Water vapor permeability (WVP) of the film was measured according to the previous study. Briefly, anhydrous calcium chloride (10 g) was put into a glass jar to achieve 0% relative humidity. After covering with film sample, the glass jar was moved into a desiccator containing the saturated sodium chloride solution (25 °C, 75% of relative humidity). Then, the weight of glass jar was recorded at 0, 2, 4, 8, 12, 24, 36, 60 h, respectively. WVP value of the film was calculated as: WVP (g·m−1·s−1·Pa−1) = (m × n)/(a × t × Δp), where m is the change in jar weight (g), n is the thickness of film (m), a is the opening area of the jar mouth (m2), t is the placement time (s) and Δp is the partial pressure difference existed between the two sides of film sample (Pa) [16 (link)].
Oxygen permeability (OP) of the film was evaluated by the oxidative dehydrogenation degree of ascorbic acid, which was determined according to 2,6-dichloroindophenol titration method [17 (link)]. Prior to the test, 1 mL of ascorbic acid solution (0.5 mg/mL) and 10 mL of metaphosphoric acid solution (20 mg/mL) were added into a glass jar. Then, the glass jar mouth was covered with film sample and moved into a box with 70% oxygen concentration atmosphere for 24 h. After that, the solution in glass jar was titrated with 2,6-dichloroindophenol titration solution to just pink, according to the detailed method in previous study. OP value of the film was calculated as: OP (g·m−1·s−1·Pa−1) = (m × n)/(a × t × Δp), where m is the content of oxidized ascorbic acid in jar (g), n is the thickness of film (m), a is the opening area of the jar mouth (m2), t is the placement time (s), and Δp is the partial pressure difference between the two sides of film sample (Pa) [16 (link)].
Oxygen permeability (OP) of the film was evaluated by the oxidative dehydrogenation degree of ascorbic acid, which was determined according to 2,6-dichloroindophenol titration method [17 (link)]. Prior to the test, 1 mL of ascorbic acid solution (0.5 mg/mL) and 10 mL of metaphosphoric acid solution (20 mg/mL) were added into a glass jar. Then, the glass jar mouth was covered with film sample and moved into a box with 70% oxygen concentration atmosphere for 24 h. After that, the solution in glass jar was titrated with 2,6-dichloroindophenol titration solution to just pink, according to the detailed method in previous study. OP value of the film was calculated as: OP (g·m−1·s−1·Pa−1) = (m × n)/(a × t × Δp), where m is the content of oxidized ascorbic acid in jar (g), n is the thickness of film (m), a is the opening area of the jar mouth (m2), t is the placement time (s), and Δp is the partial pressure difference between the two sides of film sample (Pa) [16 (link)].
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