Solubility and spinnability of cellulose-lignin blends in aqueous NMMO

The direct dissolution and joint spinning of cellulose and lignin from NMMO-water were investigated by using dissolving pulp and purified KRAFT lignin. Compared to the rather narrow dissolution window of cellulose in the NMMO-water system, lignin with concentrations up to 15 wt.-% was shown to dissolve in a range from 30 % NMMO to 70 % NMMO at room temperature. The quasi-ternary phase diagram of cellulose-lignin-(NMMO-monohydrate) is represented by a cross section at 95 °C. Dry-jet wet spinning was realized for the cellulose-lignin compound up to 50 % lignin loading. The spinnability decreases with increasing lignin content. SEM and TEM investigations of the fibers exhibit a core-shell structure with a dense core and a porous shell with lower lignin content. In accordance with the X-ray fiber diagrams, it can be concluded that cellulose governs fiber formation and fiber properties while lignin acts mainly as a filler in the core region.