*2.7. Microscopic Images*

The surface of the SA composite film sample was plated with a layer of gold, and then placed in a vacuum environment to observe the surface morphology of the prepared sample using a field emission scanning electron microscope (SEM, NOVA NANOSEM-450, FEI Co., Ltd., Hillsboro, OR, USA)

## *2.8. Water Vapor Permeability (WVP)*

The ability of SA film to block water vapor was measured referring to ASTM E96-95 standard method. Twelve grams of anhydrous silica were put into the weighing cup. The prepared film was cut to a uniform size to seal the rim of the measuring cup. Finally, the weighing cup was placed in a desiccator at 25 ◦C and 50% relative humidity. The samples were placed in a desiccator to measure the weight of the weighing cup at an interval of 1 h for a total of 12 h, and three samples were set in parallel for each type.
