## 3 Results and Discussions
### DNA Identification on Recycled PET Composites  
As a noninvasive optical technique, FTIR has already been used for the identification of DNA structure and composition from eukaryotic and prokaryotic cells [30], microbial pathogens [31], cattle, sheep, fish, and swine [32]. In this paper, for the substrate contamination, the authors used isolated DNA from rat muscle and tumor tissues, with a concentration of 90.5 ng/mL and 313 ng/mL, respectively, as determined by UV-Vis. Figure 3: Thermal behavior and characteristics. \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline \multirow{2}{*}{**Codification**} & \multicolumn{2}{c}{**Process I**} & \multicolumn{2}{c}{**Process II**} & \multicolumn{4}{c}{**Complex Melting Process**} \\ \cline{2-9}  & \multicolumn{2}{c}{**Glass Transition**} & \multicolumn{2}{c}{**Crystallization**} & \multicolumn{2}{c}{**Melting I**} & \multicolumn{2}{c}{**Melting I**} \\ \cline{2-9}  & \multicolumn{2}{c}{**T\({}_{\text{onset}}\)\({}^{\circ}\)C**} & \multicolumn{2}{c}{**\(\Delta\)CP, J/g: K**} & \multicolumn{2}{c}{**T\({}_{\text{onset}}\)\({}^{\circ}\)C**} & \multicolumn{2}{c}{**T\({}_{\text{max}}\)\({}^{\circ}\)C**} & \multicolumn{2}{c}{**T\({}_{\text{onset}}\)\({}^{\circ}\)C**} & \multicolumn{2}{c}{**T\({}_{\text{miss}}\)\({}^{\circ}\)C**} & \multicolumn{2}{c}{**T\({}_{\text{miss}}\)\({}^{\circ}\)C**} \\ \hline M1\_4 & 64.9 & 0.032 & 117.7 & 123.3 & 239.1 & 249 & \(-\) & \(-\) \\ \hline M2\_4 & 64.7 & 0.076 & 117.1 & 124.5 & 237.8 & 249.9 & \(-\) & \(-\) \\ \hline M6\_4 & 72.4 & 0.044 & 116.6 & 124.1 & 153.3 & 162.9 & 237.9 & 247.4 \\ \hline M7\_4 & 64.7 & 0.046 & 107.6 & 116.3 & 153.3 & 163.8 & 237.4 & 254.1 \\ \hline M11\_4 & 73.7 & 0.006 & \(-\) & \(-\) & 123.6 & 130.8 & 238.0 & 247.4 \\ \hline M12\_4 & 74.0 & 0.045 & \(-\) & \(-\) & 123.6 & 130.4 & 238.6 & 247.0 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Thermal behavior and characteristics. The rat DNA samples (DNA_M represents DNA isolated from muscle, while DNA_T represents DNA from tumor cells) exhibited an identical infrared spectral signature (Figure 4). As expected, the main vibrational bands specific to the molecular structure of DNA in solution were found in three different regions--namely, 3267 cm\({}^{-1}\), attributed to the stretching vibrations of the OH and NH bonds of the amino acid; 1634 cm\({}^{-1}\), assigned to C=C thymine, adenine vibrations, and N\(-\)H from guanine (the region of base vibrations) [33]; and 1044 cm\({}^{-1}\), ascribed to the C\(-\)O deoxyribose stretching [30]. The ATR spectrum of bare PET substrate (sample M1_4) is shown in Figure 5, and the absorption bands are assigned according to the main available groups. Specifically, the 2960 cm\({}^{-1}\) band was attributed to the aliphatic C-H symmetrical bond stretching, 1712 cm\({}^{-1}\) to the ester carbonyl bond stretching, 1407 cm\({}^{-1}\) for stretching of the C\(-\)O group deformation of the O-H group, 1236 cm\({}^{-1}\) for the terephthalate group, 1088 cm\({}^{-1}\) to the methylene group, 1015 cm\({}^{-1}\) to the vibrations of the ester C\(-\)O bond, 872 cm\({}^{-1}\) for the present aromatic rings, and 722 cm\({}^{-1}\) to the polar ester groups' interactions with benzene rings. These bands are in agreement with the FTIR spectra of PET obtained by [PERSON], et al. [34], [PERSON], et al. [35], and [PERSON] [36]. As observed in Table 2, all samples (M2_4, M6_4, M7_4, M11_4, and M12_4) contained PET in their composition; therefore, the specific absorption bands, as seen in Figures 5-7, were present in all ATR spectra. The presence of 5% Al nanopowder in the recycled PET (sample M2_4), PET/PP (sample M7_4), and PET/HDPE (sample M12_4) compositions could be detected in the range of 500-1000 cm\({}^{-1}\)[37], but in our case the weak peaks characteristic of the Al-O stretching and O-Al-O bond overlapped with the peaks of PET, PP, and HDPE, but with small shifts.