Moisture protection for hygroscopic materials during transport

The main point of packaging is to protect products from damages. Packaging is often made from hygroscopic materials, which means materials that absorb and hold moisture. And moisture is in itself a threat to most products, especially during transportation. This is problematic and something we want to shed light on. In addition to the problem with using packaging material that absorbs and holds water, these hygroscopic materials often change their size and shape when they become wet. They can even add water to the environment, becoming a threat rather than a protective agent.

In this article, we will go through some important facts about the right moisture protection for hygroscopic materials that we hope will be of value to you.

Before we dive into it, let’s look at some examples of hygroscopic materials. Perhaps the most commonly used as packaging are paper, cardboard and wood. Some plastics are also hygroscopic and so are sugars, powders and salts such as calcium chloride which is what we use in our desiccants.

EMC or the ability of wood

Wood has the ability to be in balance with the moisture level of the surrounding environment. Therefore, wood will either absorb or release moisture until it achieves a balance with the surrounding air, called Equilibrium Moisture Content (EMC). The EMC point depends on the relative humidity and temperature of the air.

The worst case is when wet wood pallets release moisture into the surrounding air. When the temperature drops at night, this moisture will cause container rain.

EMC and absorption of hygroscopic materials depending on the relative humidity in the environment
Figure 1. Wood absorbs or releases moisture depending on the relative humidity in the environment.

This phenomenon is not limited to wood. The same is true for paper, sugar and powders inside containers or boxes. So far, it does not seem possible to transport these materials without risking that they absorb moisture from the air, causing costly or irreparable damages.

So how do you protect hygroscopic materials from moisture damages during transport?

 

Hygroscopic substances to protect hygroscopic materials

Fight fire with fire? In the case of moisture protection for hygroscopic materials, it’s probably the best option. But first, let’s take a look at another solution – plastic wrapping the original packaging. The plastic film prevents the packaging material (i.e. cardboard) to absorb moisture from the surrounding air.

However, this solution tends to be ineffective due to material costs and installation time. Especially if it’s incorrectly installed, which is quite common. If so, or by using the wrong type of plastic, the risk is high that this method will capture moisture inside the packaging. Finally, additional plastic is undesirable in a time when we need to be as efficient as possible with the resources we use.

Alright, let’s get back to fighting fire with fire. Protecting hygroscopic materials with hygroscopic substances does not mean adding more cardboard or paper to the packaging. Unfortunately, this is also a common, expensive and ineffective solution. It’s also not very environmentally friendly, especially when there’s a much more effective option.

Moisture absorbers are what you should use. They’re made from hygroscopic substances and their purpose is to absorb moisture and keep it away from products that can be harmed by it. Silica gel, clay and calcium chloride of 94% purity (what we use in our desiccants) are some of the most well-known desiccants on the market. Their performances are very different and you can learn more about that in our guide to help you to test and compare the performance of different types and brands of desiccants.

 

Keep the relative humidity as low as possible

Now let’s look at how desiccants protect hygroscopic materials from moisture damages. One of the most common moisture damages when transporting wood is mould. The mould will usually appear when the relative humidity is around 75%  or more, and the temperature is between 20-30 °C. Wood (and paper) have another challenge in that they don’t hold moisture if the relative humidity of the surrounding air is low.

Therefore it’s important to keep the relative humidity as low as possible. This will rule out mould and other moisture damages and prevent packaging material to absorb moist from the air.

The most cost-efficient solution

The most cost-efficient and effective way to achieve that is the use of desiccants. Calcium chloride with a 94% purity has the capacity to absorb moisture up to 250% of its own weight when the relative humidity is 90% in normal field conditions. In a climate chamber, the same desiccant will absorb over 400% % (in this post we highlighted the importance of testing the desiccants in real-life conditions).

The right desiccant choice and dimensioning can keep the moisture level inside a container at harmless levels and avoid moisture damages during transport and storage.

It is however crucial that loading procedures are done correctly. It’s common that the greater part of the moisture found inside a container is actually added during loading. This will affect the dimensioning of the desiccants and potentially pose a problem.

 

Avoid adding extra moisture inside the container

Imagine a company that stores the pallets used to stuff the container in a cold and wet storeroom or even in rainy conditions outside the storage building. Those wood pallets can hold a moisture content of up to 24%. When those pallets are loaded inside the container, they will release water instead of absorbing it, adding moisture and increasing the relative humidity in the environment.

Wet pallets under the rain

Therefore, wet pallets or wet packaging materials will jeopardize the conditions the products will be loaded in.

Other conditions can affect the amount of moisture entering the container. We have explained them here.

Summary

To summarize, always consider these five key points to ensure a good moisture protection for hygroscopic materials:

  1. Avoid adding excess moisture in the container during the loading process.
  2. Use desiccants to keep the relative humidity inside the container at harmless levels for your cargo during the transport or shipping.
  3. Calculate the amount of desiccants needed by measuring the required moisture absorption. Take loading and unloading into account and then validate your calculations by conducting field tests. Keep in mind that absorption achieved in climate chambers will never be reached during field conditions.
  4. Add a plastic film wrapping if your cargo is very sensitive to e.g. dirt. It is not strictly necessary, but it might help you sleep better. However, this must be executed in a way that doesn’t trap moisture inside the packaging. If so, the desiccants will not get access to the moisture and can’t absorb it.
  5. Ask for professional help to perform points 1, 2 and 3. An expert in the prevention of moisture damages can help you choose the best protection for your cargo and optimize it. This way you will reach the highest savings in money, time and environmental impact.
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