W. Stephen Tait, Ph.D. Chief Science Officer & Principal Consultant, Pair O Docs Professionals, LLC Corrosion Corner What packaghaeps pcenors rowdhee?n spray ello everyone. Is corrosion-free spray packaging a realistic expectation? What can happen when a spray package corrodes? This month we’ll examine the various scenarios that could occur when a formula causes spray package corrosion, and the options for living with corrosion. Corrosion Basics: spray package lifetime All spray products have a lifetime during which the product and the package both perform as specified. This lifetime is often referred to as shelf life. However, the term shelf life usually applies to products with active ingredients, such as pharmaceutical products and insect control products. For example, a five-year shelf life indicates that the effective medical ingredient concentration in the package is around 50% after five years. I prefer the term service lifetime when discussing spray packages. Service lifetime is the length of time when packages perform as specified—that is, packages spray until the product is exhausted and do not leak product. Corrosion Basics: categories of spray package corrosion There are two general categories of spray package corrosion: • General • Localized o Pitting corrosion o Crevice corrosion Both categories of corrosion could affect polymers, polymer coated metals—lined traditional aerosol containers and spray packages with internal laminated film bags—and spray packages using uncoated aluminum or steel (tinplate or tinfree steel). General corrosion occurs over the entire internal package surface or in large patches on the surface. Localized corrosion occurs at small points—pits and coating/laminate blisters of 50 microns or less in diameter—or in areas where two pieces of material overlap (such as aerosol container double seams and laminated bag welds). Corrosion in overlapping areas and bag welds is referred to as crevicing. Corrosion Basics: how corrosion affects spray products Corrosion of spray packaging could: Cause product instability • Metal corrosion could catalyze active ingredient decomposition, thereby reducing effective concentrations • Metal ions from corrosion break an emulsion 42 Spray December 2014 Degrade product efficacy • Metal corrosion could discolor the product or cause a malodor • Metal corrosion could degrade active ingredients, reducing product efficacy Cause package leaking • Localized metal corrosion could cause product to leak • Localized metal corrosion causes partial or complete loss of propellant Cause packages to stop spraying • Loss of propellant through a corrosion perforation • Pieces of coating or laminate film clog dip tubes or aerosol valve orifices • Metal corrosion product accumulates in dip tubes and aerosol valves and ultimately clog the dip tube of valve orifices There are two ways to address corrosion issues. Corrosion could be prevented or controlled by reformulating with or without a corrosion inhibitor. Corrosion prevention means that corrosion is not present during the specified service life of the spray package. Corrosion prevention is typically achieved with a corrosion inhibitor or by changing to a different type of spray package. Corrosion inhibitors have effective concentration ranges, like all of a formula’s ingredients. Too much or too little of a corrosion inhibitor could actually cause or exacerbate corrosion. Consequently, quality specifications should include analysis for the corrosion inhibitor concentration in each manufacturing batch prior to spray package filling. Corrosion is present with control. However, very slow corrosion usually does not reduce service life below the specified target or appear to degrade product efficacy. In other words, package service life is extended through control and control is also probably reducing the corrosiondegradation of product efficacy. The quality specifications should also include analysis for corrosion inhibitor concentration prior to spray package filling when a corrosion inhibitor is used to control corrosion. In addition, commercial spray packages should be periodically retrieved and inspected for corrosion when using corrosion control. Determination of corrosion inhibitor concentration and measurements of product efficacy is also recommended during these inspections. Inspections should be conducted throughout the commercial life of the product. H
Spray Dec 2014
To see the actual publication please follow the link above