2.1.8.2. Absorbency Under Load (AUL) - BADA

Results showed the effect of ethanol on the swelling properties of EDTAD-AP and IZP
superabsorbent hydrogels were more preferable than isopropanol and acetone respectively,
because of the extent of swelling capacity of hydrogels which treated with isopropanol and acetone
were lower than hydrogel that treated with ethanol.
The effect of pH in buffer solutions (pH 3-12) on swelling capacity of the AP and IZP
superabsorbent was also investigated. This study provided evidence to introduce isoelectric points
in both AP and IZP superabsorbent hydrogels. The isoelectric point is importance in protein
purification because it is the pH at which solubility is frequently minimal and mobility in an
electrofocusing system is zero to form folded protein. The isoelectric points in the anionic proteins
which have anionic hydrophilic groups in their structures demonstrate at certain alkaline pH
contain uniform equilibrium charge distribution on their surface.
According to results and schematic diagrams of the AP superabsorbent (Fig.23), the isoelectric
points with maximum of swelling is around pH=9 and for IZP superabsorbent is around pH=8
(Fig.34). In this form the modified protein hydrogel surrounded by water due to minimum
repulsion compare to high concentration of charged particles in acidic or basic conditions.
As follow, the swelling kinetics AP and IZP superabsorbent were surveyed in deionized water.
Water uptake of AP and IZP superabsorbent hydrogels increased during first hour quickly and
reached a maximum water uptake level of 296 g water / g dry gel after 24 h for AP superabsorbent
hydrogel, this amount was 87 g water / g dry gel after 24 h for IZP superabsorbent hydrogel.
Among the reasons, the initial quick rate might be due to penetrate water into the hydrogels
networks by charged groups. The decrease in the swelling rate of hydrogels after the first hour
indicates to repulsion of hydrophilic groups inside the hydrogels network and difference in
osmotic pressure between the internal of the hydrogels and the external solution until the
equilibrium swelling is reached.
To this end, the infrared spectroscopy (FT-IR) was carried out to approve the chemical structure of
the unmodified and EDTAD-modified AP and IZP superabsorbent hydrogels.
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