## 3 Results and Discussion
### Characterizations of the Membranes  
Four membranes were studied and compared: cmNFC, cmNFC-PVAm, cmNFC-PVAm-AEAPTMS-A, and cmNFC-PVAm-AEAPTMS-B. The respective weight per surface unit and thickness of the membranes are displayed in the Table 1. The weight per surface unit was similar, around \(20.9\pm 0.5\) g m\({}^{-2}\), and very close to the planned value (20 g m\({}^{-2}\)). The thickness varied from 23 to 35 \(\upmu\)m. The incorporation of PVAm increased the thickness of the membranes because the water-soluble polymer might widen the distance between the nanofibers creating higher porosity.  
The FTIR spectra of amine functionalized cmNFC-PVAm membranes are showed in the Figure 5. The peaks at 1745 and 1615 cm\({}^{-1}\) were respectively assigned to the stretching vibration of the C=O  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Membranes** & **Weight Per Surface Unit (g m\({}^{-2}\))** & **Thickness (\(\upmu\)m)** \\ \hline cmNFC & 20.3 & 23.3 \(\pm\) 2.8 \\ cmNFC-PVAm & 21.2 & 35.5 \(\pm\) 3.2 \\ cmNFC-PVAm-AEAPTMS-A & 21.3 & 34.7 \(\pm\) 3.5 \\ cmNFC-PVAm-AEAPTMS-B & 20.7 & 30.8 \(\pm\) 3.0 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Characteristics of the amine-functionalized cmNFC-based crosslinked membranes.  
Figure 4: Hydrolysis-condensation kinetics curves of AEAPTMS in acidic D\({}_{2}\)O/EtOH (20/80) medium followed by liquid \({}^{29}\)Si NMR in-situ. Chemical structures and assignments of the different species obtained: dimers (**a**), linear oligomers (**b**), and three-dimensional species (**c**).  
carboxylic bond and the ionized C=O carboxylic bond of the cmNFC material. The broad peak at 1600-1500 cm\({}^{-1}\) was assigned to the deformation vibrations of the N-H bonding of the grafted aminosilane and the PVAm [81]. Regarding the cmNFC-PVAm-AEAPTMS-B membrane elaborated from the two-step process, the broad peak assigned to N-H bonding was slightly shifted from 1580 cm\({}^{-1}\) to 1530 cm\({}^{-1}\) corresponding to secondary amide bonding resulting in the presence of more crosslinking of cmNFC with PVAm and/or AEAPTMS. Moreover, the peak at 1745 cm\({}^{-1}\) assigned to the C=O carboxylic bond disappeared, meaning that the carboxylic acid functions have reacted assuming the crosslinking between the nanofillers and the matrix by amidation.  
The DSC curves of the amine functionalized cmNFC-PVAm membranes are showed on Figure 6 with the corresponding melting temperatures and enthalpies in Table 2. The cmNFC nanofiller had no melting temperature and the PVAm matrix melted at around 179 \({}^{\circ}\)C, whereas the blends of functionalized amine or neat cmNFC and PVAm had upper melting point shifted by 46 \({}^{\circ}\)C. The increase in melting temperature of the PVAm inside the composite membranes was induced by a higher crystallinity of PVAm [47; 85], which is a key parameter for gas transport properties. This could also prove the crosslinking between the cellululosic fillers and the polymer matrix [28] but no apparent glass-rubber transition temperature was found for the different membranes to confirm the crosslinking even at lower heating speed rate or using modulated DSC technique. Regarding the cmNFC-PVAm-AEAPTMS-B membrane elaborated from the two-step process, the melting point  
Figure 5: FTIR spectra of cmNFC, cmNFC-PVAm, and cmNFC-PVAm-AEAPTMS-A and B membranes.  
was only shifted by 28 \({}^{\circ}\)C instead of 46 \({}^{\circ}\)C for the membrane elaborated with the one-step process. It also displayed a lower melting enthalpy. This difference of thermal characteristics between the two processes of membrane elaboration could be explained by: (i) the crosslinked density between the filler and the matrix was lower, (ii) there was a leakage of some free PVAm polymer chains during the step of dipping into the aqueous solution of aminosilanes (as PVAm is soluble in water), or (iii) an amorphization of the cmNFC-PVAm membranes was created by dipping the membrane inside the water-based aminosilane solution [47; 85].