Corrosion Corner
The corrosion of
refillable multiple-use
packaging—Part II
Hello, Everyone. We again have a paradox—both docs
from Pair O Docs Professionals LLC. are authoring this
month’s edition of Corrosion Corner.
Last month, we discussed the structural and cosmetic failure
modes possible with refillable multi-use (RMu) packaging. This
month we’ll finish the discussion with corrosion, one cause of
package failures.
The various news articles on RMu packaging gave Steve a
strong sense of Déjà vu. Multiple decades ago, he investigated
replacing disposable single-use aerosol containers with RMu
aerosol containers. The concept was ultimately not commercially
successful due to issues with de-crimping aerosol valves, incompatible
cleaning processes and extensive corrosion issues.
As mentioned last month, glass, coated aluminum and stainless
steel are the most likely materials for RMu packaging. All
three of these materials will corrode. As always, corrosion issues
are whether the corrosion rate is low enough for the package to
have the desired service life and whether the corrosion rate is low
enough that metal ions from corrosion will not adversely affect
product performance and efficacy.
Materials research & corrosion testing needed
Glass is brittle and some annual loss is unavoidable from chipping,
cracking and breaking. However, glass packages could have
W. Stephen tait, ph.D.
Chief Science Officer & principal Consultant,
pair O Docs professionals, LLC
longer service lifetimes with proper handling, cleaning procedures
and selection of cleaning detergents. For example, our Aristartec
FlexiCell electrochemical test cell has both glass and metal components
and both types of components are designed to be re-usable.
The cells have undergone storage jostling, assembly handling,
high temperature washing and interactions with hundreds of different
test fluids, such as consumer spray products.
We do lose some of the glass-components each year from
chipping and breakage, but none of them experience etching
(glass corrosion). Most of our glass-components have been in
use for nearly two decades as a result of extensive research and
testing on different types of glass and selecting detergents that
do not etch glass while cleaning.
All of the FlexiCell metal components have been in use
for nearly two decades as a result of extensive research to find
metal alloys that are resistant to corrosion by a wide range
of liquids and by developing a cleaning process that doesn’t
corrode the metal components (which includes non-corrosive
detergents).
Common materials in spray & RMu packages
Disposable single use spray packaging and RMu packaging both
use stainless steel and aluminum. For example, stainless steel
(SS) springs are used in both package platforms for aerosol valves,
pumps and sprayers and coated aluminum is also used for both
package platforms.
A common myth is that stainless steel alloys (SS-alloys) are
corrosion-proof. However, SS-alloys do corrode under various conditions.
A common household example is the iridescent blue color
inside SS cookware. General corrosion, pitting corrosion, crevice
corrosion, weld corrosion, vapor phase corrosion and interfacial
corrosion can all affect SS-alloy RMu packaging as well as aluminum
RMu packaging.
Consequently, RMu packages need to undergo similar corrosion
testing as is conducted on traditional spray packaging.
However, the multiple cycles needed for RMu packages requires
specific testing protocols expanded beyond those used for disposable
single-use packaging to reflect the new conditions of use and
the longer service lifetimes.
Corrosion prevention
& control for metal RMu packages
Last month, we also mentioned that thicker metals would increase
the denting resistance of metal RMu packages. However, thicker
metals and thicker internal coatings do not increase stainless steel
and aluminum corrosion resistances. The important concept to
30 Spray July 2019
SUSan WhitWORth tait, ph.D.
executive Director & CFO,
pair O Docs professionals, LLC
Stainless steel alloys do corrode under various conditions; a common household
example is the iridescent blue color inside of stainless steel cookware.