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.

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 1879, Bouchardt created one form of synthetic rubber, producing a polymer of isoprene in a laboratory.

The expanded use of motor vehicles, and particularly motor vehicle tires, starting in the 1890s, created increased demand for rubber.

In 1909, a team headed by Fritz Hofmann, working at the Bayer laboratory in Elberfeld, Germany, also succeeded in polymerizing methyl isoprene, the first synthetic rubber^[1].

Scientists in England and Germany developed alternate methods for creating isoprene polymers from 1910-1912.

The Russian scientist Sergei Vasiljevich Lebedev created the first rubber polymer synthesized from butadiene in 1910. This form of synthetic rubber provided the basis for the first large-scale commercial production, which occurred during World War I as a result of shortages of natural rubber. This early form of synthetic rubber was again replaced with natural rubber after the war ended, but investigations of synthetic rubber continued.

Political problems that resulted from great fluctuations in the cost of natural rubber led to enactment of the Stevenson Act in 1921. This act essentially created a cartel which supported rubber prices by regulating production (see OPEC), but insufficient supply, especially due to wartime shortages, also led to a search for alternative forms of synthetic rubber.

By 1925 the price of natural rubber had increased to the point that many companies were exploring methods of producing synthetic rubber to compete with natural rubber. In the United States, the investigation focused on different materials than in Europe, building on the early laboratory work of Nieuwland.

Studies published in 1930 written independently by Lebedev, the American Wallace Carothers and the German scientist Hermann Staudinger 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.

The company Thiokol applied their name to a competing type of rubber based on ethylene dichloride which was commercially available in 1930.

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. The rubber designated GRS (Government Rubber Styrene), a copolymer of butadiene and styrene, was the basis for U.S. synthetic rubber production during World War II. It still represents about one-half of total world production.

Other brands included Koroseal, which Waldo Semon developed in 1935, and Sovprene, which Russian researchers created in 1940^[2].

World War II

Sheet of synthetic rubber coming off the rolling mill at the plant of Goodrich (1941)

The production of synthetic rubber in the United States expanded greatly during World War II, since the Axis Powers controlled nearly all the world's limited supplies of natural rubber by mid-1942 once Japan conquered Asia.

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 improve synthetic rubber production. A principal scientist involved with the effort was Edward Robbins.

B.F. Goodrich Company scientist Waldo Semon developed a new and cheaper version of synthetic rubber known as Ameripol in 1940. Ameripol made synthetic rubber production much more cost effective, helping to meet the country's needs during World War II.

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.^{[citation needed]} Operation Pointblank bombing targets of Nazi Germany included the Schkopau (50K tons/yr) plant and the Hüls synthetic rubber plant near Recklinghausen (30K, 17%),^[3] the Kolnische Gummifaden Fabrik tire and tube plant at Deutz on the east bank of the Rhine.^[4] 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. ^[5]

Post-war

Additional refinements to the process of creating synthetic rubber continued after the war. The chemical synthesis of isoprene accelerated the reduced need for natural rubber, and the peacetime quantity of synthetic rubber exceeded the production of natural rubber by the early 1960s.

In 2005, close to 21 million tons of rubber were produced of which around 58% was synthetic.

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

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

See also

• Butyl rubber
• Thermoplastic

Notes and references

1. ^ The Moving Powers of Rubber, Leverkusen, Germany: LANXESS AG: 20.
2. ^ Current Biography 1940, "SEMON, WALDO LONSBURY" pp723-24
3. ^ 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" 
4. ^ 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 
5. ^ 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"