Written on: January 1, 2020 by W. Stephen Tait
Happy New Year, everyone. One of the most frequent questions that I’m asked is, “When is corrosion testing required for spray packaging?”
Spray packaging corrosion risks without corrosion testing or a comprehensive company corrosion database is approximately 62% for aerosol containers and approximately 20% for laminated metal foil packaging.
Thus, high risk comes with incomplete corrosion testing or corrosion tests using the wrong test parameters. Consequently, your best defense against spray product failures and litigation from unexpected corrosion is a complete and robust corrosion testing program. Hence, I recommend that corrosion tests should be conducted on the following:
Corrosion science is not advanced enough at this time to where chemistry first principles can be used to determine if a given formula’s chemical composition is or is not corrosive toward the different types of spray packages. Consequently, corrosion testing is needed to avoid high risk.
Derivations of existing products (line extensions or derivatives)
Small changes to the chemical composition of a formula could transform a benign formula into a spray package-eater. Thus, derivative formulas (or line extensions) should be tested for corrosion compatibility with the chosen spray package, no matter how small the change to the formula.
All new insecticide formulas and derivative insecticide formulas
Insecticide chemicals are often electrochemically active and thus corrosive toward spray packaging. Typically, insecticide formulas also need a corrosion inhibitor to prevent or control spray package corrosion.
When developing a corrosion inhibitor
Corrosion testing is needed to find a suitable inhibitor for a corrosive formula. Corrosion inhibitors typically have an effective concentration range and corrosion testing is also needed to determine the effective range.
Anhydrous formulas and derivative anhydrous formulas
Anhydrous formulas are typically contaminated by small amounts of water. Water is electrochemically active and causes metal corrosion. Consequently, anhydrous formula corrosion testing is needed to determine if the formula is corrosive with a given concentration of contaminant water and to determine the safe concentration range for contaminant water.
New and derivative low pH formulas
PH is the negative log of hydrogen ion concentration in moles per liter. Hydrogen ions are electrochemically active and cause corrosion of spray package metals and metal foils. Consequently, low pH formulas should be tested for corrosion with all types of spray packages.
New and derivative high pH formulas
High pH formulas can also cause spray package corrosion. Thus, corrosion testing is also needed for high pH formulas.
Changes to an existing formula’s chemical composition
Small changes to the chemical composition of a formula could transform a benign formula into a spray package-eater. Thus, any change to the chemical composition—no matter how small the change—should be tested for corrosion.
Changing package materials for existing formulas
Changes to package materials could include different types of polymer coatings or laminate films; different coating thicknesses and/or different package metals. The chemical composition of a formula determines if a given type of package material is resistant to corrosion. Thus, corrosion tests should also be conducted when switching package materials.
Changes to raw material suppliers for existing formulas
The chemical composition of raw materials from different suppliers might be different. Consequently, corrosion testing should also be conducted when changing raw material suppliers.
Changing surfactant suppliers, types and concentrations for existing formulas
Surfactants make a surface more or less susceptible to wetting by formula ingredients, formula water and contaminant water. Thus, corrosion testing should be conducted when changing the type of surfactant or your surfactant supplier.
Changing fragrance types, suppliers and/or concentrations
Many fragrances offer some modicum of corrosion inhibition. There are also a few types of fragrances, such as those incorporating vanilla, that often cause corrosion. Consequently, changes to the type of fragrance, fragrance supplier and fragrance concentration in your formula should be tested for changes in corrosion.
Unexpected spray package corrosion can be very costly and disruptive to product development programs. Indeed, the cost of unexpected corrosion typically greatly exceeds the cost for complete corrosion testing. Consequently, the answer to the when-to-test question is virtually everything should be tested, or—if available—a proprietary, comprehensive company corrosion database should be consulted to determine if corrosion testing is needed.
In Chapter 7 of the Pair O Docs Elements of Spray Packaging Course short course we discuss various types of corrosion tests. Basically, corrosion testing could be either a storage stability test for a year or more, or a shorter electrochemical corrosion.
Test results from shorter storage times, such as three months, could be misleading and result in unexpected spray package corrosion in commercial products. Using higher temperatures to accelerate corrosion typically leads to high risk, incorrect and confusing predictions about actual corrosion. For example, three months of storage testing at 40°C (104°F) does not correspond or predict the corrosion that will occur after 2–5 years storage at room temperature.
Electrochemical corrosion tests can accurately predict 2–5 years of actual spray package corrosion in less than 100 days when the appropriate test parameters are used for the electrochemical test.
Please visit www.pairodocspro.com for more information. Thanks for reading and I’ll see you in February. SPRAY