A container is a closed system with its own “weather.” The difference with a warehouse is that the temperature variations are much greater.
It is not unusual for a container’s temperature to range from below zero to 60-70 degrees over the course of a single journey. It is a fact that warm air can contain more moisture than cold air. This means that when warm air cools down, the conditions become wetter.
When enough of the moisture cools, the condensation eventually leads to rain. This is the same phenomenon that produces dewy grass and mist on cool autumn mornings.
Even without condensation, a higher air humidity is enough to cause damage to products in a short period of time.
A humidity level of 60-70% will lead to corrosion or discolouration of metal objects. At higher levels of humidity of circa 80-90%, there will be moulding, labels will become detached and corrugated cardboard boxes will well up and become soft.
Migration of moisture:
At higher temperatures, air can contain more moisture than at lower temperatures. With a maximum relative humidity of 100% and a temperature of 30 °C, this is 30.4 g/m3. However, at 5 °C, it will only be 6.8 g/m3. This moisture cannot escape through the walls of e.g. a container when the temperature goes down.
If the goods themselves do not warm up as quickly as the air around them, there will be condensation on the surface of the goods. The reverse is also true: when the temperature rises, moisture will escape from the products and/or the packaging into the surrounding air.
While stored in a warehouse on a moist wooden pallet, the originally low relative humidity can increase from e.g. 30% to 80%.
Acute temperature differences not only occur when goods are transported through different climate zones. The difference between a hot day and the cold night that follows can result in a difference in temperature of more than 40 °C inside the container.
The most effective way to use desiccants is inside a closed and sealed water vapour barrier or in a metal container. Humidity indicators are placed inside the packaging to indicate the relative humidity and to determine whether the desiccant is in need of replacement.
Silica gel was first used to keep penicillin dry during the Second World War. The material turned out to have excellent desiccating properties. It can also be used as an air freshener, because it effectively absorbs smells and will gradually remove unpleasant odours from the entire space.
Important documents and possessions that must be stored under dry conditions for long periods of time can be stored safely in bins and other storage locations with silica gel desiccant products. These help prevent moisture and condensation.
Camera lenses are extremely sensitive to moisture when there is a change in temperature. Silica desiccants can absorb the moisture that is present on the lenses of a camera.
Digital cameras require more attention due to their sensitive nature. Silica gel will help you greatly extend the lifespan of your camera’s lenses.
Weapons and munitions must also be protected against moisture. It is therefore advisable to add silica gel bags to these products during storage. These will absorb any moisture in the environment.
Moisture on weapons and munitions will cause them to rust and compromise their reliability.
- For moisture absorption (the bags in shoe boxes, electronics, etcetera);
- To keep medication dry, the jar sometimes contains a capsule of silica gel;
- To keep machines and military material dry;
- During the production of gasoline with a high octane content;
- As a catalyst during the production of synthetic rubber;
- As a component in alcohol tests (in the mouth piece);
- In the filters of a cooling circuit (e.g. a car’s air conditioning system) to extract any moisture from the air;
- To protect cameras against moisture and fungus (they are used to keep photographic equipment dry under humid conditions);
- As a relative humidity buffer (RH buffer), e.g. in museum cabinets and pianos;
- To dry flowers (under a bell jar or in an airtight box with some silica gel added)
Silica gel filter is a desiccant that was patented in 1919 by Walter A. Patrick at Johns Hopkins University in Baltimore, Maryland. Despite its name, the product is not a gel and should not be confused with silicone gel. Silica gel is a porous, granular form of silicon dioxide, which is synthetically manufactured from sodium silicate. Silica gel is the most absorbent desiccant that is available today. It consists of small interconnected pores. Silica gel attracts moisture via adsorption and retains it with capillary condensation. Silica gel is inert, non-toxic, non-flammable and safe to be used to protect food, medicine, sensitive materials and other products against moisture. Even when the product is saturated with adsorbed moisture, silica gel will look and feel dry to the touch. Some types of silica gel are approved by the FDA to come into direct contact with food and pharmaceutical products.
Silica gel is the cheapest way to protect our products from damage caused by moisture. It can be seen as one of the most important scientific breakthroughs, although using silica gel to keep things fresh and dry can also be considered a low-tech solution.
For packaging purposes, the most commonly used desiccants are activated clay and silica gel.
What is activated clay?
Activated clay is made from montmorillonite clay. This clay has a high affinity for moisture. It is a natural product. Activated clay is chemically inert and non-corrosive. The layered structure attracts moisture and adsorbs it on the surface and between the layers. Activated clay is the most economical of all desiccants. It is a highly effective desiccant for use at normal temperatures and relative humidity levels.
It is important to understand how the desiccant does its job of protection the product. Most porous adsorbents, such as silica gel, activated clay or molecular sieves, use physical adsorption instead of chemical adsorption to achieve their functionality.
Physical adsorption involves relatively weak intermolecular forces (van der Waals forces and electrostatic interactions) between the moisture and the surface of the desiccant.
Chemisorbents, on the other hand, make use of chemical bonds. The physical adsorption of moisture is usually an exothermic process. The strength of the adsorbing obligations can therefore be determined by measuring the heat that is released during the adsorption process. The more heat is produced during the moisture’s adsorption by the desiccant, the stronger the bond and the harder it will be for the moisture to be removed later on.
Porous desiccants, such as the silica gel sold by droogzakjes.nl, remove water from the atmosphere with the help of:
- multi-layer adsorption, which involves attracting thin layers of water molecules on the surface of the desiccant. Because the desiccant is highly porous, it has a large surface area and can attract and adsorb large quantities of water;
- capillary condensation during which the smaller pores are filled with water. Capillary condensation occurs because the saturation of water (vapour pressure) in a small pore is reduced by the effect of surface tension.
Desiccants extract moisture from the surrounding air. Desiccants adsorb the moisture and retain it. This means they can be used to prevent corrosion, moulding and the clumping of powdery substances.
An absorber is also known as an oxygen scavenger. It is an ideal product with which to minimise the volume of residual oxygen inside packagings. Despite the many advantages such absorbers offer, some people believe them to be toxic. You can rest assured that this is not the case.
Our products meet the strictest EU regulations and are specifically designed to be food-safe. This means they are ideally suited for situations in which food products must be stored for long periods of time. You do not have to worry about the oxygen scavengers you order from us being toxic, because they certainly are not.
The function of an oxygen absorber is right there in its name. It absorbs oxygen (also known as the chemical element O2) from an environment and does so in a highly effective manner. That is important, because oxygen can cause products such as food to spoil or become mouldy much faster.
The more oxygen is present inside a packaging, the faster the spoiling process tends to be. It is therefore advisable to use oxygen absorbers to maximise your products’ shelf life. The amount of oxygen is reduced significantly and food will stay fresh and delicious for much longer.
Lowering the residual oxygen level inside a packaging not only improves the product’s shelf life, but also offers additional benefits with regard to the product’s scent, colour and flavour. Food products that have been stored in an environment with a lower oxygen content will smell and taste better and look more appealing to consumers.
A desiccant unit (DE) is used to indicate the absorption capacity of a desiccant. In accordance with DIN 55473, the DE must be able to absorb at least six grams of water vapour at a relative humidity of 40% and a temperature of 23 °C +/- 2 °C. As a general rule, it can be said that a desiccant unit weighs circa 30 grams. More specifically, it can be said that one desiccant unit of clay weighs circa 33 grams, a desiccant unit of silica gel weighs circa 26 grams and a desiccant unit of molecular sieves weighs circa 32 grams.
Have you ever been in this situation?
“My container was delivered and the cargo is moist. There are no holes in the container, yet the inside reeks of mould and mildew. It is almost like it’s raining inside! How is this possible?”
If your container is loaded in a tropical environment where the air is hot and humid and its destination is a country with a cooler climate, your cargo will have to deal with a phenomenon known as “cargo sweat” or “container rain.”
At certain times throughout the year, temperature fluctuations of up to 50 °C can occur during overseas transport between tropical regions and the cooler, temperate climate in Europe. Of course, similar conditions can arise when loading a container during certain humid periods in Europe and then shipping it to a tropical destination elsewhere in the world.
When the outside temperature drops, the container becomes colder, causing hygroscopic or moisture-absorbing cargo and packaging materials to release water vapour. Because of the lower temperature inside the container, the water vapour is not absorbed into the air. This happens when the temperature of the upper and side panels of the container is lower than the dew point of the air trapped inside the container and condensation starts to form on the cargo itself and on the container’s walls and ceiling, just like the droplets that form on a glass of iced tea on a hot summer day.
The moisture, which is shipped together with your cargo and packaging materials, will (given the temperature differences inside the container) be released as water vapour. The resulting effect almost looks like rain. When warm, humid air cools down to below the dew point, water vapour in the air turns to condensation – sometimes in very large volumes. This condensation can penetrate the packaging materials that protect your cargo.
Water from the container’s ceiling can fall directly onto the cargo or drip down along the container walls. The result is like having a pool on the floor of the container. All this moisture will be absorbed by the cargo or the packaging materials. However, the resulting damage is not covered by any insurance. It will be attributed to inherent flaws of the cargo or packaging materials.
Moisture damage to goods is a common occurrence in the world of container shipping and storage. In the past, these problems were attributable to a failure to use (properly performing) desiccants. These products were not strong enough to effectively protect the cargo during transport and/or storage.
Damage caused by moisture and condensation can have the following consequences: wet boxes, moist packaging materials, detached labels, torn boxes, spoilt goods, unpleasant smells, rust, stains and corrosion. Every year, these problems cost manufacturers, forwarders, shipping companies, trade companies, importers, exporters and insurance companies millions of euros.
Since sea freight is often the cheapest way to transport goods across long distances, most cargo is transported by ship. From the port of Rotterdam alone, circa 3.4 million containers were shipped to destinations all over the world in 2013. Many of these containers were – directly or indirectly – impacted by container rain.
By providing air humidity lower than condensation, stabilising it and linking it to a system that can react fast enough to absorb the excess moisture before it can begin to form droplets.