A new insight to the effect of calcium concentration on gelation process and physical properties of alginate films

A series of alginate films were prepared using constant alginate content (2 % w/v) with various calcium chloride (CaCl₂) concentrations in the crosslinking solution (0.375–6 % w/v). Then, the initial investigation of how the CaCl₂ concentration affected the gelation process and physical properties of alginate films was established. A combination of Fourier transform infrared spectroscopy, swelling test, inductively coupled plasma optical emission spectrometer, and energy-dispersive spectroscopy analysis showed that the gelation process of alginate films evolved with the increase of CaCl₂ concentration, which resulted in different crosslinking density and entanglement of alginate molecular chains. Moreover, the increase of CaCl₂ concentration improved the visual appearance, surface homogeneity, and tensile strength, while the elongation at break and swelling capacity of the film were decreased monotonously. As a compromise between film strength and flexibility, performing effective absorption capability as well as the product appearance, the concentration of 1.5 % w/v CaCl₂ in the crosslinking step was recommended. These various physical properties of obtained alginate films could be attributed to the shaped crosslinking density and molecular entanglement characteristics during crosslinking.