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Étude de méthodes d'analyse rapides de la structure moléculaire du polyéthylène

Abstract : The molecular structure of polyethylene is characterized by a long chain branching rate and a specific short chain branching distribution. The long chain branching are usually characterized by rheology whereas methods of fractionation by crystallization are used to analyze the short chain branching distribution. We studied new methods, rheology (Fourier transform rheology, exponential shear rheology) and crystallization based on self-nucleation (DSC and optical microscopy). They are easy to implement, fast and they use a small amount of polymer.In rheology, a transient large shear flow is applied on polymers with classical rheometers. In Fourier-transform rheology, large dynamic oscillations are applied and the third harmonic of the stress spectrum is analyzed according to the amplitude of the strain. In exponential shear rheology, the strain increases exponentially with time as in an elongational flow. But under such a flow, branched and linear polymers develop a strain-softening phenomenon. These methods reveal that transient shear flow is sensitive to low rates of long chain branching when large strain rates are applied. The main obstacle to the expansion of these methods is the absence of theoretical background to correlate the behavior of polymers with their molecular structure. Self-nucleation allows to increase the kinetics of crystallization of polymers. Contrary to DSC, optical microscopy gives the possibility to estimate, at each crystallization level, the maximum fraction of polymer transformed. Nevertheless, it is more difficult to obtain information on the thickness of the lamella by this method. Thus, whatever the method used, we showed that self-nucleation had the effect of decreasing the analysis time while giving more reliable theoretical basis.
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Submitted on : Thursday, December 31, 2009 - 11:52:53 AM
Last modification on : Wednesday, November 17, 2021 - 12:28:11 PM
Long-term archiving on: : Friday, June 18, 2010 - 12:12:12 AM


  • HAL Id : tel-00443616, version 1


Karine Labastie-Coeyrehourcq. Étude de méthodes d'analyse rapides de la structure moléculaire du polyéthylène. Mécanique []. École Nationale Supérieure des Mines de Paris, 2003. Français. ⟨NNT : 2003ENMP1143⟩. ⟨tel-00443616⟩



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