Swelling and dissolution mechanisms of cellulose fibres

The focus of this work was to study the swelling and dissolution of cellulose fibres by varying the quality of the solvent (N-methylmorpholine-N-oxide with various amount of water, NaOH 8% - water), the dissolution conditions, as the tension, and the fibres sources (cotton, wood pulps, regenerated fibres and cellulose derivatives). The swelling and dissolution mechanisms were investigated by high resolution microscopic observations. A selective separation of insoluble and soluble fractions was performed by a centrifugation method. Molar mass distribution, crystallinity, sugar composition, allomorphy and amount of material of each fraction were analysed. From all these investigations, we were able to better describe the swelling and dissolution mechanisms of cellulose fibres and to identify the main parameters involved in the dissolution. Our results show that structural and molecular characteristics of cellulose fibres as well as process parameters must be better controlled to improve the dissolution, (i) process parameters are linked to the solvent convection and the possibility of movements of cellulose fibres in the solvent bath. (ii) Structural parameters are linked with the removal of the external walls, the destructuration of the layer structure and the selective removal of the hemicelluloses. (iii) Molecular parameters are dealing with thermodynamic, as the chain length, the crystallinity, but also the enhancement of the conformational mobility of the chains.