Extraction Dry wood (10 g) meal was subjected to planetary
ball milling at 500 rpm for 48 h under nitrogen. The crude
lignin was isolated in the same way as described above for the
determination of extractable lignin. The obtained lignin was dissolved
in the minimum required amount (100 ml, typical 10 ml
for each gram of wood) of cold acetic acid (50%) and the solution
was filtered first over a G3 and then over a G4 glass sinter
plate. The solution was introduced slowly into water (750 ml).
The aqueous suspension was frozen and stored overnight to
destroy colloid structures. The suspension was centrifuged at
5000 rpm for more than 1 h. The clear solution was decanted
and the residue was suspended by stirring with water and centrifuged
again. This step was repeated two or more times until
the odor of acetic acid had disappeared.