Nanoindentation of edible films: A new complementary characterization of nanomechanical properties

The nanoindentation technique has recently emerged as a useful tool for measuring nano and microscale mechanical properties in various materials. In the literature few studies reported the use of this technique on edible films to determinate mechanical properties. Therefore, the aim of this study was to determine the nanomechanical properties of alginate and chitosan edible films using the nanoindentation technique. Alginate, chitosan and alginate-chitosan films were prepared by casting and solvent evaporation method. 1% solutions of alginate and chitosan were prepared with distilled water and 1% acetic acid solution, respectively. The solutions were dried at 60°C to constant weight. Small parts of films were mounted on glass slides with super glue to carry out tests. The Oliver-Pharr method was used to calculate the hardness and elastic modulus from the unloading curve. Chitosan films presented a higher hardness value of 31.92±1.24 MPa, however significant differences were not found between the chitosan and alginate/chitosan films, while the chitosan film had a higher value of 0.769±0.016 GPa. All samples exhibited a creep behavior. Nanoindentation is a new complementary technique, which can be used to characterize the mechanical properties at micro, and nano level of edible films and the obtained parameters can be useful for the design and construction of these kinds of biofilms.