Water vapor barrier and mechanical properties of starch films containing stearic acid

Polysaccharide is often used as a low-cost renewable source for the manufacture of films. Starch films present appropriate mechanical and oxygen barrier properties, but are sensitive to humidity. In order to improve their water vapor permeability the addition of lipids such as stearic acid to starch films has been studied. The films were prepared using different concentrations of stearic acid (3.76-12.24 g/100 g dry starch) and glycerol (21.76-30.24 g/100g dry starch). The suspensions were prepared as emulsions, using a stirring frequency of 200 Hz (12,000 rpm). The effects of the stearic acid concentration and glycerol on the mechanical properties, solubility in water and water vapor permeability were evaluated using response surface methodology (RSM). It was found that the addition of stearic acid to starch films affected the mechanical properties. Moreover, films elaborated with 4 g stearic acid and 24 g glycerol/100 g starch presented reductions in the water vapor permeability (WVP = 1.93 x 10(-7) gm/m(2) Pa h) and solubility in water (S congruent to 25%). This work demonstrates that the addition of stearic acid to films could be an alternative to reduce their solubility in water and water vapor permeability, thus promoting their physical properties. (C) 2012 Elsevier B.V. All rights reserved.