Swelling and dissolution of cellulose Part II: Free floating cotton and wood fibres in NaOH-water-additives systems

The swelling and dissolution mechanisms of native cotton and wood cellulose fibres in NaOH-water are studied. The cellulose fibres exhibit a heterogeneous swelling by ballooning in the best dissolving conditions (-5 degrees C, 7.6% of NaOH). This corresponds to the mode 3 of the swelling-dissolution (see companion paper). in this region of the mixture phase diagram, cellulose is only dissolved inside the balloons. A lot of insoluble parts are present. Increasing the temperature and/or the content of NaOH decreases the quality of the solvent. in this case, the cellulose fibres do not show ballooning, but only a homogeneous swelling (mode 4). Three components are tested as additives: urea, zinc oxide and N-methylmorpholineN-oxide (NMMO). The swelling and dissolution mechanisms in NaOH-water and NaOH-water-additives stay the same. Adding urea to NaOH-water (-5 degrees C, 7.6% of NaOH) gives the same ballooning mechanisms, but with a larger expansion of the balloons, indicating that the solvent is better. Zinc oxide does not increase the expansion of the balloons, but the kinetics of swelling is faster. NMMO acts as a dissolution inhibitor.