Swelling and dissolution of cellulose Part 1: Free floating cotton and wood fibres in N-methylmorpholine-N-oxide-water mixtures
Résumé
Five modes describing the behaviour of cellulose fibres dipped in a chemical have been identified: Mode 1: Fast dissolution by disintegration into rod-like fragments Mode 2: Large swelling by ballooning, and then dissolution of the whole fibre Mode 3: Large swelling by ballooning, and partial dissolution of the fibre, still keeping its fibre shape Mode 4: Homogeneous swelling, and no dissolution of any part of the fibre Mode 5: No swelling and no dissolution (case of a non-solvent) In the case of the behaviour of wood and cotton cellulose fibres in N-methylmorpholine-N-oxide (NMMO) and water mixtures, four domains of water content have been identified. Below 17% of water up to monohydrate (13%), the fibres are disintegrated into rod-like fragments and dissolve (mode 1). In NMMO - water mixtures containing 19-24% water, the cellulose fibres exhibit a heterogeneous swelling by forming balloons (composed of dissolved cellulose holds inside a membrane) separated with non-swollen sections. The whole fibre will completely dissolve (mode 2) in four successive steps (growth of the balloons, burst of the balloons, dissolution of the non-swollen sections and finally dissolution of the membrane). With still greater water contents (25-30%), only the ballooning phenomenon is observed, with a partial dissolution inside the balloon (mode 3). Above 35% of water, the fibres swell homogeneously and are not dissolving (mode 4).