Modeling Water Vapor Sorption and Permeability in Starch-Montmorillonite Nanocomposite Films

Abstract

The aim of this study was to investigate the rate of water vapor permeability (WVP) and moisture sorption of starch-montmorillonite (MMT) nanocomposite films. The nanocomposite films were prepared using the casting method andglycerol was used as a plasticizer. The effect of glycerol concentration on WVP of the films was determined at 25°C with a relative humidity of 0-99% (inside and outside of the vials). The results showed that WVP is increased with higher glycerol content in the nanocomposite samples and there is an exponential relationship between the plasticizer concentration and WVP of the nanocomposite films. Additionally, moisture sorption kinetics of nanocomposite samples was studied by placing the films in humid environments conditioned at 25°C and 75% relative humidity. In addition, the Fick's second law and four empirical equations were used to predict the films moisture sorption and the results of the modeling demonstrated that the initial stages of moisture sorption were fully supported by Fick's law. However, by the gradual relaxation of the polymer, its behavior deviated from the law. This result indicated that the concentration gradient was not the only dominant mechanism of mass transfer. The effective moisture diffusion coefficient (D) was increased with increasing MMT concentration. This was attributed to the penetration of clay layers into polymer matrix in the amorphous regions and creation of free spaces in polymer structure. The existence of free spaces in the nanocomposite structure increased the effective moisture diffusion coefficient. Additionally, plasticizer presence facilitated mobility of polymer chains and increased the effective moisture diffusion coefficient.

Keywords

• modeling
• mass transfer
• starch
• nanocomposite
• montmorillonite