How Much Desiccants To Use?

What is a Desiccant?

Desiccants are compounds whose primary purpose is maintaining a low-humidity environment by absorbing excessive moisture in the air or within a packaging. Two of the most common desiccants are silica gel and montmorillonite clay.

Desiccants are typically used in storage facilities, transportation containers and maintenance facilities. They also come in handy to keep everything from military munitions to preventing mould on shoes. Because desiccants can protect paper from high humidity, moisture absorbers are used to preserve art in display cases. The moisture absorbers also protect metal parts from rust and prevent silver tarnishing.

Desiccant packs can be placed alongside food items because food-grade desiccants are not toxic or harmful. However, desiccants should not be consumed directly. Consumption of desiccants may result in nausea, vomiting and headaches.

Desiccants and Moisture Damage

Water contamination in a closed package or container is a common problem in industrial, commercial and home settings. A desiccant can help with the following:

• Water vapour content of the air within a package
• Moisture within the material the package is made of
• Moisture on and in the walls of a package
• The penetration of moisture into a package

Minimising the Risk of Water Damage

Moisture penetration and water damage can be costly and inconvenient. Manage these risks by assessing these factors:

Product Integrity

Different materials and substances react and resist differently when they come into contact with moisture. Food products, for instance, are easily susceptible, while plastics are far less so.

Packaging Integrity

Apart from the product, the packaging of the product also plays a role in the selection of the desiccant. Consider the following when deciding on the packaging:

• Package contents
• Volume of the package that has to be protected from moisture
• Atmospheric conditions at the time and place of packaging
• Atmospheric conditions around the package before and during shipment and/or storage
• Relative humidity and temperature around the package before and during shipment and/or storage
• Duration of shipment and/or storage
• Choosing the right type of desiccant

Base Environmental Conditions

Relative humidity and temperature affect both the packaging’s integrity and the air’s moisture level. Different containers and products can withstand varying levels of environmental pressure. Determine the conditions to maximise the packaging and product’s integrity. The environment’s readings will also help select the best type of desiccant.

Evolving Environmental Conditions

Environmental conditions rarely remain unchanged over the course of shipment and/or storage. Determine factors such as:

• location
• weather
• seasonal changes
• climate control settings
• duration of protection required
• possible emergencies

Over time, the range of values of these aspects will give a clear picture of the type and level of moisture protection required. Use data loggers to monitor the humidity levels and temperature changes during transportation.

Dew Point

A dew point is a temperature at which water vapour in the air condenses to form dew if air pressure and water content remain constant.

Determine the dew point for the expected range of air pressure and water content combinations during the period of shipment and storage conditions. The right type and amount of desiccant will absorb enough water vapour so that the dew point can be managed to meet the humidity requirements.

Common Desiccants

Montmorillonite Clay

Montmorillonite clay is a naturally occurring absorbent created by the controlled drying of magnesium aluminium silicate. Desiccant clay regenerates itself for repetitive use at low temperatures without swelling or substantial deterioration.

The moisture absorber is a highly effective and inexpensive packaging solution for average temperature and relative humidity requirements.

Silica Gel

Silica gel is a compound with the chemical formula SiO₂ and is one of the most commonly used desiccants. Structurally, it is characterised by interconnected pores. These pores significantly increase the surface area of the compound, with causes the silica gel to attract and hold water or moisture through capillary condensation and absorption.

Silica gel is exceptionally effective below 25⁰C (77⁰F) but loses its absorption capabilities as the temperature rises. Find out more about silica gel uses here.

Molecular Sieve

Alternatively known as Synthetic Zeolite or aluminosilicate, the molecular sieve contains a network of empty absorption cavities and crystalline pores. The dessicant creates an internal surface area for absorption of 700 m² to 800 m².

Apart from their uniform structure, molecular sieves are better than activated clay or silica gel for low humidity level requirements.

Calcium Oxide (CaO)

Calcium Oxide (CaO) is calcined lime with a moisture absorption capacity of up to 28.5% by weight. CaO can absorb more water vapour at extremely low relative humidity levels than other materials.

Calcium Sulphate (CaSO₄)

Calcium sulphate (CaSO₄) is a general-purpose desiccant created by the controlled dehydration of gypsum and is mainly used in laboratories.

The moisture-absorbing solution is chemically stable, non-corrosive, and non-toxic and does not release absorbed moisture when exposed to higher temperatures. While relatively inexpensive, calcium sulphate can absorb up to 10% of its weight in moisture or water.

Uses of Desiccants

Desiccants are best used in enclosed spaces with high humidity but low evaporation rates. A desiccant can also function as a dehumidifier by absorbing excess moisture in the air.

• Goods Transportation

Temperature changes and moisture penetration are common challenges when products are shipped over long distances. Commercial desiccants are often used in product shipping packages with humidity indicator cards and moisture barrier bags for optimal packaging protection.

• Odour Control

Carbon is known for its ability to extract impurities, and activated carbon is especially effective. The desiccant has the ability to eliminate foul odours in enclosed containers or packaging, for example, basements, garages and storerooms.

• Natural Dehumidifiers

Desiccants are useful in both commercial and domestic settings. Pulses, spices, and other food items can rot if exposed to moisture; rice and salt as natural dehumidifiers source to prevent this.

• Preservation of Chemicals

Many chemicals react with moisture in the air to form compounds. Desiccants absorb humidity and prevent this from happening.

• Basement Storage

Basements are notorious for being the dampest rooms in the house. Containers of desiccant placed in the basement can prevent mould and fungi from forming.

How Much Desiccant Do You Need?

The decision on the amount of desiccant to use is critical. Too little and all the efforts to prevent moisture damage will go to waste, while too much might be unnecessary. The general rule of thumb is that 1.2 units of the correct desiccant will help protect approximately one cubic foot of space.

Here is an example to illustrate the calculation process:

• Size of package: 15in x 15in x 12in = 2,700 cubic inches = 1.5625 cubic feet
• Units of desiccant required: 1.2 x 1.5625 = 875 units

In this case, we round the figure up by 0.125 to 2. Hence, a 2-unit bag of desiccant is required to keep the container dry. The additional 0.125 units of desiccant give us a convenient buffer to account for unforeseen circumstances.

Conclusion

Numerous moisture control solutions are available, each with its strengths and weaknesses. Always determine the best desiccant for each different requirement. Always ensure that the correct amount of desiccant is used. Overall shipping and storage conditions also play a role, with temperature and humidity targets influencing the final decision.

Find out how to reuse desiccants, and here below is a video about desiccant bags.