Silica gel desiccants for moisture absorption: things you need to know

They’re so common that few notice them.  Bags filled with a few grams of silica gel are used for moisture protection in everything from shoe boxes to packaging for electronics. The popularity of silica gel desiccants has led to few people stopping to analyze if there aren’t superior alternatives for protecting their company’s products.

If that’s you, worry not!

In this insight, we’ve done just that for you, and by investing a couple of minutes, you’ll get a grip of how your company (and the environment too) can benefit from a switch from silica gel to calcium chloride desiccants to keep your goods safe and dry.

Let’s start by going a bit technical.

How silica gel desiccants remove moisture from the air

Silica gel and calcium chloride have different ways to remove moisture from the surrounding environment. Silica gel does it by adsorption, which means that the water molecules adhere to the surface of the silica gel. The silica gel is a very porous component with a high number of voids that may contain water when needed.

Calcium chloride, on the other hand, is hygroscopic and deliquescent which means that it absorbs moisture and turns into liquid. Hygroscopic materials can reach a balance with the surrounding environment and absorb moisture when the relative humidity is higher than the EMC, which stands for Equilibrium Moisture Content (we talked about it in this insight). Absorption means that the water molecules dissolve into the calcium chloride rather than cling to the surface of it, as it does to silica gel.

The different processes affect how they perform in different environments:

• Silica gel works well at unexceptional temperatures, while it may lose the capacity to adsorb at higher temperatures. At high temperatures, it might actually release moisture into the air.
• Calcium Chloride has a much better performance when the relative humidity is high.
• Calcium chloride increases its capacity to absorb water over time because the absorption process makes the moisture dissolve into the calcium chloride.
• Due to the physical characteristics of the adsorption process, silica gel desiccants may be full up quickly. If that happens, their capacity to remove moisture remains low and very constant.

Our first conclusion is that calcium chloride performs better than silica gel in tougher conditions, especially when the relative humidity is high. These are conditions where moisture damages such as mould, bad smell, peeled labels and collapsed packaging are more likely. Calcium chloride also improves its capacity over time, which makes it very suitable for long journeys and unpredictable shipment conditions such as longer transit times.

Absorption rate: calcium chloride outstanding performance

In other insights, we have talked about the differences in performance between calcium chloride and silica gel desiccants in both climate-chamber tests and real-life conditions.

Placed in an environment with 30 degrees Celsius and 90% relative humidity during 30 days, calcium chloride can absorb over 250% of its weight. In the same conditions, silica gel stops at 25-30%. This means that calcium chloride has 10 times the capacity of silica gel to remove moisture from the air when the relative humidity (RH) is 90%. At 50% RH, the difference is less, but calcium chloride with its absorption rate of ca. 100% in these conditions still outperforms silica gel by around 20%.

These results may affect the dimensioning of a moisture damage prevention solutions in different ways. To reach the same level of absorption, you may need 10 times more silica gel desiccants than if you’d choose calcium chloride. This means you can exchange 40kg of silica gel desiccants with approximately 4kg of 94% purity calcium chloride desiccants. This reduction of resources can also lead to significant benefits for the environment, which we’ll explain further down.

The absorption rate difference between these materials is a key factor to keep in mind when you plan certain types of shipments.

During journeys with extreme conditions such as long duration journeys, routes with high differences in temperature, shipments from the South Hemisphere to the North, transport routes during rainy seasons or from/to tropical weather conditions, calcium chloride desiccants offer a safe margin that silica gel desiccants don’t. That’s because calcium chloride’s capacity to absorb moisture increases over time, while silica gel desiccants’ capacity decreases.

Silica gel desiccants’ carbon footprint is 20 times higher than calcium chloride desiccants.

The carbon footprint is the total amount of greenhouse gases (including carbon dioxide and methane) that are generated by a product. There’s no question that calcium chloride outperforms silica gel in this area (in a good way).

The carbon footprint of a desiccant varies depending on factors such as:

• source and quantity of the raw material
• type of production
• energy used
• source of the energy used
• transport of material to production

Calculating the carbon footprint of a product is a complex procedure. But the general figures point to calcium chloride’s carbon footprint being half of silica gel’s. This is due to differences in the process of obtaining silica gel and calcium chloride respectively.

On top of this, we have to add the fact that we need 10 times as much silica gel to reach the same level of absorption as calcium chloride. The result of this is that the carbon footprint of calcium chloride desiccants is 1/20 of that of silica gel.