# Biodegradable and Compostable Shopping Bags under Investigation by FTIR Spectroscopy
## 3 Results and Discussion
### FTIR Analysis  
FTIR analysis is a spectroscopic technique exploiting electromagnetic radiations ranging from 2500 nm to 25,000 nm of wavelength. FTIR spectroscopic technique provides rapid analytic data which, if properly processed, could provide chemical information concerning samples, therefore reflecting manufacturing processes, samples quality, differences or similarities in chemical composition, appearance, physical characteristics of the samples, etc. [26]. FTIR spectroscopy, together with other chemical characterizations, is the analytic technique adopted by TUV Italy and DIN CERTCO to carry out periodic checks of all registered or certified products, and to confirm their certification during the period of validity of the mark [27]. FTIR technique has the advantages of being usable for both liquid and solid samples, requiring little or no sample preparation and no additional chemicals or consumables [28; 29]. It is non-destructive, easy to use, fast, reliable, precise, and low cost [28; 29]. By acquiring the FTIR spectrum on a sample, the instrument provides a graph composed of peaks characterized by an intensity, expressed as a percentage of absorbance or transmittance (A% or T%), as a function of wavenumbers (cm\({}^{-1}\)), usually in the range 4000-400 cm\({}^{-1}\). When the spectral data of \(n\) samples are put together in the same matrix, a matrix is achieved whose dimensions depend on the \(n\) value. Sometimes, it is possible to compare the spectral data and detect the physicochemical differences between the samples under study simply by observing the spectra obtained. Otherwise, in most cases, this is not possible, both because the differences are minimal and because the very large number of samples makes the work not feasible. Figure 3a,b report the FTIR spectra of polyethylene (PE) and PLA, respectively, acquired in transmission mode and showed in transmittance scale (T%). They were included to show the substantial differences existing in the spectra of PE and PLA, which are the two polymers typically contained in shopping bags made with old plastics and compostable ones, respectively. Figure 4 shows the FTIR spectra acquired in transmission mode and reported in absorbance scale of 10 significant samples out of the 22 analyzed in this study and reported in Section 2.2 (Table 2). Figure 3: FTIR spectrum of polyethylene (PE) (**a**) and of PLA (**b**). With the exception of the spectra of starch (thicker red spectrum), PE-based film (thicker fuchsia spectrum), and films of shopping bags, that resulted in not being compliant with the law, as Virosac-2 (thicker black spectrum) (Figure 4), all other spectra, as those acquired on the three samples provided by the Savona (Liguria, Italy) (Figure 5b), were very similar to each other, as well as similar to the spectrum of the film with thickness and with PLA content, suitable to be classified as compostable and biodegradable, and also suitable for the transport of bulk food or for hygienic purposes [namely Vincotte-S732, Figure 4 (very light blue spectrum) and blue spectrum in Figure 5a]. In particular, all the spectra obtained were characterized by the presence of an intense band at a wavenumber higher than 1700 cm\({}^{-1}\) (Figures 4 and 5a,b), which is missing in the spectra composed essentially by PE (Figures 4 and 5a), as well as in the spectrum of PE itself (Figure 3a). This band belongs to the C=O group of the PLA (Figure 3b), and clearly  
Figure 4: Comparison between the FTIR spectra of 10 significant samples out of the 22 considered in this study. The FTIR spectra of residual samples have not been shown to make it easier to identify differences between samples. Figure 5: Comparison between the FTIR spectra of starch, a PE-based film, and Vincotte-S732 (**a**); FTIR spectra of samples M1, M2, and M3 recently extruded and supplied by MecPlast for the study (**b**). indicates that all film samples effectively encompass considerable amounts of renewable raw material, whose presence and content is essential for obtaining the conformity mark.