3.2.7. Hygroscopic Behaviors

WCA and WVTR were tested to investigate the hygroscopic behaviors of the composites. Table 2 shows the results. The WVTR was a little increased at first by the addition of ChNF up to 10% and then saturated thereafter. This result shows a good agreement with the previous research for CNF and acetylated CNF [22]. Regarding the WCA of the composites, it was rather a bit decreased by adding ChNF, which indicates hydrophilic behavior of the composites. This hydrophilic behavior might be associated with the hydroxyl groups appeared on the surface of the composites. Enhancing this behavior is future work in this research.


**Table 2.** Water vapor transmission rate and water contact angle of CNF and ChNF–CNF composites.

## 3.2.8. Antioxidant Property

The antioxidant abilities of CNF, ChNF and ChNF–CNF composites were investigated and expressed in AOA%/100 mg, as shown in Figure 11. The antioxidant activities of CNF, ChNF, CTS3, CTS5, CTS7, CTS10, CTS15 and CTS20 were 16.9%, 27.9%, 19.4%, 23.4%, 23.4%, 33.4%, 47.4% and 52.0%, respectively. The CTS20 showed the highest antioxidant activity among all cases. Interestingly, although the CNF and ChNF have low antioxidant activities, when they were blended together, the antioxidant activity of the composites increased. Cellulose and chitosan are both polysaccharides, and, when they are combined, the reducing ends of the materials may open, thus increasing the antioxidant activity. Nanofibrillation can also increase the hydroxyl groups, which are good for antioxidant activities. The antioxidant activity is the interaction of free radicals with the hydroxyl groups, and free amino groups of the chitosan and cellulose [39,40]. The improvement of antioxidant activities of the composites is agreeable with the previous research [39], which showed a steady increase of the antioxidant activity of the composites by increasing the chitosan content.

**Figure 11.** Antioxidant of ChNF–CNF composites.
