## 3 Results and Discussion
### Effect of the Filler on the Barrier Properties of the Coatings  
The inherent water-resistant properties of wax-based additives [78], along with their hydrophobic characteristics [79], are acknowledged for their effectiveness in reducing the absorption of aqueous solutions within wood coatings [32; 34; 80; 81]. Hence, the samples underwent water uptake tests to validate the protective efficacy of the wax-based additive. Figure 10 illustrates the progression of water absorption by the samples during the test, with the poplar wood panel serving as a reference to underscore the barrier function of the various coatings. Indeed, the amount of solution absorbed by the wood panel is significantly higher than that observed in the four series of coated samples. The coated samples exhibit a gradual absorption, which decreases slowly over time, indicating a potential saturation of the protective layers. Simultaneously, there is a noticeable distinction in behavior between sample G0 and the three samples containing the wax-based additive. The latter exhibits superior barrier characteristics, evidenced by a reduced amount of water uptake. Additionally, samples G5 and G10 demonstrate comparable outcomes, indicating that 5 wt.% of wax-based additive is adequate to significantly enhance the barrier properties of the acrylic coating. Indeed, at the conclusion of the test, sample G5 demonstrated a decrease in water uptake of approximately 25% compared to sample G0. The error bars show remarkably tight values, indicating a high degree of consistency in the results. Similar findings were previously emphasized in a prior study [34], reaffirming the excellent barrier properties of rice bran wax. Indeed, the decreased water absorption not only enhances the barrier properties but also contributes to the improved aesthetic integrity of the coating. As depicted in the graphs in Figure 11, the three series of composite coatings exhibit minimal color change (Figure 11a) and reflectance characteristics (Figure 11b), which remain largely unaffected by the water uptake test. The heightened absorption of solution in the pure acrylic matrix coating (sample G0) correlates with a noticeable color change and a decrease in the surface's reflectance properties. The substantial presence of the bio-based additive powder within the bulk of the coating of sample G10, as observed in Figure 4c, initially raised concerns about the potential percolation phenomena of aggressive solutions at the interface with the coating matrix. However, these results demonstrate the excellent compatibility of the additive with the acrylic resin, as previously confirmed by the exposure test in a climatic chamber. Nevertheless, to better assess the superficial effects of contact with aggressive solutions, the samples underwent resistance tests to cold liquids. The results are depicted in Figure 12, showcasing the change in color (Figure 12a) and gloss (Figure 12b). The standard deviation values indicate good reproducibility of the measurements and stable behavior of the samples. According to the reference table of the standard [82], all samples exhibit excellent results, with color fading levels classified as 0-1, indicating either absent or minimal discoloration. Aside from contact with coffee, the coatings containing the green additive consistently display a slight rise in color change compared to sample G0. This is probably because tea extract is prone to discoloration when exposed for an extended period (96 h) to  
Figure 10: Water uptake evolution during the test. both aqueous and non-aqueous solutions, particularly under extreme pH conditions [77], such as those tested in this experiment (pH 1 and pH 14). Despite the tea-based additive component's susceptibility, the samples exhibited favorable behavior, including in terms of gloss (Figure 12b).