## 3 Results and Discussion
### Alginate-Starch Films  
In Figure 6, we present Raman spectra at room temperature for the 5% alginate films, starch and 5% alginate-starch films in the spectral range 1700-700 cm\({}^{-1}\). We report in Table 2 the values of each of the observed or adjusted peaks. The difference spectrum between 5% alginate-starch and 5% alginate films is shown in Figure 7.  
Figure 5: Area ratios of four vibrational modes:.\(\tau=Area_{1414}/Area_{1340}\) and \(\mu=Area_{1098}/Area_{1068}\) for the alginate and alginate–glycerol films.  
Figure 6: The 1700–700 cm\({}^{-1}\) Raman spectral range of the 5% alginate, starch and 5% alginate-starch films.  
In Figure 6, it is observed that the vibrational modes of starch seem to dominate the Raman spectra of 5% alginate-starch films. We find the specific modes of starch linked to CH\({}_{2}\) vibrations: 1463 and 865 cm\({}^{-1}\) assigned, respectively, by \(\delta\)(CH\({}_{2}\)) and \(\tau\)(CH\({}_{2}\)-OH) deformations. However, the Raman subtraction spectrum in Figure 7 better reveals the particularities of the two elements making up 5% alginate-starch showing that the Raman spectrum of the 5% alginate-starch films is indeed the superposition of those of 5% alginate and starch films taken separately. Thus, we observe in the Raman spectrum of 5% alginate-starch-water mixture the predominance of the vibrational modes linked to 5% alginate: 1630, 1570, 1500, 1414, 1305, 955 and 805 cm\({}^{-1}\) assigned to \(\
u_{\rm as}\)(COO\({}^{-}\)), hydrogen bonds, d(O-H) in plane, \(\
u\)(C-O-C) vibrations, respectively.  
Among these seven vibrational modes only the modes at 1414 and 1305 cm\({}^{-1}\) are common to 5% alginate and starch. If we observe in Figure 7 that the mode at 1414 cm\({}^{-1}\) is more dominant on the 5% alginate side, it means that the vibrational contribution of hydrogen bonds is more important from 5% alginate compared to starch in the 5% alginate-starch films. A comparison of the value of the area ratio \(\tau\) between 5% alginate and starch films prepared in water could confirm this phenomenon. From the Raman spectra of 5% alginate and starch films, we obtain for \(\tau\) the following values: 10.8 for 5% alginate films against 0.6 for starch films. So, it seems clear that the hydrogen bonds with water are made primarily with alginate. But hydrogen bonds between 5% alginate and starch can be existed. A study of the area ratio \(\tau\) for 5% alginate-starch films could give an indication on this point.  
In Figure 8, we present the evolution of the area ratio \(\tau\) according to the mass proportion of alginate in the water. From this figure, it is noted that between alginate and alginate-starch films the area ratio \(\tau\) seems to have the same evolution according to the mass proportion of alginate in the water but with lower values: a reduction with a factor of 4 for the small percentages (1%, 2% and 3%), then by a factor between 2 and 3 for 4% and 5%. These results are consistent with what we expected: a decrease in the vibrational contribution of hydrogen bonds. Compared to 5% alginate-glycerol films, this ratio \(\tau\) is even lower: we go from 7.0 to 4.4. The starch molecule being larger than that of glycerol, the intercalation of starch within the alginate matrix has the consequence of further reducing the number of hydrogen bonds of the alginate with water. Nevertheless, there may exist in this biopolymer structure different types of hydrogen bonds: between alginate with water, starch with water and starch with alginate. From our Raman study, it seems difficult to distinguish these different types of hydrogen bonds.  
Figure 7: Raman subtraction spectrum between 5% alginate-starch and 5% alginate films.