The pH of the water will have little
effect on the absorption potential within the range of 5 to 10. It must be
remembered that the pH is not a measure of the salt concentration and a
neutral pH does not necessarily mean that the water is not high in salts. In
an eight per cent calcium chloride solution swelling is reduced by a factor
of ten. In the presence of high levels of iron and aluminium an external
skin can be formed on the polymer, which greatly reduces the water retention
capacity.
WATERLOCK is virtually unaffected by short exposure to boiling water. After
prolonged exposure a certain amount of hydrolysis of the polymer may occur,
especially at high pH. This hydrolysis will have a limited effect on the
water absorbing capacity of the polymer. Water held by the polymer is fixed
and not sensitive to removal by pressure or centrifugal forces until above 5
bars is exerted.
The stability of the polymer to bacterial degradation is variable depending
on number of factors. In aerobic condition little degradation is observed
and the polymer may be expected to function well for at least five years. In
anaerobic conditions the polymer can be broken down by the ferrous ions
created by the action of sulphate reducing bacteria.
Mechanism To understand how this polymer functions to absorb
water, we can consider a simplified model of a single molecule. Each
molecule can be represented by parallel rows of the principal atoms with
periodical bridging links between them. When water comes into contact with
these rows an electrical repulsion between rows is generated, rather as in
the poles of magnet, and the rows move apart. This draws more water into the
molecule and the rows move further apart. This results in a rapid swelling
of each particle. The water can be removed from the polymer either by
evaporation or by exerting pressure beyond 5 bars. The molecule on losing
water contracts to its original size. This swell and shrink cycle can be
repeated indefinitely.