## 3 Results and Discussion
### Barrier Properties of Green Composites
\begin{table}
\begin{tabular}{l c c c c} \hline \hline
**Film** & **Thickness** & **WVP \(\times\) 10\({}^{15}\)** & **LP \(\times\) 10\({}^{14}\)** & **OP \(\times\) 10\({}^{19}\)** \\  & **(\(\mu\)m)** & **(kg\(\cdot\)m\(\cdot\)m\({}^{-2}\cdot\)Pa\({}^{-1}\cdot\)s\({}^{-1}\))** & **(kg\(\cdot\)m\(\cdot\)m\({}^{-2}\cdot\)Pa\({}^{-1}\cdot\)s\({}^{-1}\))** & **(m\({}^{3}\cdot\)m\(\cdot\)m\({}^{-2}\cdot\)Pa\({}^{-1}\cdot\)s\({}^{-1}\))** \\ \hline PHBV & 126 \(\pm\) 5 & 1.84 \(\pm\) 0.39 \({}^{\text{a}}\) & 1.41 \(\pm\) 0.12 \({}^{\text{a}}\) & 2.09 \(\pm\) 0.48 \({}^{\text{a}}\) \\ PHBV\_2\%MFC & 133 \(\pm\) 4 & 4.19 \(\pm\) 0.40 \({}^{\text{b}}\) & 1.34 \(\pm\) 0.06 \({}^{\text{a}}\) & 1.60 \(\pm\) 0.19 \({}^{\text{b}}\) \\ PHBV\_5\%MFC & 128 \(\pm\) 7 & 5.27 \(\pm\) 0.53 \({}^{\text{c}}\) & 1.07 \(\pm\) 0.09 \({}^{\text{b}}\) & 1.24 \(\pm\) 0.36 \({}^{\text{c}}\) \\ PHBV\_10\%MFC & 129 \(\pm\) 6 & 5.89 \(\pm\) 0.47 \({}^{\text{c}}\) & 1.66 \(\pm\) 0.15 \({}^{\text{c}}\) & 1.08 \(\pm\) 0.12 \({}^{\text{d}}\) \\ PHBV\_ESAO & 137 \(\pm\) 2 & 4.46 \(\pm\) 0.19 \({}^{\text{b}}\) & 2.04 \(\pm\) 0.17 \({}^{\text{d}}\) & 2.27 \(\pm\) 0.15 \({}^{\text{a}}\) \\ PHBV\_TGIC+DCP & 135 \(\pm\) 8 & 5.69 \(\pm\) 0.29 \({}^{\text{c}}\) & 3.80 \(\pm\) 0.31 \({}^{\text{e}}\) & 2.70 \(\pm\) 0.26 \({}^{\text{a}}\) \\ PHBV\_5\%MFC\_ESAO & 136 \(\pm\) 7 & 5.48 \(\pm\) 0.58 \({}^{\text{c}}\) & 0.99 \(\pm\) 0.39 \({}^{\text{b}}\) & 1.36 \(\pm\) 0.12 \({}^{\text{c}}\) \\ PHBV\_5\%MFC\_TGIC+DCP & 128 \(\pm\) 3 & 3.29 \(\pm\) 0.30 \({}^{\text{d}}\) & 0.16 \(\pm\) 0.01 \({}^{\text{f}}\) & 0.98 \(\pm\) 0.17 \({}^{\text{f}}\) \\ \hline \hline \end{tabular}  
* WVP = water vapor permeability; LP = limonene permeability; OP = oxygen permeability. Mean values and standard deviation. \({}^{\text{a}-f}\) Different superscripts in the same column indicate significant differences between formulations (\(p<0.05\)).  
\end{table} 
Table 6: Barrier properties of the films of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) with microfibrillated cellulose (MFC) and compatibilized with epoxy-based styrene-acrylic oligomer (ESAO) and with triglycerides isocyanurate (TGIC) and dicumyl peroxide (DCP). film sample showed an LP value of 1.59 \(\times\) 10\({}^{-15}\) kg\(\cdot\)m\(\cdot\)m\({}^{-2}\)\(\cdot\)Pa\({}^{-1}\)\(\cdot\)s\({}^{-1}\), which is nearly one order of magnitude lower than the permeability of neat PHBV. In this regard, one should consider that the aroma barrier performance of nanocellulose is remarkably higher than that of PHB and PHBV [68] so that the presence of highly dispersed MFC in the compatibilized film sample could successfully reduce limoneine absorption in the biopolyester matrix. Finally, in terms of oxygen barrier, one can see that permeability values followed a similar trend to the one observed in the case of aroma. Thus, the incorporation of MFC significantly reduced (\(p<0.05\)) the OP values, showing the highest improvement at fillers of 10 wt % with a value of 1.08 \(\times\) 10\({}^{-19}\) m\({}^{3}\cdot\)m\(\cdot\)m\({}^{-2}\cdot\)Pa\({}^{-1}\cdot\)s\({}^{-1}\). This result agrees with previous studies reporting on the oxygen-barrier enhancements of biopolyesters by the incorporation of nanocellulose materials. For instance, [PERSON] et al. [66] incorporated 5 wt % CNC in PLA, attaining a reduction in OTR of about 43%. Similar improvements were achieved by [PERSON] et al. [69], showing 47-64% reductions in the OP values of PLA by the addition of nanocellulose with different aspect ratios and at contents of 1, 3, 5, and 10 wt %. Higher reductions were achieved by [PERSON] et al. [70], who showed that the addition of 0.7 wt % CNC led to a decrease of 88.9% in PHB-based films. The improvement and contribution mechanism of ultrathin cellulose materials to the gas barrier property of polymers is based on the creation of a tortuous path for the diffusing gas molecules, since these nanomaterials are impervious to gases.