Chemical Polarity and Its Impact on the Performance of Elastomeric Foam Insulation - By Chum Kotcha September 15, 2019
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Chemical Polarity and Its Impact on the Performance of Elastomeric Foam Insulation By Chum Kotcha September 15, 2019
Closed-cell elastomeric foam is widely recognized as an effective insulator for pipes
and ductwork, but ask an engineer to distinguish whether a particular elastomeric
foam insulation is “NBR” or “EPDM” -based and you are likely to get a blank stare.
Many engineers designing mechanical HVAC or plumbing systems today may not even
realize that two distinct formulations for elastomeric foam exist. After all, both types
of insulation are remarkably similar in all observable aspects, most notably the pliable,
carbon-colored material and characteristically smooth skin. But despite their similarities
in both application and appearance, NBR and EPDM elastomers are very different. One
might even say they are polar opposites.
N
BR-based elastomeric foam Like Oil and Water
insulation is made of a Nitrile
Even those who haven’t cracked a
Butadiene Rubber/PVC
chemistry book since high school
polymeric blend. EPDM is made of an
probably remember that a molecule
Ethylene Propylene Diene Methylene.
— the smallest physical unit of an
Both compounds are cross-linked
element or compound — consist
during a vulcanization process,
of two or more atoms chemically
which gives them their “rubbery”
bonded to one another. All atoms,
characteristic; however they differ
whether they be carbon, hydrogen
significantly in their chemical structure.
or any of the other 118 elements on
It’s this structure that determines
the periodic table, have a specific
whether a particular polymer is
electronegativity value. This value
considered “polar” or “non-polar,”
reflects an atom’s ability to attract
characteristics which describe the
electrons. When atoms come together
behavior of the material at a molecular
to form a molecule there is a certain
level. The chemical polarity of an
amount of “push and pull” that takes
insulation gives us important insight
place between them depending on the
into how the material will react under
difference in electronegativity between
certain environmental stresses.
the atoms. (Think of a tug-of-war.)
The single most pointed difference
between NBR- and EPDM-based
insulations is that NBR is polar and The chemical polarity of an insulation gives us
EPDM is non-polar. But what does that important insight into how the material will react under
mean? And, more importantly, how certain environmental stresses.
does the polarity of the material impact
its performance as an insulation? The
answer is rooted in basic chemistry.
Chemical Polarity and Its Impact on the Performance of Elastomeric Foam Insulation I September 15, 2019 AEROFLEX I 2Sometimes it’s a fair fight — so fair What Makes An Elastomeric Foam
that the electronegativity of one atom Polar or Non-Polar?
cancels the other out and a sort of
When it comes to complex chemical
equilibrium is achieved.
compounds such as those that make up
This “balance” of charge and/or the elastomeric foam, it can be difficult to
symmetrical distribution of shared determine polarity. This is because the
electrons between atoms are what final product includes a mix of other
make certain molecules non-polar. chemicals that may include synthetic
It is why oil (non-polar) and water or non-synthetic rubber, fillers,
(polar) do not mix. Their respective curing agents, accelerators, peptizers
electronegativity characteristics drive and blowing agents. However,
them apart. On the other hand, we all the molecular structure of these
know how easily table salt (extremely compounds gives us some clues.
polar!) dissolves rapidly in water. Polar
Figure 1 below shows the molecular
molecules like to mingle — so much so
structure of both EPDM and NBR.
that this affinity for one another can
Notice that there is a lack of
cause a change in physical state and
symmetry to the NBR chain. This is
molecular structure. Water is especially
indicative of an uneven sharing of
effective at creating physical change
electrons between the elements that
as it will eventually dissolve just about
make up the molecular structure.
anything that happens to be the least
This “unevenness” destabilizes
bit polar, including highly polarized
the molecular bonds under certain
formulations of elastomeric foam.
environmental exposures, including
heat, moisture, ultraviolet light,
Figure 1 Cyanide Group > Cyanide gas (HCN) emitted when NBR is burned
Polar
C N trans 1,4 BD
trans 1,4 BD H2C H2C R
HC H2C CH HC CH HC CH CH
1,2 BD
CH2 CH CH2 CH2 H2C CH2
Acrylonitrile cis 1,4 BD HC CH2
R
Double bonds in the main polymer chain > reactive and easily broken when
attacked by HEAT, MOISTURE, UV, O3, O2, POLAR SOLVENTS, ACID AND ALKALI
Chemical Polarity and Its Impact on the Performance of Elastomeric Foam Insulation I September 15, 2019 AEROFLEX I 3ozone and oxygen. It is this polarized respective installations of EPDM and
chemical structure that makes NBR NBR insulations, but all things being
hygroscopic — meaning that it attracts equal (proper sizing, installation,
water molecules from the surrounding environmental factors, etc.) NBR-based
environment. It also makes it elastomer foam insulation will start to
more vulnerable to other types of degrade long before insulations made
environmental degradation. of EPDM-based foams. Its cells will
begin to collapse, cracking will appear
The molecular structure of EPDM,
and the material itself will start to lose
shown in Figure 2 below, is quite
its flexibility. As moisture infiltrates
different. Notice that its chain is linear
the material, its thermal properties will
and much more balanced. This, among
increasingly degrade since water is a
other things beyond the scope of this
far more effective conductor of heat
article, are indicative of its impressive
than air. Extreme moisture infiltration
molecular stability. It is hydrophobic,
will start to break down the material
meaning that it does not induce or
itself, the tell-tale sign being a kind of
react with water or moisture from
“black slime” that occurs at the surface
its surroundings. In addition, the
of the product. This can be likened to
saturated chemical structure of EPDM
the dissolution of salt in water, where
makes it less reactive to ultraviolet
water is dissolving another polar
light and ozone than NBR, so it
substance.
degrades at a slower rate than NBR
under these exposures.
It may be months or years before
these differences manifest in
Figure 2 Fully saturated backbone chain (no reactive double bond > Not reactive
to HEAT, MOISTURE, UV, O3, O2, POLAR SOLVENTS, ACID AND ALKALI
(CH2 CH2) m (CH CH2) n ( )o
No toxic element! CH3
Safe for all users!
CH-CH3
Pendant diene: This double bond will be cured during
production processes to strengthen the product only.
Chemical Polarity and Its Impact on the Performance of Elastomeric Foam Insulation I September 15, 2019 AEROFLEX I 4Comparatively speaking, the molecular wide temperature range. The most
polarity of NBR makes it markedly less notable among this is moisture. EPDM EPDM Sheet Insulation
stable than EPDM under environmental is hydrophobic (it does not dissolve in
conditions that would be most relevant water) whereas NBR is hygroscopic (it
to any type of mechanical insulation does attract water and will eventually
application. Table 1 below compares the begin to dissolve). To the specifier this
properties of both types of materials means greater precaution must be
with respect to various exposures. taken when opting for NBR over EPDM, 12 Months Control
especially for applications where there (0 Months)
Conclusion
is high humidity and/or applications
Despite their nearly identical where the potential for condensation
visual characteristics and common is high. Installers have far less room
NBR Sheet Insulation
applications in mechanical HVAC, for error as extreme care must be
(Brand 1)
plumbing and refrigeration systems, taken to protect the material from
EPDM and NBR elastomeric closed- environmental conditions, including
cell insulations are markedly different moisture and sunlight. Finally, owners
in molecular structure. The most need to be made aware that NBR
fundamental difference is polarity. foams, though slightly less in material 12 Months Control
The non-polarity of EPDM makes it a costs, will most likely have higher (0 Months)
more stable material when exposed lifecycle costs due to the shorter
to moisture, sunlight, ozone and a lifespan of the product.
NBR Sheet Insulation
Typical Operating Properties
(Brand 2)
Property EPDM NBR
Continuous low temperature, °F -297 -297
Continuous high temperature, °F 257 220
Ozone Excellent Good
12 Months Control
UV resistance Excellent Good
(0 Months)
Water vapor permeability Excellent Good
The above samples show one EPDM-
based elastomeric foam insulation and
two different brands of NBR-based
insulations after undergoing identical
ASTM G7 Exposure Test conditions,
including exposure to rain, sunlight,
wind and moisture. Samples on the right
show the unexposed control sample.
Samples on the left show the product
after 12 months of exposure testing.
Chemical Polarity and Its Impact on the Performance of Elastomeric Foam Insulation I September 15, 2019 AEROFLEX I 5About the author
Chum Kotcha is a Chemist and Ms. Kotcha would like to thank Ravina
Technical Manager for Aeroflex USA. Vitoorapakorn, Sales & Procurement
She is responsible for oversight of Manager for Eastern Polymer Group,
rubber formulations, raw materials for her assistance with this article.
and process control. She also Ms. Vitoorapakorn has a Master’s
oversees the properties testing degree in Polymer Science.
of Aeroflex finished goods.
About Aeroflex
Aeroflex USA, Inc. is a manufacturer Public Co., Ltd. (EPG). EPG is highly
of closed-cell elastomeric foam regarded throughout the world for its
insulation for HVAC, plumbing contributions to the polymer industry.
and refrigeration systems. All of The company operates eight R&D
Aeroflex insulation products are laboratories that fuel its subsidiary
made in Sweetwater, Tennessee, and companies with innovations that
are shipped throughout the USA, enhance the durability, safety and
Canada, and Mexico. Aeroflex USA sustainability
insulations are enriched by the vast of its products.
resources and expertise of parent
company, Eastern Polymer Group
Corporate office:
282 Industrial Park Road
Sweetwater, TN 37874
423.337.2493 Fax: 423.337.7675
Toll Free: 866.AEROCEL
www.aeroflexusa.com
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