Fractionation of technical lignin with ionic liquids as a method for improving purity and antioxidant activity

Alder soda lignin, a by-product of the chemical processing of black alder wood, was fractionated using ionic liquids (ILs) based on the 1-buthyl-3-methylimidazolium [Bmim] cation and the following anions: chloride ([Bmim]Cl), dimethylphosphate ([Bmim]Me2PO4), acetate ([Brhim]OAc) and tosylate ([Bmim]OTs). The aim was to obtain lignin fractions of improved purity for further application as antioxidants. The purity and properties of the IL lignin fractions were compared with those of other lignin fractions obtained using sequential extraction with organic solvents. The original lignin and the lignin fractions were characterized by analytical pyrolysis (Py-GC/MS/FID), size-permeation chromatography (GPC), electron paramagnetic resonance (EPR) spectroscopy and wet chemistry methods. The lignin treatment with [Bmim]DMP, [Bmim]OAc and [Bmim]OTs produced fractions with a lignin content of 98-99%. These fractions along with the n-propanol and methanol fractions obtained using sequential organic solvent extraction were enriched with certain structural features that had a positive impact on lignin antioxidant activity, according to the results from DPPH center dot and ORAC assays. (C) 2016 Elsevier B.V. All rights reserved.