## 3 Results
### FTIR Results  
Integration of the peaks was performed displaying the spectra in the absorption scale. The same integration limits for all the samples were chosen. These limits were chosen to encompass about 95% of the total area, excluding the band edges [17; 18]. Even though the formulation of the bioplastic used for the tested bag is proprietary and unknown, the spectra were consistent with those expected by a mixture of starch and a polyester (PEs) (Figure 4). Table 2 reports the absorption bands which characterize the functional groups for PEs, starch, ULB and LSB bags, respectively. The spectral results for ULB show an absorption band centered in 3391 cm\({}^{-1}\) due to the O-H stretching and another one centered in 2921 cm\({}^{-1}\) related to the C-H stretching; weak chemical bonds are also present in the spectral region between 1455 and 1388 cm\({}^{-1}\) assigned to C-H bending. A very strong absorption band is centered at 1712 cm\({}^{-1}\) due to C=O stretching of the ester group in association with a strong band at 1268 cm\({}^{-1}\) due to C-O stretching of the O=C-O group. Some bands are present at 1119, 1102 cm\({}^{-1}\), assigned to aliphatic ethers, and at 1080 and 1018 cm\({}^{-1}\), due to the presence of primary and secondary alcohols, in association with a weak band at 1646 cm\({}^{-1}\) due to C-O bending associated with the OH group. The spectral results for LSB are very similar to those of ULB, except for the intensity of the signals assigned to the primary and secondary alcohols that in the ULB spectrum are negligible and the CH\({}_{2}\) chains region between 1455 and 1388 cm\({}^{-1}\) stronger than in ULB. \begin{table}
\begin{tabular}{c c c c c} \hline
**Bands** & **Absorption Bands (cm\({}^{-1}\))** & **PEs** & **Starch** & **ULB** & **LSB** \\ \hline O-H groups (hydroxyl) stretching & 3600\(-\)3300 & ✓ & ✓ & ✓ & \\ C-H stretching & 2930\(-\)2900 & ✓ & ✓ & ✓ & ✓ \\ C=O stretching (carboxylic and ester groups) & 1730\(-\)1705 & ✓ & ✓ & ✓ \\ C-O bending associated with OH group & 1650\(-\)1637 & ✓ & ✓ & ✓ \\ C-H bending & 1460\(-\)1375 & ✓ & ✓ & ✓ & ✓ \\ C-O stretching & 1270\(-\)1050 & ✓ & ✓ & ✓ & ✓ \\ C-O-C stretching (aliphatic ethers) & 1180\(-\)1150 & ✓ & ✓ & ✓ & ✓ \\ C-H and C=O bending (out of plane) & 970\(-\)750 & ✓ &  & ✓ & ✓ \\ \hline \end{tabular}
\end{table} 
Table 2: Absorption bands of functional groups stretching for PEs, starch, ULB and LSB bags. Figure 4: FTIR spectra of (**a**) ULB, (**b**) LSB, (**c**) PEs, (**d**) starch. The peaks which were integrated are denoted by \({}^{\star}\) in the ULB spectrum; the peak taken as reference is indicated by r in the ULB spectrum. PEs FTIR spectrum is characterized by C=O stretching centered in 1710 cm\({}^{-1}\) of the carbonyl band of the ester group and C-O stretching in 1240 cm\({}^{-1}\) and 1090 cm\({}^{-1}\). The bands at 2950, 2910 cm\({}^{-1}\) are assigned to C-H symmetrical stretching in CH\({}_{2}\) chains and 1460-1375 cm\({}^{-1}\) are assigned to C-H bending. C-H and C=O bending (out of plane) around 700 cm\({}^{-1}\)[30; 31; 32; 33; 34; 35] is typically present in polyesters. The broad band at around 3300 cm\({}^{-1}\) for starch is due to the stretching mode of the O-H groups. The adsorption band at 1650 cm\({}^{-1}\) is attributed to C-O bending associated with the OH group together with the band at 1150 cm\({}^{-1}\) assigned to C-O stretching. The bands at 2955-2920 cm\({}^{-1}\) and 1460-1375 cm\({}^{-1}\) are assigned to C-H stretching and C-H bending, respectively. In addition, the characteristic C-O-C ring vibration on starch leads to an absorbance peak at around 1180-1150 cm\({}^{-1}\). In summary, both ULB and LSB seem to be composed of polyester and starch, as already found by the isotopic analysis approach. The diverse relative proportion of the two components in ULB and LSB explain the spectral differences found among them, confirming the higher percentage of starch in ULB than that in LSB.