Effect of plasticizers and fatty acids on mechanical and permeability characteristics of chitosan films

Chitosan films were prepared by blending with polyols (glycerol, sorbitol and polyethylene glycol (PEG)) and fatty acids (stearic and palmitic acids) and their mechanical and barrier properties studied. The tensile strength of the blended films decreased with the addition of polyols and fatty acids, whereas the percent elongation was increased in polyol blend films, but fatty acid blend films showed no significant differences. Glycerol blend films showed decrease, whereas sorbitol and PEG blend films showed increase in the water vapor permeability (WVP) values. No considerable differences in WVP were observed in fatty acid blend films. Equilibrium moisture content of all the films was low at lower water activity (a(w)), but increased at higher a(w). Eight moisture sorption models were applied to experimental data. The various constants determined by linear fitting of the sorption equation with R-2 values were in the range of 0.92-0.99. The GAB model showed the best fit over the entire range of a(w) with root mean square error (RMSE) of 2.75 and 6.36 for native and blended chitosan films, respectively. While the BET model was applicable in the low a(w) (0.11-0.45) range with RMSE values ranging from 1.95 to 9.55. (C) 2006 Elsevier Ltd. All rights reserved.