*2.3. Preparation of Cellulose Aerogel*

The solvent mixture of NaOH/urea/H2O (7:12:81 w/w) was precooled to approximately 5 ◦C. The desired amount of MWBF samples (1.5, 2, and 2.5 wt.%) was then dispersed immediately into the solvent system under vigorous stirring at this low temperature until a semitransparent or transparent gel was achieved, depending on the MWBF concentration. At the final stage, the gel was vacuumed to remove the air bubbles. The specimen thickness was controlled to approximately 2 cm using a beaker as a mold and then immersed into ethanol to obtain the 5 wt.% solution. A 100 mL of aqueous 10 wt.% H2SO4 solution was then added at ambient temperature for coagulation. The resulting cellulose hydrogels were washed with excess distilled water to remove the residual chemical reagents. The sample was then frozen in a freezer at −80 ◦C for 24 h and freeze-dried using a FTS Systems Dura-Stop Digital Control Stoppering Tray Dryer to obtain the desired cellulose aerogel (CA).
