*3.6. FESEM Analysis*

FESEM analysis was performed to observe the structure of ChNFs and polyphenols and their effect on the paper tissue structure. The brittle dusty sample deposited on aluminium foil by spraying the polyphenol-based treatment and the homogeneous and compact film formed by depositing the treatment based on ChNFs were both analysed.

In Figure 12, the different microstructures of polyphenols (Figure 12a) and ChNFs (Figure 12b) were clearly observed. Polyphenols showed the aspect of a paste consisting of round submicrometric partially united particles deposited on the surface of aluminium foil forming a nonhomogeneous film with the presence of cracks in correspondence of the particles joining lines. Instead, chitin showed a nanostructured morphology consisting of nanofibrils that form a compact structure fully covering the aluminium foil. In good agreement, a good film-forming capacity was evidenced for ChNFs [54,84].

**Figure 12.** *Cont*.

**Figure 12.** FESEM micrographs of: (**a**) polyphenols and (**b**) chitin sprayed on aluminium foil, (**c**,**d**) paper tissue, (**e**,**f**) paper tissue treated with polyphenols, and (**g**,**h**) paper tissue treated with ChNFs.

Pure tissue, as observed in the micrograph of Figure 12c,d, showed a fibrillar structure grouped in bundles that were oriented in different directions. However, the structure was not compact and it showed many empty spaces having dimensions of tenth of micrometres.

In Figure 12e,f, micrographs of paper tissues treated with polyphenols are shown. At low magnification (250×), it was not possible to identify the presence of antioxidant molecules on the fibres and the microstructure appeared unmodified by the treatment. The comparison between the high-magnification micrographs of pure tissue (Figure 12c,d) and the one treated with polyphenols (Figure 12e,f) allowed the deposition of polyphenols onto the fibrillar structure of the paper to be observed.

Micrographs of tissues coated with chitin (Figure 12g,h) showed a completely different structure with respect to the one treated with polyphenols. In fact, it was also possible to observe the coating at low magnification (250×) where the chitin completely filled the empty space between the paper fibrils, forming a continue surface. At high magnification, it was not possible to distinguish the fibrillar structure of the paper but only the nanofibrillated structure of chitin covering the treated surface.
