WATER-VAPOR PERMEABILITY AND DIFFUSIVITY THROUGH METHYLCELLULOSE EDIBLE FILMS

A model edible film made with methylcellulose was studied for its wate r vapor barrier properties. The steady-state water vapor transmission rate (WVTR) increased with both the water vapor pressure gradient and the initial water content before permeation. A decrease in water diffu sion with increasing moisture content was due to a clustering phenomen on of water molecules within the film. Water concentration profiles wi thin the film were estimated from the sorption isotherm, and differed from the theoretical linear profile based on Fick's first law. The WVT R and the diffusivity depended strongly on the water concentration bec ause of interactions between water molecules and the polymer matrix. T hus water vapor permeability (WVP) calculations used for synthetic pol ymeric packaging and based on Fick's and Henry's laws do not apply for methylcellulose edible films.