Kinetics of water sorption by chitosan and its blends with poly(vinyl alcohol)

Gravimetric and spectrophotometric studies of the kinetics of water sorption from air of various water activities by chitosan of different deacetylation degrees (and molecular weights) and chitosan/poly(vinyl alcohol) blends were conducted. Analysis of the presented results has shown a clear effect of the deacetylation degree of chitosan and the presence of poly(vinyl alcohol) in chitosan blends on water sorption rate. The character of sorption curves, calculated values of diffusion coefficients of water vapour and micropore volumes have shown that the higher chitosan deacetylation (and higher M-w) the lower the sorption of water vapour. The observed effect is explained by a rising ordering of molecular chains leading to an increase of structural packing in chitosan. odification of the chitosan structure in miscible blends with poly(vinyl alcohol) has been reflected in their sorptive properties which depend on the weight fraction of poly(vinyl alcohol) and water activity. Good compatibility of the components, resulting from the presence of hydrogen bonds between specific groups (hydroxyl, amide) of chitosan and poly(vinyl alcohol) chains, causes an increase in molecular packing and thus, a decrease of pore volume and a rate of water diffusion. (C) 2005 Elsevier Ltd. All rights reserved.