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Évolution de la microstructure d'un PET lors du bi-étirage soufflage ; corrélation au durcissement structural

Abstract : The evolution of the poly(ethylene terephthalate) microstructure was studied during uni-axial stretching as well as during stretch-blow moulding. Drawing was made between glass transition and cold crystallisation temperatures (i.e. between 90 °C and 115 °C). PET was quenched orannealed at the end of drawing. The evolution of the strain-induced microstructure and its texture was investigated by X-Ray diffraction (WAXS and SAXS). The strain-induced amorphous phase was also studied by dynamic mechanical and thermal analysis (DMTA). Whatever the kind of samples (thin or thick samples as well as preforms), the kind of drawing or the experimental conditions used (i.e. temperatures and strain-rates) are, strain-induced crystallisation do not lead to perfect crystalline microstructure in case of applying rapid quenching at the end of stretching.This means that the microstructure observed at the end of drawing is highly influenced by the post-cooling stage. Strain hardening is related to nucleation step rather to crystallisation of perfect crystal. The amorphous phase is, for its part, very constrained during drawing, showing an increasing alpha transition and better ability to crystallize during DMTA measurements. Free stretch-blow moulding tests have shown how the blown hollow parts are heterogeneous in term of microstructure, morphology and polymer chain orientation along a bottle and within the panel thickness. This observation partly explains why it is difficult to relate the end-used mechanical properties to the strain-induced microstructure.Comparative studies of free and industrial stretch-blow moulding demonstrate that the mould could impact the kinematics of blowing. As a consequence, the mould could severely impact the final induced microstructures and properties.
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Submitted on : Monday, December 1, 2008 - 11:29:15 AM
Last modification on : Wednesday, October 14, 2020 - 4:02:44 AM
Long-term archiving on: : Monday, June 7, 2010 - 10:11:16 PM

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  • HAL Id : tel-00343353, version 1

Citation

Martine Picard. Évolution de la microstructure d'un PET lors du bi-étirage soufflage ; corrélation au durcissement structural. Mécanique [physics.med-ph]. École Nationale Supérieure des Mines de Paris, 2008. Français. ⟨NNT : 2008ENMP1557⟩. ⟨tel-00343353⟩

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