Definitions

synthetic rubbers

Synthetic rubber

Synthetic rubber is any type of artificially made polymer material which acts as an elastomer. An elastomer is a material with the mechanical (or material) property that it can undergo much more elastic deformation under stress than most materials and still return to its previous size without permanent deformation. Synthetic rubber serves as a substitute for natural rubber in many cases, especially when improved material properties are needed.

Advantages of synthetic rubber

Synthetic rubber can be made from the polymerization of a variety of monomers including isoprene (2-methyl-1,3-butadiene), 1,3-butadiene, chloroprene (2-chloro-1,3-butadiene), and isobutylene (methylpropene) with a small percentage of isoprene for cross-linking. Furthermore, these and other monomers can be mixed in various desirable proportions to be copolymerized for a wide range of physical, mechanical, and chemical properties. The monomers can be produced pure and addition of impurities or additives can be controlled by design to give optimal properties. Polymerization of pure monomers can be better controlled to give a desired proportion of cis and trans double bonds.

History

The first synthetic rubber polymer was created by Lebedev in 1910. Practical synthetic rubber grew out of studies published in 1930 written independently by American Wallace Carothers, Russian scientist Lebedev, and the German scientist Hermann Staudinger. These studies led in 1931 to one of the first successful synthetic rubbers, known as Neoprene, which was developed at DuPont under the direction of E.K. Bolton. Neoprene is highly resistant to heat and chemicals such as oil and gasoline, and is used in fuel hoses and as an insulating material in machinery.

In 1935, German chemists synthesized the first of a series of synthetic rubbers known as "Buna rubbers". These were "copolymers", meaning the polymers were made up from not one but two monomers, in alternating sequence. One such Buna rubber, known as "GRS" (Government Rubber Styrene), is a copolymer of butadiene and styrene, became the basis for U.S. synthetic rubber production during World War II.

Worldwide natural rubber supplies were limited and by mid-1942 most of the rubber-producing regions were under Japanese control. Military trucks needed rubber for tires, and rubber was used in almost every other war machine. The U.S. government launched a major (and largely secret) effort to develop and refine synthetic rubber. A principal scientist involved with the effort was Edward Robbins.

By 1944 a total of 50 factories were manufacturing it, pouring out a volume of the material twice that of the world's natural rubber production before the beginning of the war.

After the war, natural rubber plantations no longer had a stranglehold on rubber supplies, particularly after chemists learned to synthesize isoprene. GRS remains the primary synthetic rubber for the manufacture of tires.

Synthetic rubber would also play an important part in the space race and nuclear arms race. Solid rockets used during World War II used nitrocellulose explosives for propellants, but it was impractical and dangerous to make such rockets very big.

During the war, California Institute of Technology (Caltech) researchers came up with a new solid fuel, based on asphalt fuel mixed with an oxidizer, such as potassium or ammonium perchlorate, plus aluminium powder, which burns very hot. This new solid fuel burned more slowly and evenly than nitrocellulose explosives, and was much less dangerous to store and use, though it tended to flow slowly out of the rocket in storage, and the rockets using it had to be stockpiled nose down.

After the war, the Caltech researchers began to investigate the use of synthetic rubbers instead of asphalt as the fuel in the mixture. By the mid-1950s, large missiles were being built using solid fuels based on synthetic rubber, mixed with ammonium perchlorate and high proportions of aluminium powder. Such solid fuels could be cast into large, uniform blocks that had no cracks or other defects that would cause non-uniform burning. Ultimately, all large military rockets and missiles would use synthetic rubber based solid fuels, and they would also play a significant part in the civilian space effort.

Table of common synthetic rubbers

ISO Standard Code Chemical Name Common Names
BR Polybutadiene
CIIR Chloro Isobutylene Isoprene Chlorobutyl, Butyl
CR Polychloroprene Chloroprene, Neoprene
CSM Chlorosulphonated Polyethylene Hypalon
ECO Epichlorohydrin ECO, Epichlorohydrin, Epichlore, Epichloridrine
EP Ethylene Propylene
EPDM Ethylene Propylene Diene EPDM, Nordel
EVA Ethylene Vinyl Acetate EVA
FKM Fluoronated Hydrocarbon Viton, Kalrez, Fluorel
HNBR Hydrogenated Nitrile Butadiene HNBR
IR Polyisoprene (Synthetic) Natural Rubber
IIR Isoprene Butylene Butyl Butyl
NBR Butadiene Acrylonitrile NBR, Nitrile, Perbunan, Buna-N
PU Polyurethane Polyurethane
SBR Styrene Butadiene SBR, Buna-S, GRS
SI Poly-Siloxane Silicone Rubber

In addition, to distinguish the tree-derived Natural Rubber [code NR] from the synthetic Natural Rubber [code IR] the term Gum Rubber is sometimes used.

Trade names

References

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