Heat treatment of calcium alginate films obtained by ultrasonic atomizing: physicochemical characterization

Planar films of calcium alginate were obtained using an ultrasonic atomizing device. Sodium alginate solutions of 0.6% and 0.9% (w/v) were nebulized with calcium gluconolactate solutions (gelling agent) of 0, 1, 2 and 3% (w/v) at a flow rate of 0.3 mL min−1 for 20 min. After drying, thickness and mechanical properties were determined. In view of the results of mechanical properties, manageability and flexibility, calcium alginate films obtained using 0.9% sodium alginate and 2% calcium gluconolactate were selected as “optimum dry film” samples. These samples were cut into rectangular pieces and heated at 180 °C for 0, 4, 8, 12, 20 and 24 min. Thickness, mechanical and optical properties, differential scanning calorimetry (DSC) thermograms, Fourier transform infrared spectroscopy (FTIR) spectra, and scanning electron microscopy (SEM) micrographs were analyzed in order to characterize the physicochemical properties of heat-treated samples. The heat treatment produced thickness reduction, a yellow ochre color development and an increase in the brittleness of the films. DSC, FTIR and SEM studies suggested that heat treatment produced further dehydration of dry films and thermal dehydration–degradation of alginate macromolecules.