## 3 Results and Discussion
### WVTR Measurements
Comparing both single layer of 80 \(\upmu\)m coated samples, but with different application speeds, the lower speed (50 mm/s) corresponds to a lower WVTR. This suggests a more uniform coating distribution and a higher penetration capacity in the paper support. In accordance with this assumption, grammage data (Table 2) show higher values at a lower coating speed. The WVTR data for the first set samples were plotted in a graph (Figure 5) versus coating grammages, showing a linear inverse relationship (R\({}^{2}\) = \(-\)0.986; \(\alpha\) < 0.01). The lowest WVTR values reached were 80d and 100d, and they resulted statistically different from single layer-coated samples (namely, 80s50, 100s and 80s80). In the second set, calendered paper was coated with PHBV and PCL, also considering the influence of PEG addition as plasticizer (from 0% to 20% \(w\)/\(w\) of polymer). By comparison of WVTR values of PHBV 80d sample (first set) and PHBV (second set) it could be assumed that the modification of coating solution preparation allowed a better distribution on the paper sheet, with positive effect on moisture barrier performances (Figure 6). Figure 4: WVTR values (g 24 h\({}^{-1}\) m\({}^{-2}\)) of PHBV coating at different thickness. Bars represents the average value of three determinations, error bars report standard deviation. Different letters indicate statistically significant differences (\(p\) < 0.05). “UCP” refers to base paper, “Fluo” to fluorinated paper, while “Poli” to polyethylene-coated paper. See Table 1 for other samples codification. Concerning the addition of PEG to PHBV, a general increase of WVTR in presence of plasticizer can be observed. These results could be explained considering the hydrophilic nature of PEG and its plasticizing action, according with previous studies that attribute this behavior to a free volume increase (which promotes molecular diffusion) and to the PEG hydrophilic nature, which tends to increase sorption capacity, solubility and water  
Figure 5: Linear correlation between coating grammage and WVTR of first set samples. Grammage equal to 0 corresponds to uncoated paper sample. Figure 6: WVTR values (g 24 h\({}^{-1}\) m\({}^{-2}\)) of PHBV and PCL coated samples both pure and with PEG addition at different concentrations (set 2). Bars represents the average value of three determinations, error bars report standard deviation. Different letters indicate statistically significant differences (\(p<0.05\)). “UCP” refers to base paper, “Fluo” to fluorinated paper, while “Poli” to polyethylene-coated paper. See Table 1 for other samples codification. permeability of plasticized films [17]. In particular, WVTR values significantly increased in presence of plasticizer up to 10%, and then decreased at 20% PEG concentration, while maintaining a value higher than PHBV not plasticized and not significantly different compared with PHBV with 5% PEG. This trend agrees with a study about PHBV extruded films incorporated with PEG1000 at 5%, 10%, 20%. The WVTR decrease was explained in the study assuming a demixing between plasticizer and PHBV, which could, given the relatively low PHBV permeability, allow a reduction in water vapor permeability [22]. This hypothesis is not necessarily in contrast with the SEM structure observed for these samples, which appeared as more uniform compared to non-plasticized films and could be explained as the result of a beginning demixing between the two materials, not always detectable by SEM images. According to Figure 6, pure PHBV coating showed lower, although not significantly, WVTR values compared to PCL. It is possible that discontinuities observed at SEM on PCL coatings could facilitate water vapor permeation.