## 3 Results
### Characterization of the Extracted Chitosan  
Chitin extracted from cicada sloughs collected in 2020 has subsequently been deacetylated to obtain chitosan. In order to assess the effectiveness of the deacetylation process and to characterize the extracted chitosan, the FTIR spectrum of the latter has been compared to the spectra of three commercial chitosan (CS-80, CS-90 and CS-95). Even though the spectra (shown in Figure 5) present high similarities among them, the extracted chitosan shows two additional peaks at 1556 and 1631 cm\({}^{-1}\). According to [PERSON] et al. [16], the peak at 1631 cm\({}^{-1}\) may indicate a specific hydrogen bond between C=O and the hydroxymethyl group (CH\({}_{2}\)-OH) of the next chitin residue of the same chain. Since C=O belongs to the acetyl group, which is characteristic of chitin rather than chitosan, its presence suggests that a high amount of acetyl groups are still present in the extracted chitosan. [PERSON] et al. [16] also report that after the deacetylation of chitin, the peak at 1556 cm\({}^{-1}\), corresponding to amide II (N-H bending), disappeared along with the appearance of a new sharp peak at 1595 cm\({}^{-1}\)(NH\({}_{2}\) bending). Since these two peaks (i.e., 1556 and 1631 cm\({}^{-1}\)) are more characteristics of chitin rather than chitosan, their presence suggests that the deacetylation process was only partially efficient. This can be confirmed by observing the peak at 1320 cm\({}^{-1}\), which is more intense for the extracted chitosan, while its intensity decreases as the \(DD\) increases (CH-95 has the less intense peak). This is due to the fact that the peak at 1320 cm\({}^{-1}\) corresponds to the \(N\)-acetyl-D-glucosamine, which belongs to chitin (and for this reason included in the calculation of the \(DA/DD\)[11]). The degree of deacetylation of the four chitosan samples has been calculated using the Equations (1) and (2) from their FTIR spectra. In order to assess the accuracy of the calculation of the \(DD\) for the extracted chitosan, we used the same method to calculate the \(DD\) of the three commercial chitosan (whose \(DD\) was stated in the product specification sheet obtained from Heppe Medical Chitosan, HMC\({}^{+}\) (refer to Section 2.1)). Table 4 shows the measured average \(DD\) of the extracted chitosan, CS-80, CS-90 and CS-95 as well as their \(DD\) obtained from the product specification sheets. The results show that the FTIR method employed for the calculation of the \(DD\) is highly efficient for chitosan with high \(DD\). In fact, the measured value of \(DD\) for CS-90 and CS-95 (91.1 \(\pm\) 1.1 and 93.7 \(\pm\) 0.7, respectively) falls in the expected values of \(DD\) indicated by the company HMC\({}^{+}\) (87.6-92.5% and \(\geq\)92.6%, respectively). However, for the CS-80, we measured a higher \(DD\) (89.9 \(\pm\) 1.6%) compared to the expected one (77.6-82.5%). According to the employed method, the extracted chitosan has a degree of deacetylation of 66.2 \(\pm\) 1.6%. The low \(DD\) measured is not surprising considering the presence of the peaks at 1320, 1556 and 1631 cm\({}^{-1}\) described above. Figure 5: FTIR spectra of: (a) extracted chitosan, (b) CS-80, (c) CS-90 and (d) CS-95. We then looked at the crystallinity of the extracted chitosan. The XRD spectra of the extracted chitosan, CS-80, CS-90 and CS-95 are shown in Figure 6. All the spectra are very similar and present peaks at approximately \(12^{\circ}\) from (020) plane and \(19.5^{\circ}\) from (110) plane, which are characteristics of chitosan. The peak at approximately \(12^{\circ}\) is indicative of the efficiency of the deacetylation process. In fact, while chitin (which is more crystalline than chitosan) present two distinct peaks at \(8.9^{\circ}\) and \(12.5^{\circ}\) (see Figure 6), chitosan only presents one large peak between \(11.6\) and \(12.7^{\circ}\)[17]. Our result shows that the extracted chitosan still presents a small peak at \(8.9^{\circ}\) from (020) plane, suggesting that the deacetylation process was not totally efficient.