Etude du procédé d'homogénéisation de polyéthylènes à distribution bimodale des masses molaires par extrusion en conditions supercritiques

Abstract : Polyethylenes having a bimodal molecular weight distribution are of great interest because they combine the good processability of the low molecular weight (LMW) component and the superior mechanical properties of the high molecular weight (HMW) fraction. However, the presence of HMW gels in the continuous phase hinders the final product quality. A method for the homogenization of these polymers by supercritical fluid assisted extrusion has been investigated. After having assessed the contribution of supercritical carbon dioxide in the reduction of the melt viscosity of polyethylene, the influence of operating conditions like screw rotation speed, polymer flow rate or CO2 content on the product morphology was evaluated. It was shown that under certain conditions, the mixing efficiency reached 98 % upon injection of CO2. The elaboration of an experimental strategy led to the modeling of morphological properties and the specific energy. The development of these models required the use of the experimental data for parametric identification. Both experimental and statistical validations were carried out. The modeling of the homogenization process was then used to propose an optimized extrusion process. Multicriteria analysis of the process consisted in obtaining the best compromise from the fixed objectives, that is maximization of the mixing efficiency along with the lowest specific energy possible. Collectively, this work provides a better understanding of the efficiency and the limits of the supercritical fluid assisted extrusion of bimodal polyethylenes
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Matthieu Nobelen. Etude du procédé d'homogénéisation de polyéthylènes à distribution bimodale des masses molaires par extrusion en conditions supercritiques. Autre. Institut National Polytechnique de Lorraine, 2006. Français. ⟨NNT : 2006INPL005N⟩. ⟨tel-01748882⟩

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