Dislocation Movement Induced by Molecular Relaxations in Isotactic Polypropylene

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

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 (epsilon = 1.2) in order to introduce a high number of dislocation lattice defects and immediately stored in liquid nitrogen afterward. Then, stepwise annealing was applied from 180 degrees C up to above the melting temperature (165 degrees C) while synchrotron X-ray diffraction patterns were recorded at each step. The resulting low noise, high angular resolution diffraction patterns were 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. Two significant decreases of the dislocation density were found at annealing temperatures of about 10 and 85 degrees C. These distinct changes in the dislocation density could be identified as the mechanisms of beta- and alpha-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 (beta-relaxation) occurs because the stabilizing effect of backstresses originating from the amorphous phase is lost. At the alpha-relaxation the reduction in the dislocation density is attributed to defect propagations within the crystalline lamellae as well as in the amorphous phase and the recrystallization of intralamellar mosaic blocks (i.e., grains).

Organisation(s)
Physics of Nanostructured Materials, Physics of Functional Materials
External organisation(s)
Montanuniversit├Ąt Leoben, Lab Polymer Engn LKT TGM, Elettra Sincrotrone Trieste
Journal
Macromolecules
Volume
50
Pages
6362-6368
No. of pages
7
ISSN
0024-9297
DOI
https://doi.org/10.1021/acs.macromol.7b00931
Publication date
09-2017
Peer reviewed
Yes
Austrian Fields of Science 2012
Polymer physics
Keywords
Portal url
https://ucris.univie.ac.at/portal/en/publications/dislocation-movement-induced-by-molecular-relaxations-in-isotactic-polypropylene(4a82e1e4-cc74-48e3-b111-e93c8bf2a2a4).html