## 3 Results  
### Characterization of the Prepared Membranes  
* FTIR and DSC Analysis  
Figure 1 shows the FTIR spectra (4000-400 cm\({}^{-1}\)) obtained from the PAA polymer, blank CA membrane (M0), and membranes obtained by blending CA with PAA at 8 wt. % (M8) and 15 wt. % (M15), respectively. In particular, PAA spectrum reveals the typical bands for carboxylic acids such as the characteristic stretching absorption of the hydroxyl groups (O-H) in 3522 cm\({}^{-1}\) and the absorption peak characteristic of carbonyl (C=O) in 1719 cm\({}^{-1}\). In addition, the bands that appeared at 1219 cm\({}^{-1}\) and 1458 cm\({}^{-1}\) can be assigned, respectively, to the C-C stretching and the in-plane bending of the hydroxyl group. The spectrum of M0 membrane presented the distinctive bands of CA ascribable to the stretching of different characteristic functional groups: O-H (3250-3700 cm\({}^{-1}\)), C-H (2850-2990 cm\({}^{-1}\)), C=O (1740 cm\({}^{-1}\)), C-H (1372 cm\({}^{-1}\)) of -CH\({}_{3}\), and C-O-C (917 cm\({}^{-1}\)) of ether [35; 36]. The FTIR spectrum of the blend membranes M8 and M15 revealed the effect of the presence of PAA on the chemical nature of CA membranes. The enlargement and the remarkable decreasing of the intensity of the band between 3200 and 3700 cm\({}^{-1}\) indicated the hydrogen interactions between the two polymers favouring a homogeneous blend. Thus, the bands attributed to the hydroxyl and acetyl groups of CA significantly decrease [37]. Moreover, the bands situated between 1150 and 1500 cm\({}^{-1}\) appeared to overlap, which may be due to the interconnection between the two polymers via hydrogen bonding. DSC is a widely used thermal analytical tool that helps to understand the thermal behavior of polymers. It serves, basically, to identify the compatibility of polymer blends and to detect the different temperatures of phase transitions of the polymers and their blends. The DSC thermogram of PAA and the prepared membranes M0, M8, and M15 are given in Figure 2a,b. A comparison of the glass transition temperature (Tg), melting temperature (Tm), and degradation temperatures (Td) is summarized in the Table 3. Thermogravimetric analyses are summarized in Table 3, revealing the presence of three thermal events in every sample; two of them are endothermic, as reported in Figure 2b. The endothermic peaks were attributed to the glass transition (Tg) and the melting point (Tm), whereas the exothermic peak was due to the polymer degradation (Td). The presence of a single Tg in M8 and M15, similar to M0 (63.71 \({}^{\circ}\)C), indicated an optimal miscibility between the two polymers. In fact, two well-distinguished glass transition temperatures characteristic of each polymer are usually detected in the case of a heterogeneous blend [38]. Indeed, the compatibility of the two components was assured by the hydrogen interconnections as confirmed by the FTIR result. Moreover, the observed Tg were in the range of 64.51 \(\pm\) 0.80 \({}^{\circ}\)C whereas Tm decreased from 231.80 \({}^{\circ}\)C for M0 to 226.55 \({}^{\circ}\)C for M15, indicating a minimal effect of PAA on the thermal properties of the membranes. Definitely,  
Figure 1: FTIR spectra of pure CA membranes (M0) and CA/PAA blend membranes (M8 and M15). \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Samples** & **Tg**[\({}^{\circ}\)**C] & **Tm**[\({}^{\circ}\)**C] & **Td**[\({}^{\circ}\)**C] \\ \hline PAA & 44.5 & 147.23 & 252.78 \\ \hline M0 & 63.71 & 231.80 & 369.40 \\ \hline M8 & 65.30 & 227.47 & 362.68 \\ \hline M15 & 64.12 & 226.55 & 361.01 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Values of glass transition temperature (Tg), melting temperature (Tm), and degradation temperature (Td) of the CA and CA/PAA blended membranes. the observed values of Tg and Tm were similar to those reported in previous studies for CA membranes [39; 40].