2.4. Lignin extraction
Kenaf (50 g) was extracted with 2 L of 2% aqueous ammonium
hydroxide for 2 d [22]. The extract was centrifuged (5000g) for 10 min at 4 C to remove the solid kenaf residue. The supernatant
was rotary evaporated with heating to remove excess aqueous
ammonium hydroxide to precipitate crude lignin, which was
recovered by centrifugation (5000g) for 10 min at 4 C. The crude
lignin was dissolved in DMSO and centrifuged (5000g) 10 min at
4 C. The supernatant, which contained lignin, was collected, dried
using rotary evaporator. Most of the residual DMSO could be
removed by repeatedly (8-times) adding 5 mL distilled water and
drying using rotary evaporation.