Corrosion Corner
The corrosion of
refillable multiple-use
packaging—Part I
Hello, Everyone. We have a paradox—both docs from Pair
O Docs Professionals LLC are authoring the June and
July editions of Corrosion Corner. Those of you who have
worked with Pair O Docs know Sue from our Elements of Spray
Package Corrosion short course, as well as her work in the Pair O
Docs laboratory operations and on corrosion test design.
This issue, we begin a two-part discussion on the corrosion of
refillable multiple-use (RMu) packaging.
The RMu package platform has been much in the news and
appears to be a promising new element for “Green” packaging.
Indeed, some of the articles we’ve seen indicate that RMu packages
might replace traditional, disposable single-use packages for a
variety of spray products and pump products (see SPRAY, March
2019, p.35).
Based on what we’ve read, it appears that the main types of materials
being considered for RMu packaging are coated aluminum,
glass and stainless steel. All of these materials will eventually fail
and the failure modes could be either structural or cosmetic. The
possible structural failure modes are:
• Chipping—glass
• Fracturing (cracking and breaking)—glass and internal
polymer coatings
• Aging/Memory—glass and internal polymer coatings
• Corrosion—metals and coated metals
The possible cosmetic failure modes are:
• Etching (glass)
• Fracturing (glass and polymer coatings)
• Denting (metals) and scratching (all materials)
Scratching
Scratching does not lead to metal failure, but it could subsequently
lead to glass fracturing or a breach in a polymer coating that
allows the environment (e.g.,
your formula) to contact the
metal under the coating.
Etching
Etching is glass corrosion
brought about by chemical attack.
It causes the glass to have
a frosted look.
Aging
Glass, polymer coatings and
polymer films have amorphous
molecular structures instead
of the orderly, metal, repeating
geometrical structure.
Amorphous materials typically
become more brittle with age
and thus become more susceptible
to cracking, chipping and
W. Stephen Tait, Ph.D.
Chief Science Officer & Principal Consultant,
Pair O Docs Professionals, LLC
fracture. Consequently, aging
ultimately leads to glass and
polymer failures.
Memory
We have all experienced the manifestations of long-term material
memory. Remember that favorite glass or ceramic mug that you
used over and over? You dinged it here and there, plus probably
knocked it over a few times. Then one day when you were using it,
you dinged it just a little and the mug broke. Glass and ceramics
are brittle and micro-cracks formed each time you bumped your
favorite mug, dropped it and knocked it over. The micro-cracks
26 Spray June 2019
SUSAN WHIT WORTH Tait, Ph.D.
Executive Director & CFO,
Pair O Docs Professionals, LLC
Scratching could lead to glass fracturing…
Glass can get a frosted look through
etching, which is glass corrosion
brought about by chemical attack.
While this looks attractive when
used intentionally for aesthetic purposes,
it is not a desirable outcome
when chemicals accidentally come
in contact with your glass package.
Micro-cracks accumulate
and grow in a mug until the
final bump causes it to fail.