*2.2. Hydrolytic Treatment*

The proper material (3 g) was treated with 70 mL of 6 M HCl under stirring at 100 ◦C overnight [4,26]. After cooling at room temperature, the mixture was centrifuged (8247× *g*, room temperature, 15 min) and the precipitate washed with water until neutrality and freeze dried. The recovery yields were 58% (chestnut wood fiber), 68% (exhausted chestnut wood) and 83% (quebracho exhausted wood).
