**4. Conclusions**

In this paper, two coatings based on chitin and polyphenols were successfully applied on paper tissues. As a result, antibacterial properties due to ChNFs and antioxidant properties due to polyphenols were positively detected. In particular, the correlation between the concentration of functional coatings and the expected properties was confirmed, resulting in an increase in antibacterial and antioxidant properties at higher contents of active molecules. ATR-IR analysis confirmed the presence of a homogeneous coating on the surface of the paper tissues and showed a higher concentration of chitin on the top surface with respect to the bottom part, revealing its affinity for the cellulosic substrate. Mechanical properties of treated and untreated tissues were also studied considering the effect of the application technique with water. The results showed that, in all mechanical tests, the water treatment had a toughening generalized effect. In the literature, it was reported that the change in swelling and moisture can induce anisotropic shrinkage or relaxation of the microcompression created during the manufacturing [85]. The latter described phenomenon is in agreement with the generalized toughening effect. Regarding the tissues treated with ChNFs or polyphenols, it was also possible to observe different effects. In fact, the addition of polyphenols resulted in a reduction in mechanical resistance, while the addition of ChNFs resulted in its enhancement, which was confirmed by the statistical analysis of results. The observation of mechanical properties in the different directions for tensile and tearing tests confirmed the general orientation of paper fibres in

the machine direction, in agreement with industrial methodologies for paper production. The effect of coatings on mechanical properties can be better explained by observing FESEM micrographs. ChNFs increased the density of the tissue, filling the empty spaces between the paper fibres and obtaining a more compact structure that can justify the increase in mechanical resistance. Conversely, polyphenols did not significantly affect the structure of the tissue, as they were impregnated but had no film-forming capacity. Therefore, the decrease in mechanical properties of tissues treated with polyphenols cannot be attributed to a change in the structure but to a detrimental effect due to the presence, along all the tissue thickness, of the polyphenols extract showing a limited compatibility with the cellulosic fibres of the paper tissue. As polyphenols derive from a natural extract that contains several molecules, it might be reasonable to assume a chemical degradation of the fibres. On the whole, the results of the present paper can be useful for developing, in the near future, functional coatings for cellulosic products in the skin care or packaging sectors considering the effects of interesting biomass waste derivatives.

**Author Contributions:** Conceptualization, L.P. and M.-B.C.; methodology, L.P.; investigation, L.P.; data curation, L.P.; writing—original draft preparation, L.P. and M.-B.C.; writing—review and editing, S.G., M.C.G. and A.H.; supervision, A.L. and P.C.; project administration, P.C.; funding acquisition P.C. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was funded by the Bio-Based Industries Joint Undertaking under the European Union Horizon 2020 research program (BBI-H2020), ECOFUNCO project, grant number G.A 837863.

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

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