Absorcare Desiccant Technology

What is desiccant and what does it do?
A desiccant is a dehumidifying agent which attracts moisture from the atmosphere. It adsorbs and holds particles of water to itself.

The three most common types of desiccants are clay, silica gel, and molecular sieve.

What are clay desiccants?
Clay desiccants are non-hazardous, moisture adsorbent substances created by the controlled drying of a calcium (bentonite) aluminosilicate clay. This naturally occurring montmorillonite clay has a special affinity for moisture and is chemically inert and non-corrosive. The layered structure of clay desiccant attracts and adsorbs moisture onto its surface and between its layers.

Absorcare Clay Desiccant will protect the contents of a properly sealed container during shipping and storage (i.e., the contents of a sealed container will be in the same condition as when they were packaged for shipment or storage).

Clay is the least expensive of all desiccants and highly effective within normal temperature and relative humidity ranges. It is used in most industrial applications requiring humidity control. Clay desiccant can adsorb up to 28% of its weight in water vapor at 77°F (25°C) and 80% relative humidity. At full moisture vapor capacity, Desi Pak remains dry and free-flowing. There is no apparent change in size, shape, or texture of the desiccant.

Clay desiccant works satisfactorily below 120°F (49°C). Above 120°F (49°C), there is a possibility that the clay will give up moisture rather than pull it in (silica gel or molecular sieve are suitable for such temperatures). Accordingly, anticipated storage and transportation conditions should be considered when deciding whether or not to use clay.

What is silica gel?
Silica gel is silicon dioxide (SiO2), an amorphous form of silica which is manufactured from sodium silicate and sulfuric acid. It is a naturally occurring mineral that is purified and processed into beaded or granular form. Like clay desiccant, silica gel is also non-corrosive and chemically inert.

Much like a sponge, silica gel's interconnected pores form a vast surface area that will attract and hold water by adsorption and capillary condensation, allowing silica gel to adsorb about 40% of its weight in water vapor at 100% humidity.

As a desiccant, silica gel has an average pore size of 24 angstroms (24A). Silica gel desiccant will pull in moisture at temperatures up to 220°F (104°C). As temperatures increase above 100°F (38°C) the rate of moisture pick-up will slow down, but the silica gel will still work. Silica gel performs best at room temperatures between 70°F to 90°F (21°C to 32°C) and at high humidity between 60% to 90% relative humidity.

Absorcare Silica Gel Desiccant is designed to control moisture levels within a properly sealed container during shipment and storage. At 77°F (25°C) and 80% relative humidity, Sorb-It can adsorb approximately 35% of its weight in water vapor. However, unlike a sponge, Sorb-It remains dry and free-flowing at maximum adsorption capacity.

Desiccant City also offers several types of bulk silica gel.

What is indicating silica gel?
Indicating silica gel is a bead or granule that has been washed with a concentration of cobalt chloride (a heavy metal salt). The cobalt chloride is a deep blue color when dry and turns from blue to purple to pink as it becomes saturated with moisture.

Desiccant City also carries orange indicating silica gel. This type is a bright orange color when dry and turns green as it becomes saturated with moisture.

The most common form sold by Desiccant City is bulk silica gel, primarily used in air drying applications.

Another use of indicating silica gel is with a moisture sensitive product that will be inspected regularly, as the indicating silica gel gives a quick visual indication of how well the product is doing. Due to the presence of cobalt chloride, indicating silica gel desiccant should never be used in contact with products for consumption, such as food or pharmaceuticals.

Indicating silica gel desiccant is also available in special packet sizes for use in electronics, pharmaceutical, or food packaging.

What is molecular sieve?
Molecular sieve is a synthetically produced crystalline metal alumosilicate zeolite. Molecular sieve particles have a uniform pore structure (created during the manufacturing process). This enables molecular sieve to separate molecules by size. It is also non-hazardous and derived from naturally occurring materials.

Molecular sieve is the desiccant of choice for the most demanding and unique applications. The pore structure of molecular sieve desiccant provides a higher capacity for water adsorption than either silica gel or clay at very low humidity levels. Molecular sieve also retains a higher percentage of moisture capacity at elevated temperatures; in fact, molecular sieve can hold moisture at temperatures well past 450°F (232°C). Because of its high affinity for moisture, molecular sieve is able to bring the relative humidity in packages down as low as 10% relative humidity.

The most commonly used pore size for drying applications is 4 angstroms (4A). Molecular sieve desiccant is also available in 3 angstroms (3A), 5 angstroms (5A) and 10 angstroms (13X) sizes for specific molecule separation, including gases.

Molecular sieve is the most aggressive of the primary desiccants (in terms of adsorption rate), so additional handling procedures may need to be considered.

Absorcare Molecular Sieve is for controlling moisture levels in sealed containers during shipment and storage. Desiccant City also offers several types of bulk molecular sieve.

What is a desiccant "unit"?
In desiccant terminology, a "unit" is the quantity of desiccant required to meet the U.S. Military's specification (MIL-D-3464E) for packaged desiccant products. Under this specification, a unit is the quantity of desiccant which will adsorb 3.00 grams of water vapor at 20% relative humidity or 6.00 grams of water vapor at 40% relative humidity at 77°F (25°C).

When do I need to include a humidity indicator card in my package?
You need a humidity indicator card if you are concerned as to whether or not the desiccant in your package is still active. Desiccant becomes inactive under the following conditions:

if your package is not properly sealed
if you don't use enough desiccant in your package to draw down the relative humidity
if the barrier material (i.e., plastic bag) you use to package your product has a high moisture vapor transmission rate (which means that a significant amount of humid air is entering your package through the barrier material itself).

How does desiccant most effectively protect my product or package?
In order to achieve optimal protection, desiccants should be used within a closed/sealed moisture barrier or a rigid/sealed container. Humidity Indicator Cards are generally placed inside the container to show the humidity level and to indicate when the desiccant needs to be replaced.

What industries and products use desiccant?
The largest users of desiccants are the industrial, pharmaceutical, and the electronic components packaging industries. The following list shows examples of the types of industries and products that use desiccant products:

Industries

• Aerospace
• Automotive
• Communications
• Dental
• Diagnostic
• Electronics
• Filmmaking
• Food packaging
• Industrial
• Medical
• Military
• Nutraceutical
• Optics
• Packaging
• Pet food
• Pharmaceutical
• Textiles

Products

• Batteries
• Bulk powdered chemicals
• Cholesterol tests
• Circuit boards
• Documents and paper storage
• Electronic components
• Foodstuffs
• Glucose tests
• Industrial equipment
• Instruments
• Leather products
• Medical equipment
• Metal and machine parts
• Metal powders
• Military instruments and armaments
• Motors
• Museum storage
• Oceanographic devices
• Optical devices
• Pet foods
• Photographic equipment and film
• Powdered or beaded glass
• Pregnancy tests
• Relays and communication devices
• Safes
• Semiconductors
• Vitamins

How much desiccant do I need?
It depends. The amount of desiccant required is usually dependent on the following factors:

• volume of air space to be desiccated
• nature of the material to be protected
• moisture surrounding the package
• type of desiccant to be used
• length of time for protection
• atmospheric conditions (temperature and relative humidity) when/where the product is sealed and during subsequent shipment and storage

To determine the number of "units" required to protect medium to large products/packages/areas, refer to the Desiccant Requirements Chart Unit Sizes.

To determine the number of "grams" required to protect small products/packages/areas, refer to the Desiccant Requirements Chart Gram Sizes.

You may also use our Desiccant Calculator to determine the amount of desiccant for your application.