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MT16 Elastomers, Rubber Compounds and Synthetics

 

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Tutorial                                                                                                                                                                                                            rht July 2010

Elastomers are long-chain polymers which are capable of cross-linking which is referred to as vulcanization.  The vulcanization process cross-links the polymer chains via chemical bonds creating the elastic or “rubbery or memory properties”.

Elastomers are typically descried by type or family based on the base polymer used in the formulation.  These classifications are summarised per the ASTM D 1418 standard below and more detail is available for each of the families by clicking on the Chemical Description contained in the summary.

ELASTOMER RUBBER COMPOUNDS TYPES AND REFERENCES
General Description
Chemical Description
Abbreviation (ASTM 1418)
ISO/DIN
1629
Other Trade names & Abbreviations
ASTM D2000 Designations
     Nitrile

Acrylonitrile-butadiene rubber

NBR NBR Buna-N BF, BG, BK, CH
     Hydrogenated Nitrile Hydrogenated Acrylonitrile-butadiene rubber
HNBR (HNBR) HNBR DH
     Ethylene-Propylene Ethylene propylene diene rubber EPDM EPDM EP, EPT, EPR BA, CA, DA
     Fluorocarbon Fluorocarbon Rubber FKM FPM Viton , Fluorel HK
     Chloroprene Chloroprene rubber CR CR Neoprene BC, BE
     Silicone Silicone rubber VMQ VMQ PVMQ FC, FE, GE
     Fluorosilicone Fluorosilicone rubber FVMQ FVMQ FVMQ FK    
     Polyacrylate Polyacrylate rubber ACM ACM ACM EH
     Ethylene Acrylic Ethylene Acrylic rubber AEM AEM Vamac EE, EF, EG, EA
     Styrene-butadiene Styrene-butadiene rubber SBR SBR SBR AA, BA
     Polyurethane Polyester urethane / Polyether urethane AU / EU AU / EU AU / EU BG
     Natural rubber Natural rubber NR NR NR AA

Vamac and Viton are registered trademarks of E. I. du Pont de Nemours and Company or affiliates.
Fluorel is a registered trademark of Dyneon LLC

General Properties - Classes of  Elastomer and Compounds:

Very Good = 1 Good = 2 Average = 3 Poor = 4 Temperature in F
Basic Property NBR HNBR EPDM FKM CR ACM AEM SBR AU/EU VMQ FVMQ NR
     Economy of Material 1 4 2 3 2 3 4 1 3 3 4 1
     Compression Set Resistance 1 1 1 1 2 4 2 2 3 2 2 1
     Resilience (Rebound) 2 2 2 2 2 3 2 2 2 2 2 1
     Tear Strength 2 1 2 2 2 3 2 3 2 4 3 1
     Heat Aging Resistance 3 2 2 1 3 1 1 3 1 1 1 3
     Ozone Resistance 4 2 2 1 2 2 1 4 1 1 1 4
     Resistance to Oil & Grease 2 2 4 1 2 1 3 4 2 3 1 4
     Fuel Resistance 4 3 4 2 4 1 4 4 3 4 2 4
     Water Swell Resistance 2 2 1 2 3 4 2 1 4 1 1 1
     Gas Impermeability 2 2 3 2 2 3 2 3 2 4 4 3
     Dynamic Service / Abrasion Res. 2 2 2 3 2 2 2 1 1 4 4 1
     High Temperature - Standard 212 300 300 390 250 300 300 212 175 450 400 220
     High Temperature - Special 250 - - - - - - - - 480 - -
     Low Temperature - Standard -22 - 22 -60 5 -40 -60 -40 -50 -60 -75 -75 -60
     Low Temperature - Special -60 -40 - -30 - - - - - - - -
NATURAL RUBBER (NR)
Natural rubber is a product coagulated from the latex of the rubber tree, hevea brasiliensis. Natural rubber features low compression set, high tensile strength, resilience, abrasion and tear resistance, good friction characteristics, excellent bonding capabilities to metal substrate, and good vibration dampening characteristics.
Temperature Range (dry heat)
low high
- 60 F
-51 C
220 F
104 C
Application Advantages

excellence compression set
good resilience and abrasion
good surface friction properties



Primary Uses Application Disadvantages
O-rings, rubber seals and custom molded rubber components for:

rubber to metal bonded vibration isolators and mounts
automotive diaphragms
FDA applications for food and beverage seals

poor resistance to attack by petroleum oils
poor ozone, UV resistance

FLUOROSILICONE (FVMQ)
Fluorosilicones combine most of the attributes of silicone with resistance to petroleum oils and hydrocarbon fuels.
Low physical strength and abrasion resistance combined with high friction limit fluorosilicone to static seals.
Fluorosilicones are used primarily in aircraft fuel systems.
Temperature Range (dry heat)
low high
-75 F
-59 C
450 F
232 C
Application Advantages

excellent extreme temperature properties
excellent compression set resistance
very clean, low odor and taste


Primary Uses Application Disadvantages
O-rings, rubber seals and custom molded rubber components for:

seals (static) for extreme temperature applications
food applications
medical devices
FDA applications

typically not good for dynamic seals due to friction properties and poor abrasion resistance

SILICONE (VMQ)
Silicone is a semi-organic elastomer with outstanding resistance to extremes of temperature with corresponding resistance to compression set and retention of flexibility. Silicone elastomers provide excellent resistance to ozone, oxygen, and moisture.
Low physical strength and abrasion resistance combined with high friction properties limit silicone to static seal applications.
Silicone utilises a flexible siloxane backbone rather than a carbon backbone like many other elastomers and has very low glass transition temperatures.
Temperature Range (dry heat)
low high
-75 F
-59 C
450 F
232 C
Application Advantages

excellent extreme temperature properties
excellent compression set resistance
very clean, low odor and taste

Primary Uses Application Disadvantages
O-rings, rubber seals and custom molded rubber components for:

seals (static) for extreme temperature applications
food applications
medical devices
FDA applications

typically not good for dynamic seals due to friction properties and poor abrasion resistance

POLYURETHANE (AU) (EU)
Millable polyurethane exhibits excellent abrasion resistance and tensile strength as compared to other elastomers providing superior performance in hydraulic applications with high pressures, abrasive contamination and shock loads. Fluid compatibility is similar to that of nitrile at temperatures up to approximately 175 F. At higher temperatures, polyurethane has a tendency to soften and lose both strength and fluid resistance advantages over other elastomers.
Temperature Range (dry heat)
low high
- 60 F
- 51 C
175 F
79 C
Application Advantages

excellent strength and abrasion resistance
good resistance to petroleum oils
good weather resistance

Primary Uses Application Disadvantages
O-rings, rubber seals and custom molded rubber components for:

seals for high hydraulic pressure
highly stressed parts subject to wear

poor resistance to water
poor high temperature capabilities



STYRENE BUTADIENE (SBR)
Styrene-Butadiene (SBR) is a copolymer of styrene and butadiene.
SBR compounds have properties similar to those of natural rubber. SBRs primary custom molded application is the use in hydraulic brakes system seals and diaphragms, with the major of the industry usage coming from the Tyre Industry.
SBR features excellent resistance to brake fluids, and good water resistance.
Temperature Range (dry heat)
low high
- 50 F
-46 C
212 F
100 C
Application Advantages

good resistance to brake fluids
good resistance to water

Primary Uses Application Disadvantages
O-rings, rubber seals and custom molded rubber components for:

hydraulic brake systems seals and diaphragms
plumbing applications

poor weather resistance
poor petroleum oil and solvent resistance


ETHYLENE ACRYLIC (AEM)
Ethylene-acrylic (Vamac ) is a terpolymer of ethylene, methyl acrylate, and an acid-containing monomer as a cure site. It exhibits properties similar to those of Polyacrylate, but with extended low temperature range and with enhanced mechanical properties.
Ethylene-acrylic offers a high degree of oil, ozone, UV and weather resistance.
Temperature Range (dry heat)
low high
- 40 F
- 40 C
300 F
149 C
Application Advantages

excellent vibration dampening
excellent heat aging characteristics
good dynamic property retention over a wide temperature range
resistance to transmission fluids, water, glycol mixtures, and alkalies

Primary Uses Application Disadvantages
O-rings, rubber seals and custom molded rubber components for:

Automotive sealing applications.
Automotive transmissions
Power steering seals

not recommended for exposure to fuel, brake fluid, aromatic hydrocarbons or phosphate esters.

POLYACRYLATE (ACM)
Polyacrylates are copolymers of ethyl and acrylates which exhibit excellent resistance to petroleum fuels and oils and can retain their properties when sealing petroleum oils at continuous high temperatures up to 300 F. These properties make polyacrylates suitable for use in automotive automatic transmissions, steering systems, and other applications where petroleum and high temperature resistance are required.
Polyacrylates also exhibit resistance to cracking when exposed to ozone and sunlight.
Polyacrylates are not recommended for applications where the elastomer will be exposed to brake fluids, chlorinated hydrocarbons, alcohol, or glycols.
Temperature Range (dry heat)
low high
-60 F
-51 C
300 F
149 C
Application Advantages

petroleum fuel and oil resistance
resists flex cracking
good ozone resistance
good heat resistance

Primary Uses Application Disadvantages
O-rings, rubber seals and custom molded rubber components for

Automotive transmissions.
Automotive steering systems

poor compression set performance relative to NBR
lesser water resistance and low temperature performance than some other elastomers

NEOPRENE / CHLOROPRENE (CR)
Neoprene homopolymer of chlorobutadiene and is unusual in that it is moderately resistant to both petroleum oils and weather (ozone, UV, oxygen). This qualifies neoprene uniquely for certain sealing applications where many other materials would not be satisfactory. Neoprene is classified as a general purpose elastomer which has relatively low compression set, good resilience and abrasion, and is flex cracking resistant.
Neoprene has excellent adhesion qualities to metals for rubber to metal bonding applications.
It is used extensively for sealing refrigeration fluids due to its excellence resistance to Freon and ammonia.
Temperature Range (dry heat)
low high
- 40 F
- 40C
250 F
121C
Application Advantages

moderate resistance to petroleum oils
good resistance to ozone, UV, oxygen
excellence resistance to Freon and ammonia

Primary Uses Application Disadvantages
O-rings, rubber seals and custom molded rubber components for

refrigeration industry applications
general purpose seals, hose and wire

moderate water resistance
not effective in solvents environments

FLUOROCARBON (FKM)
Fluorocarbon exhibits resistance to a broader range of chemicals combined with very good high temperature properties more so than any of the other elastomers. It is the closest available approach to a universal elastomer for sealing in the use of o-rings and other custom seals over other types of elastomers.
Fluorocarbons are highly resistant to swelling when exposed to gasoline as well as resistant to degradation due to expose to UV light and ozone.
When exposed to low temperatures, fluorocarbon elastomers can become quite hard (-4 F) but can be serviceable at low temperatures, although FKM compounds are not recommended for applications requiring good low temperature flexibility.
In addition to standard FKM materials, a number of special materials are available with differing monomer compositions and fluorine content (65% to 71%) for improved low temperature, high temperature, or chemical resistance performance.
Fluorocarbons exhibit low gas permeability making them well suited for hard vacuum service and many formulations are self-extinguishing. FKM materials are not generally recommended for exposure to hot water, steam, polar solvents, low molecular weight esters and ethers, glycol based brake fluids, or hot hydrofluoric or chlorosulfonic acids.
Temperature Range (dry heat)
low high
5 F
- 15 C
390 F
199 C
Application Advantages

excellent chemical resistance
excellent heat resistance
good mechanical properties
good compression set resistance

Application Disadvantages

poor low temperature flexibility
poor resistance to hot water and steam

Modifications

differing monomer compositions and fluorine content (65% to 71%) for improved low temperature, high temperature, or chemical resistance performance

Primary Uses Specialised Applications
O-rings, rubber seals and custom molded rubber components for

Automotive fuel handling
Aircraft engine seals
High temperature applications requiring good compression set
General industrial seals and gaskets

degree of fluorination (A, B, F, GB, GF, GFLT, GBLT, GLT, ETP)
copolymer or terpolymer of fluorinated hydrocarbon monomers

ETHYLENE-PROPYLENE (EPDM)
Ethylene-propylene compounds are prepared from ethylene and propylene (EPM) and usually a third monomer (EPDM). These compounds are used frequently to seal in brake systems, and for sealing hot water and steam.  Ethylene propylene compounds have good resistance to mild acids, detergents, alkalis, silicone oils and greases, ketones, and alcohols. They are not recommended for applications with petroleum oils, mineral oil, di-ester lubricants, or fuel exposure.

Ethylene Propylene has gained wide seal industry acceptance for its excellent ozone and chemical resistance properties and is compatible with many polar fluids that adversely affect other elastomers.

EPDM compounds are typically developed with a sulphur or peroxide cure system. Peroxide-cured compounds are suitable for higher temperature exposure and typically have improved compression set performance.
Temperature Range (dry heat)
low high
-60 F
-51 C
300 F
149 C
Application Advantages

excellent weather resistance
good low temperature flexibility
excellent chemical resistance
good heat resistance

Application Disadvantages

poor petroleum oil and solvent resistance

Modifications

sulphur-cured and peroxide-cured compounds
third comonomer EPDM, copolymer ethylene and propylene EPM

Primary Uses Specialised Applications
O-rings, rubber seals and custom molded rubber components for

Water system seals, faucets, etc.
Brake systems
Ozone exposure applications
Automotive cooling systems
General Industrial Use

glycol-based brake system seals
FDA approved applications
NBR NSF standard 61 for potable water applications
NBR WRc, KTW water applications

HYDROGENATED NITRILE (HNBR)
HNBR is created by partially or fully hydrogenating NBR. The hydrogenating process saturates the polymeric chain with accompanying improvements to the ozone, heat and aging resistance of the elastomer and improves overall mechanical properties.
HNBR, like Nitrile, increasing the acrylonitrile content increase resistance to heat and petroleum based oils and fuels, but decreases the low temperature performance.
Temperature Range (dry heat)
low high
-22 F
-30 C
300 F
149 C
Application Advantages
excellent heat and oil resistance
improved fuel and ozone resistance (approximately 5 times) over Nitrile
abrasion resistance
Application Disadvantages

increased cold flow with hydrogenation
decreased elasticity at low temperatures with hydrogenation over standard nitrile

Primary Uses Modifications
O-rings, rubber seals and custom molded rubber components for:

Oil resistant applications
Oil well applications
Fuel systems, automotive, marine, and aircraft
General Industrial Use

acrylonitrile content (ACN) from 18% to 50%
peroxide vs. sulphur donor cure system

NITRILE (NBR)
Nitrile is the most widely used elastomer in the seal industry. The popularity of nitrile is due to its excellent resistance to petroleum based oils and fuels, and its ability to be compounded for service over a temperature range of -22F to 212F.
Nitrile is a copolymer of butadiene and acrylonitrile. Variation in proportions of these polymers is possible to accommodate specific requirements. An increase in acrylonitrile content increases resistance to heat plus petroleum base oils and fuels but decreases low temperature flexibility. Military AN and MS O ring specifications require nitrile compounds with low acrylonitrile content to insure low temperature performance.
Nitrile provides excellent compression set, tear, and abrasion resistance. The major limiting properties of nitrile are its poor ozone and weather resistance and moderate heat resistance, but in many application these are not limiting factors.
Temperature Range (dry heat)
low high
-22 F
-30 C
212 F
100 C
Application Advantages

excellent compression set,
superior tear resistance
abrasion resistance

Application Disadvantages

poor weather resistance
moderate heat resistance

Modifications

acrylonitrile content (ACN) from 18% to 50%
peroxide vs. sulphur donor cure system
XNBR improved wear resistance formulation

Primary Uses Specialised Applications
O-rings, rubber seals and custom molded rubber components for:

Oil resistant applications
Low temperature applications
Fuel systems, automotive, marine, and aircraft
General Industrial Use

NBR NSF standard 61 for potable water applications
NBR WRc, KTW water applications
NBR FDA white list compounds

 

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