Vapour / Volatile corrosion protection.

A volatile corrosion inhibitor (VCI) / Vapour Phase corrosion inhibitors (VPCI) agent/s are characterized as being primarily in the solid or liquid state at ambient temperatures and pressures, but with some fraction in the vapour phase at equilibrium.

The vapour phase corrosion inhibitor in the vapour stream adsorbs on the exposed metal surfaces forming a thin, protective layer that provides continuous protection against corrosion from exposure to moisture, salt, oxygen, carbon dioxide, or other corrosive elements.

Even if the layer is disturbed by moisture or other corrosive components entering the interior volume, the corrosion inhibiting characteristics remain effective.

In some embodiments, the VCI agent is supplied in a solid form. Solid-phase particles have diameters of less than 50 microns. 

The VCI agent may be enclosed in a vapour permeable pouch or package.

VCI agents can also be added to the polymer melt intended for melt extrusion or blow molding, thus resulting in a packaging material (film or hard material) out of which the VCI components are able to sublime continuously because of the structurally induced porosity.

A VCI is a “noncontact inhibitor”. The performance of any VCI inhibitor depends on the effectiveness of the packaging seal around the metal object, i.e. to prevent the inhibitor from escaping into the atmosphere.

There are 3 Groups of Vapour Phase Inhibitors

Group IGroup IIGroup III
Low vapour pressure inhibitorsMedium vapour pressure inhibitorsHigh vapour pressure inhibitors
Vapour pressure of less than 10-4 mm Hg at 20° CVapour pressure between 10-3 – 10-4 mm Hg at 20° CVapour pressure above 10-3 mm Hg at 20° C
Long term but slow effect as VCIMedium Term effect and effect as VCIShort term quick effect as VCI

Some of the VCI Chemicals are as follows.

Benzotriazole Cyclohexylamine Benzoate    
Cyclohexylamine carbonateCyclohexylammonium Benzoate
Dicyclohexyl ammonium benzoateDicyclohexyl ammonium salicylate
Dicyclohexyl ammonium nitriteDicyclohexylamine Nitrite                 
Dicyclohexylamine Chromate            Diethanolamine Benzoate     
icyclohexylaminebenzotriazoleDiisopropyl ammonium nitrite
Diisopropyl ammonium benzoateMorpholine
Monoethanolamine BenzoateOctylcaprilamide
Nitro naphthalene ammonium nitriteOctylstearamide

Contact corrosion protection

Contact corrosion protection works only when the VCI product (film, paper, tape, and sheet) is in direct contact with the product which is to be protected. Most of the time the film, paper, or sheet is tightly wrapped around the object to prevent exposure to moisture, or corrosive environment. Contact corrosion inhibitors are transferred to the metal surface by creeping of the inhibitors from the wrapping material directly to the metal. This allows the corrosion inhibitor to remain with the metal even if the package is not sealed properly.

Contact corrosion inhibitors

Chemical NameChemical Name
Ammonium dimolybdatePotassium benzoate
Cesium benzoatePotassium Nitrite
Cesium NitritePotassium Pyrophosphate
Lithium benzoateSodium Benzoate
Lithium NitriteSodium Molybdate

Barrier Protection

Any VCI film requires effective barrier protection to prevent corrosion from corrosive environment.  One way to improve the barrier protection properties is by using additives to improve the film barrier properties.

Another option is to co-extruded VCI film with multiple layer of film with specific characteristics used to prevent corrosion, provide additional barrier protection, and increase durability and puncture resistance over mono-extruded VCI films. This additional protective layer serves as a barrier, preventing moisture, salt, dirt, oxygen, and other corrosion-causing materials from depositing directly on the metal. In addition additives such as UV Inhibitors, Anti-Static compound, low slip are added to prevent outer film degradation.

However there need to be a balance between barrier protection and film permeability to allow VCI components are able to sublime continuously because of the structurally induced porosity in the film. This can be achieved by either using 2 separate coatings to the 2 sides of the film or by using multiple layers. Selecting the correct Resin (HDPE, LDPE, PE, and PP) also helps in improvements in barrier properties of the VCI Film.

Benefits  of Sodium benzoate (Micronised) as Corrosion Inhibitor in VCI Films / VCI Papers.

Sodium Benzoate widely used as contact corrosion inhibitor in VCI Films. It is also used in Radiators & Engine coolants and metal treatment as corrosion inhibitor. Use of Sodium benzoate in VCI Films as effective contact corrosion inhibitor is well documented.

US Patent: 7763213 , 7588820, 6540959, 6752934

Polymer Add Thailand supplies special grade of Sodium Benzoate called (Micronised VCI Grade) which is widely used to manufacture VCI Film and Paper.

Some of the benefits offered by Sodium Benzoate (Micronised VCI Grade) are as follows.

Sodium Benzoate (Micronised VCI Grade) from Polymer Add Thailand Co Ltd has very small micron particle size (D50 less than 5 microns) which enables complete, uniform dispersion in solid form in the VCI Film during extrusion.

Better dispersion during extrusion means improvement in barrier properties and improvement in physical properties of VCI film. This is particularly useful where the VCI Packing has to be opened and closed several times during the usage cycle and effect of VCI additives is minimised due to constant opening and closing of the packing.

Sodium Benzoate (Micronised VCI Grade) from Polymer Add Thailand Co Ltd improves the flexural modulus without affecting the tensile strength of the film which can be verified by actual testing.

Sodium Benzoate (Micronised VCI Grade) from Polymer Add Thailand Co Ltd is thermally stable upto 400 degrees C making it preferred VCI additive for harsh weather conditions from sub zero to high temperatures applications.

Compatible with almost all VCI Film grade polymers ( PP, LDPE, HDPE, PE, ETC)

Sodium Benzoate does not react with other additives in the film.

Sodium benzoate is cost effective & safe for the environment, as compared with other contact corrosion inhibitors used in VCI films.

Sodium Benzoate (Micronised VCI Grade) from Polymer Add Thailand Co Ltd is available in 10 Kg paper bags with inner liners.