3.4. Water vapor permeability (WVP) Water is an important factor in the transfer of infections to food. Because of this, the water vapor flow rate (WVTR) and water vapor permeability (WVP) of food packaging polymers, especially biopolymers, are very important characteristics. The results of measuring the permeability rate of PLA films and nanocomposites are shown in Fig. 6. As can be seen, the permeability of neat PLA film is about 1.87 1011 (g/m S Pa), which is quite consistent with reported values in a previous study [32].With the addition of 1 and 3 wt% CNF to PLA matrix, WVP slightly increased,
reaching 2.01 1011 and 2.04 1011 (g/m S Pa), respectively. The addition of 1 and 3 wt% acetylated CNF not only
improved the mechanical properties of the nanocomposites, but also maintained the initial value of permeability due to better distribution and high compatibility with the matrix. However, the WVP values of specimens containing 5 wt% CNF increased by 38.5%. Generally, the flow rate of water vapor and water vapor permeability in manufactured layers are strongly influenced by the hydrophilic or hydrophobic nature of materials,manufacturing process, type, quantity and distribution of applied additives, the presence of voids and cracks, and final arrangement in polymer structure [33].