Seals, gaskets, and o-rings for high pH applications, including organic acid
technology ("OAT") coolant, require precise definition. Unfortunately, there is a
lot of loose talk regarding base resistant elastomers, or
BREs, in the world of fluoroelastomers. However, a hot,
high pH fluid will distinguish a counterfeit base resistant
elastomer within a couple thousand hours.
engineer should be careful selecting a base resistant seal
material for highly alkaline or caustic environments. There are sealing products loosely referred to
as base resistant, which in fact are not base resistant. An
old adage says that a woman
cannot be "kind of" pregnant. She is either pregnant or
she is not. So it goes with fluoroelastomers: they are
either base resistant or they are not. The
presence of any vinylidene fluoride ("VDF")
in the elastomer
backbone will render the elastomer susceptible to
dehydrohalogenation. In other words, the elastomer is not
base resistant if VDF is present.
It is common knowledge that a typical FKM class elastomer
(fluoroelastomer), containing 40% to 80% vinylidene
fluoride (also known as VF2 or VDF) will fail in a
moderately basic environment. The polymer manufacturers have
never suggested otherwise. However, in the early 1970’s
DUPONT had just developed a fluoroelastomer, now called
VITON® GF, with only 7% of VF2. Many suppliers and
distributors, to this day, suggest that having only a
little bit of VF2 induces base resistance.
The low vinylidene fluoride or VF2 elastomers
referred to as a BRE polymers often suggest the same. This
is simply not true.
In the early 1970’s, Seals Eastern performed testing for
the Johns-Manville Supertemp-Tite ® line of steam/hot water
AS568-214 o-rings of a low VF2 content fluorocarbon were
aged in a time sequence up to 12,000-hours of 150C continuous
The saturated steam / hot water was a controlled pH of
7.0-7.5 that would simulate a factory steam loop.
Usually, a slightly basic pH is maintained to prevent
corrosion in all such steam systems.
The o-rings aged in the steam loop represented a fluorocarbon
elastomer containing only a small amount of VF2. The results
illustrated the degrading effect on the elastomer backbone
of any VF2 in a mildly basic environment. Remember, a pH scale
is logarithmic so each pH point (1 thru 14) is
10X greater than the previous point (e.g. 7-8-9-10 is
1-10-100-1000x more aggressive in terms of nucleophilic
major breakdown product of a VF2 containing elastomer is
hydrogen fluoride and is the cause of the black corrosion
noted in both our SAE Paper 2000-01-0923 (Fluoride Ion
Concentration) and numerous field failures. Professor H.J.
Harwood, in his peer-reviewed paper developed for the
"Third Geothermal Seals Technical Session-1980",
defined the breakdown process in great detail. His paper was
subsequently published in ASTMs prestigious "Journal
of Testing & Evaluation" and is available (JTVEA,
Vol. 11, No. 4, July 1983, pp. 289-298. This work and data
is twenty-five years old: nothing has changed since
Harwoods 1980 work.
Dr.W.W. Schmiegel (Dupont Dow Elastomers), in his 2003 paper
entitled "A Review of Recent Progress in the Design and
Reactions of Base-Resistant Fluoroelastomers" presented
at The International Rubber Congress, states "[i]t is
an inescapable fact that amorphous fluoroelastomers of the
VF2/HFP/TFE and VF2/HFP/PMVE can not be made resistant to
gross dehydrofluorination and subsequent embrittlement due
to overcrosslinking on contact with strong nucleophilic
bases." This has been a market reality for more than
twenty-five years. This is why Seals Eastern has spent so
much time and money to develop its 7182™ brand AFLAS ®
technology. Further evidence is found in DuPonts recent
introduction of their TBR ( VTX-8802 ) polymer in an effort to
share in this growing market.
the major fluoroelastomer producers and fabricators not
having a non-VF2 offering have resorted to
“bad-mouthing” AFLAS by pointing out what was perceived
to be the low-temperature shortcomings of Aflas.
Specifically, the material possesses a glass-transition
point (“Tg”) slightly above 0˚C. Tg is the
temperature at which a polymer becomes "glassy". Seals Eastern has
repeatedly found, that in many engine applications, a high Tg is
simply not an issue regarding seal integrity. Nevertheless,
we have the same situation today. Fabricators, who have nothing
to offer for high-temperature, high pH environment
potential end-users of Aflas ® or DuPont’s TBR with the
low-temperature issue. The confusing premise is that a low
VF2 content FKM polymer with a (-12°C) Tg will somehow perform
better than an Aflas with its 7ºC Tg. The tragedy of this
argument is that attention is diverted from the catastrophic
consequences of a high temperature, high pH solution (i.e.
hot engine coolant / oil) in
contact with a VF2 containing polymer, no matter how small
the VF2 content.
rubber offers no reprieve for hot OAT coolants. It is a
widely know fact that silicone, a condensation polymer, will
simply revert in the presence of a strong base under
elevated temperatures such as you might find in engine
"hot spots". One simply has to research the
massive warranty issues (seal and gasket failures) experienced by several of the major
Fortunately, there is something
called "the market place". Whether or not a VF2
containing elastomer works in the market for alkaline
sealing applications, such as OAT coolants, will be discovered.
Unfortunately, the truth is often only realized after
considerable expense and the damage done.
Seals Eastern Inc.
Dan Hertz, Jr., President & Technical Director