Can you use desiccant together with VCI?
The operating principles
Desiccant is designed to absorb moisture out of the atmosphere. As a rule of thumb, it is enough to keep relative humidity (RH) below 50%, although pharmaceuticals and certain compounds require RH below 10%. VCI and desiccant do not interfere with each respective function, meaning that VCI will not reduce a desiccant's ability to absorb moisture. The desiccant will not stop the VCI from releasing its molecules. This in itself is a bit of a paradox in that VCI uses the water molecules to hydrolyze itself on the surface. This creates what is in many ways an electrolyte, as we know it from batteries. The difference is that an electrolyte with VCI will not conduct current between anode and cathode, and thus corrosion ceases.
In other words, moisture is not a danger to VCI-protected components. But everything in moderation. There is, after all, a limited amount of VCI molecules present. VCI can be flushed away if there are large amounts of free water. Therefore, it may be appropriate to combine desiccant and VCI.
VCI and silica combo
It is important to give the VCI packaging an optimal starting point. We have described this in a separate blog coming out next week about how to pack with VCI plastic. In those cases where it has nevertheless been difficult to ensure dry goods when packing, we have let the desiccant do the work first by removing excess moisture, as e.g. silica gel does a very quick job to begin with. Later, the ability to absorb new moisture flattens out a bit, but it does nothing. When the desiccant has removed moisture, the VCI has time to slowly but surely build up on dry and clean surfaces.
Another effective proven packaging design using VCI and desiccants for overseas shipments is to apply 2 layers of plastic, with desiccants placed between the two layers. The innermost layer, closest to the parts, must be VCI, and the outer bag can be pure poly/plastic, preferably shrink plastic that has UV resistance.
The desiccant between the two liner bags will reduce the moisture inside without compromising the protection of the metal.
Store desiccant correctly
We have seen boxes, pails and barrels of desiccant sitting on the packaging workstation, without a lid or cover on the container. The desiccant absorbs moisture from the atmosphere when exposed to an open environment. It is therefore possible that the effect has worn off before it is ever placed inside the shipping container.
Proper storage of silica gel is critical. The simple solution is to securely close the original box with double plastic bags, but even then it will deteriorate over time. Our best suggestion is to invest in a plastic container with an indicator at the top . Keep the lid of the desiccant container closed.
We offer a complete range of corrosion-inhibiting packaging and desiccants. In Norway, we have an agency at Zerust, the world's largest supplier of (VCI) poly technology. Do you have a challenging corrosion prevention need, such as shipping overseas or storage in corrosive environments? We can help you find the right solutions.
Also find articles on Zerust's blog.