2.3.1. Swelling Test

The PEG-PU film (the mass labeled m₀) with a size of 20 mm × 20 mm × 2 mm was immersed in sterilized seawater. At regular intervals, the sample was taken out and rinsed with running water, then its surface water was soaked up with filter paper and weighed (the mass labeled m_t).

The swelling rate of the film can be calculated by the following formula:

The density of seawater was about 1 g/cm³ and the density of the PEG-PU film was about 1.08 g/cm³ which was measured in our laboratory. Thus, the swelling rate in volume Sv≈Sm. The swelling degree is the swelling rate reached swelling equilibrium.