## 3 Results and Discussion
### Composition and Structure of CHT Films
#### 3.1.4 X-ray Diffraction (XRD)  
Figure 4 shows the diffractograms of the samples of pristine chitosan, pristine HNa, and chitosan mixed with HNa at 15% (Figure 4a) and 30% (Figure 4b) crosslinked with GA and PEGDE at different concentrations. The diffraction pattern of pristine CHT showed the two characteristic sharp peaks at 20 = 9.5\({}^{\circ}\) and 20 = 20\({}^{\circ}\), which are typical of the hydrated conformation of chitosan [37]. In contrast, completely amorphous sodium hyalurone was obtained after film preparation.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Films** & \multicolumn{3}{c}{**T\({}_{\textbf{d}}\)**(\({}^{\circ}\)C)} & \multicolumn{3}{c}{**_T (\({}^{\circ}\)C) at 50\% of Weight Loss_**} \\ \hline CHT & 65 & 297 & & 351 \\ \hline \multirow{4}{*}{CHT-HA} & HNa 15 \% & HNa 30\% & HNa 15\% & HNa 30\% \\  & T\({}_{\text{d1}}\) & T\({}_{\text{d2}}\) & T\({}_{\text{d1}}\) & T\({}_{\text{d2}}\) & \\ CHT-HA & 68 & 386 & 60 & 292 & 295 & 360 \\ CHT-HA-PEGDE 1 & 70 & 344 & 63 & 285 & 295 & 349 \\ CHT-HA-PEGDE 2 & 70 & 348 & 63 & 295 & 290 & 340 \\ CHT-HA-PEGDE 3 & 64 & 338 & 62 & 300 & 298 & 340 \\ CHT-HA-GA & 56 & 354 & 61 & 272 & 276 & 358 \\ \hline \hline \end{tabular}
\end{table}
Table 2: Decomposition temperatures and weight loss of CHT films, CHT/HNa at 15% and 30% films crosslinked with GA and PEGDE.  
Figure 3: TGA and DTGA thermograms of GA crosslinked and PEGDE crosslinked chitosan/HNa films. TGA (**a**,**b**) and DTGA (**c**,**d**). HNa content of 15% (**a**–**c**), HNa content 30% (**b**–**d**).  
Regarding X-ray diffraction of hyaluronic acid, [PERSON] suggested that high molecular weight hyalurones may contain some non-glycosidic bonds that act as branch points. The removal of these branches by acid treatment can cause depolymerization and, at the same time, can allow crystalline organization [38]. [PERSON] et al. reported that the conformation of hyalurone chains in the solid state is dependent on the nature of the cations that are presented, the pH, and the temperature at which the crystallization is carried out, but not on the ionic strength of the solution from which films are molded. Depending on the cation, successful crystallization of these conformations requires the presence of various water molecules [39]. Hyaluronates peaks at approximately 20 = 26\({}^{\circ}\) and 32\({}^{\circ}\) have been reported, but these were not observed in our samples [40]. In contrast, X-ray diffraction studies have shown that hyaluronic acid films or fibers are amorphous in nature [41]. CHT/HNa uncrosslinked blends showed an additional peak at 20 = 5\({}^{\circ}\), similar to those reported by [PERSON] et al. [42] and by us [28]. They pointed out that this outcome can be attributed to the formation of more ordered complexes, inducing a change in crystallinity.  
Films crosslinked with PEGDE at different concentrations exhibited peaks like those of films without crosslinking but with a peak reduction in intensity as PEGDE concentration increased. There were no obvious changes in the diffractograms at both HNa contents but in the 30% HNa films, the intensity of the peak at 20 = 20\({}^{\circ}\) slightly increases in the PEGDE3 crosslinked samples. Likewise, GA crosslinked samples were amorphous and did not show different diffraction patters for both HNa concentrations.  
The crystallinity of the chitosan samples with sodium hyalurone decreased in the presence of the HNa and when the sample was crosslinked. Hence, one way to modify crystallinity without resorting to heat treatment or crosslinking is by adding a second polymer phase. For a more accurate comparison, Table 3 summarizes the results obtained from the calculation of the crystallinity index (CrI) of each of the films.  
Figure 4: XRD pattern of GA crosslinked and PEGDE crosslinked chitosan/HNa films. HNa content of 15% (**a**), HNa content 30% (**b**).