## 3 Results and Discussion
### Morphology of the Membranes and Elemental Quantification  
The SEM pictures of neat and amine-functionalized cmNFC based membranes are showed on Figure 8 and observed on the top surface. The diameter of the individual cmNFC fibers was estimated between 10 and 30 nm. Nanopores were observed on the cmNFC films. The diameter of the nanopores was estimated at 24 \(\pm\) 10 nm (calculation by Image J from FEG-SEM pictures (x30,000) over 100 pores). No nanoporosity was observed for cmNFC-PVAm and cmNFC-PVAm-AEAPTMS-A in one-step process maybe due to the covering of the nanopores by the polymer. However, nanoporosity was observed for the membrane cmNFC-PVAm-AEAPTMS-B elaborated in a two-step process. The diameter of the nanopores was estimated at 22 \(\pm\) 9 nm (similar to cmNFC nanopores diameter). The step of dipping inside water in two-step process might cause the solubilization of free PVAm polymer chains and generated nanoporosity as observed for cmNFC. The FEG-SEM pictures with EDX mapping on C, O, N, and Si elements of cmNFC, cmNFC-PVAm, and cmNFC-PVAm-AEAPTMS-A and -B with the corresponding EDX spectra are showed on Figure 9. The elemental semi-quantitative calculation from FEG-SEM-EDX characterization was reported on Table 3. All the membranes presented the characteristic C and O elements of cellulose respectively observed at 0.28 and 0.53 keV. The I\({}_{\text{O/C}}\) value of the cmNFC film was lower than the theoretical one (expected at 0.83) certainly because of the carbon layer deposited on the film essential for the EDX characterization. The membranes containing PVAm polymer displayed the characteristic peak of N element at 0.39 keV with good dispersion of the element on the mapping pictures. This result proved the effective dispersion of the polymer matrix inside the membranes. The N atomic percentages were similar (around 11 \(\pm\) 1%) since the same amount of PVAm was used and the I\({}_{\text{O/C}}\) value decreased because only C and N elements were added by the polymer in the calculation. The presence of the aminosilane was observed with the appearance of the Si peak at 1.74 keV and some Si dots spread out on the mapping pictures for both one-step and two-step processes. However, its intensity was low and its atomic percentage close to the detection limit of the apparatus, but the one-step process seemed to be better for the grafting of the aminosilane with higher Si content. Traces of Na and Cl elements were also observed on the EDX spectra, which were originated from tap water used to prepare cmNFC. Figure 8: FEG-SEM pictures of cmNFC (**Ai**), cmNFC-PVAm (**Bi**), cmNFC-PVAm-AEAPTMS-A (**Ci**), and cmNFC-PVAm-AEAPTTMS-B (**Di**) on individual fibers (**i = 1**) and surface (**i = 2**) [x30,000]. The elemental analyses of C, H, O, N, and Si atoms were performed on cmNFC, cmNFC-PVAm, and cmNFC-PVAm-AEAPTMS-A and -B membranes. The results in terms of elemental weight concentration are summarized in Table 4. The proportion in oxygen in all samples was higher than the theoretical value. The difference could be explained by the presence of some O-rich impurities and by experimental errors [86]. The degree of substitution of OH groups from cellulose by COOH in cmNFC materials was estimated at 0.32 using the Equation (3) and was very close to the value of the degree of oxidation equal to 0.26 obtained by titration for cmNFC with 1540 umol g\({}^{-1}\) as charges rate.