The apparatus for the determination of absorption under
load (AUL) is shown in Fig. 2. Xerogel (0.2 g) was
weighed and spread uniformly inside the cylinder with filter
paper on metal mesh at the base. It was covered with
Teflon disc which could slip freely inside the cylinder but
preserve water absorbed by the hydrogel. Metal cylindrical
load was placed on it (pressure load: 53 g cm2). It was
placed on a filter plate with plastic base inside water basin
and water or 0.9% NaCl solution was added to the level of
the filter plate. The effect of pH was investigated by using
buffer solutions of pH 4, 8 and 9 in place of water. The
weight of the cylinder and moistened filter paper were predetermined.
The moisture content of the Xerogels was also
predetermined with a moisture content analyzer (Sartorius,
Edgewood, NJ, USA). AUL was calculated by the increase
in weight of the hydrogel after specific time
intervals up to 4 h using the following equation.
AUL ¼
WH
WX
ð3Þ
WH ¼ W3 W1 ð4Þ
WX ¼ W2 ðW2 MtÞ=100 ð5Þ
WX = corrected weight of xerogel
WH = weight of hydrogel
Mt = %moisture content of the xerogel
W1 = weight of moistened filter paper + Teflon
disc + cylinder
W2 = weight of xerogel taken
W3 = total weight after absorption