## 5 Conclusions  
The effectiveness of the protection against moisture uptake of GNP-rich films has been investigated through a moisture uptake test in an environmental chamber. The behaviour of Kevlar sandwich panels, representative of a regional aircraft composite part, in a humid environment, has been investigated, and the ability of GNP films to protect Kevlar/epoxy panels from water absorption has been demonstrated.  
After 41 days in a humid environment, the maximum sorption is reduced by \(-35\%\) in samples protected with films @70 wt% of GNPs, compared to the unprotected system. Moreover, an evident delay in the absorption rate into the composite panels due to the presence of the protective layer has been observed, with a reduction of \(-80\%\) after 3 days. A Ground-Air-Ground (GAG) test has been carried out to reproduce the actual flight envelope. The GAG test showed that after 10 cycles, the maximum sorption of the panel coated with s film @70 wt% of GNPs is about 70% lower than that of the uncoated one. NDI analysis with lock-in thermography revealed the absence of damage in all panels after the test.  
The nanocomposite nanostructure plays an important role in the barrier's properties, reducing the absorption rate and the maximum moisture uptake. The GNP protective films reported an efficiency against moisture absorption between 80% and 62% at short times  
Figure 14: Thermal images: (**a**) before performing the test; (**b**) after the moisture uptake test at 0.1 Hz.  
Figure 15: Thermal images: (**a**) before performing the test; (**b**) after the moisture uptake test at 0.04 Hz.  
(3 days) and between 35% and 14% at saturation, based on the filler/matrix composition. Thanks to the nanoplatelet alignment and the intrinsic hydrophobicity of GNPs, the film acts as barrier to moisture regardless the nanofiller content, with a diffusivity coefficient of the same magnitude of aluminium (\(\sim\)10\({}^{-12}\) m\({}^{2}\)/s) [61].  
However, the overall behaviour is affected by the filler content. Although the theoretical model indicates that the tortuosity factor increases with increasing nanoplatelet content, an opposite trend was found. Films at 70 wt% of GNPs showed the best protection against moisture uptake. By increasing the filler content, the nanostructure is affected by dry areas and the surface of the film becomes more hydrophilic, promoting moisture absorption.  
Nanostructured films with 70 wt% of GNPs represent a promising technology to be employed as barrier coating in the aeronautics field, thanks to the significant reduction of moisture permeation inside composite panels. Compared to existing technologies, these innovative films are lightweight, easily integrated in the manufacturing processes, and are not susceptible to corrosion. In addition, thanks to their low electrical resistivity, they provide additional functionalities as shielding against electrostatic discharges and electromagnetic waves.  
Conceptualization F.C. and A.M.; methodology B.P., G.B. and R.V.; Investigation F.C., G.B., C.C.T. and C.T.; data curation F.C., B.P. and C.T.; writing--original draft preparation F.C., B.P. and R.V.; writing--review and editing A.M., G.G. and M.G.; supervision A.M., M.G. and G.G.; funding acquisition M.G., A.M. and G.G. All authors have read and agreed to the published version of the manuscript.  
This work has been supported by the Research Project AMICO (code ARS01_00758) funded by the Italian Ministry of Education, University and Research.  
Not applicable.  
The data presented in this study are available in the article.  
The authors would like to thank [PERSON] and [PERSON] for their precious advice and discussions.  
The authors declare no conflict of interest.