A desiccant is a hygroscopic substance that induces or
sustains a state of dryness that is nothing but called as
desiccation, in its local vicinity and in a moderately well-sealed
container. Commonly the encountered pre- packaged desiccants are
solids, that work through absorption or adsorption of water, or
combination of both. Desiccants
may be in forms other than solid that are used for specialized
purposes, and may work through other principles, like chemical
bonding of water molecules.

Pre- packaged desiccant is the most commonly used, to remove
excessive humidity from the package products that would normally
degrade or sometimes even destroy the products sensitivity to
moisture. silica gel, activated charcoal, calcium sulfate, calcium
chloride, montmorillonite clay, and molecular sieves, etc, are some
of the commonly used desiccants. Silica gel is mostly used in musical
instrument cases. Rice is other common \"low-tech\"
alternative that is used frequently as desiccant. Rice, however, is
not a good “general purpose desiccant”, unless it is immersed in
pure concentrated salt, an organism-hostile environment, which
results in degrading of the creatures or bacteria in meantime, that
might contaminate the product that is preserved. Salt itself is an
effective desiccant, used in preparation of dried food and also to
mummify the corpses.

A specific usage of a desiccant would be placing it inside the
spacer between the air spaces and window edge in an insulated window.
This prevents moisture to condensate between the panes. All the
products offered are highly equipped with facilities approved by the
US FDA. It is important to understand how the desiccant does
its job that is protecting a product from environmental humid and
moisture that help in growth of fungi, bacteria under non recoverable
conditions. Most porous adsorbents, such as silica gel, activated
clay or molecular sieves rely upon the phenomenon of physical
adsorption rather than chemical adsorption to vanish the bacteria,
and that is nothing but acting as oxygen
adsorbents, sucking out the filled in air
or oxygen present in pores of planes, in which product is stored.

Let us actually discuss this desiccant phenomenon of physical
adsorption that is oxygen adsorption. Physical adsorption is the
phenomenon that involves relatively weak intermolecular forces (van
der Waals molecular forces and electrostatic interactions) between
the moisture and surface area of the desiccant. Process of Physical
adsorption of moisture is typically exothermic. Measuring the heat of
adsorption can tell us the strength present between the absorptive
bonds. The higher is the heat of adsorption for moisture on
desiccant, the stronger is the bonding and the lesser is the chances
that the moisture can be subsequently removed easily.

It is otherwise for porous desiccants, such as the silica gel used
by a Dri-Box, water is removed from the airspace by following 2
mechanisms, that can be laid as multi-layer adsorption, in which, the
attraction between thin layers of water molecules is to the surface
area of the desiccant. Because the desiccant is very porous in
nature, the surface area is high and significant amounts of water in
large can be attracted and adsorbed. And the second mechanism is by
capillary condensation in which the smaller pores present, get filled
with water, and this can be termed as Capillary condensation, that
occurs because of saturation of the water vapor pressure in a small
pore and is reduced by the effect of surface tension.

Are
Desiccants Rated? If yes, How?

Packaging engineers face a confusing array of variables while
selecting the moisture adsorbents, partly because moisture control is
known to be a multifaceted challenge. There are four sources of water
contamination in a closed container or package, to elaborate this:
one is the water vapor present in the air, inside the package; second
is the water vapor being adsorbed by the materials inside the
package;
and then the third is the water vapor presenting
themselves on the walls of the package; and then the last fourth
sequence would be the permeation of water vapor into the package. So,
it can be clearly stated that a desiccant acts as nothing but
clearly as an oxygen adsorbent.

Following the history, desiccants are chosen by
application-testing method, often known as trial and error method.
These trial and error variables being selected can be classified into
two main groups of the variable molecules those pertaining to the
product, its package and its environment and the various available
commercial properties of desiccants. Through firsthand testing and
published research, the packaging engineer determines the conditions
and the surround cover around the optimum product preservation and
performance. In attempting to meet and maintain these suitable and
necessary conditions, anyone would often encounter moisture and its
acquaintance career hazards like corrosion, rust, mold, mildew,
fungus, swelling and other undesirable factors that are regularly
affecting product integrity. Do we have answers for that now?

As a result, the packaging engineer may be at a loss of choosing
with confidence whether which particular desiccant is best for each
of the project application. Thus, an engineer must move outside from
the limited scope of military specifications, into the real world of
moisture-proof packaging, thats nothing but a product\'s environmental
package, and thats a desiccant.