*2.4. Alkaline Lignin Extraction*

The lignin extraction was performed according to Klupsch [9] and Schütt et al. [11]. Twenty grams of dry material was treated with 1.6 g (8% of dry raw material) sodium hydroxide and filled up with water to a consistency of 10% solid content. The treatment was carried out at 90 ◦C for 60 min. The filtered extract was acidified with 6 mL glacial acetic acid to a pH below 4. The precipitated lignin was separated by centrifugation at 18,000× *g* for 10 min.

The fiber residue was washed with hot deionized water and the solid content was determined for yield calculations. The lignin fraction was vacuum dried for 24 h and, afterward, the yields were determined gravimetrically.
