Dissolution of less-processed wood fibers without bleaching in an ionic liquid: Effect of lignin condensation on wood component dissolution

This study evaluated the solubility of low-processed wood fibers produced from a low temperature acid hydro tropic fractionation (AHF) in an ionic liquid (IL) 1,5-diazabicyclo[4.3.0]non-5-enium acetate (DBNHIOAcl. Un-bleached wood fibers produced from AHF using p-Toluenesulfonic acid (p-TsOH) with or without post treatments with lignin and hemicelluloses content up to 15% and 25%, respectively, were dissolved directly into the IL DBNH[OAc]. Post-AHF treatments using dilute alkaline and glycerol swelled the cellulose and partially removed residual lignin resulting in improved dissolution. Semi-quantitative 2D HSQC NMR analyses revealed that the undissolved wood fiber residues were enriched with G units and condensed S units (S-cond), demonstrating, as expected, that G units and condensed lignin substructures have a negative effect on dissolution in DBNH [OAc]. Therefore, AHF with rapid fractionation at low temperatures offers a promising advantage over existing high temperature pulp dissolving fiber (PDF) processes in terms of reducing energy input, lowering lignin content as well as reducing lignin condensation for producing man-made cellulosic fibers (MMCF). Published by Elsevier B.V.