## 3 Results and Discussion
### Properties of the Membranes  
Mechanical properties were determined for the neat and amine functionalized cmNFC-PVAm membranes (Figure 7a). cmNFC membranes displayed a Young's Modulus around 7.5 GPa. This modulus decreased until 6.2 GPa with the addition of PVAm which could be inconsistent with crosslinking but could be explained by the lower value of the Young's Modulus of PVAm which has less rigid polymer chain [47]. Besides, the Young's Modulus were divided by 2 when the membrane was elaborated by the two-step process. This could be explained by the dipping of the cmNFC-PVAm membranes into an aqueous solution of AEAPTMS during the second step of the elaboration of the membrane, which lowered the mechanical performance.  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Materials** & **T\({}_{\text{m}}\)**(\({}^{\circ}\)**C**) & **H\({}_{\text{m}}\) (J/g)** \\ \hline cmNFC & - & - \\ PVAm & 179 & 71.4 \\ cmNFC-PVAm & 225 & 96.1 \\ cmNFC-PVAm-AEAPTMS-A & 221 & 106.1 \\ cmNFC-PVAm-AEAPTMS-B & 207 & 42.3 \\ \hline \hline \end{tabular}
\end{table}
Table 2: Values of melting temperature (Tm) and enthalpy (Hm) obtained by DSC.  
Figure 6: DSC curves of cmNFC, cmNFC-PVAm, and cmNFC-PVAm-AEAPTMS-A and -B membranes.  
The intrinsic air permeability was measured for the neat and amine functionalized cmNFC-PVAm membranes (Figure 7b). cmNFC membranes displayed an intrinsic air permeability value around 1.1 10\({}^{-17}\) m\({}^{2}\). The intrinsic air permeability was multiplied by around 5 with the addition of PVAm. This observation confirmed that PVAm has a higher permeance that pure cmNFC films. The polymer chains were dispersed in the cmNFC network and increased the distance between the nanofibers. The network was less dense and the pore size slightly increased. Consequently, air can cross the membrane more easily. On the contrary, the addition of aminosilane improved the barrier properties of the membranes against air with similar results to cmNFC membrane is probably because of the formation of a denser second network.  
The water contact angle (WCA) on the upper surface of the neat and amine functionalized cmNFC-PVAm membranes was measured (Figure 7c). The WCA value on cmNFC surface was measured at 80\({}^{\circ}\) confirming that the surface was still hydrophilic due to the presence of carboxylic acid functions on the surface of the nanofibers. The WCA values of the films prepared with amine-functionalized cmNFC-PVAm were above 90\({}^{\circ}\)--around 105\({}^{\circ}\) for both membranes--meaning that the surface of the films became hydrophobic despite their hydrophilic amines groups, which reinforced the hypothesis that the amine groups have reacted. The addition of PVAm enhanced the hydrophobicity of the surface with WCA values around 120\({}^{\circ}\) due to the presence of grafted linear polymer chains with an olefin backbone.  
The liquid water absorption measurements (Cobb60) on neat and amine-functionalized cmNFC-PVAm membranes are showed on Figure 7d. The Cobb60 value for cmNFC membrane was high around 50 g m\({}^{-2}\). Despite their hydrophobic surface, the membranes absorbed a large amount of liquid water with Cobb60 value above 30 g m\({}^{-2}\), since PVAm has a good affinity to water. Moreover, a visual swelling of the membranes in presence of liquid water was observed while the  
Figure 7: Properties of cmNFC, cmNFC-PVAm, cmNFC-PVAm-AEAPTTMS-A and -B membranes: Young’s modulus (**a**), intrinsic air permeability (**b**), water contact angle (**c**), and Cobb60 measurements (**d**).  
integrity of the sample remained intact. This observation supports the crosslinking effect between the filler and the matrix as suggested.