Butyl Rubber - IIR Rubber - definition, production, properties, applications

What is butyl rubber?

Butyl rubber, also known as isobutylene-isoprene rubber, is a synthetic rubber produced by copolymerising isobutylene with small amounts of isoprene. The material is distinguished by its chemical inertness, gas impermeability and weather resistance.

That is why butyl rubber is used in the inner linings of car tyres and in other specialised applications.

What does IIR stand for?

IIR stands for "Isobutylene Isoprene Rubber".

How is butyl rubber produced?

Butyl rubber is produced from isobutylene and isoprene. Both compounds are usually obtained by thermal cracking of natural gas or lighter fractions of crude oil.

At normal temperature and pressure, isobutylene is a gas and isoprene is a volatile liquid. For conversion to IIR, isobutylene (cooled to very low temperatures) is diluted with methyl chloride.  Later, low concentrations (1.5% to 4.5%) of isoprene are added.

The presence of aluminum chloride in the process initiates a reaction in which the two compounds copolymerize (i.e., their individual molecules join together to form large, multi-unit molecules).

Because the base polymer, polyisobutylene, is stereoregular (i.e., its pendant groups are arranged in regular order along the polymer chains) and because the chains crystallize quickly when stretched, IIR rubber is as strong as natural rubber.

What are the properties of butyl rubber?

To some extent, the properties of butyl rubber are unique in that it is the only known elastomer that does not transmit gases. Butyl rubber is a flexible type of rubber and has good vibration-damping properties at room temperature.

IIR rubber is biocompatible, resistant to many acidic and alkaline chemicals, ozone, heat and weathering, and has good aging properties.

Butyl rubber also features resistance to phosphate ester and ketone-based hydraulic fluids, but does not perform well in the presence of mineral or petroleum-based fluids, hydrocarbons and flames.

IIR rubber also has good electrical insulating properties.

Bromine or chlorine can be added to the small isoprene fraction of IIR to make BIIR or CIIR (known as halobutyls). The properties of these polymers are similar to IIR, but they can be cured faster using different and smaller amounts of curing agents.

How long does butyl rubber last?

Butyl rubber lasts about 5-10 years (according to the official shelf life). However, the actual lifespan of butyl rubber products depends on various factors and can vary depending on the conditions in which they are stored and used.

How flexible is butyl rubber?

Butyl rubber is moderately flexible. It fares better than many other types of rubber in this regard, as it contains more than 50% butyl polymer.

Is butyl rubber waterproof?

Yes, butyl rubber is waterproof. It is characterized by very high impermeability to gases and moisture.

Does butyl rubber dry out?

No, butyl rubber does not dry out.

Is butyl rubber flammable?

Yes, butyl rubber is flammable at high temperatures.

What is the temperature range of butyl rubber?

The temperature range of butyl rubber extends from -45°C to 120°C. However, consider that the damping properties decrease in hot environments. However, the upside is that the rubber remains flexible at lower temperatures.

Does butyl rubber melt?

In general, butyl rubber does not melt, but it does soften at high temperatures. Butyl rubber melting is not a well-defined property, as different manufacturers use different versions of the basic chemical compound.

Can butyl rubber be welded?

Yes, butyl rubber can be welded.

What are the applications of butyl rubber?

Butyl rubber's applications are manifold due to a number of practical properties of the material.

Since it has low gas and vapor permeability, it is an important material in the manufacture of tubeless tires, inner tubes, sports ball bladders, gloves, etc.

In addition, rubber is used as a liner in tanks and ponds as a waterproofing material.  It is also used as a patching material for membrane roofs and as a sealant for insulated windows.

In combination with other chemicals, polyisobutylene also forms oil and fuel additives and defogging agents for machining lubricants.

What's more, as a vibration damping agent, butyl rubber is used in shock absorbers, suspension bushings and body mounts for cars and trucks. The edges of speaker cones are now often made of butyl rubber, while they were once commonly made of foam.

Stoppers for laboratory utensils and medical equipment are also made from this material.

In addition, because of its low permeability, butyl rubber is used to make gas masks. Although not as soft and pliable as silicone rubber, it is flexible enough to provide a good facial seal.

Butyl rubber is also used to produce rubber hoses. As IIR rubber is suitable for contact with food, butyl rubber is used to produce food hoses.

Butyl rubber in its food contact form is also used for the production of chewing gum. It has completely replaced Chicle tree rubber (with the exception of a few specialized natural products).

What are the trade names of butyl rubber?

Trade names of butyl rubber are as follows:

• Enjay-Butyl, 
• Hycar-Butyl, 
• Petrolex-Butyl, 
• Polysar-Butyl, 
• Soca-Butyl, 
• Esso-Chlorobutyl,
• Esso-Brombutyl.

Who invented butyl rubber?

Butyl rubber was invented by American chemists William Sparks and Robert Thomas at the Standard Oil Company of New Jersey (now Exxon Corporation) in 1937.

Earlier efforts to produce synthetic rubbers involved the polymerization of dienes (hydrocarbon molecules containing two carbon-carbon double bonds), such as isoprene and butadiene. Sparks and Thomas defied convention by copolymerizing isobutylene, an olefin (hydrocarbon molecules containing only one carbon-carbon double bond) with small amounts (e.g., less than 2%) of isoprene.

As a dien, isoprene provided the additional double bond required to crosslink the neutral polymer chains, which were essentially polyisobutylene. Before the experimental difficulties were resolved, butyl rubber was called "futile butyl," but after improvements it gained wide acceptance.

During World War II, the copolymer was called GR-I (Government Rubber-Isobutylene).

However, it is worth mentioning that other people also contributed to the development of rubber.

Isobutylene itself was discovered by Michael Faraday in 1825. And polyisobutylene (PIB) was first developed by BASF IG Farben in 1931 using a boron trifluoride catalyst at low temperatures. The company sold the product under the trade name Oppanol B.

Interestingly, PIB remains BASF's core business to this day.

Is butyl rubber EPDM?

No, butyl rubber is not EPDM. In both cases, we are talking about synthetic rubbers, but they differ in construction and properties.

What is the difference between EPDM and butyl rubber?

The difference between EPDM and butyl rubber can be found in the properties and characteristics of both materials. EPDM is more flexible, holds up better, and has good resistance to weathering, UV radiation, ozone, and aging. Butyl rubber, on the other hand, has better puncture resistance, air and gas impermeability, and good vibration-damping properties.

What is the difference between natural rubber and butyl rubber?

The main difference between natural rubber and butyl rubber is primarily that the former is made from the sap of rubber trees, while the latter is a synthetic elastomer produced from isobutylene and isoprene.

Therefore, they also differ in their properties. Natural rubber is usually more flexible and resistant to stretching or deformation. Butyl rubber, on the other hand, is more resistant to aging, chemicals and better blocks the flow of gases through the material.

Is Viton a butyl rubber?

No, Viton is not butyl rubber. Viton is a trade name for fluorine-based synthetic rubber that is produced by the copolymerization reaction of fluorine-containing monomers. Butyl rubber, on the other hand, is a synthetic rubber made by combining isobutylene and isoprene.

What are the advantages of butyl rubber?

The advantages of butyl rubber are flexibility, gas impermeability, moisture resistance, durability, vibration damping, resistance to certain chemicals.

Is butyl rubber recyclable?

Yes, butyl rubber is recyclable. There are various methods for recovering the material without losing its quality.