SUPERCRITICAL CO_2 DRYING OF POLYSACCHARIDIC MEMBRANES PRODUCED IN IONIC LIQUID: APPLICATION TO CELLULOSE AND CHITIN

摘要

New generation processes of solid chitin and cellulose using ionic liquids have been studied. Butyl Methyl Imidazolium Acetate ([BMIm]Ac) has been chosen to be the solvent of both polysaccharides. The main steps of the process are the following: -step 1: gelation of ionic liquid and solute solution at room temperature, -step 2: extraction of the solvent and membrane formation by addition of an anti-solvent (water or ethanol), -step 3: drying of the membrane with supercritical CO_2 (extraction of the anti-solvent and ionic liquid residues). The solids before and after processing have been characterised by different techniques: Fourier Transform Infra-Red Spectrophotometry (FTIR), and Scanning Electron Microscopy (SEM). Preliminary measurements of the solubility have been done as function of temperature: at 70°C, the saturation is 9 g/100g solution for chitin and 16.5 g/100 g solution for cellulose. A method based on the conductivity measurement has been set up to follow the extraction of ionic liquid during step 2 and to quantify the ionic liquid residue in the membrane. A complete ionic liquid removing is necessary since, residues induce alteration of the solid. The drying by supercritical CO_2 permits to remove the major part of the anti-solvent and ionic liquid in the membrane. A porous and compact membrane is obtained.