VCI Technology

Zerust^® corrosion engineers go beyond VCI technology by offering a comprehensive system called Integrated Corrosion Technologies (“ICT^®”).  ICT^® is our term for the various material and chemical sciences that comprise our Zerust^® / Excor^® packaging product system including VCI (Vapor Corrosion Inhibitor) technology. Depending on the corrosion protection requirements and economic targets, Zerust^® / Excor^® ICT^® products can be designed in one or more of the following combinations to provide the optimum corrosion protection system.

Top VCI Products:

VCI Poly Bags and Film

Vapor Capsules and Diffusers

VCI Packaging Paper 

Health & Safety Discussion About VCIs

About VCI Technology

Volatile Corrosion Inhibitors (“VCI”) plastic packaging generally consists of polyethylene film that has been impregnated with chemical formulations that are unique to each manufacturer. While the underlying formulations can vary significantly, the finished products all function similarly in that they release very low concentrations (typically in parts per ten-thousandth) of invisible corrosion inhibiting vapors into the surrounding air. The vapor molecules subsequently condense onto exposed metal surfaces and form a molecular corrosion shield that can protect against rust and other forms of corrosion for up to five (5) years, and even longer in some cases. When the VCI packaging is later removed, all vapor corrosion inhibiting molecules rapidly evaporate. This leaves the metal parts clean and ready for immediate use.

About Zerust® VCI Poly Bags

ZERUST® VCI Film is produced by incorporating a formulation of patented contact and volatile corrosion inhibitors into the film during the production stage ZERUST®VCI Films are not coated.  The inhibitors become an integral, inseparable component of the film. The ZERUST® vapor molecules counteract the corrosive effects of humidity, salt and pollutants. ZERUST® VCI Film is available in bags, sheeting, tubing and liners to meet specific needs of industry.

Features:

•             Heat sealable with standard equipment.  Bags or shroud closures, however, can be tied, folded, or stapled closed for protection equivalent to that experienced with a heat sealed enclosure.
•             Large items can be protected for years without supplemental protection.
•             Protects when used in conjunction with acid bearing packing materials, e.g., corrugated board, chipboard, wood, etc.
•             Has no coating of chemicals to flake off, stick to, or otherwise damage or soil components or machinery.
•             Inhibitors will not affect any electrical or mechanical properties of a packaged item.
•             Chemical effectiveness is not impaired by rough handling.
•             May be used in conjunction with neutral or light rust preventative oils.
•             No special handling precautions required.
•             Available from stock in popular bag, sheeting and tubing sizes.
•             Can be supplied in special sizes and forms to meet specific needs.
•             Five-year in-service life.

Typical automotive industry applications include corrosion protection for:

•             Spare parts
•             Assembled engines
•             Engine components including blocks, cylinders, pistons, and connecting rods
•             Body panels
•             Frames
•             Electronic sensors and assemblies

In addition, ZERUST® products are so safe that they have been featured on the American Environmental Review on public television and have also been cleared by the US Food & Drug Administration for protecting metal food containers and processing equipment.

Health & Safety Discussion About VCI
Early VCI Technology

Globalization has meant that most component manufacturers today ship metal parts to assembly plants around the world. The success of these shipments, in turn, hinges upon properly protecting the parts from the destructive effects of the rust caused by the extreme climatic stresses common to long ocean voyages and storage in staging warehouses. Traditionally, coating metal parts with waxy oils provided this rust protection. Cost reduction and environmental concerns, however, have led most manufacturers to abandon this antiquated method in favor of the current standard that involves shipping their products “dry”, without oil, in Vapor Corrosion Inhibiting (VCI) plastic packaging. VCI plastic packaging generally consists of polyethylene film that has been impregnated with chemical formulations that are unique to each manufacturer. While the underlying formulations can vary significantly, the finished products all function similarly in that they release very low concentrations (typically in parts per ten-thousandth) of invisible corrosion inhibiting vapors into the surrounding air. The vapor molecules subsequently condense onto exposed metal surfaces and form a molecular corrosion shield that can protect against rust and other forms of corrosion for up to five (5) years, and even longer in some cases. When the VCI packaging is later removed, all vapor corrosion inhibiting molecules rapidly evaporate. This leaves the metal parts clean and ready for immediate use. Like most innovations, VCI technology has undergone several generations of product evolution before reaching its current level. The first generation appeared in 1937, when the Shell Oil Company introduced a product with the trademark name of “Dichan” to the market. Dichan, or more appropriately, dicyclohexylamine-nitrite (sometimes also dicyclohexylammonium-nitrite), was described in the patent as a “Vapor Corrosion Inhibitor” that had a sufficient vapor pressure to release corrosion inhibiting molecules into its surrounding atmosphere. Other companies licensed dicyclohexylamine-nitrite from Shell and began to coat it on paper, either by itself, or as a delivery system for a range of other corrosion inhibitors. These licensors shortened the technical name to VPI, and also to “Vapor Corrosion Inhibitor” or “VCI”, and launched VCI paper, as well as other VCI coatings and powders. A market developed for VCI products with applications requiring limited corrosion protection for up to a few months. This application range and market size was limited, however, by inherent weaknesses of the product. Due to the paper porosity and the high vapor pressure of dicyclohexylaminenitrite the protection was relatively short life. If the VCI was applied as a coating it also tended to flake off. Furthermore, the hydrophilic (water absorbing) properties of the porous paper tended to hold corrosion accelerating moisture in direct contact with the very metal surfaces that the product was supposed to protect. A further blow that limited the expansion of this initial phase of VCI technology was the revelation in the early 1970s that the Shell dicyclohexylamine-nitrite, the foundation of most then existing VCI formulations, was a carcinogenic agent.

The Risks of Secondary Amines in Metal Working Fluids and VCI Products

Due to their many useful properties, amines as a whole have been used for decades as the principal components of a full range of metalworking products, including some vapor corrosion inhibiting (VCI) formulations. This is despite the fact that most amines were known to be mildly toxic as well as skin, eye and respiratory irritants. Historically, these safety concerns were controlled by ensuring that workers use gloves and safety glasses in properly ventilated workshops. However, this proved to no longer be sufficient in the early 1970’s, when researchers began to suspect that secondary amines, a subset of the amine family, were carcinogenic agents. These early researchers correctly determined that secondary amines readily convert into carcinogenic N-nitrosamines when exposed to “nitrosating” agents. When these initial findings regarding the health and safety of secondary amines first surfaced, responsible manufacturers stopped making products that combined secondary amines and nitrosating agents, including “nitrites”, in their formulations. The first newly hazardous material to be targeted this way was dicyclohexylamine-nitrite, the direct combination of a secondary amine with a nitrosating agent, used in so many VCI formulations at the time. Subsequent advances in research in the early 1990’s, however, showed that using secondary amines without nitrites was still not safe. Researchers came to understand that the carcinogenic Nnitrosoamines are most likely to form when secondary amines combined with nitrogen oxides. Nitrogen oxides are a fundamental component of the air we breathe, and are actually more concentrated in the air of cities and industrial environments. In short, they’re everywhere amines might be used. Even worse, by 2001, German researchers confirmed that some N-nitrosoamines, including those generated by dicyclohexylamine-nitrite, were not only carcinogenic, but genotoxic as well (Refs 2, 3).

The increased health and safety concerns led a fair number of VCI product manufacturers to abandon secondary amines altogether in favor of primary and tertiary amines. This approach subsequently proved to be flawed, however, since technical (commercial) grades of primary and tertiary amines are generally not pure, containing 10% or more secondary amines. Once heat is applied during manufacturing processes, these components of relatively “safe” amines may also convert into N-nitrosamines. The conversion of secondary amines may also continue during the storage and application of the resulting products (Ref. 4). Evidence of these amine conversions was found in a German study, in which 40 commercially available VCI products were chemically analyzed (Ref. 5). It was found that 23 out 40, or slightly more than half of the products purchased on the market at the time, tested positive for the presence of secondary amines, and some of these products also contained carcinogenic N-nitrosamines. The other 17 products were nitrite based, and were found to be free of amines and nitrosamine by-products. These products were pronounced completely safe, based on all current scientific findings and worldwide regulations. All of this accumulated scientific evidence is being incorporated into evolving health and safety regulations worldwide, the most recent being German Technical Regulation TRGS-615 that came into effect in late 2003. TRGS 615 is specifically written to protect factory workers from exposure to carcinogenic, and possibly genotoxic, N-nitrosamines. It seeks to accomplish this by prohibiting all metalworking products, including VCI products that contain secondary amines or hidden secondary amines. This prohibition included known useful corrosion inhibitors like diamine carboxylates, diamine benzoates, diethanolamines, and of course dicyclohexylamine. Today, more than 30 years after the initial discovery that combinations of secondary amines and nitrosating agents can form hazardous N-nitrosoamines, a false association still persists that “nitrites” in VCI products are dangerous. The research summarized above, however, has clearly proven the reverse to be true. It is the secondary amines in all metalworking and VCI product that pose the risk. At the same time, there are still many perfectly safe amine based products on the market.

The Use of Nitrites in VCI Products

In the late 1970s, VCI product manufacturers were at a peak in their search for safe and effective new components that they could incorporate into their formulations. Dicyclohexylamine-nitrite, the foundation of so many VCI formulations in the past, had recently been identified as a carcinogen (later as a genotoxin), and was being abandoned by responsible VCI product manufacturers. Many manufacturers tried developing alternative amine-based formulations without nitrites. Still others, wisely, decided to take their search in the opposite direction and took a closer look at what nitrites had to offer. In 1979, Northern Technologies International Corporation (NTIC) made two significant innovations. NTIC not only managed to introduce a new VCI chemical system to the market that was founded on common food additives, but it was also the first to successfully impregnate these VCI formulations into plastic films on a commercial basis (Ref. 6). Today, subsequent generations of these initial innovations are still being successfully marketed by NTIC in almost 50 countries around the world under either the Zerust® or Excor® brand names. Of particular significance was that the Zerust®/Excor® products did not contain any amines whatsoever. Rather, they relied on nitrites, specifically sodium nitrite, as the foundation of their VCI rust inhibitor systems.  The value of sodium nitrite as a contact corrosion inhibitor had long been known. Nevertheless, conservative chemists had not considered its utility in a VCI system, due to an extremely low vapor pressure that was almost immeasurable at that time. The efficacy of sodium nitrite in VCI formulations has, however, since been proven in thousands of commercial and military applications worldwide, as well as recognized standard test methods for vapor corrosion inhibitors also used by U.S. and NATO military organizations, such as those listed in Ref. 8. The uniquely low vapor pressure of sodium nitrite also contributes to much longer-lasting corrosion protection in comparison to higher vapor pressure aminebased alternatives. In addition to its proven efficacy in rust protection, the use of sodium nitrite in VCI products also has an excellent health and safety record on three separate tiers.

First of all, the safety of sodium nitrite as a chemical substance is particularly well studied and monitored because of its primary use as a popular and critical preservative for meats (Ref. 7). There is evidently no alternative that can prevent the growth of the bacterium that causes botulism poisoning. Nitrites are also an integral part of the human and animal digestion of foods, particularly vegetables. Saliva and stomach acids convert the nitrates from food into nitrites as part of the overall “nitrogen cycle”, the most important nutrient cycle in ecosystems (Figure 1). Nitrites, as with most chemicals, can be poisonous if the pure material is ingested in sufficient quantities. However, the quantities distributed in Zerust® and Excor® packaging films, for example, approach the low levels found in foods. Furthermore, rather than being used as a loose powder, the nitrites and other VCI additives are imbedded (melted) into the plastic, effectively locking in all but what appears on the surface (Refs. 1 and 4), and, of course, there are only trace quantities in the surrounding air because of the extremely low vapor pressure. Consequently, exposure to the materials is safe and well below permitted levels for humans and animals, whether by directly eating or touching a VCI packaging product, or by breathing the trace concentrations of VCI molecules released into the air. That is why safety regulations like the German TRGS-615 restate the long-standing acceptability of corrosion inhibitors that contain less than 1% of their weight in nitrites. Secondly, unlike amines, the low levels of nitrites in Zerust® and Excor® VCI packaging, for example, have been demonstrated not to cause eye, skin or respiratory irritations. Therefore, these VCI products do not require additional safety gear such as gloves, respirators or safety glasses and will not cause any harm despite prolonged direct contact with skin, eyes or mucous membranes. The use of gloves is still highly recommended while handling metal parts, however, to protect them from the corrosive acids emanating from human skin. Finally, there was considerable concern that the “nitrites” in these VCI films would readily combine with secondary amine residues found on metal parts and subsequently form carcinogenic N-nitrosoamines. Several studies tried to deliberately create this affect in laboratory settings. However, they failed in each case, proving that the use of nitrite based VCI films is safe under these conditions, too.

The Specific Health and Safety of VCI Products

As specifically stated at the beginning of this article, certain VCI formulations and products have been proven hazardous via the accumulation of a rigorous body of scientific evidence. That, of course, is no reason to falsely condemn VCI technology as a whole. All VCI manufacturers and products are subjected to continuous, rigorous screening in order to ensure that worker safety is at the highest level. Remember that the ranks of VCI product manufacturers today include several respected “bluechip” public companies. Regardless of size, however, all chemical companies are subject to the laws and regulations that have been established around the world and are continually updated as on-going research provides new insights into protection of individual health and the environment. Secondly, to preempt frivolous lawsuits that are so pervasive these days, corporations go to extreme lengths to ensure product safety by subjecting any new formulations to rigorous toxicological testing and legal review before releasing them for sale. Once offered for sale, these same products are screened yet again for safety by governmental and certifying agencies in various countries. Finally, as a third level of rigor and scrutiny, industrial chemical products are reviewed by the in-house toxicology departments of all major manufacturing companies and military services before they are approved for use by employees of these organizations. At all three levels cited here, a complete disclosure of all raw materials in a product formulation is required. Consequently, a VCI manufacturer could not even begin to sell any product without first having successfully navigated all of these hurdles. In the meantime, interested readers can consult the references below showing a few of many scientific papers and reviews about specific VCI additives and formulations that have been tested, as well as reviews by agencies including the US EPA, the California EPA, the National Toxicology Center, and their counterparts in other countries, particularly in the European Union, Japan and Russia.

Conclusion

Significant advances have been made in the performance and scientific understanding of vapor corrosion inhibitors (VCIs). These advances also support evolving governmental regulations that protect worker health and safety. In particular, it is now clear that the use of secondary amines is hazardous, both alone (in the presence of air) and in molecular combination with other “nitrosating agents”. It is also clear that the class of corrosion inhibitors that uses nitrites without the presence of amines is safe and has proven for several decades to give effective long-term corrosion protection.

VCI product manufacturers include “blue chip” companies as well as other responsible public and private companies that are not only subject to existing laws and regulations, but also actively respond to advances in scientific knowledge. Such companies ensure product safety by subjecting new products to rigorous toxicological testing and legal review. Once offered for sale, there is also ongoing monitoring of product safety as well as associated safety labeling and documentation by governmental and certifying agencies in the various countries. Additional rigorous reviews are performed by in-house toxicology departments of all major manufacturing companies and military services, including detailed reviews of formulations and sometimes even confirmatory chemical analyses of actual products. These hurdles and reviews, as well as the intent to provide products and services with integrity, are a realistic basis for understanding the current acceptability of VCIs and related corrosion inhibitors.

By G. Patrick Lynch, gplynch@ntic.com
and A. James Henderson, jhenderson@zerust.com