Water vapour permeability and mechanical properties of mixed starch-monoglyceride films and effect of film forming conditions

The effect on water vapour permeability (WVP) and mechanical properties of an addition of various amounts of an acetylated monoglyceride (Acetem) to native potato starch (NPS) films was studied. Phase separation was also evaluated by drying the films at different temperatures, since phase separation between starch and Acetem is affected by temperature. Films were gel-cast from a heated solution of NPS (3%). Five different concentrations (0-10%) of Acetem based on NPS were added to the solution and the films were dried at three different temperatures (23, 35 and 50 °C). The film properties were evaluated by measuring thickness, moisture content (MC), WVP and mechanical properties and the results were then evaluated with multivariate analysis. The MC was slightly reduced in the films dried in higher temperatures, despite reconditioned samples, and the film thickness increased with an increasing amount of Acetem. The WVP of a pure NPS film was decreased by 27 and 37% with addition of 10% Acetem or high drying temperature, respectively. The mechanical properties were affected mainly by changes in Acetem concentration. A greater amount of Acetem decreased Young's modulus, stress at break and strain at break. Micrographs showed extensive phase separation in the films, but pure bilayer films were not formed.