae as ell as in the amorphous phase and the recrystallization of intralamellar mosaic blocks (i.e., grains).

Organisation(en)

Physik Nanostrukturierter Materialien, Physik Funktioneller Materialien

Externe Organisation(en)

Montanuniversität Leoben, TGM - Technologisches Gewerbemuseum, Elettra Sincrotrone Trieste

Journal

Macromolecules

Band

50

Seiten

6362-6368

Anzahl der Seiten

7

ISSN

0024-9297

DOI

https://doi.org/10.1021/acs.macromol.7b00931

Publikationsdatum

09-2017

Peer-reviewed

Ja

ÖFOS 2012

103023 Polymerphysik

Schlagwörter

ASJC Scopus Sachgebiete

Materials Chemistry, Polymers and Plastics, Inorganic Chemistry, Organic Chemistry

Link zum Portal

https://ucrisportal.univie.ac.at/de/publications/4a82e1e4-cc74-48e3-b111-e93c8bf2a2a4