*2.3. Cellulose Nanofiber Preparation*

To isolate CNF, a combination of chemical method, TEMPO-oxidation and the ACC method was adopted to further decrease the size of CNF. Dried bleached softwood kraft pulp was dipped in DI water for at least 30 min followed by disintegration under high speed food mixer for 10 min. The pulp was then subjected to TEMPO-oxidation treatment by using the chemicals: TEMPO 0.013 g/g, NaBr 0.13 g/g and NaClO 12% 4 mL/g-cellulose. The pH 10 was adjusted by addition of 0.1 M NaOH, and the reaction time was set to 90 min. After the reaction, the TEMPO-oxidized cellulose was neutralized with HCl 0.1 M, followed by the addition of methanol to stop the reaction. The TEMPO-oxidized cellulose was washed several times with DI water.

The TEMPO-oxidized softwood cellulose was first homogenized by using a homogenizer (IKA T25, IKA, Staufen, Germany) for 10 min at 10,000 rpm to strip off any bundled fibers before going to ACC for smooth treatment. The cellulose suspension was passed through the ACC machine for 10 passes. The transparency and morphology of the prepared CNF were determined by using UV spectroscopy, FE-SEM and AFM.
