## 3 Results and Discussion
### WVTR Measurements  
Water vapor transmission rate (WVTR) is one of the main characteristics of food packaging materials, being always included in technical sheets; it may be considered as an indicator of the food packaging material sensitivity toward water vapor and low WVTR values are often requested to assure an acceptable shelf life for many food products. The diffusional performances of biopolymers, such as PHBV and PCL, have been extensively measured and considerable scientific literature can be found [33; 34; 35]. In a recent review [36] on the barrier performance of biodegradable polymers, PHBV and PCL, together with other biopolymers, have been classified as a function of their diffusion performances. PHBV has been considered a medium barrier grade, for both oxygen (16-160 cc\(\cdot\)mil/m\({}^{2}\) day atm) and water vapor permeability (16-40 g\(\cdot\)mil/m\({}^{2}\) day kPa), while PCL has been classified as a poor barrier against oxygen (>1600 cc\(\cdot\)mil/m\({}^{2}\) day atm) and water vapor (>120 g\(\cdot\)mil/m\({}^{2}\) day kPa). In another recent study [37], different commercial biopolymers, PHBV and PCL included, were transformed into films via extrusion and the permeation performances were measured. The results obtained for water vapor permeability (WVP) were the following: PCL, around 2.0 g 100 mm m\({}^{-2}\) day\({}^{-1}\) mbar\({}^{-1}\); PHBV, 0.5 g 100 mm m\({}^{-2}\) day\({}^{-1}\) mbar\({}^{-1}\), the latter being close to values of PET-BO. PHBV seems to be a good candidate for the improvement of paper performances. In a study on double-layer composites using PHB and cellulose paper, different amounts of PHB (2%, 5%, 10%, 15%) were deposited via solvent casting (using chloroform as solvent) on control paper [38]. The authors observed that the permeation decreased with the amounts of PHB due to its low permeation but only if the concentration reached the value of 10%, concluding that it is necessary for the biopolymer to form a continuous layer above the paper sheet in order to fill all of the valleys of its structure. PCL may be considered as possible coating layer; authors [32] who evaluated the water vapor transmission of uncoated and coated paper (via bar coating, with a wet coating thickness of 24 \(\upmu\)m and a dry coating thickness of \(\sim\)6 \(\upmu\)m) concluded that the PCL layer determines a decrease in permeability of around 15% if compared with the control paper. In another study [39] on the abilities of different coating formulations (zein, WPI, PCL and chitosan) to decrease the water vapor transmission of paperboard, PCL coating resulted to be effective at significantly (\(p\leq 0.05\)) reducing the WVTR of the cellulosic substrate from 513 to 320 g/m\({}^{2}\) 24 h, i.e., a percentage decrease around 37%. Literature data for different biopolymer types coated on papers and paperboards can be found, in terms of their barrier properties, but sometimes is not easy to compare the data because of the different substrate used and coating techniques, as well as coat weight and function of coating, together with different methods of calculation and units used [40]. Figure 4 shows the WVTR values calculated in this work for coated samples (first set) and for commercial reference samples. Figure 3: Cross section of pure PHBV (**a**) and PCL (**b**) of the second set. As expected, the polyethylene-coated paper (Poli) is characterized by an extremely low WVTR (average value of 71.91 g 24 h\({}^{-1}\) m\({}^{-2}\)). Conversely, the fluorinated treatment (Fluo) slightly improved the barrier against water vapor (average value of 2825 g 24 h\({}^{-1}\) m\({}^{-2}\)) compared to the uncoated calendered paper (sample UCP) (average value of 3468 g 24 h\({}^{-1}\) m\({}^{-2}\)). Compared with base paper, WVTR value of PHBV coated samples significantly decreased, as a function of both coating thickness and number of layers. Single layer 100 \(\upmu\)m (100 s) coating resulted to have a lower WVTR than single layer of 80 \(\upmu\)m coating obtained at 80 mm/s (80s80).