The two
parameters most commonly used to characterize the properties of absorbent
products are the rate of absorbency and the total absorbent
capacity. The former determines the rapidity with which fluid is imbibed
while the latter determines the total capacity of the material to absorb
and hold fluid. A schematic diagram of the Gravimetric Absorbency Testing
System (GATS) is shown in the figure below.
Figure 1
In this device set up, the fluid is absorbed radially outward along the
plane of the sample from a single point of 1/4 inch diameter in the bottom
of the test plate. The GATS is interfaced with a recorder which provids
a plot of the amount of fluid absorbed as a function of time. The samples
used were die-cut from test fabrics with a circular die of 3.5 inch diameter
(62 cm2) and weighed.
To conduct a test, a test specimen is positioned on the sample plate.
There is a 2 mm diameter hole at the center of this sample plate that
is connected to a fluid reservoir. The level of the cell is adjusted to
give zero hydrostatic head. This guarantees that absorbency takes place
strictly on demand. A solenoid valve supplies fluid from the fluid reservoir
equal to the amount the specimen can absorb. A fluid sensor automatically
weighs the amount of water supplied, maximum absorbent capacity, V. This
resultant absorbency rate is measured in the range between 20% and 80%
of the maximum absorbent capacity. A computer system plots it with time
function. A typical graph of amount absorbed against time is shown below.
From the output, specific maximum absorbent capacity, C, and flow rate, Qo,
are determined in the unit of grams fluid/minute. Specific flow rate, Q,
is calculated by dividing the flow rate, Qo, by the weight of the dry fabric,
W, (grams fluid/grams dry fabric.min). Specific details are given below.
Experimental Conditions:
Test fluid: distilled water
Parameters:
Maximum absorbent capacity, V, total amount of fluid absorbed in grams for
a given sample area of 62 cm2
Weight of dry fabric, W, in grams.
Time, T, in seconds.
Specific absorbent capacity, C = grams of fluid/grams dry fabric weight:
C=V/W
Flow rate, Qo = grams fluid/min:
Qo =V/T
Specific Flow Rate,
Q = grams fluid/grams dry fabric·min:
Q=Qo /W
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