## 3 Results and Discussion
### Oxygen Absorption Capacity
In contrast, for the PE/PA/PB13 formulation no differences in the absorbed volume of oxygen with irradiation time were found, hence the lower irradiation time was considered as the optimum. Based on this, different amounts of films (0.25, 0.5, 0.75 and 1 g) were irradiated at the optimum UV irradiation time, obtaining the results shown in Figure 4A. Taking as an example a packaging for 200 g of nuts, with an area of 0.0432 m\({}^{2}\) and considering a 1.5% of O\({}_{2}\) residual, the required absorption capacity of the film was 195 mL O\({}_{2}\) m\({}^{-2}\). Based on the results obtained in this study, the PE/PA/PB5 films irradiated for 10 h presented an oxygen absorption capacity of 177.5 mL O\({}_{2}\) m\({}^{-2}\) measured after 6 days whereas the formulation PE/PA/PB13 irradiated for 5 h achieved 222.5 mL O\({}^{2}\) m\({}^{-2}\), being suitable for the selected application. When comparing the obtained results with those reported previously in the literature, [PERSON] et al. [17] developed TiO\({}_{2}\) catalyzed hydroxyl terminated polybutadiene (HTPB) based oxygen scavenging blends with LDPE, obtaining an oxygen absorption capacity of 30 mL O\({}_{2}\) g\({}^{-1}\) film after 30 days for the LDPE/PB (10 wt %)/TiO\({}_{2}\) (5 wt %). However, without the incorporation of TiO\({}_{2}\) as metal catalyst, after 30 days, only a value of 5 mL O\({}_{2}\) g\({}^{-1}\) film was achieved for LDPE/PB (10 wt %) formulation. In another study, polybutadiene films were developed by using an iron complex \(N_{\lambda}N^{\prime}\)-bis(salicylidene)ethylenediamine-benzylimidazole as a catalyst and methyl linoleate [14]. The oxygen scavenging capacity of the films was up to 200 mL (oxygen gas at STP) g film\({}^{-1}\) after 30 days, but the toxicity of the iron complex makes them inadequate for food packaging applications. In the present work, a value of 3.8 mL O\({}_{2}\) g\({}^{-1}\) film was achieved for LDPE/PB (5 wt %) formulation after 56 days without applying the UV treatment being in accordance with the previous reported results [17]. Using the UV irradiation treatment applied in this work, values of 4.4 mL and 2.7 mL O\({}_{2}\) g\({}^{-1}\) film were obtained for PE/PA/PB13 and PE/PA/PB5, respectively, after 6 days (Figure 4). The results presented in this work proved the suitability of the UV irradiation treatment in improving the oxygen absorption capacity without the need of a metal catalyst, avoiding the limitations associated with the catalysts such as the reduction in transparency of the films, mixing difficulties in the extrusion process and toxicity concerns [40]. Figure 3: O\({}_{2}\) absorbed (%) by PE/PA, PE/PA/PB5 and PE/PA/PB13 films after UV radiation for 5, 10 and 20 h (mean \(\pm\) SD, \(n\) = 3). Different superscripts within the same formulation indicate statistically significant different values (\(p\) < 0.05). Figure 4: Relationship between oxygen absorption (mL, Q \(\rm{g}^{-1}\) film) and the amount of film (g) (**A**), FTIR spectra of PE/PA (**B**) after UV irradiation for 5 (RR5 h), 10 (RR10 h) and 20 h (RR20 h) and of PE/PA/PR5 (**C**) and PE/PA/PB13 (**D**) films after UV irradiation for 10 and 5 h, respectively and after 6 days of oxidation (RR10 h-6 d and IRR5 h-6 d) in air at 30 \({}^{\circ}\)C.  
To follow the chemical changes taking place during the oxygen absorption after UV activation, film's FTIR spectra were registered after the UV treatment and at 6 days of oxidation in air at 30 \({}^{\circ}\)C (Figure 4C,D). The oxidation of double bonds of PB led to a production of epoxides (bands between 800 and 1200 cm\({}^{-1}\)), carbonyl groups (band at 1750 cm\({}^{-1}\)) and hydroxyl groups (signal at 3400 cm\({}^{-1}\)) [14; 16]. These changes were more noticeable for the PE/PA/PB13 formulation, whereas for the PE/PA/PB5 formulation these changes were less pronounced, although this film suffered from a higher UV exposure. These results support the conclusion that UV optimum activation time depended on the PB concentration with lower times needed for higher PB concentrations.