ALTANA BYK-Gardner Permeability Cup - Manual (Page 4)

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section of fi lm.. Knowing the fi lm thickness,
area of fi lm, elapsed time, and the difference
in water vapor pressure on both sides of the
fi lm, a value of the permeability of the fi lm
can be determined in terms of the number of
milligrams of water which permeate through 1
cm² of fi lm, 1 mm thick in 24 hours, at a given
temperature and at a given vapor pressure
differential.
2. The procedure can be reversed. The
desiccator then holds the desiccant and the
aqueous salt solution of known vapor pressure
is placed inside the cup. Again, it is important
to use a solution rather than pure water, or
condensation will occur on the surface of the
test fi lm. This would alter the permeability
values because the permeability of fi lms to
liquid water is usually much different than that
towards water vapor.
The use of the BYK-Gardner cup is not limited to
water alone. By using an active absorbent, such
as charco) or silica gel, the cup can be used to
determine permeability towards organic vapors,
using either of the two techniques described
above. In place of salt solution, it is recommended
that a dilute polymer solution be used so that the
organic solute will not affect the fi nal results. Any
other non-volatile organic solute can also be used
to lower the solution vapor pressure. In working
with organic vapors, it is advisable to condition
the cup and the fi lm in an atmosphere containing
the vapor to be studied. Likewise, when water
permeability measurements have to be highly
accurate, both the cup and the fi lm should be
allowed to equilibrate under some standard set
of conditions. (For example, 20°C, 50% relative
humidity, for 24 to 48 hours before use.)
Description