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.
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Comparison of natural and synthetic rubber
Natural rubber coming from latex is mostly polymerized isoprene with a small percentage of impurities in it. This will limit the range of properties available to it. Also, there are limitations on the proportions of cis and trans double bonds resulting from methods of polymerizing natural latex. This also limits the range of properties available to natural rubber, although addition of sulfur and vulcanization are used to improve the properties.
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. 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
In 1909, a team headed by Fritz Hofmann, working at the Bayer laboratory in Elberfeld, Germany, succeeded at polymerizing methyl isoprene, thereby creating the first synthetic rubber.[1] The first rubber polymer synthesized from butadiene was created by Sergei Vasiljevich 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 two monomers in alternating sequence. One such Buna rubber, known as GRS (Government Rubber Styrene), is a copolymer of butadiene and styrene, was the basis for U.S. synthetic rubber production during World War II.
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. Operation Pointblank bombing targets of Nazi Germany included the Schkopau (50K tons/yr) plant and the Hüls synthetic rubber plant near Recklinghausen (30K, 17%),[2] the Kolnische Gummifaden Fabrik tire and tube plant at Deutz on the east bank of the Rhine.[3] The Ferrara, Italy, synthetic rubber factory (near a river bridge) was bombed August 23, 1944.[1] Three other synthetic rubber facilities were at Ludwigshafen/Oppau (15K), Hanover/Limmer (reclamation, 20K), and Leverkusen (5K). A synthetic rubber plant at Oświęcim, Poland, was under construction on March 5, 1944. [4]
Post-war
After the war, natural rubber plantations no longer had a stranglehold on rubber supplies, particularly after chemists learned to synthesize isoprene. Styrene-Butadiene Rubber (GR-S) 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-fuel rockets during World War II used nitrocellulose explosives for propellants, but it was impractical and dangerous to make such rockets very large. 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), and aluminium powder. This new solid fuel burned more slowly and evenly than nitrocellulose explosives, and was much less dangerous to store and use, but 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 to replace asphalt in their solid fuel. 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 | Technical Name | Common Names |
|---|---|---|
| BIIR | Bromo Isobutylene Isoprene | Bromobutyl |
| 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 Monomer | EPDM, Nordel |
| FKM | Fluoronated Hydrocarbon | Viton, Kalrez, Fluorel |
| FVQM | Fluoro Silicone | FVQM |
| HNBR | Hydrogenated Nitrile Butadiene | HNBR |
| IR | Polyisoprene | (Synthetic) Natural Rubber |
| IIR | Isobutylene Isoprene Butyl | Butyl |
| MVQ | Methyl Vinyl Silicone | Silicone Rubber |
| NBR | Acrylonitrile Butadiene | NBR, Nitrile, Perbunan, Buna-N |
| PU | Polyurethane | PU, Polyurethane |
| SBR | Styrene Butadiene | SBR, Buna-S, GRS |
| SI | Polysiloxane | Silicone Rubber |
| XNBR | Acrylonitrile Butadiene Carboxy Monomer | XNBR, Carboxylated Nitrile |
In addition the term Gum Rubber is sometimes used to describe the tree-derived Natural Rubber [code NR], and to distinguish it from synthetic Natural Rubber [code IR].
Trade names
- Buna S
- Hypalon
- Kalrez
- Neoprene
- Silastic
- Tecnoflon
- Viton
Related
- Elastomer
- Thermoplastic
Notes and references
- ^ The Moving Powers of Rubber, Leverkusen, Germany: LANXESS AG: 20.
- ^ Stormont, John W. (March 1946). AAFRH-19: The Combined Bomber Offensive; April through December 1943. Dwight D. Eisenhower Presidential Library: Collection of 20th Century Military Records, 1918-1950 Series I: Historical Studies Box 35: AAF Historical Office; Headquarters, Army Air Force. pp. 74-5,81. "SECRET ... Classification Cancelled ... JUN 10 1959"
- ^ Gurney, Gene (Major, USAF) (1962), The War in the Air: a pictorial history of World War II Air Forces in combat, New York: Bonanza Books, pp. 215
- ^ Williamson, Charles C.; Hughes, R. D.; Cabell, C. P.;Nazarro, J. J.; Bender, F. P.; & Crigglesworth, W. J. (5th MARCH 1944), Plan for Completion of Combined Bomber Offensive (Appendices C & F), Dwight D. Eisenhower Presidential Library: SMITH, WALTER BEDELL: Collection of World War II Documents, 1941-1945; Box No.: 48: HQ, U.S.S.T.A.F, "DECLASSIFIED ... 4/24/74"