## 3 Results and Discussion
### Fourier-Transform Infrared (FTIR) Spectroscopy  
Figure 2 shows the spectra obtained from the natural polymers--starch, chitosan, and maltodextrin--where a broad band associated with bond stretching is observed in the large region from 3600 cm\({}^{-1}\) to 3100 cm\({}^{-1}\). This band corresponds to the O-H stretching of the multiple hydroxyl groups present in both the participating molecules (glycerol, A) and macromolecules (biopolymers). In this same region, the vibration of the amino group (N-H) corresponding to chitosan (CH) and acetaminophen appears to be located. Next, defined bands corresponding to asymmetric and symmetric stretching of C-H bonds were observed between 2925 cm\({}^{-1}\) and 2850 cm\({}^{-1}\), respectively. These vibrations are related to the hydrocarbon chain, methyl, and methylene groups present in the different organic compounds. At a wavelength of \(\sim\)1680 cm\({}^{-1}\), the vibrational stretching mode of the carbonyl (C=O) present in the amides of chitosan is shown, which is partially deacetylated (up to 75%) and acetaminophen [35]. A nearby band appears at 1695 cm\({}^{-1}\) of the water molecule, which achieved strong interactions with the other components until crystallization was achieved in the system. Another region of great importance in the spectrum corresponds to C-O interactions (ether zone) that begin at \(\sim\)1300 cm\({}^{-1}\) up to 949 cm\({}^{-1}\)[36]. In this area, significant changes are evident corresponding to hydrogen bond interactions between the different components as has been discussed and published in previous works. Finally, it was found that in the area known as fingerprints, bands appear at 838 cm\({}^{-1}\) and 514 cm\({}^{-1}\) which are related to characteristic vibrations of the disubstituted aromatic ring in the para (p-) position and the deformation of the phenyl ring outside the plane, respectively. For the TPS-CH-M-A samples, some intensity changes can be seen in characteristic bands for APIs over the control (TPS-CH-M) as a result of the addition of =C-OH groups of the phenol (as part of the molecule of acetaminophen). Also, a change is observed in the ratio of bands 1016 cm\({}^{-1}\) and 990 cm\({}^{-1}\) that becomes similar to the API in the TPS-CH-M-A with respect to TPS-CH-M. This broadening is attributed to limited intermolecular interactions due to the incorporation of the aromatic molecule, which induces steric hindrance and reduces polarity in the mixture. Overall, no new bands indicative of intramolecular reactions among the components were detected. This is crucial for application purposes, as maintaining the active component's structural integrity is essential. Previously, the presence of functional groups in the polysaccharides used--starch, maltodextrin, and chitosan--was discussed. The prominent -OH and -NH\({}_{2}\) groups confer hydrophilic properties. Furthermore, chitosan exhibits biosorbent qualities, including cationic and macromolecular structures with excellent sorption capacity [37]. According to studies conducted by [PERSON] et al. (2023) [38], various interaction mechanisms involving biopolymers have been identified, such as electrostatic attraction, electron donor-acceptor interactions (\(\pi\)-\(\pi\)), and hydrogen bonding [39]. In this case, acidic conditions are employed to solubilize chitosan and achieve optimal miscibility within the film-forming mixture, which subsequently transitions to the solid state. In solution, the capacity for interaction among components is enhanced through mechanical and ultrasonic means during mixing. The slightly acidic pH, which remains close to neutrality, maintains the positive charge of the -NH\({}_{2}\) group, thereby maximizing adsorption. This phenomenon has been discussed by other authors through the calculation of thermodynamic properties, demonstrating that the process is spontaneous, endothermic, and based on a physisorption mechanism [40].