**4. Conclusions**

In this study, PdNPs were mixed with CTAB and TEOS surfactants to have better dispersion in electrospun PHB fibers. The resultant fibers were annealed at 160 ◦C to form continuous PHB films of direct application interest. Morphological analysis carried out by SEM and TEM showed that a better dispersion was achieved for the electrospun PHB/PdNP/CTAB film. DSC indicated that the presence of the PdNPs reduced both the melting point and the degree of crystallinity of PHB, thus acting as an anti-nucleating agent, which was further confirmed by FTIR analysis. WVP and LP measurements indicated that the nanocomposite films, including those modified with surfactants, presented lower barrier performance than the neat PHB film. These results were ascribed to the reduced crystallinity degree and to existence of unbonded interfacial regions and/or voids between the biopolymer matrix and the inorganic nanoparticles that may serve as preferential ways for the diffusion of gas molecules. Finally, the oxygen scavenging activity of the PHB materials was evaluated at different RHs. Although the electrospun films presented lower capacity to absorb oxygen that their counterpart fibers, these still presented significant activity at 100% RH. The here-developed and -characterized electrospun PHB films are suitable potential candidates as coatings or interlayer systems for active food packaging applications and the followed methodology represents a new route to prepare these films due to the relative high dispersion achieved of the PdNPs.

**Author Contributions:** Conceptualization was devised by J.M.L.; Methodology, Validation, and Formal Analysis was carried out by A.C., M.G., H.T.S., S.T.-G., and J.M.L. Investigation, Resources, Data Curation, Writing-Original Draft Preparation and Writing-Review & Editing was performed by A.C., M.G., H.T.S., S.T.-G., and J.M.L.; Supervision J.M.L; Project Administration, J.M.L.

**Funding:** This research has received funding from the Spanish Ministry of Economy and Competitiveness (MINECO, project AGL2015-63855-C2-1-R) and the EU H2020 project YPACK (reference number 773872).

**Acknowledgments:** A.C. and S.T.-G. would like to thank the Brazilian Council for Scientific and Technological Development (CNPq) and MINECO for her predoctoral gran<sup>t</sup> (205955/2014-2) and his Juan de la Cierva contract (IJCI-2016-29675), respectively.

**Conflicts of Interest:** The authors declare no conflicts of interest.
