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Stabilité en extrusion des polymères fondus. Effets de la pression et de la structure des copolymères triblocs de type ABA

Abstract : Extrusion is a processing operation widely used in various industries such as polymer processing, metallurgy, ceramics or still in the food industry. Materials undergo high pressures and stresses when extruded at acceptable rates. The aim of this thesis is to gain some insight on the pressure and stress conditions and to better understand theirs effects on the properties and extrusion stability of polymers. Moreover, these effects will be related to the mesoscopic structure of polymers.
4 polyethylenes (PEs) with different structures have been considered to study the effects of pressure. Firstly, the precise experimental conditions allowing to isolate pressure effects from temperature effects and the distinction between stable and unstable flows has been established. Our results show that pressure effects in shear and in elongation can be considered as being equal for 3 out of the 4 PEs. In the case of the fourth one, pressure effects in shear were found to be 30% higher than in shear.
Our results also show that it is a critical shear stress criterion that characterizes the appearance of viscoelastic instabilities. Moreover, we show that this critical shear stress is independent of mean pressure.
In the second part of this thesis, three SEBS block copolymers showing microphase separation, have been considered. Firstly, the macroscopic defects and the propagation of surface cracks during extrusion have been studied. We have shown the origin of flow split at the die exit and an original extrusion regime has been identified: “continuous peeling”. Then, the effects of extrusion on structure have been studied by SAXS with an in-house developed rheometer.
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https://tel.archives-ouvertes.fr/tel-00011316
Contributor : Enric Santanach Carreras <>
Submitted on : Friday, January 6, 2006 - 11:38:09 PM
Last modification on : Friday, November 6, 2020 - 3:45:39 AM
Long-term archiving on: : Tuesday, April 6, 2010 - 4:36:15 PM

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  • HAL Id : tel-00011316, version 1

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Citation

Enric Santanach Carreras. Stabilité en extrusion des polymères fondus. Effets de la pression et de la structure des copolymères triblocs de type ABA. Mécanique [physics.med-ph]. Université Joseph-Fourier - Grenoble I, 2005. Français. ⟨tel-00011316⟩

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