Solubility and spinnability of cellulose-lignin blends in specific ionic liquids

The direct dissolution and joint spinning of cellulose and lignin in BmimChc and EmimAc were investigated by using blends of dissolving pulp and kraft lignin as a model for subsequent processing real lignocellulosics wood-TMP and wheat straw. The solubility of cellulose and lignin in the solvents is represented by ternary phase diagrams. The limits of solubility for different cellulose/lignin ratios were found to be an approximately linear function of the lignin content. Air-gap spinning was realized for the model compound with up to 50 % lignin loading with both ionic liquids, whereas TMP and wheat straw could be processed acceptably only with BmimChc. The resulting bicomponent model fibers exhibit a rather high level of tenacity (33 to 46 cN/tex) and modulus (1500 to 2000 cN/tex). The cellulose fraction is dominating the fiber morphology while the lignin is incorporated in the core and somewhat leached out from the shell region.