A new method for the isolation of lignin in high yield from
wood and pretreated wood is presented, avoiding the
liquid-solid extraction step of the classical milled wood
lignin (MWL) isolation. Dissolved wood lignin (DWL) was
obtained by total dissolution of ball milled wood in
dimethylsulfoxide and N-methylimidazole (DMSO/NMI)
followed by precipitation in dioxane/water in the course
of which lignin and carbohydrate fractions were separated.
The lignin fraction was purified. High lignin yields and
the low number of separation steps belong to the advantages
of the described method. DWL lignin was isolated
from beech wood (Fagus sylvatica L.) and the sample
was compared to MWL obtained by the classical Bjo¨ rkman
method. Elemental analyses, methoxyl group content,
potassium permanganate oxidation, infrared spectroscopy,
and 1D and 2D nuclear magnetic resonance
spectroscopy indicated that both lignin preparations are
quite similar. However, MWL contained significantly more
phenolic hydroxyl groups than DWL. The results indicated
that MWL contains higher amounts of smaller fractions
with broken b-O-4 linkages than DWL.