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Influence d'un cisaillement sur les premiers stades de la cristallisation du polypropylène

Abstract : The effect of a shear flow on the early stages and the kinetics of isothermal crystallization of an isotactic polypropylene is studied experimentally. In the shear rate region where crystallization proceeds through point-like precursors, the magnitude of the shear rate, the shearing time, as well as the instant in time at which the deformation starts are varied, in combination with a well-defined flow field and the use of rheo-optical measurements. Above a critical shear rate and a critical shearing time, the crystallization kinetics are enhanced. The kinetics are on the other hand not affected by the instant in time at which flow is applied, only the shearing time and primarily the magnitude of the shear rate experienced by the material matter. The influence of flow parameters are compared to the measurements of global chain extension. The early stages of crystallization are investigated by small-angle light scattering experiments, which detect changes in the polarizability fluctuations. Density fluctuations are always detected prior to orientation fluctuations and they are coupled to shear flow. Measurements explicitly compare the effect of temperature and shear on the kinetics and the intensity of the density fluctuations. The evolution of these density fluctuations is then compared to the optical observations of nucleation and growth.
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Submitted on : Monday, April 21, 2008 - 10:29:36 AM
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  • HAL Id : tel-00274692, version 1

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Nicolas Devaux. Influence d'un cisaillement sur les premiers stades de la cristallisation du polypropylène. Mécanique [physics.med-ph]. École Nationale Supérieure des Mines de Paris, 2003. Français. ⟨NNT : 2003ENMP1198⟩. ⟨tel-00274692⟩

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