This complexation might decrease the free volume of the polymeric matrix and lead to the formation of a denser polymeric matrix,thus decreasing the diffusion rate of water molecules through the bilayer coatings.
The enhanced water-vapor-barrier properties of composite films as compared with those obtained from the pure polymers have been reported for gelatin/chitosan (2013) and gelatin/gellan (2007) composite edible films.
However, Pereda, Aranguren, and Marcovich (2009) found increased WVP of caseinate based edible films when chitosan was added. These authors concluded that the high-humidity conditions (100/64.5 RH gradient) might affect the interactions between chitosan and caseinate and cause a conformational change in the microstructure of the blend film, as a result of swelling.