Chemical Database

Monday, April 20, 2009

Silicone Rrubber MQ MPQ MVQ and MPVQ

As you can see, a number of symbols have been designated for significant variations within the silicone rubber family. The reader may refer to ASTM D 1418 for abbreviations for elastomeric materials. Since all of the symbols for silicone rubber end in Q, this is the convention that will be used for silicone rubber in general. Most elastomers have a carbon main chain, while Q has a silicone oxygen backbone. Silicone has an upper continuous heat aging temperature in the region of 205°C. Caprino and Macander give a table of estimated service life for Q as follows: 40 years at 90°C, 2-5 years at 200°C and two weeks at 315 °C. Moisture, such as might be found in a poorly ventilated environment, can be a problem at high temperature. Silicone is among the best elastomers for both high and low temperature resistance. PVMQ heads the low temperature list at around -100°C. Silicone rubber has excellent ozone, weather resistance and electrical insulation. Like CR, Q has a measure of flame retardant ability. Mechanical properties such as tensile strength, are low, but change very little when measured at higher temperatures; at 150°C, it is catching up with other elastomers. Oil resistance is about the same as that of CR, acid and alkali resistance are not good. Applications include aerospace, medical, food contact, and automotive ignition cable. The cost of the raw gum elastomer is higher than any of the rubbers mentioned so far.

Reference: An Introduction to Rubber Technology by Andrew Ciesielski 1999

Sunday, April 19, 2009

Butyl Rubber IIR and Halobutyl Rubber CIIR and BIIR

Butyl rubber is a copolymer of isobutylene and isoprene, hence IIR. Its grades vary in isoprene content and viscosity, which is related to molecular weight. If a halogen, such as chlorine or bromine, is introduced into the polymer architecture, it becomes CIIR or BIIR, respectively. IIR has some properties similar to those of EPDM, such as good mineral acid and base resistance (like EPDM some concentrated mineral acids are a problem), and weather resistance which is similar to that of EPDM. IIR has excellent resistance to permeability by gases. For example, Fusco mentions its permeability to air being as low as 10% that of NR, at 65°C. Like EPDM, the polarity of IIR is low which means poor resistance to petroleum oils and conversely low swell in many polar solvents, such as ketones. Resilience is poor, which translates to good damping ability. The upper continuous heat aging temperature limit is around 121°C, which can be distinctly improved with IIR compounds containing resin (polymethylol-phenol) cure systems. For low temperature properties the vulcanizate becomes stiff and leathery at around -18°C, although it is not brittle until around -70 0C, Applications naturally following from these properties include mounts and bumpers for vibration and shock prevention, roof and tank linings, curing bladders and inner tubes for tires. A significant use is inner liners for tubeless tires, where halobutyl is preferred due to improved interply adhesion with the rest of the inner tire. Halobutyls can be blended with unsaturated elastomers such as NR, whereas for IIR it is not recommended. Blending is not recommended for IIR since the rate of cure of the 'other elastomer' in the blend is often much faster than the rate of cure of the IIR, resulting in under cured IIR in the blend. IIR and halobutyl are used for pharmaceutical closures using high purity zinc oxide as the curative. Zinc oxide, is 'generally regarded as safe' by the United States Food and Drug Administration, i.e., has historically been in common use in contact with food or skin for many years without ill effect. Recent elastomer modifications (from Exxon) are p-methylstyrenelisobutylene copolymers, which have the low permeability and high damping of IIR with the environmental and aging resistance of EPDM, and 'star branched' butyls, which have improved processing properties, prior to cure.

Reference: An Introduction to Rubber Technology by Andrew Ciesielski 1999

Thursday, April 16, 2009

Nitrile NBR

To the chemist this rubber is known as acrylonitrile butadiene rubber, to others it is called Buna-N but to many people in the industry, simply, nitrile. It is the workhorse of the marketplace for its oil resistant properties. The grades offered differ in the percentage of acrylonitrile (ACN) in the polymer chain as well as the overall viscosity of the polymer. The higher the amount of ACN in the elastomer the better the oil resistance; the lower end of the ACN distribution range being approximately equivalent to the oil resistance of CR and therefore only having a moderate level of oil resistance. NBR also has superior fuel resistance. The terms oil and fuel used here refers loosely to those products derived from petroleum. The weather resistance of NBR is poor, similar to NR and SBR, although it can be enhanced by blending with the plastic, polyvinyl chloride (PVC), at some 'cost' to its low temperature properties. This latter attribute of NBR also varies with ACN content; the lower the percentage of ACN in the polymer, the better the low temperature flexibility, and the poorer the oil resistance. A compound which has a nitrile raw gum elastomer in it, with a medium (33%) ACN content would have good oil resistance and low temperature resistance down to the region of -40°C. A low ACN (18%) nitrile would be useful down to -55°C. NBR has better heat aging resistance than CR and is in the region of 107°C for continuous (defined approximately as 1,000 hours) use. Special compounding ingredients can be added to increase heat aging resistance. Like SBR, NBR needs reinforcing fillers to give good mechanical properties.

NBR use is dominant in the oilfield, used in blowout preventions, packers and seals. However, sour gas wells containing hydrogen sulfide and amine corrosion inhibitors have been a problem for NBR based components because both chemicals can degrade nitrile elastomers causing embrittlement. The other major use for NBR is in the automotive sector. However, as 'under the hood' temperatures increase with reduced airflow and smaller engine compartments, NBR producers are searching for ways of increasing this elastomer's upper region of heat aging resistance. The term sour gas is also used in automotive applications, but here it means hydro peroxides (rather than hydrogen sulfide), which sometimes form in unleaded gasoline; this can be damaging to the 'average' NBR. Very high ACN NBR or NBRJPVC might be used in this situation. The use of alcohol (methanol and ethanol) in gasoline, the so called oxygenated fuels, has made NBR processors look very closely at the effect of such a mixture on this elastomer, since alcohol concentrations at a certain level (around 10%) could be a problem. The alcohol causes NBR in contact with the gasoline alcohol blend to swell significantly. Blends above 5% should be treated with caution unless a resistant rubber type is used. It is worth noting that many applications of NBR exclude contact with oxygen (from the surrounding air), since the product is immersed in oil. This can increase the heat aging resistance temperature mentioned above. NBR is a distinctly polar rubber; hence it’s excellent resistance to non polar petroleum oils. This also means that NBR has poor resistance to polar liquids such as ketones, esters, chlorinated solvents, and highly aromatic solvents such as benzene
and toluene.

Reference: An Introduction to Rubber Technology by Andrew Ciesielski 1999 Page 18

Sunday, April 12, 2009

Some Types of Rubbers and their Properties

BUTYL RUBBER (IIR)

BUTYL RUBBER (IIR) has very low permeability rate, good electrical properties, resistance to weathering and Ozone.

TEMP: 40⁰C to 120⁰C

Chemical Resistance: Hot Water, Steam, Ozone, Ageing, & Weather Resistance, Silicon Oil & Grease.

POLYTETRAFLUOROETHYLENE (PTFETEFLON ®)

PTFE exhibits outstanding chemical resistance to the harshest media, Non flammable, inert, self lubricating are some of its special properties.

TEMP: 200⁰C to 260⁰C

Other Filled grades of PTFE viz. BRONZE, CARBON, GLASS, MOS2 have better mechanical properties than virgin PTFE.

NATURAL RUBBER (NR)

The oldest rubber available having outstanding resistance to tear, abrasion and cut growth.

Chemical Resistance: Water Oxidation, Alcohol and Ketones, Moderate Resistance to Acids, Alkalis.

ORings are manufactured from over 15 different Polymers which include Nitrile (NBR), Fluorocarbon (Viton®), Silicon (VMQ), Fluorosilicone (FVMQ), Polyurethane, PTFE (Teflon®), Natural Rubber (NR), Ethylene Propylene (EPDM), Hydrogenated Nitrile Rubber (HNBR), Carboxylated Nitrile Rubber(XNBR), Styrene Butadiene Rubber (SBR), Perfluoroelastomer (FFKM), Chloroprene (Neoprene®).

ETHYLENE PROPYLENE RUBBER (EPDM)

EPDM is a CoPolymer of Ethylene and Propylene and is mostly used in Break systems having Glycol based Fluids.

TEMP: 55⁰C to 150⁰C

Chemical Resistance: Hot Water and Steam, Glycol based brake fluids, Organic And Inorganic Acids, Phosphate Ester Based Fluids, Soda, Potassium, Silicon Oil and Grease, Ozone, Aging and weather resistant.

ACRYLONITRILE BUTADIENE (NBR NITRILE)

Nitrile Rubber (NBR) is the general term for Acrylonitrile Butadiene Polymer. Acrylonitrile content varies from 18 to 50%. Higher the Acrylonitrile content, better the resistance to fuel and oil, at the same time affecting elasticity & compression set.

TEMP: 30⁰C to 100⁰C

Chemical Resistance: Propane, Butane, Petroleum, Mineral Oil, Grease, Diesel Fuel, Fuel Oils, HFA, HFB, HFC Fluids, Dilute Acids, Alkali, Salt Solutions and Water.

CARBOXYLATED NITRILE (XNBR)

Carboxylated Nitrile has proven tear and abrasion resistance compared to NBR. It is often used for dynamic applications.

TEMP: 30⁰C to 100⁰C

HYDROGENATED NITRILE (HNBR)

NBR compounds exhibits improved heat resistance to the general NBR compounds. They also possess superior mechanical properties particularly high strength.

TEMP: 40⁰C to 150⁰C

FLUOROCARBON (FKM VITON ®)

FLUOROCARBON (FKM VITON ®) has excellent resistance to High temperature, Ozone, Oxygen, Mineral Oils, Aliphatic and Aromatic Hydrocarbons and many chemicals.

TEMP: 20⁰C to 204⁰C

Chemical Resistance: Mineral Oil, Grease, Non Flammable Hydraulic Fluids, Aliphatic and Aromatic Hydrocarbons, Ozone Weathering, Aging, High Vacuum, Steam and Alcohol.

SILICON (VMQ)

Silicon has best Cold flexibility, Excellent heat resistance, Good Insulating properties, Good Ozone and weathering resistance, as well being neutral in its properties.

TEMP: 50⁰C to 232 ⁰C Chemical Resistance: Ozone, Aging, Weathering, Animal & Vegetable oil, Grease, Moderate Resistance to Mineral Oil.

FLUOROSILICONE (FVMQ)

Fluorosilicone (FVMQ) offers improved fuel and oil resistance in comparison to regular Silicon (VMQ), Mechanical and Physical properties being the same. TEMP: 70⁰C to 175⁰C

POLYURETHANE (AU)

POLYURETHANE have the highest Wear resistance, Tensile strength and Elasticity. They have high volume applications in seals for hydraulic cylinders.

TEMP: 30⁰C to 80⁰C

Chemical Resistance: Ozone, Aging, Mineral Oil, Aliphatic Hydrocarbons, Water (upto 50⁰C)

STYRENEBUTADIENE RUBBER (SBR)

SBR previously known as ' BUNA S' was first produced as a replacement to natural rubber.

TEMP: 40⁰C to 105⁰C

Chemical Resistance: Water, Alcohol, NonMineral Oil fluid, Silicon oil and Grease, Weak Acids.

CHLOROPRENE RUBBER (CR NEOPRENE®)

Chloroprene popularly known as NEOPRENE exhibits good Ozone, Aging, chemical, Abrasion & Flex Fatigue Resistance.

TEMP: 40⁰C to 120⁰C

Chemical Resistance: Silicon Oil And Grease, Water and its solvents, Refrigerants, Ammonia and Carbon Dioxide, Ozone, Weathering and Aging.

CHLOROSULFONATED POLYETHYLENE (CSM HYPALON ®)

Chlorine in the Polymer imparts resistance to Flame and Mineral Oils and also improves cold flexibility. TEMP: 20⁰C to 120⁰C Chemical Resistance: Oxidising Media, Water, Aging, Grease, Many Acids.

PERFLUOROELASTOMER (FFKM)

PERFLUOROELASTOMER (FFKM) exhabits unique resistance even in the harshest environments. It exhabits unbeatable resistance to Acids, Alkalis, Steam, Ketones.

TEMP: 25⁰C to 300⁰C

Chemical Resistance: Aliphatic, Aromatic and Chlorinated Hydrocarbons, Organic And InOrganic Acids, Water, Steam and Vacuum.

TETRAFLUOROETHYLENE PROPYLENE (TFPE)

TFEP has excellent chemical resistance to a wide range of materials

TEMP: 5⁰C to 232⁰C

Chemical Resistance: Bases, Engine Oil, Steam, Radiation, Amines Phosphate Esters.

Saturday, April 11, 2009

What exactly does the word 'rubber' mean?

Rubber seems to be a fairly straightforward word. The French call it caoutchouc recognizing its historically South American 'native' origin. The word derives from a South American Indian word, meaning 'weeping wood' [18, 19]. The dictionary definition of rubber is, 'a material that when stretched returns quickly to its' approximate original shape'. This definition fits the vulcanized material quite well. ASTM Standard D 1566¬98 [1] has a detailed definition of rubber implying the vulcanized material. Unfortunately the rubber industry tends to be somewhat casual in the use of the term rubber. When a rubber product is made, the primary raw material is a polymer. This polymer often has some elasticity, but not always. It is then mixed with chemicals to make a rubber 'compound' which is subsequently vulcanized. This compound is simply a physical mixture of chemicals and indeed a number of ingredients in the vulcanizate might be present only as a physical blend. The industry often calls both the polymer and the uncured compound, 'rubber'. Unvulcanized silicone, for example, (both polymer and uncured compound) does not fit the dictionary definition too well, since it can have the consistency of butter. The word used in this book for the primary raw polymer will be raw gum elastomer.

Some people use the term rubber, to mean NR only, but there have been instances when a customer asked for rubber (expecting the vendor to choose the right type, neoprene, natural, etc.), the vendor however assumed the customer was specifically asking for natural rubber, which in that case turned out to be the worst choice. Naturally, the vulcanized material is also called rubber, as indeed it should be. The word 'elastomer' and 'rubber' are often used by the industry to mean exactly the same thing, which is a waste of such an interesting word (elastomer), which maybe, could have been reserved exclusively to describe the raw polymer. Blow [20] makes comments similar to these, about the word 'rubber' having several meanings. He suggests that the vulcanized material be called 'elastomer'. ASTM Standard D 1566-98 defines 'elastomer' as 'a term often used for rubber and polymers that have properties similar to those of rubber'.