2.1.8.2. Absorbency Under Load (AUL) - BADA

The first step was weighted a 30 mg (0.03g) of dried sample in non-woven heat-sealable pouch
(like to a tea bag).The sealed pouch was immersed in 200 ml deionized water for 24h at room
temperature (25 ± 2 o C).Then the pouches were centrifuged in a clinical centrifuge at 214 × g with
sample holders containing plastic wire mesh for suitable drainage of the excess water from the
swollen gel (The Vivaspin 20ml centrifugal concentrators from Sartorius). The sample was
weighted instantly and the wet weight of swollen gel was determined. Afterward the wet pouch
with swollen gel was dried in oven at 104 o C to constant weight. Finally, the water uptake of gel
was measured in different times by the weight of wet gel divided by the weight of dried gel
according to the following equation (1):
111111111111111111111 W – Wo
Water uptake (g/g) =
(1)
Wo
Where W is the weight of swollen gel and W0 is the weigh of dried matrix [17] .
2.1.6. Swelling Kinetics
Absorption rate or swelling rate contains diffusion of liquid into the polymer networks. Several
methods have been employed to achieve swelling kinetics of hydrogels [1] . In this study, the
equilibrium swelling of crosslinked protein hydrogels upon immersion in liquids as a function of
time have been investigated. Figure 24, 34 show the swelling rates of the EDTAD-AP and
EDTAD-IZP hydrogels in deionized water. By this way, swelling rates were measured for all
samples of AP and IZP-superabsorbent hydrogels at 25±2° C by gravimetric technique. A weighed
amount of dried gels were pocketed in heat-sealable pouches and allowed to swell in deionized
water. After the exact time, the bags removed and centrifuged at 214 × g for 5 min in a clinical
centrifuge with sample holders containing plastic wire mesh for accepted drainage of the excess
water to the bottom of the holder, thereafter the weight of swollen gels were determined
immediately. The wet pouches were dried in an oven at 104 o C to constant weight. As a result,
absorbency was calculated as a gram of water per gram of dried gel (g/g) according to Eq.1 at
period of constant time.
37