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.