Therewas no difference in the water vapor permeability
of the uncoated TPS25/PLA and TPS30/PLA sheets, i.e., the
glycerol concentration in the blend did not affect the permeability of the sheets, as also observed for the solubility.
This behavior may be due to the presence of PLA,
which stabilized the water vapor barrier properties of these materials.
The spray-coated TPS25/PLA sheets presented around
35% lower permeability than the uncoated sheet. The
permeability of TPS30/PLA sheets, with and without
coating, showed no differences except for the sheet coated by immersion (2x).
The process of water molecule permeation through the
sheet occurs via the simultaneous effects of the solubilization process and the diffusion of water molecules in the
polymeric matrix. Thus, a reduction in the permeability
was expected for the chitosan coated sheets due to
a reduction in the overall solubility and diffusion coefficients, since chitosan has a hydrophobic character.
However, only a few sheets showed a significant difference.