## 3 Results and Discussion
### Composition and Structure of CHT Films
#### 3.1.3 Thermogravimetric Analysis (TGA)  
Figure 3 shows TGA and DTGA thermograms of GA crosslinked and PEGDE crosslinked chitosan/HNa films at 15% (Figure 3a,c) and 30% (Figure 3b,d). It was observed that the degradation profile for all films presented two stages. The first stage (T\({}_{\rm d1}\)) was located between 56-70 \({}^{\circ}\)C for CHT-HNa 15% films and 60-63 \({}^{\circ}\)C for CHT-HNa 30% films. The second stage (T\({}_{\rm d2}\)) was detected at 285-300 \({}^{\circ}\)C for CHT-HNa 15% films and 272-300 \({}^{\circ}\)C for CHT-HNa 30% films. The first weight loss for all films was between 7-12%. This change was related to the loss of water and residual acid by evaporation, which means that the water is physically retained by weak hydrogen bonds on chitosan surface. The second weight loss was located between 52-66%. This loss of mass corresponded to the thermal degradation of chitosan, and simultaneous removal of volatile products. The maximum rate of thermal decomposition of the pristine chitosan (T\({}_{\rm d2}\)) took place at 297 \({}^{\circ}\)C, while HNa decomposed at 222 \({}^{\circ}\)C although [PERSON] et al. reported that degradation of hyaluronate occurred at 210 \({}^{\circ}\)C [36].  
When HNa at 15% was added to CHT an increase in T\({}_{\rm d2}\) temperature was also observed. This increase was from 297 \({}^{\circ}\)C for pure chitosan to 386 \({}^{\circ}\)C for chitosan with 15% HNa. For the uncrosslinked blend with 30% HNa films T\({}_{\rm d2}\) remained unchanged (292 \({}^{\circ}\)C). This outcome indicates that by increasing the HNa concentration does not decrease the thermal stability of the material although T\({}_{\rm d2}\) of pristine HNa was lower than CHT. In PEGDE1 and PEGDE2 crosslinked films with 15% of HNa, a slight increase in T\({}_{\rm d1}\) was observed (Table 2), i.e., from 65 \({}^{\circ}\)C (pure chitosan) to 70 \({}^{\circ}\)C (chitosan with 15% of HNa) but for PEGDE 3 no change was observed. In contrast, T\({}_{\rm d2}\), increased for all PEGDE crosslinked films (Table 2). When HNa was added at 30%, PEGDE crosslinked films, T\({}_{\rm d1}\) and T\({}_{\rm d2}\) were slightly reduced except for PGDE3, which remind the same in agreement with [PERSON] et al. [16] who reported that as the amount of hyaluronic acid increases in CHT cryogels, the thermal stability and the amount of char decrease. In comparison with pristine CHT films, GA crosslinked films exhibited higher T\({}_{\rm d2}\) at 15% of HNa but lower T\({}_{\rm d2}\) when used at 30%. Table 2 summarizes the thermal properties of these films.  
The higher thermal stability of CHT/HNa blends was achieved with 15% without crosslinking agent (386 \({}^{\circ}\)C). The higher thermal stability of CHT/HNa/PEGE crosslinked films was achieved with low PEGDE concentrations and 15% of sodium hyaluronate (344-348 \({}^{\circ}\)C). In addition, the one with the highest thermal stability was the chitosan film crosslinked with GA (354 \({}^{\circ}\)C). Presumably, this outcome was due to the double crosslinking with GA, i.e., the formation of interpenetrated network as well as to the secondary interactions between the chitosan and hyaluronic acid chains [16].  
The temperature of 50% of loss of mass (Table 1) of pristine CHT decreased almost 50 \({}^{\circ}\)C when CHT film was mixed with 15% of HNa and crosslinked with PEGDE but slightly decreased when 30% was added. This temperature slightly increased for GA crosslinked samples with 30% of HNa.