Thermodynamic study of water sorption and water barrier properties of nanocomposite films based on brea gum

Water transport in edible films based on hydrophilic polymers is a complex phenomenon due to the strong interactions of sorbed water molecules with the polymeric structure. The effect of montmorillonite (Mt) nanoparticle incorporation into brea gum (BG) based films was studied through thermodynamic and phenomenological analyses. Moisture adsorption isotherms at three different temperatures of BG based films and BG/Mt nanocomposite films were obtained. Thermodynamic parameters showed an exothermic process that results less favourable when Mt is incorporated into the BG matrix, reducing the water uptake. Entropy change and net isosteric heat of adsorption showed a peak at monolayer water content, which is greater in composite films, indicating a more stable and ordered structure when Mt was added. Gibb's energy was indicative of process spontaneity and of the lower affinity to water composite films. Water vapour permeability depends on the tortuosity of the pathway formed by Mt nanoparticles and solubility of water molecules into the BG film matrix. Mt incorporation reduces the hydrophilic character of BG based films and thus their water vapour permeability.