Proper selection of the right desiccant can be inexpensive insurance
for protecting your packaged product. Product quality can be improved,
resulting in reduced or eliminated customer rejections.
When dealing with moisture problems in packaging, a wide array
of variables can make it difficult or confusing to develop solutions.
These variables can be classified into two main groups:
1) those pertaining to the product, its package, and the environment;
2) the physical and chemical properties of commercially available
Formal testing can become quite costly in time and money, and the
purpose of this entry is to provide basic information about currently
available desiccants and their properties. We hope it will help
you to make better informed selections.
What Size Desiccant Do I Need?
It depends. The answer to the size of desiccant needed depends on
the size of the air space to be desiccated, the nature of the material
in the package, the moisture barrier surrounding the package, the
type of desiccant being used, the desired shelf life, the atmosphere
conditions where the package is sealed, the type of seal on the
Dri-Box has an approximate effective desiccating area of three
feet of sealed cubic space, an area our Moisture Control System
barrier bags are careful not to exceed. In the case of other desiccants,
you should contact us.
We will usually ask a new customer a number of questions to determine
the above variables, so that we can calculate which size desiccant
will work best in a particular application.
How Does The Environment Factor In?
Temperature, relative humidity and other considerations constitute
the product's environment, which must be controlled to match the
conditions of optimum product preservation and performance. Before
selecting the correct desiccant, professional packaging engineers
review the conditions surrounding the shipment and storage of the
product: the extremes of temperature and relative humidity to which
the product will be exposed and the average duration of such exposures.
The most useful combined measure of temperature and relative humidity
is the dew point. Dew point is the temperature at which the water
vapor content of the air exceeds saturation and the excess water
is squeezed out, forming dew or condensation. The dew point varies
with the amount of water vapor in the air. It is low with dry air,
and high with saturated air.
For example, at zero°C, the air can hold no more than 4.84
gm/m3 of water vapor; at 40°C the air can hold no more than
50.7g/m3 of water vapor (see the related chart for more details.)
An effective desiccant will adsorb the water vapor in the air,
lowering the relative humidity to the point where water cannot condense.
Is Packaging An Issue?
The container in which the product will be packaged, shipped and
stored is vital in determining how much of a particular desiccant
is needed and in what packaging form. Before the adsorbent selection
process itself, a packaging engineer determines the size of the
container based on the flexibility of the container's wall structure.
An important factor in the efficiency of the selected desiccant
is the bag material (cover stock) of the desiccant. The cover stock
must allow the desiccant to do its job without harming the product.
This means maintaining an acceptable adsorption rate and conforming
to the product's dusting requirements.
The selected desiccant's adsorption rate is greatly affected by
the water vapor transmission rate of its cover stock. This is the
measure of the gain or loss of water vapor through the package of
the bagged desiccant. By their nature, certain products require
a very non-dusting desiccant bag to maintain their integrity. While
dealing with dusting requirements, however, the packaging engineer
encounters another problem: in preventing the release of dust into
the container, the water vapor transmission rate is often adversely
The search for a solution has led to the development of substances
such as a spunbonded, high-density polyethylene material known commercially
as Tyvek®. Created by DuPont, Tyvek resembles a waxy paper with
good whiteness and exceptional strength, maintaining its size and
shape with changes in humidity. It will not allow dust to be released
into the container, is resistant to staining, mold and mildew growth,
and will not reduce the adsorption rate of the desiccant it holds.
Because of its special properties, Tyvek is more expensive than
conventional desiccant package materials. The Moisture Control System's
barrier bags are composed of polyethylene bonded to a specialized
grade of aluminum foil for extra strength. See our specific page
on the system for more detailed information.