## 3 Results
### Barrier Properties of Paper Multilayers  
The permeance values of the water and limonene vapors and oxygen gas of the uncoated paper sheet, PHBV and PET films, and multilayer paper sheets are shown in Table 5. Permeance is the expression of permeability with the removal of the thickness factor, used to determine the barrier of multilayer structures and the actual performance of a film at given conditions of temperature and %RH. For this reason, the thickness values of each film and sheet samples were also included. Regarding the water vapor, one can observe that the permeance of the paper sheet was 1.10 \(\times\) 10\({}^{-8}\) kg/m\({}^{2}\).Pa-s, resulting in a permeability value of 3.21 \(\times\) 10\({}^{-12}\) kg.m/m\({}^{2}\).Pa-s. The low water vapor barrier of paper is due to the fact that it is a hydrophilic and highly fibrous material and, therefore, has a high porosity, as observed previously during the FESEM analysis. In relation to the 10-m PHBV film, it presented a permeance of 4.78 \(\times\) 10\({}^{-10}\) kg/m\({}^{2}\).Pa-s, yielding a permeability of 5.73 \(\times\) 10\({}^{-15}\) kg.m/m\({}^{2}\).Pa-s. This permeability value is slightly higher than that reported for thermo-compressed films of PHB [49] and PHBV with 2-3 mol% 3 HV [50], that is, 1.70 and 1.82 \(\times\) 10\({}^{-15}\) kg.m/m\({}^{2}\).Pa-s, respectively. This difference is due to the higher comonomer content in the PHBV tested herein, which induces lower crystallinity and, hence, higher diffusivity to the vapor and gas molecules [18; 51]. In the case of the commercial PET multilayer film, the permeance value was 2.32 \(\times\) 10\({}^{-11}\) kg/m\({}^{2}\).Pa-s, which corresponds to a permeability of 2.25 \(\times\) 10\({}^{-15}\) kg.m/m\({}^{2}\).Pa-s, considering it as a monolayer material. The resultant WVTR was approximately 6.3 g/m\({}^{2}\).day, which is in the range but lower than the one reported by the manufacturer at 38 \({}^{\circ}\)C and 90% RH, that is, 16 g/m\({}^{2}\).day [52] due to the lower temperature and humidity employed herein. Moreover, this water vapor permeability value is slightly lower than that of PET, that is, 2.3 \(\times\) 10\({}^{-15}\) kg.m/m\({}^{2}\).Pa-s, measured at 38 \({}^{\circ}\)C and 90% RH [53]. This can be related to the presence of a layer of polyolefin, such as LDPE, with a lower permeability, that is, 1.2 \(\times\) 10\({}^{-15}\) kg.m/m\({}^{2}\).Pa-s, at 38 \({}^{\circ}\)C and 90% RH [54]. This polyolefin layer is generally placed in the external part of the film in order to perform heat sealing at lower temperatures. In a food packaging context, both materials presented water vapor permeability between that of polyamide 6 (PA6), that is, 2.06 \(\times\) 10\({}^{-14}\) kg.m/m\({}^{2}\).Pa-s, and PP, that is, 7.26 \(\times\) 10\({}^{-16}\) kg.m/m\({}^{2}\).Pa-s [54]. One can further observe that the water permeance of the resultant PHBV/paper/PHBV multilayer was in the range of the PHBV film, but still significantly lower (_p_ < 0.05), with a value of 4.48 \(\times\) 10\({}^{-10}\) kg/m\({}^{2}\).Pa-s. This enhancement in the permeance can be mainly related to the increase in the thickness sample. However, it can also be ascribed to the fact that the hydrophobic PHBV film successfully protected paper from moisture and, thus, the barrier of paper improved in dry conditions. Similarly, the PET/paper/PET multilayer resulted in a value of 1.91 \(\times\) 10\({}^{-11}\) kg/m\({}^{2}\).Pa-s due to the higher water barrier performance and thickness of the petrochemical film.