Desiccant suppliers will always tell you that the most important factor to consider when selecting a desiccant is the absorption capacity. It seems perfectly logical that the more moisture a desiccant can absorb the better it should be. However, what they are not telling you is that you also need to consider the application (where is the desiccant being used) and unique characteristics of the desiccant when making your decision.
Let’s illustrate this point using the example of bentonite clay and calcium chloride desiccants, both of which are offered by Micro-Pak. Calcium chloride can absorb up to 300% of its own weight in moisture, compared to 30-40% for clay. Surely the ability to absorb 10X more moisture makes calcium chloride a far superior desiccant? This is not necessarily the case. It’s like saying a sports car is always better than a 4X4 because it is faster, but what if you’re driving on a muddy trail…
Application – Inside a Package Versus Inside a Shipping Container
Where the desiccant is being used is fundamentally important. Calcium chloride needs high levels of sustained moisture to perform, which you do not find inside packages. Inside packages the humidity is less extreme and is not sustained, and under these conditions calcium chloride absorbs poorly. It is not able to absorb much moisture and the rate of absorption is very slow. Clay desiccants thrive in such conditions and will outperform calcium chloride, reducing the humidity inside the package faster and to significantly lower levels.
The opposite is true inside shipping containers where the humidity is extreme and sustained. Calcium chloride performs optimally in these conditions and has the capacity to remove the necessary amount of moisture to prevent container rain. It is therefore an ideal ingredient for container desiccants and we use a high quality calcium chloride in Micro-Pak Container Desiccants. Clay desiccants will be overwhelmed under such extreme conditions and they do not have the capacity to remove sufficient moisture. Clay is not a suitable ingredient for container desiccants.
Desiccant Characteristics
A second factor to consider is what happens to the desiccant when it absorbs moisture. Calcium chloride turns into a highly corrosive liquid gel which presents a risk of leakage. Clay desiccants stay dry at all times, even at full water vapour capacity. This is another reason why you may not want to use calcium chloride inside a package. If it leaks it can cause irreparable damage to your products. In fact, we do not recommend using calcium chloride with electronics or metal parts due to its corrosive nature.
Sustainability
Packaging materials comprise 95% of a desiccant’s makeup. How a desiccant is packaged is therefore an important, but often overlooked, factor.
To prevent leakage, calcium chloride desiccants require two layers of packaging; an inner plastic pouch with an outer non-woven layer. As a result, they tend to use 4X more packaging materials than other desiccants. Clay desiccants like Micro-Pak Dri Clay® Kraft can be packaged in plastic-free and biodegradable Kraft paper.
Summary
- When selecting a desiccant you should consider the application, desiccant characteristics and material makeup in addition to the absorption capacity.
- Clay desiccants are ideal for packages
- Calcium chloride is ideal for container desiccants