DESICCANTS: HOW THEY WORK, TYPES AND APPLICATIONS

Desiccants are a tried and tested means of preventing corrosion damage. How do desiccants work, what types are there and are they environmentally friendly?

It is, therefore, essential to protect these products securely from moisture. A tried and tested means for this is desiccants, which can be used flexibly and easily. Among other things, they are excellently suited to protecting metal parts and electronic components from corrosion. 

Using desiccants in everyday packaging is as easy and flexible as there is so much know-how behind it. Britwrap protective packaging gives a comprehensive overview of the questions: 

• How do desiccants work?
• Are desiccants environmentally friendly, and how do I dispose of them?
• What new challenges are there with desiccant packaging, and what are the trends (keyword, e.g., ESD, automation)?

HOW DO DESICCANTS WORK?

There are two categories of desiccants that work fundamentally differently: 

1.      Physically acting desiccant moisture by absorbing the water vapor in their pores. These physically acting desiccants do not change their form during the adsorption process, i.e., they remain fixed, retain their size (no change in volume) and are chemically inert. It is impossible to tell from the outside whether desiccants with a physical effect are saturated or still active (except silica gels with indicators such as orange gel or ruby ​​gel, which change color as adsorption progresses). By adsorbing humidity, these desiccants only change their weight: the more water vapor is adsorbed, the heavier the desiccants become. 

2.      Chemical desiccants absorb moisture and condensed water during a chemical reaction. These desiccants usually work with calcium chloride as the central active ingredient, which is mainly effective in ​​very high relative humidity and absorbs condensation. Chemical desiccants change their shape during absorption. Often, once absorbed, granules (in the unsaturated state) become a soft/gel-like mass that more than doubles in volume. 

WHAT TYPES OF DESICCANTS ARE THERE, AND WHAT ARE THEY USED FOR?

·         Desiccants with a physical effect can almost always come into direct contact with sensitive products (such as food and medicines) and components (electronics, optics). Therefore, physically acting desiccants are used in primary packaging or during operation as a component of machines and systems.

·         Within the group of physically acting desiccants, a distinction is made between the following desiccants:

o   Alumina: the "standard desiccant" for container desiccant, the most commonly filled desiccant in desiccant containers that conform to DIN 55473 (from the smallest 1/6 unit to the largest 32 unit desiccant containers). Clay is a natural product mined in bentonite mines around the world

o   Silica gel: due to the significantly higher adsorption capacity than alumina, the "standard desiccant" for very small desiccant containers (0.25g to 5g filling weight) or applications with very limited installation space (higher adsorption capacity = space-saving). Often the preferred desiccant in pharmacy, diagnostics and the food industry. It is also filled into DIN 55473 desiccant containers but has the same adsorption capacity as DIN 55473 desiccant containers filled with alumina. Silica gel is an amorphous silicon dioxide chemically produced by acidifying water glass.

o   Orange gel/ruby ​​gel (silica gel with indicator): A color indicator can be added to silica gels to visually check the saturation of the desiccant. The discoloration of the desiccant tells the user when the silica gel is saturated and needs to be replaced. 

·         Drying agents with a chemical effect, in particular calcium chloride (salts), are not suitable as primary packaging materials, as these can damage products if they come into direct contact. The main application of chemical desiccants is container desiccant containers placed outside primary packaging (wooden crates, big bags, closed cardboard boxes) on the sea route. These bags aim to absorb the condensation water drips down from the inner ceiling underside of sea containers. The chemically acting desiccants are particularly suitable for use in sea containers outside the primary packaging, as they are particularly efficient at high relative humidity and absorb condensation ("container rain"). The absorption capacity can reach up to 300% of its filling weight (at very high relative humiditiy over 80% RH).

·         Suppose a desiccant is not just used as packaging material but also as a component in the ongoing operation of components.

ARE DESICCANTS ENVIRONMENTALLY FRIENDLY, AND HOW DO I DISPOSE OF THEM?

Physically acting desiccants are environmentally friendly because they do not unduly affect the natural environment. Accordingly, all desiccants with a physical effect can be disposed of in household waste (private end customers) or normal commercial waste (corporate customers).

Alumina – the most commonly used desiccant – is even used as an additive in composting, for example, to adsorb tannic acids when composting certain organic waste and thus prevent the compost from becoming acidic. However, the common desiccant containers in the dust-tight version "B" usually consist of a fleece material with a plastic coating as a sealing medium on the inside (bi-component). Therefore, these desiccant containers are not 100% recyclable.

Chemically acting desiccants used as container desiccant containers outside of primary packaging for sea transport are not environmentally friendly. Therefore, desiccants with a chemical effect, which usually contain calcium chloride, must be disposed of as hazardous waste. 

WHAT ARE THE NEW CHALLENGES IN DESICCANT PACKAGING, AND WHAT ARE THE TRENDS?

Automation: Irrespective of whether container desiccant is used as part of the packaging or as a component (e.g., for electronic controls): the fully automatic introduction or placement of desiccant containers in packaging or housing is increasingly becoming the focus to avoid the costs of manual work steps. There are numerous technical possibilities to store dry bags protected from water vapor as bulk goods in silos, separate them from there automatically, and supply precise packaging, e.g., via pick-and-place robotic arms or a "chute." 

It is helpful to consider the integration of a container desiccant infeed from the outset when planning packaging lines. Existing systems can also be expanded to include a drying bag feed system, although retrofitting is usually less flexible. In addition to the more efficient packaging process, automated feeds have another positive side effect. By storing them in water vapor-tight silos, the packaging units of desiccant containers can be made significantly larger, which saves costs and reduces packaging waste.

More than just moisture: There is increasingly sophisticated packaging in which the moisture absorption provided by standard desiccant containers is insufficient to protect products adequately. More and more specific properties of different desiccants are required, especially regarding the adsorption kinetics (the speed at which moisture is absorbed) and the adsorption behavior under different climatic conditions (e.g., cold chains with low relative humidity). It is also becoming increasingly important. In addition to pure water vapor, other molecules, such as gases, can react with moisture to adsorb. In chemical analysis, there are possibilities to choose desiccants with a precisely defined pore diameter, which enables such targeted adsorption of certain molecules.