Butyl Rubber (IIR)
Butyl rubber is a synthetic rubber, a copolymer of isobutylene with isoprene.
The abbreviation IIR stands for Isobutylene Isoprene Rubber. Polyisobutylene, also known as "PIB" or polyisobutene, (C4H8)n, is the homopolymer of isobutylene, or 2-methyl-1-propene, on which butyl rubber is based. Structurally, polyisobutylene resembles polypropylene, having two methyl groups substituted on every other carbon atom.
Polyisobutylene is a colourless to light yellow viscoelastic material. It is generally odorless and tasteless, though it may exhibit a slight characteristic odor. A synthetic rubber, or elastomer, butyl rubber is impermeable to air and used in many applications requiring an airtight rubber.
Polyisobutylene was first developed by the BASF unit of IG Farben in 1931 and sold under the trade name Oppanol B.
It was later developed into butyl rubber in 1937, by researchers William J. Sparks and Robert M. Thomas, at Standard Oil of New Jersey's Linden, N.J., laboratory.
In 1950s and 1960s, halogenated butyl rubber (halobutyl) was developed, in its chlorinated (chlorobutyl) and brominated (bromobutyl) variants, providing significantly higher curing rates and allowing covulcanization with other rubbers such as natural rubber and styrene-butadiene rubber. Halobutyl is today the most important material for the inner linings of tubeless tyres.
First commercialized in 1943, the primary attributes of butyl rubber are excellent - impermeability/air retention and good flex properties, resulting from low levels of unsaturation between long polyisobutylene segments.
Tyre innertubes were the first major use of butyl rubber, and this continues to be a significant market today.
The majority of the global supply of butyl rubber is produced by just two companies, ExxonMobil and LANXESS.
The Reliance-Sibur JV will be the first manufacturer of butyl rubber in India and following this, India’s import dependency is expected to come down subsequently.
In India there is no production capacity currently. The total demand for Butyl Rubber in 2011 was 87 KTA and is expected to touch 102 KTA in 2016-17.
Polyisobutylene and butyl rubber are used in the manufacture of adhesives, agricultural chemicals, fiber optic compounds, ball bladders, caulks and sealants, cling film, electrical fluids, lubricants (2 cycle engine oil), paper and pulp, personal care products, pigment concentrates, for rubber and polymer modification, for protecting and sealing certain equipment for use in areas where chemical weapons are present, as a gasoline/diesel fuel additive, and even in chewing gum.
The first major application of butyl rubber was tyre inner tubes. This remains an important segment of its market even today. Butyl rubber is used for the bladders in basketballs, footballs, soccer balls and other inflatable balls to provide a tough, airtight inner compartment.
Butyl rubber sealant is used for rubber roof repair and for maintenance of roof membranes (especially around the edges). It is important to have the roof membrane fixed, as a lot of fixtures (i.e., air conditioner vents, plumbing and other pipes, etc.) can considerably loosen it.
Butyl rubber is one of the most robust elastomers when subjected to chemical warfare agents and decontamination materials.
It is a harder and less porous material than other elastomers, such as natural rubber or silicone, but still has enough elasticity to form an airtight seal. Many varieties of chewing gum utilize food-grade butyl rubber as the central gum base.
Butyl (and its primary derivative, halobutyl) is and will continue to be a high value polymer particularly well suited for its primary application of air retention in tyres. Its unique combination of properties (excellent impermeability, good flex, good Weatherability, co-vulcanization with high unsaturation rubbers, in the case of halobutyl) makes it a preferred material for this application.
As miles driven, tyre size, and market sensitivity to pressure retention are all increasing the demand for butyl rubber.
Butyl Rubber typically contains about 98% polyisobutylene with 2% isoprene distributed randomly in the polymer chain. To achieve high molecular weight, the reaction must be controlled at low temperatures (-90 to -100 deg C). The reaction is highly exothermic.
The most commonly used polymerization process uses methyl chloride as the reaction diluent and boiling liquid ethylene to remove the heat of reaction and maintain the needed temperature. It is also possible to polymerize butyl in alkane solutions and in bulk reaction.
1. Butyl rubber or butyl polymer is generally prepared in a slurry process using methyl chloride as a vehicle and a Friedel-Crafts catalyst as part of the polymerization initiator.
2. The use of methyl chloride is advantageous because AIC13, a relatively inexpensive Friedel-Crafts catalyst, is soluble in methyl chloride, as are the isobutylene and isoprene comonomers.
3. Additionally, the butyl rubber polymer is insoluble in the methyl chloride and precipitates out of solution as fine particles.
4. The polymerization is generally carried out at temperatures of about -90° C. to -100° C.