Crystallisation of cellulose/N-methylmorpholine-N-oxide hydrate solutions
Résumé
N-methylmorpholine-N-oxide (NMMO) hydrates are direct solvents for cellulose used commercially in the preparation of cellulose spinning dopes for fibre and film manufacturing. The fact that the cellulose/NMMO/water solutions can crystallise under cooling is important in the process of preparing fibres and films and in their structure formation. It is shown here that the major difference with classical polymer solutions is that the crystallisation of cellulose/NMMO/water solutions is only due to the crystallisation of the solvent, not of the cellulose. The reason for the decrease in crystallisation velocity with the increase in the cellulose concentration is the reduction in the crystallisable part of the solution. The concentration of water in solutions with the same cellulose content is found to strongly influence the crystallisation velocity and the morphology of crystallised solutions. The variation of the crystallisation velocity values with the type of cellulose can be explained by different amounts of free water bound to NMMO, that depend on the cellulose origin.