Do you remember the first time when you found a small pack inside the new shoes’ box, or in a food container and wondered what it was? Well, I don’t remember exactly but I do remember times when I wondered what they were, I also opened them and put a few beads on my tongue (I think my dad told me to) just to feel how they stick to it. Well, most of the time, these small packs that we find are silica gel desiccant packs used to absorb humidity, but there are more types of desiccants with many more and diversified used. In the following article I will discuss about the most important ones so read on.
The most known and used type of desiccant is silica gel. It is a natural occurring mineral called silicon dioxide (SiO2) that is purified and processed into beaded or granular form. Silica gel has an average pore size of 24 angstroms and has a strong affinity for moisture molecules. It will absorb moisture at temperatures up to 220°F (105°C). As temperature goes above 100°F, the rate of moisture absorption will slow down but it will still work.
Silica gel performs best at room temperatures and high humidity (60- 90% RH) and will drop the relative humidity in a container down to around 40% RH. It is widely used in food and pharmaceutical applications as it is the only desiccant approved by FDA for direct contact with these items.
Silica gel desiccant has a wide range of pore sizes so it has the ability to absorb not only water but alcohols, aromatics, ammonia, olefins, diolefins and paraffins too.
Indicating Silica Gel
Indicating silica gel is a silica gel bead or granule that has been washed with a concentration of a heavy metal salt, cobalt chloride which has a deep blue color when dry but it turns from blue to purple to pink as it becomes saturated with moisture. Indicating silica gel should not be used in contact with products for consumption such as food or pharmaceuticals because of the addition of cobalt chloride.
Activated carbon or activated charcoal how it is also called is different from normal charcoal because it went through an activation process and it is also free of fossil fuels that are poisonous. Its surface area is dramatically increased in the activation process which adds the superior absorbing ability.
Activated carbon has the ability to absorb pollutants, poisons or chemical spills when used in agriculture. It has great medicinal qualities being used to treat infections and colic, diarrhea, open wounds, spider bites or bees, ants and scorpion bites, food poisoning. It also treats drug overdose, gas, diabetic ulcers, heartburns and indigestion.
As it possesses such great absorption capability, activated carbon is also used for water and air filters. It will absorb gases and odors, plastic fumes, cigarette smoke, furniture glues, carpet odors, bacteria and viruses. Activated charcoal also filters out harmful elements from water like chlorine, copper or carbohydrates.
Molecular sieves are porous synthetic desiccants that have a very strong affinity for moisture molecules. Compared to the other desiccants, the distinctive feature of the molecular sieve structure is the uniformity of the pore size openings in the crystal lattice structure.
Part of the manufacturing process, the pore size on the molecular sieve particles is controlled allowing the selection of a product which can absorb water, yet exclude most other molecules, such as volatile organics, which might be present in the package or others that can absorb a wide range of molecules as well as moisture.
Molecular sieve can hold moisture to temperatures well past 450°F (230°C), and because of its high affinity for moisture, molecular sieve is able to bring the relative humidity in packages down as low as 10% RH.
FDA has not approved sieve for direct contact with consumable items in the United States but it is used with pharmaceuticals in Europe.
There are many other types of desiccant packs used for different applications but maybe this article gave you some introduction to the most important ones. Before using any of them, ask your desiccant supplier for more specific details so you will be safe.