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.

BR-based elastomeric foam Like Oil and Water insulation is made of a Nitrile Even those who haven’t cracked a Butadiene Rubber/PVC N 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 2 Sometimes 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 burnt

Polar

C N trans 1,4 BD trans 1,4 BD H2C H2C R HC H C CH HC CH HC CH CH 2 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 3 ozone 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

CH No toxic element! 3 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 4 Comparatively 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 5 About 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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