## 4 Discussion  
Maximum WL (weight loss) was reported for all samples at INT1152, while maximum SM (sorbed moisture) was observed at INT1728. At INT2880, the ZnO-loaded composites exhibited the lowest WL, reaching a state of stabilization. SEM images complemented by EDS analyses revealed that the higher the ZnO loadings, the higher the protection against AWE treatment. This is evident in SEM images where ZnO-loaded samples did not contain surface pores and crack canals were shallower. These images, complemented with X-Ray diffraction patterns, revealed that effective ZnO dispersion was achieved. FTIR analysis showed that the decomposition of the composite's surface was less as the ZnO filler content increased. C0.5 and C2 samples exhibited better stability of-C-O-C groups, together with the increase of -OH groups. On the other hand, C0 samples exhibited a high reduction in -OH and -C-O-C groups, denoting increased decomposition as corroborated by the presence of pores in SEM images. The wettability measurements revealed mild hydrophilicity that turned to hydrophobicity as ZnO content increased, due to the increasing surface roughness. In addition, AWE treatment only affected wettability of C2 samples by further increasing their hydrophobicity. In the same manner, only C2 samples underwent distinct gloss reduction due to filler incorporation and, consequently, due to AWE treatment. Additionally, C0.5 samples exhibited the lowest gloss reduction due to AWE treatment. UV-Vis measurements revealed that ZnO presence enhanced UV blocking capability as filler content increased up to 0.5 wt%, above which no significant changes were observed. Additionally, 2880 h aging only slightly reduced transmittance, most prominently at the 400-500 nm range for the ZnO-loaded samples. Colorimetric measurements showed that bare samples (C0) suffered significant yellowing at INT2304 due to AWE treatment, while C0.1 and C0.5 were the least affected. This constituted a border AWE treatment interval, after which reduction in b* value at INT2880 was observed only for low ZnO loadings (C0, C0.1), denoting the initiating decomposition of -OH groups, as observed in FTIR measurements. Additionally, the \(\Delta\)E parameter revealed that the least colour change occurred to C0.1 and C0.5 samples. A very interesting phenomenon is the'self-healing' process of the epoxy matrix. Although the epoxy resin of the present study is thermosetting with an irreversible network structure, the'self-healing' phenomena would occur at a very low degree [56]. Indeed, the presence of residual thermoplastic epoxy resin would facilitate the crosslinking of unreacted epoxy groups in the presence of free OH functionalities and UV radiation impact. Based on the FTIR measurements, ether/epoxy linkages are present even after 2880 h of AWE treatment, and the presence of OH functionalities are also evident. Additionally, radial induced scissions, by the presence of the aforementioned functionalities, are certainly possible. It should be noted that, although mechanical properties were not part of this study, according to the literature [18], improved mechanical strength is also expected for our high content samples, namely for the C0.5 and C2 ones. This assumption can be substantiated by the interaction between ZnO filler and epoxy resin, where hydrogen bonding is expected between free OH groups on the nanoparticle surface and epoxide groups of the resin [27]. Finally, dielectric properties were dominated by epoxy resin. Particularly, tan\(\delta\) was unaffected by ZnO incorporation during all stages of AWE treatment. Interestingly, the relative permittivity, compared to that of bare epoxy, underwent significant reduction in C0.1 and C0.5 samples that was maintained up to INT1152; it suffered a small increase from INT1728 up to INT2880, but was still lower than the bare resin. On the other hand, k' of C2 samples remained increased, compared to C0/INT0 samples, throughout the full AWE treatment period.