## 3 Results and Discussion
### Investigation of the Uvradiation Action on Polyesters PHB and PLA by a Method of IR Spectroscopy  
The chemical structure of PLA and PHB exposed to UV-C radiation for 2, 5, 24, and 144 h was studied with the use of FTIR spectroscopy. It was found that the spectral characteristics of chitosan, subjected to UV radiation, remained practically unchanged, in contrast to PLA and PHB ones. For this reason, the analysis of the effect of UV radiation was carried out by the spectra of PLA and PHB only. Figure 5 shows the changes in the IR spectra of PHB exposed to UV radiation. As can be seen in the figure, significant changes in spectrum structure occurred. The transformations already begin to appear after 2 h of radiation and are expressed in altering the shapes of the bands related to the stretching vibrations of the ester group C-O-C (1280 cm\({}^{-1}\), as shown in the Supplementary File as Figure S1 and Table S2) and asymmetric vibrations C-O-C (1332 cm\({}^{-1}\), Figure S1). There is also a change in the shape of the 1724 cm\({}^{-1}\) (Figure S3 and Table S2) band relevant to the carbonyl group (C=O). At 1745 cm\({}^{-1}\) (Figure S3), an additional spectral band is formed, indicating the presence of the C=O group, which is different from the original PHB. The band related to the stretching vibrations of the crystalline regions of the C-C bond (980 cm\({}^{-1}\), Figure S4 and Table S5) remains practically unchanged. There is no shift of the bands at 1379 cm\({}^{-1}\) and 1358 cm\({}^{-1}\) (Figure S1), which belong to the wagging vibrations and strain vibrations of the CH\({}_{3}\) group, respectively. The band at 1447 cm\({}^{-1}\) (Figure S1), which is related to the asymmetric bending vibrations of the CH\({}_{3}\) group, is shifted by 6 cm\({}^{-1}\) from the initial value of 1453 (1454) cm\({}^{-1}\) (Figure S1), which is characteristic of the initial PHB. The greatest changes are observed in the samples after 144 h of UV radiation, expressed in the appearance of a band at 1402 cm\({}^{-1}\) (Figure S1) and two broad bands at 3132 cm\({}^{-1}\) and 3045 cm\({}^{-1}\) (Figure 5). These three bands refer to the -OH stretching vibrations of the carboxyl group (Figure S4 and Table S5) and show that, after 144 h of UV irradiation of PHB  
Figure 5: FTIR spectrum of PHB films before (A) and after UV radiation during 2 (B), 5 (C), 24 (D), 144 (E) hours. samples, a relative broadening and a decrease in the intensity of the band at 1182 cm\({}^{-1}\) related to C-O-C vibrations in the amorphous region of the polymer takes place. It can be assumed that the process of PHB photodegradation mainly affects the amorphous phase of the polymer, while the spectral region (1000-800 cm\({}^{-1}\)) (Figure S6 and Table S7), characterizing the crystalline phase, remains practically unchanged. Figure 6 shows the IR spectra of PLA exposed to UV radiation. As can be seen from figure, the most significant changes in the PLA spectrum are observed in the region of 1225-1170 cm\({}^{-1}\). This range is mixed and is defined by two bands with maxima at 1211 and 1184 cm\({}^{-1}\) (Figure S8), related to asymmetric vibrations of the C-CO-O group and bending vibrations of CH\({}_{3}\) (Table S9). As the duration of UV radiation increases, their broadening occurs, which indicates a change in the structural features of this fragment. Bands at 1087 cm\({}^{-1}\) and 1047 cm\({}^{-1}\) are referred to as the symmetric vibrations of C-O-C groups and vibrations and of C-CH\({}_{3}\) stretching vibrations, respectively (Figure S8 and Table S9). The 1269 cm\({}^{-1}\) band is mixed and consists of CH strain vibrations and C-CO-C stretching asymmetric vibrations (Table S9). The band at 1130 cm\({}^{-1}\) refers to the asymmetric rocking vibrations of the CH\({}_{3}\)-group (Figure S8 and Table S9). The regime of asymmetric strain vibrations of CH\({}_{3}\) appears at approximately 1454 cm\({}^{-1}\) in the form of an intense band (Figure S10 and Table S11). The frequency stability reflects a pure asymmetric oscillation mode.