Rubber is an elastomer—that is, a polymer that has the ability to regain its original shape after being deformed. Rubber is also tough and resistant to weathering and chemical attack. Elastomers can be naturally occurring polymers, such as natural rubber, or they can be synthetically produced substances, such as butyl rubber, Thiokol, or neoprene. For a substance to be a useful elastomer it must possess a high molecular weight and a flexible polymer chain.
Natural rubber is one of nature's unique materials. The Native Americans of tropical South America's Amazon basin knew of rubber and its uses long before Christopher Columbus's explorations brought it to the attention of Europeans. The Indians made balls of rubber by smoking the milky, white latex of trees of the genus Hevea that had been placed on a wooden paddle, to promote water evaporation and to cure the substance.
Spanish navigator and historian Gonzalo Fernández de Oviedo y Valdes (1478–1557) was the first European to describe these balls to a European audience. In 1615 a Spanish writer enumerated the practical uses of rubber. He reported that the Indians waterproofed their cloaks by brushing them with this latex and made waterproof shoes by coating earthen molds with it and allowing these coatings to dry.
In 1735 interest was revived in this unusual substance when French mathematical geographer and explorer Charles-Marie de La Condamine (1701–1774) sent several rolls of crude rubber to France with an accompanying description of products made from it by the South American natives. Although it met with some use in waterproofing boots, shoes, and garments, it largely remained a museum curiosity. Crude rubber possessed the valuable properties of elasticity, plasticity, strength, durability, electrical nonconductivity, and resistance to water; however, products made from it hardened in winter, softened and became sticky in summer, were attacked by solvents, and smelled bad.
Rubber, sometimes called "gum-elastic," was known to the Indians by the name of caoutchouc (from caa, "wood," and o-chu, "to flow or to weep"). In 1770 English chemist and Unitarian clergyman Joseph Priestley (1733–1804), the discoverer of oxygen, proposed the name "rubber" for the substance because it could be used to erase pencil marks by its rubbing on paper in lieu of previously used bread crumbs.
In 1791 rubber was first used commercially when English manufacturer Samuel Peal patented a method for waterproofing cloth by treating it with a solution of rubber in turpentine. In 1820 the modern rubber industry began when English coachmaker and inventor Thomas Hancock (1786–1865) established the first rubber factory. He was the first to compound rubber with other materials to be shaped into molds, a common modern industrial practice.
In 1823 Scottish chemist and inventor Charles Macintosh (1766–1843) began to manufacture double-textured rainproof garments known as "mackintoshes." He made these by introducing a coal tar naphtha solution of rubber between two pieces of fabric, thus circumventing the sticky (when warm) and brittle (when cold) surfaces associated with single-textured rubber-containing garments.
Composition and Structure
Crude rubber is primarily hydrocarbon in nature. In 1826 English chemist Michael Faraday (1791–1867) analyzed natural rubber and found it to have the empirical (simplest) formula C5H8, along with 2 to 4 percent protein and 1 to 4 percent acetone-soluble materials (resins, fatty acids, and sterols). In 1860 English chemist Charles Hanson Greville Williams (1829–1910) confirmed Faraday's analysis and in 1862 distilled natural rubber to obtain the pure monomer, which he named isoprene . He determined isoprene's vapor density and molecular formula, and he showed that it polymerizes to a rubbery product—an observation that led to the notion that rubber is a linear polymer of isoprene, proposed in 1910 by English chemist Samuel Shrowder Pickles (1878–1962).
The molecular weights of rubber molecules range from 50,000 to 3,000,000. Sixty percent of the molecules have molecular weights of greater than 1,300,000. The repeating unit in natural rubber has the cis configuration (with chain extensions on the same side of the ethylene double bond), which is essential for elasticity. If the configuration is trans (with chain extensions on opposite sides of the ethylene double bond), the polymer is either a hard plastic (naturally occurring gutta-percha, obtained from the leaves of Palaquium, a species of sapotaceous Malaysian and East Indies trees) that was used for wire and cable coating during the nineteenth century; or a substance like gutta-percha (balata, obtained from Mimusops globosa, trees native to Panama and South America), used for modern golf ball covers.
Because there are few (if any) cross-links in the chains of rubber molecules, natural rubber is thermoplastic; that is, it becomes soft and sticky in summer and hard and brittle in winter. It is also malodorous and softened or dissolved by various solvents, as noted. These undesirable properties of natural rubber were not overcome until 1839, when American inventor Charles Goodyear (1800–1860), at the end of five years of constant experimentation, accidentally placed a sample of rubber mixed with sulfur and litharge (lead oxide, PbO) on a hot stove in Woburn, Massachusetts. The operation converted rubber into a heavily cross-linked, and therefore insoluble and infusible, thermosetting polymer or "thermoset." William Brockedon, a friend of Hancock's, named Goodyear's curing process "vulcanization" (after Vulcan, the ancient Roman god of fire and metalworking). Goodyear later used the term, but only reluctantly.
In practice, vulcanization was so simple that many persons used it without paying royalties, and Goodyear spent much of his time contesting approximately sixty infringements of his patent. He died a pauper and left behind debts estimated at between $200,000 and $600,000. His name lives on in Goodyear tires and Goodyear blimps.
Paradoxically, neither Goodyear nor any of his family members or descendents were involved with the Goodyear Tire and Rubber Company, whose founder, Frank A. Seiberling, named it to honor one of America's most famous inventors and the founder of an industry that is indispensable to modern life. In 1851 Goodyear's brother Nelson used sulfur to convert natural rubber into ebonite, the first thermosetting plastic.
The Modern Rubber Industry
Vulcanization marked the birth of the modern rubber industry, and although later discoveries have somewhat modified Goodyear's original procedure, today it remains essentially the same as his process of 1839. Vulcanization is still an imperfectly understood chemical reaction between rubber and sulfur. It results in cross-linking between linear chains of rubber molecules and prevents slippage of the chains as the material retains the desired elasticity.
Temperatures of 140–180°C (184–356°F) are used for modern vulcanization, and additives other than sulfur are often used. Accelerators permit the reaction to occur at lower temperatures and in less time, and antioxidants prolong the life of rubber products by reducing the deterioration that is caused by atmospheric oxygen (or ozone), which breaks covalent bonds and lowers the molecular weight. Reinforcing agents (e.g., carbon black) increase stiffness, tensile strength, and resistance to abrasion. Coloring agents and fillers are sometimes added.
The Search for Substitutes
The earliest synthetic polymers were synthetic rubbers. Before 1920 natural rubber was the only available elastomer, but constant attempts, with varying degrees of success, to develop commercial rubber substitutes had been made previously, especially by English and German chemists, who competed with each other in the search.
As mentioned, natural rubber is a polymer consisting of repeating units of isoprene, its "mother substance." Scientists at first sought an exact chemical equivalent. But they attained their first success in preparing a suitable substitute only when they abandoned their attempts to synthesize rubber from isoprene, butadiene, or other dienes (hydrocarbons with two double bonds) and tried to synthesize an original polymer that possessed the physical properties of natural rubber.
The development of a synthetic rubber was a slow process, because it was almost impossible for the early synthetic products to compete economically with cheap natural rubber and because they were not as good as natural rubber for most uses. The driving force in the search for synthetic rubber was the shortages created by wartime needs.
CARL "SPEED" MARVEL (1894–1988)
During World War II, the United States was almost entirely blockaded from its rubber suppliers. Carl Marvel became a part of the successful effort to meet the demand for synthetics. Along with others, he worked to increase the efficiency and production of existing rubber syntheses.
During World War I German chemists, whose country was cut off from its sources of natural rubber by the British blockade, polymerized 3-methylisoprene (2,3-dimethyl-1,3-butadiene) units, (CH2 = C(CH3)C(CH3) = CH2), obtained from acetone, to form an inferior substitute called methyl rubber. By the end of the war Germany was producing 15 tons (13.6 metric tons) of this rubber per month. The USSR (Union of Soviet Socialist Republics), which built a pilot plant at Leningrad (now St. Petersburg) in 1930 and three factories in 1932 and 1933, was the first country to institute a fullscale synthetic rubber industry.
Two Serendipitous Discoveries
During World War II the United States, cut off from India, Ceylon (now Sri Lanka), Malaysia, and the Dutch East Indies (areas which, since the late nineteenth century, had replaced South America as the main suppliers of natural rubber), developed several superior synthetic rubbers. The U.S. synthetic rubber industry originated from two discoveries that were serendipitous; that is, they occurred while the researchers were searching for something else.
In 1922 independent inventor and physician Joseph C. Patrick (1892–1965) was trying to make ethylene glycol (HOCH2CH2OH) to be used as antifreeze. Instead he discovered Thiokol (a trade name that has become generic), a rubbery polysulfide condensation product of ethylene dichloride and sodium tetrasulfide. This early product is still used for gaskets, sealants, sealer adhesives, and hoses because it is resistant to oil and organic solvents.
In 1931 Arnold Collins, a chemist in the Du Pont research group of Wallace Hume Carothers (1896–1937), the discoverer of nylon, discovered neoprene accidentally while studying the by-products of divinylacetylene (H2C = CH−C=CH). There are several types of neoprenes. They have high tensile strength, high resilience, and excellent resistance to oxygen, ozone, other chemicals, and oil. They also resist heat, flame, and tearing. They are good general-purpose rubbers, but they are limited to uses requiring rubbers with special properties because of their high cost.
Other Synthetic Rubbers
In 1937 Robert McKee Thomas (1908–1986) and William Joseph Sparks (1904–1976) at the Standard Oil Development Company (now Exxon) synthesized butyl rubber via the copolymerization (polymerization of a mixture of monomers) of isobutylene (2-methylpropene (CH3)2C = CH2) with a small amount of isoprene.
By 1929 the German firm I. G. Farben developed a series of synthetic rubbers similar to those produced in the USSR. They were called Buna rubbers ("Bu" for butadiene, one of the copolymers, and "na" for sodium, the polymerization catalyst ). They included the oil-resistant Buna S (S for styrene) and Buna N (N for nitrate). Buna S, styrene butadiene rubber, is currently called SBR, and it is produced at about twice the volume of natural rubber, making it the most common synthetic rubber. Buna N, acrylonitrile-butadiene rubber, is now called NBR. During World War II the United States produced these rubbers for the American war effort.
While earlier attempts to produce satisfactory synthetic rubber from isoprene were unsuccessful, in 1955 American chemist Samuel Emmett Horne Jr. (b. 1924) prepared 98 percent cis -1,4-polyisoprene via the stereospecific polymerization of isoprene. Horne's product differs from natural rubber only in that it contains a small amount of cis -1,2-polyisoprene, but it is indistinguishable from natural rubber in physical properties. First produced in 1961, BR (for butadiene rubber), a rubberlike polymer that is almost exclusively cis -1,4-polybutadiene, when blended with natural or SBR rubber, has been used for tire treads.
Polyurethane (PU) was first synthesized in the 1930s by German chemist Otto Bayer (1902–1982), who was trying to prepare a nylonlike fiber. PU is a versatile polymer that is used for rigid and flexible foams, bristles, coatings, fibers, and automobile parts, such as bumpers. Other synthetics are used in products such as stretchable fabrics and binders for paints.
After the end of World War II the American synthetic rubber industry declined sharply. However, by the early 1950s, as better and more uniform synthetic rubbers became available, it underwent a renaissance. By the early 1960s the amount of synthetic rubber produced worldwide equaled that of natural rubber, and it has increased steadily ever since. Although natural rubber performs well for most uses, some of the newer synthetics are superior to it for specialized purposes. Today rubber is indispensable for a variety of products and industries, and our modern world, with its many necessities and luxuries, would be unthinkable without it.
see also Polymers, Natural; Polymers, Synthetic.
George B. Kauffman
Carraher, Charles E., Jr. (2000). Seymour/Carraher's Polymer Chemistry, 5th edition, revised and expanded. New York: Marcel Dekker.
Kauffman, George B. (1989). "Charles Goodyear—Inventor of Vulcanisation." Education in Chemistry 26(6): 167–170.
Kauffman, George B., and Seymour, Raymond B. (1990). "Elastomers I: Natural Rubber." Journal of Chemical Education 67(5): 422–425.
Kauffman, George B., and Seymour, Raymond B. (1990). "Elastomers II: Synthetic Rubbers." Journal of Chemical Education 68(3): 217–220.
Morris, Peter J. T. (1986). Polymer Pioneers: A Popular History of the Science and Technology of Large Molecules. Philadelphia: Beckham Center for the History of Chemistry.
Morris, Peter J. T. (1989). The American Synthetic Rubber Research Program. Philadelphia: University of Pennsylvania Press.
Seymour, Raymond B. (1988). "Polymers Are Everywhere." Journal of Chemical Education 65(4): 327–334.
Rubber is an essential component of modern industry, especially the automotive industry. Although it has thousands of uses, over half of world production is for tires and other automotive parts. Rubber is derived from two different sources: natural rubber, produced from the latex of a tropical rainforest tree, and synthetic rubber, derived from petroleum. For nearly a century it has been one of the dominant commodities in world trade, its production transforming tropical ecosystems and consuming immense quantities of petroleum.
Until the 1940s natural rubber was the only type available. Even this type only became available after Charles Goodyear invented a process to stabilize it by bonding rubber with sulfur (vulcanization) in Akron, Ohio in 1839. He soon fashioned the new material into raincoats and rubber shoes; by the late 1800s it had a widening variety of commercial and industrial uses, and Akron became the world's greatest producer of processed rubber.
Demand for rubber accelerated rapidly from the 1890s onward, to make tires for bicycles and then for automobiles. Until then almost all rubber was produced from a tree native to the Amazonian rainforest. Rubber tappers combed wide reaches of the remote forest and sold the latex they collected to buyers at trading posts along the river for shipment to Europe and North America. This was the first deep industrial penetration into the world's tropical forests. But the process of collecting and processing the latex was difficult and expensive because in the natural forest rubber trees grow mixed with many other species. This dispersion protects the rubber trees from a leaf blight that destroys them if they are planted in concentrated rows, so mass production of rubber from plantations could not be done in Brazil.
But British experimenters beginning in the 1870s transplanted seedlings via Kew Gardens in London to their Southeast Asian colonies of Ceylon and Malaya, where they succeeded in growing large, blight-free plantations. Dutch and French planters similarly transformed their colonial forests in Indonesia and Indochina into rubber groves. By 1910 these plantations produced half the world's supply, and by 1920 they produced 90 percent, a proportion of natural rubber that has remained steady ever since, whereas the Brazilian industry collapsed and never recovered. In Southeast Asia many thousands of acres of natural forest were cleared by a concentrated labor force recruited on multiyear indenture contracts, many of them from overcrowded, poverty-stricken Java and southern China. Dutch plantation overseers in particular became notorious for harsh working conditions.
The international trade in plantation rubber was largely controlled by a British and Dutch cartel centered in Singapore with extensions in Amsterdam and London. These two colonial powers attempted to stabilize rubber prices, which were highly unstable, reflecting widely fluctuating demand but inflexible production. France had its own colonial sources, but German industry, lacking a major tropical colonial base, had to buy its rubber on the open market. The rapidly expanding U.S. auto industry also had to pay whatever price the Dutch and British cartel demanded. American industrialists became determined to develop their own sources of rubber, and fledgling U.S. rubber companies, closely allied with the auto industry, invested in large plantations in British and Dutch colonies in Malaya and Sumatra.
There were also colonial experiments in equatorial Africa's rainforest belt. King Leopold of Belgium, ruler of most of the vast Congo basin since 1885, used notoriously brutal forced-labor practices, coercing Congolese forest people to deliver latex to European buyers. Many Africans died of beatings, imprisonment, or malnutrition when they failed to meet their quotas.
From the start the rubber industry was directly linked to the rapid expansion of the automobile industry. Then came the urgent demand for rubber as a critical military material in World War I, the first war fought on wheels with rubber tires. The war convinced Americans to reconsider their strategic situation, since their sources halfway around the world were vulnerable to potential enemy attack. In 1926 Harvey Firestone, in close cooperation with Henry Ford and the U.S. government, established the world's largest plantation of Brazilian rubber trees on 90,000 acres leased from the government of Liberia.
After the rapid expansion of the auto industry in the 1920s, the global Great Depression resulted in the near-collapse of the rubber industry. Tropical plantations were hit hard; many thousands of laborers were laid off and had to return to subsistence farming. In the process they demonstrated that they could plant and manage rubber trees, often as their primary cash crop, just as successfully as industrial plantations could on a vastly greater scale. It was risky to devote precious crop land to rubber trees because they could be tapped only after they were seven years old, and widely fluctuating prices on the international market made profits unpredictable. But small-holders were more flexible than concentrated plantation laborers, who depended on company commissaries for their food and other supplies. Smallholder production also avoided the ecological costs of the large monocrop plantations. In Thailand, which was becoming the world's second-largest producer after neighboring Malaya, nearly all rubber was produced on small plots.
By the late 1930s a second world war loomed. Japan, rapidly becoming the newest major industrial power, looked toward the West's colonies in Southeast Asia as its potential rubber salvation. Within three months after it struck the U.S. base in Pearl Harbor, Hawaii, Japan conquered most Western colonies in Southeast Asia, depriving the Allies of their primary supplies. U.S. sources in Liberia were protected, and before the United States entered the war it had stockpiled a year's supply, much of it from recycled tires. But additional sources of rubber were urgently needed.
Germany was even more desperate for rubber, because its purchases were cut off. Since World War I German chemists had been experimenting with types of rubber derived from petroleum, but early forms of synthetic rubber were unreliable, either turning stiff and brittle when cool or melting in hot weather. In the 1930s I. G. Farben in Germany and DuPont, Firestone, and Standard Oil in the United States developed new types of synthetic rubber primarily for military vehicles and planes. By the end of the war in 1945 the European industrial economies were using mostly synthetic rubber.
In the aftermath of the war the civilian industrial economies boomed, and vast numbers of new car owners demanded sets of tires, which used a high proportion of synthetic rubber. In the thirty years after 1945 total world consumption of rubber rose 500 percent; two-thirds of this rubber was synthetic. Almost all petroleum-based rubber was produced by a few multinational rubber and petroleum firms whose aggressive investment in new products research created a steadily widening range of products. Tropical rubber production for world markets grew more gradually in the postwar mass affluence, but by the late 1970s it was 50 percent higher than thirty years before. Old plantations in Southeast Asia were replanted, this time with hybridized trees which used intensified applications of chemical fertilizers and pesticides, raising yields several times over. Throughout Southeast Asia, after former colonies became independent, Western companies sold controlling interests to local investors and governments, but remained their primary customers. In 2004 90 percent of the world's natural rubber was produced in tropical Asia. Throughout the tropics as a whole, smallholder acreage has expanded faster than plantations. But the overall environmental impact is similar: reduction of tropical rain forest.
The sudden quadrupling of oil prices in 1974 hit synthetic rubber much harder than natural rubber: it doubled production costs of synthetic rubber, but raised the production costs of natural rubber by less than half. The years of much faster growth in petroleum-based rubber were over. Then radial tires entered the market. Radials require the flexibility of natural rubber for their walls and use a higher percentage of natural rubber than older tire types. Pioneered by Michelin in France in the 1960s, radial-tire production expanded rapidly in Europe and then in the United States and Japan. By the early 1980s more than 80 percent of all new tires were radials. The two types of rubber, roughly equal in amounts produced, were clearly complementary for an industry that thrives on ever-growing global consumer affluence and places ever-increasing pressure on global natural resources.
SEE ALSO Africa, Labor Taxes (Head Taxes); Agriculture; Automobile; Blockades in War; Brazil; Disease and Pestilence; du Pont de Nemours Family; Empire, Belgian; Empire, British; Empire, Dutch; Empire, French; Empire, Japanese; Ford, Henry; Germany; Great Depression of the 1930s; Imperialism; Indonesia; Laborers, Coerced; Laborers, Contract; United States; Vietnam.
Coates, Austin. The Commerce in Rubber: The First 250 Years. Singapore: Oxford University Press, 1987.
Dean, Warren. Brazil and the Struggle for Rubber. Cambridge, U.K.: Cambridge University Press, 1987.
Firestone, Harvey S. Men and Rubber: The Story of Business. Garden City, NY: Doubleday, 1926.
Grilli, Enzo R., Agostini, Barbara Bennett, and HooftWelvaars, Maria J. The World Rubber Economy: Structure, Changes, and Prospects. Baltimore, MD: Johns Hopkins University Press, 1980.
Hochschild., Adam. King Leopold's Ghost. New York: Houghton Mifflin. 1998.
Schidrowitz, P., and Dawson, T. R., eds. History of the Rubber Industry. Cambridge, U.K.: Heffer, 1952.
Stern, H. J. Rubber, Natural and Synthetic. New York: Palmerton, 1967.
Szekely, Ladislao. Tropic Fever: The Adventures of a Planter un Sumatra. Kuala Lumpur: Oxford University Press, 1979.
Richard P. Tucker
RUBBER. Although rubber-yielding plants are native to Africa and Asia as well as to the Americas, the first mention of rubber in the West was made by Pietro Martire d'Anghiera, the Italian representative to the court of Spain (De Rebus Oceanicis et Novo Orbe, 1516). In the early seventeenth century, Juan de Torquemada (Monarquía Indiana, 1615) described how the Mexican Indians used a milk-like fluid drawn from a tree for religious rites and sport, and for making crude footwear, waterproof bottles, and garments. Although a little rubber was used in Europe in the eighteenth century to make erasers—it derived its name "rubber" for its property of rubbing out (erasing) pencil marks—along with elastic thread, surgical tubes, and experimental balloons, the rubber manufacturing industry was not established until the nineteenth century.
The first record of rubber in the United States is a patent for gum elastic varnish for footwear issued to Jacob F. Hummel in 1813. This was followed by a patent for a grinding and mixing machine granted to John J. Howe in 1820. Prompting these first steps was the profitable trade in crude rubber shoes imported into Boston and New York City from Brazil. By 1833, America's pioneering rubber factory was established at Roxbury, Massachusetts. Other rubber shoe and clothing factories soon appeared elsewhere in Massachusetts, as well as in New Jersey, Rhode Island, Connecticut, New York, and Pennsylvania. By 1840, the infant industry had experienced a speculative boom (about $2 million in stock was issued) and a disastrous collapse. The primary cause for the loss of confidence was that rubber products had not proven reliable—they softened in the heat and stiffened in the cold—but the downturn in general business conditions that began in the fall of 1837 only added to the industry's distress. So great were the industry's troubles that in 1843 the Roxbury Rubber Company sold the "monster" spreading machine (built by Edwin Marcus Chaffee in 1837) for $525; it had been purchased for $30,000.
Although experiments to cure rubber have been attributed to the eighteenth-century Swedish physician and pharmacist Petter-Jonas Bergius, it remained for Charles Goodyear to solve the basic technical problem confronting early rubber manufacturers. He did so in 1839, at Woburn, Massachusetts, when he developed the "vulcanization process," which gives rubber durability and consistent qualities across a broad range of temperatures by treating it with sulfur and white lead at a high temperature. His samples of "cured" rubber, with which he tried to raise funds in England, prompted the English inventor Thomas Hancock to make his own "discovery" of vulcanization. The "elastic metal" provided by these two inventors would soon prove indispensable to the Western world.
Nowhere was this more marked than in the development of the automobile industry. Yet long before the automobile appeared at the end of the nineteenth century, America's consumption of raw rubber had grown twenty fold—from 1,120 short tons in 1850 to 23,000 tons in 1900 (two-fifths of the world total of 59,000 short tons). Wherever elastic, shock-absorbing, water-resistant, insulating, and air-and steam-tight properties were required, vulcanized rubber was used. Most of the raw rubber came from Brazil, with Africa the second-most important source. The problem was not to find rubber but to find the labor to collect it in the almost inaccessible forests and ship it to the factories of the Northern Hemisphere. Until the systematic development of plantation rubber in Southeast Asia in the twentieth century made collection and transportation a comparatively easy task, the growing demand for crude rubber could only be met at increased cost. In 1830, Para rubber was 20 cents a pound; in 1900 the annual average wholesale price had risen to about a dollar.
Between 1849 and 1900, the industry's output of manufactured goods—chiefly footwear, mechanicals (for use with machinery), proofed and elastic goods, surgical goods, bicycle tires, and toys—increased in value from $3 million to $53 million. In the same years, the industry's workforce grew from 2,500 to 22,000. Because of the economies of scale and the absence of product differentiation, the market for rubber products was fiercely competitive—hence the tendency for the early rubber manufacturers to band together. Before the Civil War, marketing arrangements were already in existence to control the sale of footwear and other products. By the eve of World War I, production had come to be dominated by the "Big Four": Goodyear Tire and Rubber Company, United States Rubber Company, B. F. Goodrich Company, and Firestone Tire and Rubber Company. Partly to be close to the carriage-making industry—at the time the rubber industry's major consumer—the center of rubber manufacture had shifted from the towns of New England to Akron, Ohio. The industry's first branch factories were established in Western Europe in the 1850s.
The most dramatic phase of the industry's growth followed the introduction of the internal combustion engine, cheap petroleum, and the widespread use of the pneumatic tire in the early 1900s. Between 1900 and 1920, consumption of raw rubber increased tenfold—to 231,000 short tons. Even the world depression of the early 1930s only temporarily halted the industry's rapid expansion. By 1940, the United States was consuming 726,000 tons of a world total of 1,243,000 tons of crude rubber. Between 1900 (when the first four tons of Southeast Asia plantation rubber had reached the market) and 1910, the annual average wholesale price per pound of crude rubber doubled from $1 to $2. By 1915, more than twice as much rubber was coming from the plantations of Southeast Asia than from America and Africa combined, and prices had fallen to a quarter of their 1910 level; on 2 June 1932, the price was just three cents a pound.
Partly because of the great fluctuations in the price of crude rubber, and partly because the plantation industry of the Far East was largely in British hands, the industry began a search for rubber substitutes in the 1920s. In the next decade, manufacturers produced a few hundred tons a year of a special type of synthetic rubber. As Japan seized the rubber lands of Southeast Asia during World War II, U.S. production of synthetic rubber increased a hundredfold—from 9,000 short tons in 1941 to 919,000 tons in 1945, at which point synthetic rubber met four-fifths of America's needs. By 1973, of a world output of 6.3 million metric tons, the United States produced about 40 percent, almost three times more than the next greatest producer, Japan. That year, the United States had consumed only 696,000 metric tons of a world output of approximately 3.5 million tons of natural rubber.
Chemists succeeded in not only synthesizing rubber by making a wide range of elastomers and plastomers available, they changed the character of the industry until it was no longer possible to distinguish between rubber and rubber substitutes. The price of the synthetic compared favorably with that of the natural product, and for some uses synthetic rubber was preferable.
The rise of other industrialized nations in the twentieth century reduced America's domination of the industry; even so, its output in 1970 (including plastics) was worth about $15 billion and the industry employed more than half a million workers. In 1987, the American rubber industry shipped $24.9 billion in goods, of which automobile tires accounted for $10.5 billion of that amount. According to the Environmental Protection Agency, more than 230,000 people were employed in the rubber industry in the United States in 1987. Although rubber was used in thousands of ways, automobile tires—with which the major technical developments in manufacture have been associated—continued to account for more than one-half of the industry's consumption of raw materials. The overwhelming size of the major rubber corporations (a fifth giant was added to the Big Four in 1915 when the General Tire and Rubber Corporation was formed at Akron) did not lessen the industry's competitive nature. After World War II, the tendency toward global expansion increased, and, in the late twentieth century, the major rubber manufacturers were worldwide in scope and operation.
Allen, P. W. Natural Rubber and the Synthetics. New York: Wiley, 1972.
EPA Office of Compliance Sector. Profile of the Rubber and Plastic Industry. Washington, D.C.: U.S. Environmental Protection Agency, 1995.
Howard, Frank A. Buna Rubber: The Birth of an Industry. New York: Van Nostrand, 1947.
Phillips, Charles F. Competition in the Synthetic Rubber Industry. Chapel Hill: University of North Carolina Press, 1963.
Schidrowitz, Philip, and T. R. Dawson, eds. History of the Rubber Industry. Cambridge, U.K.: Heffer, 1952.
Woodruff, W. "Growth of the Rubber Industry of Great Britain and the United States." Journal of Economic History 15, no. 4 (1955): 376–391.
rubber, any solid substance that upon vulcanization becomes elastic; the term includes natural rubber (caoutchouc) and synthetic rubber. The term elastomer is sometimes used to designate synthetic rubber only and is sometimes extended to include caoutchouc as well.
Chemistry and Properties
All rubberlike materials are polymers, which are high molecular weight compounds consisting of long chains of one or more types of molecules, such as monomers. Vulcanization (or curing) produces chemical links between the loosely coiled polymeric chains; elasticity occurs because the chains can be stretched and the crosslinks cause them to spring back when the stress is released. Natural rubber is a polyterpene, i.e., it consists of isoprene molecules linked into loosely twisted chains. The monomer units along the backbone of the carbon chains are in a cis arrangement (see isomer) and it is this spatial configuration that gives rubber its highly elastic character. In gutta-percha, which is another natural polyterpene, the isoprene molecules are bonded in a trans configuration leading to a crystalline solid at room temperature. Unvulcanized rubber is soluble in a number of hydrocarbons, including benzene, toluene, gasoline, and lubricating oils.
Rubber is water repellent and resistant to alkalies and weak acids. Rubber's elasticity, toughness, impermeability, adhesiveness, and electrical resistance make it useful as an adhesive, a coating composition, a fiber, a molding compound, and an electrical insulator. In general, synthetic rubber has the following advantages over natural rubber: better aging and weathering, more resistance to oil, solvents, oxygen, ozone, and certain chemicals, and resilience over a wider temperature range. The advantages of natural rubber are less buildup of heat from flexing and greater resistance to tearing when hot.
Natural rubber is obtained from the milky secretion (latex) of various plants, but the only important commercial source of natural rubber (sometimes called Pará rubber) is the tree Hevea brasiliensis. The only other plant under cultivation as a commercial rubber source is guayule (Parthenium argentatum), a shrub native to the arid regions of Mexico and the SW United States. To soften the rubber so that compounding ingredients can be added, the long polymer chains must be partially broken by mastication, mechanical shearing forces applied by passing the rubber between rollers or rotating blades. Thus, for most purposes, the rubber is ground, dissolved in a suitable solvent, and compounded with other ingredients, e.g., fillers and pigments such as carbon black for strength and whiting for stiffening; antioxidants; plasticizers, usually in the form of oils, waxes, or tars; accelerators; and vulcanizing agents. The compounded rubber is sheeted, extruded in special shapes, applied as coating or molded, then vulcanized. Most Pará rubber is exported as crude rubber and prepared for market by rolling slabs of latex coagulated with acid into thin sheets of crepe rubber or into heavier, firmly pressed sheets that are usually ribbed and smoked.
An increasing quantity of latex, treated with alkali to prevent coagulation, is shipped for processing in manufacturing centers. Much of it is used to make foam rubber by beating air into it before pouring it into a vulcanizing mold. Other products are made by dipping a mold into latex (e.g., rubber gloves) or by casting latex. Sponge rubber is prepared by adding to ordinary rubber a powder that forms a gas during vulcanization. Most of the rubber imported into the United States is used in tires and tire products; other items that account for large quantities are belting, hose, tubing, insulators, valves, gaskets, and footwear. Uncoagulated latex, compounded with colloidal emulsions and dispersions, is extruded as thread, coated on other materials, or beaten to a foam and used as sponge rubber. Used and waste rubber may be reclaimed by grinding followed by devulcanization with steam and chemicals, refining, and remanufacture.
The more than one dozen major classes of synthetic rubber are made of raw material derived from petroleum, coal, oil, natural gas, and acetylene. Many of them are copolymers, i.e., polymers consisting of more than one monomer. By changing the composition it is possible to achieve specific properties desired for special applications. The earliest synthetic rubbers were the styrene-butadiene copolymers, Buna S and SBR, whose properties are closest to those of natural rubber. SBR is the most commonly used elastomer because of its low cost and good properties; it is used mainly for tires. Other general purpose elastomers are cis-polybutadiene and cis-polyisoprene, whose properties are also close to that of natural rubber.
Among the specialty elastomers are copolymers of acrylonitrile and butadiene that were originally called Buna N and are now known as nitrile elastomers or NBR rubbers. They have excellent oil resistance and are widely used for flexible couplings, hoses, and washing machine parts. Butyl rubbers are copolymers of isobutylene and 1.3% isoprene; they are valuable because of their good resistance to abrasion, low gas permeability, and high dielectric strength. Neoprene (polychloroprene) is particularly useful at elevated temperatures and is used for heavy-duty applications. Ethylene-propylene rubbers (RPDM) with their high resistance to weathering and sunlight are used for automobile parts, hose, electrical insulation, and footwear. Urethane elastomers are called spandex and they consist of urethane blocks and polyether or polyester blocks; the urethane blocks provide strength and heat resistance, the polyester and polyether blocks provide elasticity; they are the most versatile elastomer family because of their hardness, strength, oil resistance, and aging characteristics. They have replaced rubber in elasticized materials. Other uses range from airplane wheels to seat cushions. Other synthetics are highly oil-resistant, but their high cost limits their use. Silicone rubbers are organic derivatives of inorganic polymers, e.g., the polymer of dimethysilanediol. Very stable and flexible over a wide temperature range, they are used in wire and cable insulation.
Pre-Columbian peoples of South and Central America used rubber for balls, containers, and shoes and for waterproofing fabrics. Mentioned by Spanish and Portuguese writers in the 16th cent., rubber did not attract the interest of Europeans until reports about it were made (1736–51) to the French Academy of Sciences by Charles de la Condamine and François Fresneau. Pioneer research in finding rubber solvents and in waterproofing fabrics was done before 1800, but rubber was used only for elastic bands and erasers, and these were made by cutting up pieces imported from Brazil. Joseph Priestley is credited with the discovery c.1770 of its use as an eraser, thus the name rubber.
The first rubber factory in the world was established near Paris in 1803, the first in England by Thomas Hancock in 1820. Hancock devised the forerunner of the masticator (the rollers through which the rubber is passed to partially break the polymer chains), and in 1835 Edwin Chaffee, an American, patented a mixing mill and a calender (a press for rolling the rubber into sheets).
In 1823, Charles Macintosh found a practical process for waterproofing fabrics, and in 1839 Charles Goodyear discovered vulcanization, which revolutionized the rubber industry. In the latter half of the 19th cent. the demand for rubber insulation by the electrical industry and the invention of the pneumatic tire extended the demand for rubber. In the 19th cent. wild rubber was harvested in South and Central America and in Africa; most of it came from the Pará rubber tree of the Amazon basin.
Despite Brazil's legal restrictions, seeds of the tree were smuggled to England in 1876. The resultant seedlings were sent to Ceylon (Sri Lanka) and later to many tropical regions, especially the Malay area and Java and Sumatra, beginning the enormous East Asian rubber industry. Here the plantations were so carefully cultivated and managed that the relative importance of Amazon rubber diminished. American rubber companies, as a step toward diminishing foreign control of the supply, enlarged their plantation holdings in Liberia and in South and Central America.
During World War I, Germany made a synthetic rubber, but it was too expensive for peacetime use. In 1927 a less costly variety was invented, and in 1931 neoprene was made, both in the United States. German scientists developed Buna rubber just prior to World War II. When importation of natural rubber from the East Indies was cut off during World War II, the United States began large-scale manufacture of synthetic rubber, concentrating on Buna S. Today synthetic rubber accounts for about 60% of the world's rubber production.
See P. W. Allen, Natural Rubber and the Synthetics (1972); M. Morton, Rubber Technology (3d ed. 1987).
Rubber was first used to manufacture tires in the mid-nineteenth century. By the turn of the twenty-first century, there were about three billion waste tires stockpiled or clogging leak pollutants intolandfills in the United States alone. Worldwide, about 700 million scrap tires are generated annually. This waste rubber has become a major source of pollution .
Although rubber, made from latex secreted by trees, has been used for thousands of years, it wasn't until 1839, when Charles Goodyear invented vulcanization, that rubber became important for manufacturing. Vulcanization uses sulfur to cross-link the latex fibers into a rubber that is strong, flexible, durable, and resistant to heat and cold. Like natural rubber, modern synthetic rubbers are polymers (long chains of similar molecules) that are cross-linked by vulcanization. Tires consume 60–70% of all rubber produced, twothirds of which is synthetic.
Of the 273 million waste tires generated annually in the United States, about 25% end up in landfills. There they leak pollutants into soil and groundwater and tend to rise to the surface, harming landfill covers. The largest tire dump in the Northeast United States holds an estimated 20–30 million tires. The majority of states now ban tire disposal in landfills and collect disposal fees on tires or require that the tires be chipped or ground before disposal. An additional 800 million tires are stockpiled in the United States, however, and many more are dumped illegally. These mountains of tires can fill up with water and become breeding grounds for rats and mosquitoes. They also can ignite, have a high heat output, and are very difficult to contain. These fires can burn for months or years, producing toxic smoke and oils that pollute the air, water, and soil.
Rubber is difficult to recycle because of its chemical cross-linking. Furthermore most tires contain a mixture of three or four types of synthetic rubbers, as well as natural rubber, other fibers, and steel. Nevertheless in the United States, markets now exist for 76% of newly-scrapped tires, up from 17% in 1990. About 42% of scrapped tires are used for fuel in facilities such as pulp and paper mills and cement kilns. As a fuel, tires are equivalent to oil and produce 25% more energy than coal . Because of new technologies and pollution controls, tire combustion now proceeds at higher temperatures with less air pollution .
About 33 million retread or recapped tires are sold annually in the United States. A retread tire reuses 75% of the old tire and requires 70% less oil than manufacturing a new tire.
In 2001 about 40 million scrap tires were used in the construction of playground equipment, artificial reefs, boat bumpers, crash barriers, stabilizers for slopes, and erosion control for dams . Tire material is used for mulch , mats, septic systems, building products, coatings and sealants, and in hazardous waste containers.
Many new products contain material from recycled tires. In the United States about 24.5 million scrap tires annually are ground up, cut, stamped, or punched for new products. Ground tires are used for running tracks, playgrounds, flooring, and the soles of shoes, or mixed with asphalt for road paving. Rubber crumb is used in products such as athletic turf and auto parts.
In typical rubber recycling , the tires are cut up into small pieces and ground, or frozen in liquid nitrogen and shattered or pulverized. The steel is extracted with magnets and filters separate the rubber from other synthetic fibers. However 15–50% of the original tire remains as a useless rubber-fiber blend that goes to the landfill. The U.S. Department of Agriculture is attempting to develop more efficient methods of separating the rubber from the other fibers.
The development of new tire recycling technologies is an active area of research. Ground-up rubber can be mixed with virgin rubber and vulcanized to form new cross-links, restoring its strength and elasticity. About 5% of scrap tires are recycled in this way. Improved methods for rejuvenating old rubber, without mixing it with newly-manufactured rubber, would enable tire manufacturers to increase the recycled content of new tires.
Another area of research uses heat and pressure to combine the powder from ground-up tires with powder made from asphalt. This asphalt-modified rubber is superior to asphalt for roads, construction materials, and roofing shingles. Likewise, researchers are experimenting with adding rubber crumb to fresh concrete to increase strength and durability. A composite that contains 50% rubber crumb could potentially replace plastics such as polyvinyl chlorides for various applications. Other researchers are studying whether the oils produced by waste tire combustion can be reprocessed into carbon black for use in various products.
[Margaret Alic Ph.D. ]
"Arizona State University Research Finds Recycling Cure for Used Tires." ScienceDaily Magazine September 13, 2001 [cited July 7, 2002]. <http://www.sciencedaily.com/releases/2001/09/010913074634.htm>.
"Recycling Research Institute." Scrap Tire News Online. 2002 [cited July 7, 2002]. <http://www.scraptirenews.com>.
U.S. Environmental Protection Agency. Jobs Through Recycling. May 31, 2002 [cited July 7, 2002]. <http://www.epa.gov/epaoswer/non-hw/recycle/jtr/comm/rubber.htm>.
U.S. Environmental Protection Agency. Municipal Solid Waste. May 9, 2002 [cited July 7, 2002]. <http://www.epa.gov/msw/tires.htm>.
"Umass Polymer Scientists Aiming to Turn Scrap Tires into Environmentally Friendly Products." ScienceDaily Magazine March 6, 2002 [cited July 7, 2002]. <http://www.sciencedaily.com/releases/2002/03/020306073739.htm>.
International Tire & Rubber Association Foundation, Inc., PO Box 37203, Louisville, KY USA 40233-7203 (502) 968-8900, Fax: (502) 964-7859, Toll Free: (800) 426-8835, Email: [email protected], <http://www.itra.com>
Recycled Materials Resource Center, 220 Environmental Technology Building, Durham, NH USA 03824 (603) 862-3957, Email: [email protected], <http://www.rmrc.unh.edu>
rub·ber1 / ˈrəbər/ • n. a tough elastic polymeric substance made from the latex of a tropical plant or synthetically. ∎ (rubbers) rubber boots; galoshes. ∎ Baseball an oblong piece of rubber or similar material embedded in the pitcher's mound, on which the pitcher must keep one foot while delivering the ball. ∎ inf. a condom. ∎ Brit. an eraser for pencil or ink marks. DERIVATIVES: rub·ber·i·ness n. rub·ber·y adj. rub·ber2 • n. a contest consisting of a series of successive matches (typically three or five) between the same sides or people in tennis, cricket, and other games. ∎ (usu. rubber match or rubber game) a game played to determine the winner of a series: Clemens will pitch in the rubber game of this tied-up series. ∎ Bridge a unit of play in which one side scores bonus points for winning the best of three games.
rubber stamp a person or organization that gives automatic approval or authorization to the decisions of others, without proper consideration (literally, a hand-held device for inking and imprinting a message or design on a surface).