Types of rubber

A natural cis-polyisoprene.

This is “the real thing”. The outstanding strength of natural rubber has ensured its position as the preferred material in many engineering applications. It has a long fatigue life and high strength (even without reinforcing fillers unlike SBR). The resistance to high temperatures is limited. The rubber is suitable for continuous use up to 70 degrees Celsius, intermittent exposure up to +100 degrees Celsius. It can maintain flexibility down to – 60 degrees Celsius if compounded for this purpose.

It’s main disadvantage is the poor aging and weather resistance, as its lack of resistance to oxygen, ozone and oil.

Acrylic rubber is used in the tyre industry and shock isolators.

Synthetic cis-polyisoprene has a high tear, pull and abrasion resistance. The aging properties of this synthetic alternative are better in comparison to natural rubber and also the machine-ability of cis-polyisoprene is better. Temperature resistance is also considerably better in comparison to natural rubber.

Despite the synthetic composition, this rubber is mechanically weaker in comparison to natural rubber, because it is not 1--% the cis-isomer. The ageing and weather properties are poor. Cis-polyisoprene also has poor resistance to mineral oils.

This rubber is used in the tyre industry and shock isolators.

When first introduced the name Buna S was used (“Bu” for Butadiene”, “Na” for Sodium” and “S” for Styrene). SBR is a copolymere of styrene and butadiene and is developed as a alternative for natural rubber.

SBR has a better properties where  high temperatures are concerned. With suitable fillers it is a strong rubber although not approaching natural rubber of polychloroprene. Otherwise it has similar chemical and physical properties to natural rubber, with general better abrasion resistance.

SBR is used in the tyre industry and in shock isolators, but also in shoe heels and even in chewing gum.

Polybutadiene (BR)

Butadiene rubber has a strong resistance to low temperatures. It has a low Tg (Glass Transition temperatures) in the region of – 75 degrees Celsius to – 100% degrees Celsius. This rubber has good flexibility and low hysterisis at ambient temperatures and these properties are maintained to temperatures well below zero.

Butadiene rubber has poor “wet traction” qualities as a result of the low Tg. This can be improved by combining BR with other elastomeres such as natural rubber or SBR.

Butadiene rubber is used in car tyres, treads, side walls and in compounds as a blend with natural rubber and SBR.

Isobutylene-isopropene copolymere (IIR)

A copolymerised version of isobutene and isoprene. IRR has been first commercially applied in 1943.

IRR has a low gas permeability and a good flexibility. Also the electrical, chemical, moisture and abrasion properties are good. The rubber is suitable for continuous use at temperatures from – 50 degrees Celsius up to 120 degrees Celsius. Butyl rubber also has good ozone and ageing properties.

Butadiene rubber has poor “wet traction” qualities as a result of the low Tg. This can be improved by combining BR with other elastomeres such as natural rubber or SBR.

Chlorobutyl Rubber (CIIR)

A isobutylene-isoprene copolymere derived from a reactive butyl rubber with a chlorine component.

The properties of CIIR are similar to the properties of Butyl rubber. However, the ozone and high temperature resistance is better. CIIR rubber is suitable for continuous use at temperatures from – 50 degrees Celsius (Tg – 65 degrees Celsius) up to 120 degrees Celsius.

CIIR is mostly used in car tyres.

Polychloroprene, CR

A chlorined polyisoprene. It is an all round elastomere, with properties similar to natural rubber. The world wide production of CR amounts to 300.000 tons per year.

Because of its versatility, Chloroprene does not really excel at specific properties. However the equilibrium between the various properties is unique in the World of synthetic elastomeres.  

Generally speaking, the mechanical equilibrium of properties and abrasion resistance is good. Also the chemical, water, oil and heat resistance is good.

Polychloroprene also has a good ozone, heat ageing, dissolved acids and alkaline resistance. 

Chloroprene contains chlorine, which reduces the reaction to oxidising components. It is also moderately resistant to high molecular oils and a base for flame retardant.

It’s not advised to use Polychloroprene for fuel resistance.

Polychloroprene is widely used, varying from rubber gloves and pre-moulded foams to a mean of improvement of bitumen.

Alkyl Acrylic copolymer, ACM

Strong resistance to hot carbohydrate oils an to oxidation, especially the sulphurised type. The rubber is suitable for continuous use at temperatures up to 150 degrees Celsius. Intermittent exposure up to +/- 175/180 degrees Celsius.

Poor resistance to water and moisture, acids and bases. This rubber is not advised to be used under minus 10 degrees Celsius.

Ethylene Acrylic, AEM

A terpolymere of ethylene, methyl acrelate and a monomere where vulcanisation is concerned.

Comparing to ACM, this elastomere has a better cold resistancy. Good temperature performance up to – 40 degrees Celsius. This rubber also has better dynamic properties. AEM is resistant to aliphatic hydrocarbons and has good heat ageing and weather ageing properties.

The oil resistancy of AEM is poor in comparison to ACM. Also the resistance to aromatic hydrocarbons, polarised fluids and strong acids and bases is poor.

AEM is used for flexible applications ranging from hoses, dampers to seals and gaskets.

Chloronated Polyethylene (CPE)

A chlorined polyethylene rubber.

Good chemical resistancy to fluid hydrocarbons at elevated temperatures. CPE is also resistant to many oxidising and corrosive chemicals.

CPE has poor mechanical qualities at temperatures above + 100 degrees Celsius.

Chlorosulphonated Polyethylene (CSM)

Also known as “Hypalon” by Dupont. CSM demonstrates durability in harsh environments and is known for its use in products that require high performance in extreme conditions (such as extreme temperatures, and ultra violet light, but also resistance to chemicals, etc.).

This rubber has excellent resistance to oxygen, water, oil, acid, ozone and many chemicals. The physical qualities are excellent. Also high temperature resistance is good (up to + 130 degrees Celsius) as are the abrasion properties. CSM has strong flame retardant properties and the gas density is good.

Epichlorhydrin (CO)

CO has poor cold, electrical and wear properties. Epichlorhydrin is not advised in combination with ketones, esters, alcohols, phosphate ester hydraulic fluids, acid gasses, water and steam. Rubber metal adhesion is difficult to achieve.

Ethylene Propylene Copolymer EPM or EPDM

It’s the best water resistant rubber available, also in combination with high temperatures. Steam resistancy can be improved by use of compounding. It has excellent atmospheric ageing properties, and is resistant to oxygen and ozone up to approximately 150 degrees Celsius. Acid resistancy is good. This rubber also performs well when exposed to high energy radiation.

A remarkable fact is that this rubber can be made resistant to phosphate ester hydraulic fluids of for instance aeroplanes, an unusual aggressive fluid that even FKM is not resistant to.

EPM/EPDM has poor resistancy to mineral oils and di-ester based lubricants.

EPM/EPDM has many applications such as seals, hoses, washers, etc. 

Fluorelastomere, FKM/FPM, also known as Viton Elastomer by DuPont

The following elastomere types can be discerned: Copolymere (2 monomers, 65% - 66% fluorine), Terpolymere (3 monomeres, 65% - 71% fluorine) and Tetrapolymere (4 monomeres, 67% - 69% fluorine) types. Also bisphenol vulcanised types and peroxide vulcanised types can be discerned. The fluorine content and the different monomer types including the different kinds of vulcanisation, lead to different properties as well as chemical and high and low temperature resistancy’s.

This elastomere is very resistant to many chemicals and performs well at high temperatures. It also has a good oil and high energy radiation resistancy. FKM/FPM has a high density and a high price per kilogram. The lowest possible Shore hardness is 50 – 60 Shore A. It also has an excellent resistancy to aliphatic and aromatic hydrocarbons, chlorinated solvents and petroleum based fluids.

VMQ Silicone rubber modified with fluorine offers good resistance to high and low temperatures, resistance to liquids, such as mineral oils and fuels, and in addition outstanding ozone resistance and resistance to oxidation and to the weather. It also does not readily adhere to anything. The resistance to low temperatures to -50 to -60 deg Celsius is better than that of FKM. The tensile strength and tear strength are lower at room temperature than those of other fluoroelastomers. Its specific gravity is also lower than that of FKM, at around 1.4.

Performs poorly with respect to gas impermeability.

Particularly in the aviation industry.

Nitrile Butadiene Rubber, NBR

First introduced to the market by Bayer in 1930 under the name Buna-N.

Based on 2 monomers, acrylonitrile and butadiene. The higher the acrylonitrile content, the more resistant the elastomer is to aliphatic hydrocarbons. The lower the ACN content, the better it resists low temperatures.

A subdivision can be made:

High ACN content, higher than 45%

Medium ACN content, between 30% and 45%

Low ACN content, lower than 30%

Gas permeability is low. Low compression set, heat ageing, ozone resistance and abrasion resistance can be improved by means of special compounding. Normally usable up to +100 deg C, and with special compounding up to around +120 deg C. This is an inexpensive rubber with high resistance to aliphatic hydrocarbons, oils and fuels. However, resistance to aromatic oils is poor.

Not ozone or weather resistant. Not resistant to aromatic oils, chlorinated hydrocarbons (trichloroethylene) or strong acids.

Patented by Bayer in 1975 and first introduced to the market in 1986 under the name Therban.

This is a saturated version of NBR with much greater temperature resistance. With ACN contents of 18 – 49% and a degree of saturation of 80 to 99%. Temperature resistance options from -45 deg C to above 165 deg C, with peaks up to 180 deg C.

This is a mechanically robust elastomer with good compression set, good "hot tear" and good ozone resistance. HNBR is highly resistant, showing resistance to mineral oils, including unrefined oils containing amines, sulphur, nitrogen oxides, and is also resistant to high-energy ionising radiation.

Also shows good resistance to hot water and steam. You could say that HNBR fills the gap between NBR and FKM. HNBR remains resistant to aggressive media at higher temperatures.

The major advantages of the considerably more expensive HNBR over NBR are the greater temperature resistance (sustained +150 C, with higher peaks), ozone resistance and the better mechanical properties. However, HNBR shows poor resistance to certain oxygenated solvents and aromatic hydrocarbons.

Not resistant to chlorinated hydrocarbons, polar solvents (ketones, ethers and esters) and strong acids.

First introduced to the market by DuPont under the name Kalrez.

Has greater heat and chemical resistance and especially acid resistance than fluoroelastomer (up to +320 deg C). Poor machinability, extremely high price and high density (around 2.0), poor mechanical properties at high temperatures, poor resistance to low temperature (around -10 deg C). There are various types of FFKM offering better resistance to high temperatures (+260 to 320 deg C), or respectively better chemical resistance to for example amines or steam. Also resistant to aliphatic and aromatic hydrocarbons and chlorinated hydrocarbons, polar solvents (ketones, ethers and esters), organic and inorganic acids.

DuPont is no longer the sole manufacturer of FFKM. Currently at least three other manufacturers of FFKM have been added.

Not resistant to fluorinated refrigerating agents and perfluorolubricants.

Frequently used in the chemical and oil industries.

Introduced to the market by Thiokol Chemical Corporation in 1943.

Extremely high resistance to mineral oils, fuel, solvents, oxides and ozone. Good gas impermeability.

Unpleasant to process, unpleasant odour.

In the automotive industry. Poor mechanical properties and poor heat resistance.

Polyurethane Elastomer, AU or EU

Bayer was the first to introduce Vulkollan to the market in the 1950's, developed from Otto Bayer's discovery in 1937.

This is on the market in various forms. There are millable types that may be processed like many other elastomers, but that need considerably more time to vulcanize, and the liquid versions. The hot-vulcanizable types possess better mechanical characteristics than the millable types, but these liquid types also have a long vulcanization (curing) time.
High tear strength, high abrasion resistance. Outstanding weather resistance and resistance to oxidation. Polyurethanes are resistant to hydrocarbons and mineral oil. Hydrolysis, water resistance, is poor, but better up to +60 deg C in the case of polyether polyurethane. The polyether version of the polyurethanes also show the highest low temperature resistance up to around -35 deg C. Unusual for this rubber is that the higger the hardness, the better the mechanical properties. Can normally be used up to around 80deg C, although a particular composition can be used up to around 150 deg C for a brief period.

Among the elastomers, polyurethane shows the greatest resistance to high doses of ionising radiation. A point to note is that, in the event of high-energy radiation doses, polyurethane must not be adhered to aluminium, as an acid is produced that attacks aluminium.

One disadvantage of this elastomer is that it loses heat poorly and thus builds up heat. Temperature resistance and hydrolysis resistance are further weak points.

In situations where abrasion is high or where  large forces are generated.

Dow Corning (a joint venture between Dow Chemicals and the Corning Glass Company) first produced silicone

rubber in 1943. General Electric followed with the production of silicone rubber in 1947. They patented their production method.

The rubber with the largest temperature range (-100 deg C (phenyl silicone rubber) up to more than +300 deg C). Superior ageing and ozone resistance, high electrical insulation values. Broad scale of chemical resistances. Good compression set at higher temperatures. PVMQ especially resistant to high energy ionising radiation. Its mechanical properties are not highly regarded, although this does not have to be the case. The tensile strength of silicone may not exceed around 11 MpA at room temperature. If desired, there are other elastomers with higger tensile strength. However, if temperatures are higher we see the values for other elastomers decline. At these higher temperatures, the values of silicone rubber remain much more constant. In addition we have silicone compounds with extremely high tear strengths for silicone rubber. As a result of its high degree of physiological inertness, silicone rubber is also used in food and medical applications. Silicone rubber is also resistant to bacteria and fungi.

Silicone rubber adheres poorly, for example to PTFE. We have been bounding silicone rubber to PTFE for almost 44 years. We can also make silicone rubber flame resistant. When silicone rubber is totaly burned, a white silicium powder remains. We are also able to produce silicone rubber that is an electrical conductor. We are able to make the compound suitable for gas chromatic applications, such as septa, that have to continue to close after a great number of perforations and may not emit any substances that could interfere with the readings measurements.

We are also able to make silicone rubber of extremely low hardness, around 10 deg Shore A.

Poor impermeability to gas, not resistant to hydrocarbon-based fuels, aromatic hydrocarbons (benzene, toluene), low molecular weight silicone oils, strong acids and alkalis. It is regarded as mechanically weak.

Extremely diverse.

Tetrafluoroethylene Propylene, FEPM

Initially introduced to the market in 1975 by the Asahi Glass Company under the name Aflas.

This is sold by the Asahi Glass Company under the brand name Aflas, designated FEPM in accordance with ASTM D1418. This elastomer has an extremely broad range of resistances, such as strong resistance to mineral oils, gas, acids and strong alkalis, bases, ozone and the weather, hot water and steam, alcohols, amine corrosion inhibitors, water-based drill oils and completion fluids, high pH completion fluids and high-energy ionising radiation. It is also highly gas-impermeable. In addition, electrical insulation is better than that of FKM.

However, FEPM is not resistant to aromatic hydrocarbons, chlorinated hydrocarbons, organic acetates and organic refrigerant liquids.

FEPM can withstand dry heat of 230 deg C for lengthy periods, and steam with peaks of 260 deg C. The price per kg is extremely high. The specific gravity is 1.51 to 1.6. This elastomer is used primarily in the chemical and oil industries. Resistance to cold: brittle point is –40 deg C, TR10 is 0 deg C.

Frequently used in the chemical and oil industries.

Viton Extreme from DuPont

DuPont has produced a variation on the basis of Aflas, officially also designated FEPM in accordance with ASTM D1418. This is a revolutionary Advance Polymer Architecture (APA) polymer bisphenol vulcanized TFE/Propylene, with a fluorine content of 67%. As a result of its structure, Viton Extreme from DuPont combines the best of FEPM and Special FKM.

There are ETP and TBR versions.

Viton Extreme ETP has the following important properties and probably combines the best of FEPM and Special FKM:

It is resistant to acids, hydrocarbons, low molecular weight esters, ketones and aldehydes, strongly caustic solutions, amines and hot water. Resistance to cold Tg10 is 10 deg C. Note this is not TR 10.

Viton Extreme TBR has the following important properties:

It is resistant to caustics and amines, hydrocarbon oils, acids and steam. It has superior compression set values, lower swelling percentages in the case of long-life seals, and high abrasion resistance.

As a result of its chemical structure, Viton Extreme TBR, like all TFE/Propylene products, is not recommended for fuel seals in the automotive or aviation industries.