DESICCANT KNOWLEDGE HUB
AS ANY SEASONED PACKAGING ENGINEER DEALING WITH MOISTURE-SENSITIVE PRODUCTS WILL TELL YOU, THE MOST CRITICAL QUESTION TO ASK IS, "WHAT RH DO YOU NOT WANT YOUR PRODUCT TO SEE?
Figure 1: 3.5 Gram 13X StayDry Molecular Sieve Desiccant Packet
Purchase at these links, available 5,000 per case or 100 packets per pouch
Why Molecular Sieve is the best desiccant;
- Highest adsorption capacity at low relative humidity.
- Ability to extract moisture contained in other products.
- Will not desorb moisture into the package when temperatures rise (unlike Silica Gel).
The answer to the question, what relative humidity do you not want your product to see is, in this case, 10 percent.
Example: You’re in product development developing a medical instrument, or a diagnostic test. You’ve decided that you need to maintain the humidity in the package at 10 percent or less. Thus….to answer that Packaging Engineering question “what relative humidity do you not want your package to see?” The answer, in this case, is 10 percent relative humidity (see the graph above and note circle around 10 percent relative humidity.) And if you are working at 10 percent RH note the circle which is now the environment. In that environment, the capacity for silica gel is 4.6 percent (Data obtained from IMPAK QA Lab). The capacity for Molecular Sieve is 19.8 percent. In other words, a 3.5-gram packet of molecular sieve working in a 10 percent environment has more than three times the capacity of silica gel. This is the most important concept to understand in all of the adsorbent technology. *
10 percent is often a target relative humidity to maintain long shelf life in lateral flow diagnostic devices. Five percent is the target relative humidity in the bake-out procedure for some semiconductor and microprocessor devices.
One of the more well-known specifications that utilize two specific relative humidity environments is military packaging. MIL D3464 Revision E is all based on a specific set of results. The military specification references two particular environments based upon humidity. The humidity environments are 20 percent RH, relatively low, and 40 percent RH, relatively higher but still low enough to prevent corrosion. The military specification calls out that the sorbent utilized to produce a military-grade desiccant package must be able to adsorb three grams at 20 percent relative humidity and six grams in a 40 percent relative humidity environment. What does this mean? As the Technical Director of our company in the 1990’s used to say --- “If for some reason the dirt in your backyard was so prone to accept moisture that 10 grams of it would pick up three grams in a 20 percent environmental chamber and also pick up 6 grams in a 40 percent environmental chamber you could enter the military the military-grade desiccant packaging immediately.” Why is this? To meet that specific characteristic that is the prime directive of the MIL D3464 desiccant package it must be able to pick up 3 grams at a 20 percent environment and 6 grams in a 40 percent environment. Most sorbents, i.e., silica gel and clay tend to need 30 to 33 grams to meet the requirement. Molecular Sieve needs less, almost 20 percent less. Unfortunately, Molecular Sieve is not only 20 percent more expensive than silica gel or clay. It is significantly more expensive or despite the reduction in total packaging cost it needs as a product, it would be the dominant sorbent used in military applications. Does this make sense to you? If you can read this only one time and it makes sense to you, you should obtain an honorary Packaging Engineering degree in the area of sorbent technologies.
*No, Calcium Oxide has an extremely high capacity despite its very slow adsorption rate. The use of Calcium Oxide is almost exclusively found in the United States in military applications due to its flammability in wet environments. It is also commonly seen worldwide in Japanese dried seaweed products where it is often referred to as slaked lime. We reference this only to demonstrate the knowledge that is part of the global sorbent knowledge and is IMPAK Corporations skillset.
For more information on desiccants and humidity indicators click the links below: