Use of transient and steady-state methods and AFM technique for investigating the water transfer through starch-based films

► Preparation of starch-based films ► Measurement of the diffusion coefficient using two methods: stationary and transient. ► Evaluation of film surfaces at different RHs. The aim of this study was to investigate the water transfer properties of starch films using steady-state and transient methods and to evaluate the influence of air relative humidity on the film roughness using atomic force microscopy (AFM). Films were prepared with 3% starch and 0.3g glycerol/g dry starch. Composite-films were prepared with the addition of 0.3g cellulose/g dry starch. Water transfer through the films exhibited a dependence on the relative humidity RH. Using AFM, film roughness was observed to increase from a few nanometers to 45nm over 1.5h when the films were exposed to high RH. Results indicated that the equilibrium conditions at the film surface were not reliable boundary conditions and that the diffusion coefficients determined by both transient and steady-state methods may be different because they were determined at different conditions. Further studies of water permeability, assisted by AFM, could be performed for a better understanding of film barrier properties.