## 3 Results and Discussion
### Characterization of Nanocellulose Gels and Films
#### 3.2.3 FTIR of CNF Gels and CNF Films  
The spectra of the CNF gels are presented in Figure 5, where the full overlaps of both spectra stand out. Three bands can be observed as follows: one quite pronounced at 3300 cm\({}^{-1}\), representing hydrogen bonds. This band is related to the stretching vibration of the O-H groups essentially due to the presence of water and hydroxyl groups of cellulose. The hydroxyl group is confirmed by the presence of another band at 1634 cm\({}^{-1}\), which signals the results from H-O-H bending of absorbed water. This pick is typical for samples with a large  
Figure 4: Rheological study. amount of water [24]. At the fingerprint region, a clear band appears with a pick near 600 cm\({}^{-1}\), which may be related to out of plane C-H bending. Figure 6 shows the FTIR spectra of the CNF films, uncoated CNF\({}_{1}\) and CNF\({}_{2}\) and the wax-coated, respectively, WC CNF\({}_{1}\) and WC CNF\({}_{2}\). The spectra of the uncoated films show similar peaks, indicating that they assign common functional groups but with different peak intensities, suggesting variations in composition or surface chemistry [19]. Specific peaks appear between 1200 and 1700 cm\({}^{-1}\) for CNF\({}_{1}\) and CNF\({}_{2}\) film FTIR spectra, recording the oxidative process TEMPO. One band, near 1600 cm\({}^{-1}\), is attributed to the C=O bond in the COONa groups, and another band is assigned to C-O symmetric stretching of dissociated carboxyl groups. The CNF\({}_{2}\) film shows higher intensity at 3300 cm\({}^{-1}\) compared with the CNF\({}_{1}\) film. This band is associated with the stretching vibration of the O-H groups of cellulose, followed by the presence of another band at 1634 cm\({}^{-1}\), which also has higher intensity. Two peaks arise between 2800 and 3000 cm\({}^{-1}\) corresponding to C-H bond stretching vibrations of cellulose. The CNF\({}_{1}\) film shows a more intense peak, probably due to the greater number of alkyl groups. This result could indicate more hydrophobicity of these films, which is confirmed by the greater water contact angle compared with CNF\({}_{2}\) films. Between 1720 and 1620 cm\({}^{-1}\), two absorption bands appear in the CNF\({}_{1}\) film that are not detected for the CNF\({}_{2}\) film. These bands may be associated with C=O double bonds, since sulfite pulps contain a higher content of carbonyl groups compared with sulfate pulps [19]. Also, at the fingerprint region, between 900 and 1200 cm\({}^{-1}\), different intensities for both CNF films are  
Figure 5: FTIR of CNF gels. Figure 6: FTIR of uncoated and wax-coated CNF films. detected; CNF\({}_{2}\) shows greater intensity for C-O stretching and C-O-C vibrations related to the glycosidic bonds. This result reveals that both CNFs have different surface chemistries. The spectrum of wax-coated films, displayed in the same figure, also shows a similar profile. However, compared with uncoated films, a reduction in the intensity of absorption at 3300 cm\({}^{-1}\) and an increase in absorption bands between 2800 and 3000 cm\({}^{-1}\) is observed. This intensification may result from the stretch, symmetrical or asymmetrical, of the C-H group of alkanes and the CH\({}_{2}\) group of methylene in the lipid chains. This result confirms the effectiveness of the wax coating. Between 2800 and 3000 cm\({}^{-1}\), C-H stretching takes place; in this region, the WC CNF films show a more pronounced peak comparative with the uncoated films. This result suggests the presence of additional alkyl (-CH, -CH\({}_{2}\), -CH\({}_{3}\)) functional groups from the wax [25], which is expected since the waves are composed of long-chain hydrocarbons. In the range of 1620 and 1670 cm\({}^{-1}\) where the carbonyl group (C=O) responds, the peaks that appear in CNF\({}_{1}\) do not appear on the coated film. The fingerprint region between 1000 and 1500 cm\({}^{-1}\) shows subtle differences, suggesting additional functional groups associated with wax.