Desiccant methods were originally developed for the safe storage of military and transported goods. They offer reliable protection against corrosion through the insertion of a defined amount of desiccant in a packaged good. The following data are required to calculate the necessary quantity of desiccant units according to DIN 55474:
The air in a package, as well as the packed goods and the desiccant, is separated from the external climate by a barrier envelope. It is important that this envelope is as impermeable to water vapour as possible. The air trapped in the envelope is dried so that no moisture damage can take place during the transport and/or storage period. On request, we would be pleased to send you a copy of our desiccant calculation program acc. to DIN 55474.
Desiccant methods protect against corrosion on metal parts and, more generally, against unwanted moisture within packaging. The following environmental conditions influence corrosion:
The temperature determines how much water vapour can be found in the air. The higher the temperature, the greater the potential amount of water vapour. The relative humidity is the relationship between the amount of water vapour present in the air and the maximum possible amount of water vapour at a particular temperature.
Conventional adsorption agents (such as bentonite, silica gel or molecular sieves) store water by means of physical forces in narrow cavities (layers, pores, channels) on their inner and outer surfaces, and mostly bind it through electrostatic interactions. Adsorption agents are insoluble and chemically inert. They can be regenerated using intense heating. The temperatures for regeneration to less than 1% water by weight are: 130°C for bentonite, silica gel and orange gel, and at least 300°C for molecular sieves.
Bentonite is a natural product and thus environmentally friendly and easy to dispose of. It has a layered structure. The water vapour is adsorbed between these layers. The material thus remains dry and free-flowing even when fully loaded. The uptake of water vapour is dependent on the ambient conditions and ranges from about 10 per cent by weight in dry environments to up to 30 per cent by weight in humid environments.
Silica gel is a synthetically produced, highly porous and amorphous silicic acid in the form of hard grains with a glass-like appearance. Silica gel absorbs between 7 per cent by weight and 35 per cent by weight depending on the relative humidity of its surroundings.
Molecular sieves are synthetically produced zeolites with a regular crystalline structure – and thus a uniform pore diameter. They are particularly suitable for flash drying (up to a dew point of 80°C). Unlike bentonite and silica gel, however, they absorb 16 - 22 per cent of water vapour by weight regardless of the particular relative humidity. They are therefore principally used in desiccant cartridges to protect sensitive electronic and optical devices.
Desiccants are only effective if the air within the packaging is separated from the external atmosphere by an airtight barrier. Flexible barriers are generally used for export packaging. These are materials that are largely impermeable to water that can be sealed using heat sealing or thermal pulse welding.
are adsorption agents for humidity that is captured within their porous structures. The effectiveness of desiccants must meet defined specifications that are laid down in a variety of standards, such as DIN 55473, MIL D 3464E or AFNOR NFH 00321.
Desiccants reduce the air humidity within a closed barrier layer as soon as they are placed inside it.
They already start working at <5% relative humidity. The adsorption capacity depends on the relative humidity (RH) of the surrounding air. Desiccants according to DIN, MIL or AFNOR standards have an adsorption capacity of at least 6 g of water per desiccant unit at 23°C and 40% RH. Bentonite, silica gel and molecular sieves are used as desiccants. The adsorption capacity of these differing desiccants is between 16.5 and 19.5 per cent by weight at 23°C and 40% RH. This results in a weight per desiccant unit of about 30 g – 38 g adsorption agent. The relative humidity can be reduced to considerably below 40% by using desiccants, achieving effective corrosion protection.
You can obtain an overview of our range of desiccant bags in our desiccant bag product description.