## 4 Discussion  
In this study, homogenous ultrathin PLA fibers incorporating GA polyphenol at 40 wt% with a mean diameter of ca. 0.9 \(\upmu\)m were successfully produced by the electrospinningning technique. The incorporation of GA into the PLA fibers increased the roughness surface and also slightly flattened the fibers shape mainly due to the conductivity increase observed in the solutions used for electrospinningning. The GA-containing submicron PLA fibers were then used to build nano-sized bi- and multilayers structures based on previously prepared cast-extruded 200-\(\upmu\)m PLA films. For the bilayer structures, the electrospun mats were applied as a coating on the PLA films for 1, 2, and 3 h. Electrospun coatings of approximately 60, 85, and 100 \(\upmu\)m were then obtained on the PLA films after 1, 2, and 3 h of deposition during electrospinningning. The electrospinningning process successfully yielded the formation of continuous coatings made of submicron PLA fibers, but they were not strongly adhered to the PLA film and the resultant bilayer PLA films also lacked of transparency. To produce the multilayer PLA films, the cast films of PLA were first one side coated with electrospun GA-loaded PLA fibers, also processed for 1, 2, and 3 h, and then sandwiched with a thin PLA film of 10 \(\upmu\)m on the other side by the application of a thermal post-treatment without pressure, the so-called annealing. It was also observed that the thickness of the electrospun nanostructured interlayers increased as a function of the during the electrospinningning process though they were relatively difficult to discern due to their low thicknesses. The resultant multilayer films interestingly presented sufficient adhesion between layers as a result of the large surface-to-volume ratio of the electrospun fibers that efficiently coalesced and adhered strongly to both PLA film sides during annealing. The multilayer PLA films showed relative high transparency when the containing nanostructured interlayers were produced for up to 2 h of electrospinningning due to their very little porosity. Results also showed that the incorporation of the natural polyphenol positively delayed the thermal degradation of PLA for up to 10 \({}^{\circ}\)C and all films were thermally stable up to 345 \({}^{\circ}\)C. This thermal enhancement was more pronounced in the case of the bilayer films, being this phenomenon ascribed to the presence of the antioxidant in regions close to the films surface. During the in vitro release studies, the GA release amounts from all PLA films increased but the release rates decreased with increasing the thickness of the electrospun GA-containing layer. The bilayer PLA films showed that the cumulative release amount of GA increased rather rapidly for the first 5 h of immersion time. Further increase in the submersion time resulted in a gradual increase in the cumulative amount of the polyphenol up to it finally reached a _plateau_ value after 45-250 h. On the contrary, the PLA multilayers offered a highly sustained release of GA, having the capacity to release the polyphenol for over 1000 h and being the release diffusionally controlled. Therefore, whereas the bilayer PLA films can provide a quick release of antioxidant into saline food simulant that can be of interest for functional food in packaging materials of a relatively short life cycles, that is, 1-2 weeks, the multilayer systems can be interesting from a point of view of food products stored in water-based media with a much longer shelf life. Finally, the antioxidant activity assessment of the GA released from the PLA films was carried out by measuring its capacity to scavenge the DPPH radicals. During the first days, the bilayer PLA films performed as a potent source of antioxidant while the multilayer films offered comparatively weaker activities. In the long term, however, the GA released from the multilayer PLA films were able to show a stronger DPPH inhibition.