Acetylation was carried out using the experimental conditions
described below. Dry lignin samples (1.00 g) were dispersed in formamide
(25 mL) about 3 h, until complete solubilization. Pyridine
(40 mL) was added, followed by acetic acid anhydride (6.6 mL). After stirring at room temperature for 3 h, another portion of acetic
anhydride (6.6 mL) was added, followed by the same amount after
another 3 h. After 30 h, the viscous dark solution was poured (under
vigorous stirring) into 1.3 L of 2% ice-cold hydrochloric acid. The
precipitate was filtered on a buchner funnel with filter paper and
washed with excess (0.5 L) deionized water and then with 0.5 L
diethyl-ether. The samples were then dried in a over at 50 ◦C during
24 h.