2.1.8.2. Absorbency Under Load (AUL) - BADA

The increase in water uptake at pH 8 might be due to increase in the no net electrical charge at the
surface of the zygomycetes protein, it seems that around pH 8 might be the isoelectric point (pI) of
IZP-hydrogel. It should be mentioned that increasing swelling capacity of hydrogel is not directly
related to the binding of water molecules to ionized carboxyl groups. It could be related to
untangling of the protein chain due to electrostatic repulsion inside the hydrogel network, resulting
in maximum water absorption.
Swelling (g/g)
100
80
60
40
20
0
0 2 4 6 8 10 12 14
Figure 34. Effect of pH in buffer solutions on swelling capacity of the IZP-Hydrogel
3.6.Ⅱ. Kinetics of Swelling
Figure 35 illustrates the swelling kinetic of EDTAD-IZP hydrogel in deionized water as a function
of time. Swelling behavior of the IZP-hydrogel was shown during the 24 h a maximum water
uptake of 87 g water/g dry gel after 24h at 25±2° C. The maximum rate of water uptake was
obtained during first hour, afterward slope increase very slowly up to 24 hours. In fact, the
swelling kinetic of superabsorbent is better to determine up to first hour of immersion.
pH
62