# Biodegradable and Compostable Shopping Bags under Investigation by FTIR Spectroscopy
## 3 Results and Discussion
### Principal Component Analysis (PCA)
#### 3.3.1 Conformity Prediction  
Figure 6 showed the PCA results obtained processing the matrix containing the spectral data of all 22 samples, using R software, represented both as a score plot (Figure 6a)  
and a loading plot (Figure 6b). Accordingly, all three new MecPlast films were found to be part of the population of films clustered in the right side of the score plot, considered compostable and biodegradable, due to the presence of starch (Figure 6a). This population, circled in light blue, was well separated from the population of films considered to be of irregular plastic, due to the presence of PE-based shopping bag (circled in red) on the principal component 1 (PC1), explaining the 59.3% of variance. The compostable population resulted furtherly separated into two subgroups, in turn separated from the sample named Vincotte-1 and from starch, on component 2 (PC2), explaining the 20.4% of variance. In particular, a group of compostable samples was detected, including M1 and Vincotte-S303 (circled in yellow), separated from a group including M2, M3, and Vincotte-S732 (circled in green). They were differently distant from starch, representing the renewable material. Rationally, M2, M3, and their group, appearing  
Figure 6: PCA results as score plot (**a**) and loading plot (**b**) obtained by using R software. more close and consequently similar to starch, should have a PLA content higher than that of M1, Vincotte-S303, and their group, which was more distant and consequently different from starch, as was confirmed developing the PLRM (Section 3.4). Similarly, Vincotte-1, which resulted in being separated from both groups and located very close to starch, should have the higher content in renewable material, as was confirmed developing the PLRM (Section 3.4). Unfortunately, the PCA results highlighted that only in the delimited area of Genoa, up to 4 films out of a population of 20 (20%), despite being marked for compliance, were found not included in the cluster of the compostable population. Surprisingly they were found very distant from starch, and in the cluster where the entirely non-degradable plastic-based film (PE-shopper) was included (Figure 6a, circled in red). With insights on the three MecPlast samples (M1, M2, and M3) using selected compostable samples as references, Figure 7 shows the PCA results obtained processing the small matrix collecting spectral data of M1, M2, M3, and of the MecPlast films, which received the TUV Italy mark in 2017 (Vincotte-303), and that was inserted as a reference for films approved by TUV Italy. Figure 8 shows PCA results obtained handling the matrix gathering the FTIR data of M1, M2, M3, Vincotte-303, and Vincotte-S732, i.e., the film with PLA content \(\geq\) 40% and thickness \(<\) 15 \(\upmu\)m. It was included as a reference for films with the requirements to be classified as suitable for contact with bulk foods. The PCA were performed using R software, and the results were represented both as score plots (Figures 7a and 8a) and loading plots (Figures 7b and 8b). In both cases, all samples were well separated on PC1 in two clusters (Figures 7a and 8a), thus highlighting a substantial difference between samples S303, M1, and M2, located in the right side of the score plot (circled in light blue), and M3, located in the left side of the score plot (circled in green). These results confirmed what was already visible in the PCA reported in Figure 6a, where M1 and M3, although belonging to the compostable population separated on PC1, belonged to different populations separated on PC2. It is interesting to note that, concerning separation on PC2 in Figure 6a, M2 was included in the same population of M3, but observing this group, a further separation of M2 from such group (on PC1) is observable, announcing some significant difference between M3 and M2, as confirmed by PCAs in Figures 7a and 8a. In the presence also of the Vincotte-S732 spectral data, additional information on the samples was obtained (Figure 8a).