Pre-test of water uptake kinetics showed no further increase
of sample quality after 30 min. Thus, all water uptake tests were
fixed on 30 min to determine the final weight of soaked chitosan
films. Typically, weighted chitosan films (w1) were immersed in
100 ml distilled water for 30 min in a water bath with temperature
controlled at 20 ◦C. Then the swollen samples were vacuum
filtered for 30 s to remove the surface water. Finally, the weight
of swollen sample (w2) was measured. The water uptake capacity
of chitosan film was calculated from the formula of (w2 −
w1)/w1.
For testing the effects of pH and salt concentration on the water
uptake capacity, the solutions were adjusted with 0.01 mol/l HCl or
NaOH, or added sodium chloride with concentration in the range
of 0.05–0.2 mol/l.