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Étude physico-chimique des solutions de cellulose dans la N-Méthylmorpholine-N-Oxyde

Abstract : Cellulose is a natural linear polymer that does not melt below its degradation temperature. It can be processed by means of various techniques, more or less complex and polluting. Among numerous cellulose solvents, N-methylmorpholine-N-oxide (NMMO) is the only solvent used in industrial way for fibres spinning. Despite the fact that this process has been used for nearly fifteen years, it remains empirical. The scientific objective of our work was to clarify various questions concerning the stages of dissolution, forming and regeneration. The main characteristic of this process is the continuous change of NMMO/water mixture composition. Thus, a complete NMMO/water phase diagram was built. The existence of the NMMO monohydrate with a melting temperature of 80°C was confirmed, the existence of the dihydrate (Tm=40°C) instead of the 2,5 hydrate was proposed and a new hydrate with 8 water molecules per NMMO molecule with a melting temperature of - 45°C was found. The investigation of the interactions between cellulose and NMMO/water mixtures in the whole concentration range showed that cellulose II swells and dissolves more readily than cellulose I. For NMMO/water mixtures with high water contents, swelling affects only amorphous regions; it is accompanied by the organisation of the amorphous phase when water content is between 28% and 50%. The predominant role in the crystallisation process of the cellulose/NMMO/water solutions belongs to the solvent. The crystallisation velocity does not depend on the viscosity for given temperature and cellulose concentration. It depends on the properties of the solvent - its amount and water content, and on the dispersion of cellulose in solution. This dispersion depends on the cellulose origin. When the cellulose crystallinity is high, the dispersion of cellulose chains is low. This leads to a high crystallisation velocity of the solvent. The precipitation of cellulose from cellulose/NMMO/water solutions occurs during solution immersion in the water bath. The precipitation velocity is defined by the diffusion of the solvent (NMMO) from the cellulose/NMMO/water solution to the water bath and by the diffusion of the non-solvent (water) from the bath to the cellulose solution. The diffusion of the non-solvent is affected by NMMO content in the water bath while the diffusion of the solvent is also influenced by cellulose concentration of the cellulose/NMMO/water solution. We demonstrated that the diffusion of the non-solvent is ten times more rapid than the diffusion of the solvent. This result was linked to the particular morphology of cellulose solutions regenerated in molten state.
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  • HAL Id : tel-00443727, version 1

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Olga Biganska. Étude physico-chimique des solutions de cellulose dans la N-Méthylmorpholine-N-Oxyde. Mécanique [physics.med-ph]. École Nationale Supérieure des Mines de Paris, 2002. Français. ⟨NNT : 2002ENMP1098⟩. ⟨tel-00443727⟩

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