Major Volatile Corrosion Inhibitor (VCI) packaging manufacturers tout the ability of VCIs to desorb once the protected metal part is unwrapped. This design feature is key to providing the clean metal part to be assembled, put in use, or further machined without the need for the part to be cleaned. Most VCIs rely on high vapor pressures and low binding affinities to desorb from the metal surface effectively. This paper describes a latent protective film that remains on the part after unwrapping. Furthermore, we evaluated how the relative humidity (RH) of the environment affects the VCI's ability to desorb from the metal surface.
The use of volatile corrosion inhibitor packaging continues to be a mainstay in protecting metal parts in shipping and storage. Initial protective packaging applications of VCIs involved coated paper1-4 which was used to wrap or interleave metal parts for transportation and/or storage. This type of wrapping evolved into film packaging where the inhibitors were extruded into film.5 In either form, paper or film, the packaging allows for the protection of metal fabricated parts without complications of rust preventative (RP) oils, which would typically have to be washed off. As VCI chemistries vaporize from the film or paper and diffuse throughout the package, they are attracted to the polar nature of the metal part, forming a protective molecular layer on metal surfaces.6,7 This occurs even when the part is not in direct contact with the paper or film.
In contrast to VCI adsorption during packaging, what happens when metal part is unpacked from the VCI material? How long does VCI desorption take? Is there going to be an effect on downstream processes if there is still VCI remaining? These are some of the questions that end users will ask of VCI packaging manufactures. There seems to be no real general understanding of the inhibitor film longevity. Furthermore, there does not appear to be any reports in the literature on VCI desorption. As more and more suppliers try to enter the marketplace, it is imperative that these valuable technologies be used and understood appropriately.
