*3.5. Oxygen Permeability of Films of PLA/PBAT/GR Formulations*

*3.5. Oxygen Permeability of Films of PLA/PBAT/GR Formulations*  Since these materials are intended for food packaging applications, the barrier performance against oxygen is very relevant to protect the foodstuffs from oxidation processes. Thus, the oxygen transmission rate was measured and Table 5 summarizes the OTR\*e values of the obtained formulations. PLA showed significantly better oxygen barrier performance than PBAT (*p* < 0.05). The incorporation of 20 wt.% of PBAT into the formulation led to a significant increment of the oxygen permeation of PLA (increment of 72%) reaching values close to that of PBAT. This behavior was due to the low miscibility of PLA and PBAT in this formulation, which allowed oxygen diffusion through the porous/defects present in the film. The incorporation of 5 phr of GR into the PLA/PBAT blend significantly reduced the oxygen permeability by 19.5%, mainly due to the homo-Since these materials are intended for food packaging applications, the barrier performance against oxygen is very relevant to protect the foodstuffs from oxidation processes. Thus, the oxygen transmission rate was measured and Table 5 summarizes the OTR\*e values of the obtained formulations. PLA showed significantly better oxygen barrier performance than PBAT (*p* < 0.05). The incorporation of 20 wt.% of PBAT into the formulation led to a significant increment of the oxygen permeation of PLA (increment of 72%) reaching values close to that of PBAT. This behavior was due to the low miscibility of PLA and PBAT in this formulation, which allowed oxygen diffusion through the porous/defects present in the film. The incorporation of 5 phr of GR into the PLA/PBAT blend significantly reduced the oxygen permeability by 19.5%, mainly due to the homogeneous dispersion of GR into the PLA/PBAT blend matrix. This dispersion contributed to a reduction of the defects observed in PLA/PBAT as well as to the increased crystallinity of the formulation, which

geneous dispersion of GR into the PLA/PBAT blend matrix. This dispersion contributed to a reduction of the defects observed in PLA/PBAT as well as to the increased crystallinity

served in the PLA-based blends [19]. Higher amounts of GR, 10 phr, led to the best result, showing a significant reduction of 35% in the oxygen permeability (*p* < 0.05) with respect of PLA/PBAT formulation and being closer to that of PLA (12% higher than PLA), in good agreement with the highest crystallinity observed in this formulation. Those formulations with higher contents of GR, 15 and 20 phr, resulted in a worse oxygen barrier than

led to a better oxygen barrier performance as was already observed in the PLA-based blends [19]. Higher amounts of GR, 10 phr, led to the best result, showing a significant reduction of 35% in the oxygen permeability (*p* < 0.05) with respect of PLA/PBAT formulation and being closer to that of PLA (12% higher than PLA), in good agreement with the highest crystallinity observed in this formulation. Those formulations with higher contents of GR, 15 and 20 phr, resulted in a worse oxygen barrier than PLA/PBAT\_10GR but were still better than PLA/PBAT. The saturation effect of GR into the PBAT domains generated pores/defects that allowed oxygen diffusion through the film. Nevertheless, the good adhesion between the increased PBAT domains due to the GR presence with the PLA matrix at the interface still allowed to obtain better barrier performance than PLA/PBAT. The oxygen transmission results obtained here were higher than traditional petrochemical plastics widely used in the packaging sector, such as EVOH (OTR\*e < 4 cm3mm/m2/day) [53] or PET (OTR\*e < 3 cm<sup>3</sup> mm/m2/day), but substantially lower than that of LDPE (OTR\*e between 160 and 240 cm3mm/m2/day) [54]. Thus, the materials developed here could be used in several food packaging applications as a potential alternative to some packaging materials made of conventional plastics (i.e., polyolefins) directly as films or in more complex formulations (i.e., multilayers systems).

**Table 5.** Oxygen permeability measurements of PLA, PLA/PBAT, and PLA/PBAT with 5, 10, 15, and 20 phr of GR resin.


a–f Different letters within the same property show statistically significant differences between formulations (*p* < 0.05).
