Depending on application area and packaging form, different desiccants can be used: silica gel or molecular sieve. These desiccants behave hygroscopically, which means that by attracting moisture, they keep it away from the packaging contents.
A barrier layer (in this case, the plastic packaging) separates the air as well as the contents and the desiccant in the packaging from the outside climate. This creates a so-called microclimate. It is essential that the packaging is moisture vapor proof to the greatest possible extent. The desiccant dehumidifies the air inside the packaging to such an extent that no moisture damage will occur to your product. We use either silica gel or molecular sieve as desiccants.
Silica gel is the most commonly used moisture adsorbent offering a wide application range. It consists of an amorphous, granulated and porous form of hydrated silica whose raw materials are mainly water glass (sodium silicate) and sulphuric acid. Silica gel is compatible with all materials except strong alkaline agents and hydrofluoric acid. It is completely odorless and emission-free and is not corrosive. The extensive internal surface area of silica gel particles consists of a large number of tiny pores and may adsorb up to 36% of its own weight of moisture without changing its structure.
Silica gel adsorbs moisture more slowly, and with less dependence on temperature than molecular sieve. Furthermore, it offers an adsorption capacity that increases with the amount of humidity.
It is ideal for applications where a particular level of residual moisture is desired in the packaging (e.g. with gelatine capsules) and for high relative humidity.
Molecular sieves are synthetically manufactured zeolites. They are characterized by a regular pore diameter and their crystalline structure. Their use is the first choice where fast drying is required. They adsorb 20 to 22 % by weight of vapor independently of relative humidity. Molecular sieves have lower residual moisture and optimum adsorption capacity.
In addition, they adsorb moisture rapidly even at low temperatures and humidity and show constant adsorption characteristics.
Molecular sieves represent an ideal solution for very low humidity in the packaging or when used in arid countries since their adsorption capacity is not as related to temperature as it is with silica gel.
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