Charles Goodyear Discovers the Process for Creating Vulcanized Rubber
Charles Goodyear Discovers the Process for Creating Vulcanized Rubber
In 1839, a perpetually impoverished inventor who referred to a succession of debtors' prisons as his "hotels" rescued an ailing industry and made it a multimillion-dollar enterprise. Charles Goodyear (1800-1860) discovered a process for curing rubber, which transformed this remarkable but flawed natural substance from a curiosity fit for museums into the first of the modern plastics.
During his second visit to the New World in 1493-96, Christopher Columbus (1451-1506) noted that native villagers in Hispaniola played a soccer-like game with a light and bouncy ball made from the milky, white sap of a tree. The Indians cured the sap, called latex, by smoking it to evaporate out the water before forming the latex into balls. Subsequent explorers from Europe learned that latex, which was both elastic and sticky, could be pressed not only into objects for games but also into usable articles such as waterproof cloth, inflatable bags, and molded bottles and boots.
In 1735, the French mathematical geographer Charles Marie de la Condamine (1701-1774) sent back samples of crude rubber from South America, and described its botanical nature and the products that could be made from it. The French called the material cautchouc, from the Mayan word for weeping wood, and excitedly advertised its springiness and resistance to water. It came to be called rubber after the British chemist Joseph Priestley (1733-1804) noted in 1770 that it was superior to breadcrumbs for rubbing out lead pencil marks.
The fact that latex hardened on drying spurred a search for solvents so that products could be made far away from where the rubber was collected. In 1763, two Frenchmen found that turpentine successfully dissolved rubber but left it sticky. Experiments with ether a few years later solved the problem of stickiness. Rubber was first used commercially by the English manufacturer Samuel Peal, who applied a solution of rubber in turpentine to waterproof cloth. In 1820 the Scottish chemist Charles Macintosh (1766-1843) found that immersing raw rubber in naptha produced a liquid rubber substance that could be brushed on sheets of cotton canvas. Two pieces of this rubberized cloth pressed together like a sandwich appeared to make an ideal waterproof raincoat, or mackintosh. The first rubber factory was founded in 1820 by English inventor Thomas Hancock (1786-1865), to manufacture footwear and clothing with rubber components. One of Hancock's innovations was a machine called a masticator that welded bits of waste rubber into solid masses that could be reused. Hancock and Macintosh eventually became partners.
The remarkable qualities of rubber were immediately obvious. Elastic, plastic, strong, durable, electrically inert, and water-resistant, it was a material that begged for exploitation. But at the time it was also intractable: Macintosh's raincoats, which worked so well in the London fog, melted in the heat of the American South. In the winter cold, rubber overshoes turned hard and brittle. And the smell of rubber was unpleasant. Although demand for the light, pliant, waterproof material from Brazil was initially high, factories that sprang up in the 1830s in a wave of "rubber fever" quickly went under. Millions of dollars were lost in rubber ventures. Rubber products seemed destined to remain a marginal article of commerce.
In 1834, a bankrupt young inventor from Connecticut named Charles Goodyear tried to sell an improved airtight valve for life preservers to the Roxbury India Rubber Company. The company refused his invention on the grounds that it made no sense until someone could come up with a better rubber. Goodyear had always been enamored of rubber, and needed little encouragement. Although he was penniless and had no knowledge of chemistry, he set about to find the full range of rubber's potential. During this time, Goodyear, who had a wife and small children, was in and out of debtors' prison, where he cajoled the prison guards into letting him conduct experiments in the prison kitchen.
Goodyear plunged into a trial-and-error orgy of mixing natural latex rubber with anything he could find, including witch hazel, castor oil, and ink. Because rubber was naturally adhesive, he wondered what he might do to absorb the stickiness. He tried adding two drying agents to his rubber, first magnesia, then both magnesia and quicklime, with limited improvement. His first success occurred in 1836 when he treated rubber with nitric acid and bismuth and copper nitrates—the so-called acid-gas process—which made the rubber as smooth and dry as cloth and appeared to improve its resistance to heat. He found a financial backer to begin production of his material, but bad economic times ended the scheme, and Goodyear was reduced to fishing to keep his family alive. In 1837 he accepted a friend's contract to manufacture nitric-acid-cured rubber mailbags. But in the summer heat the mailbags crumbled, and Goodyear realized that the nitric acid had only cured the surface of the rubber. He redoubled his attempts to solve what he called the "riddle of rubber."
Five years into his investigations, and the year he turned 40, Goodyear accidentally spilled some raw latex mixed with sulfur on a hot stove. Instead of melting like ordinary rubber, the substance charred evenly, like leather. He applied extremes of heat to the mixture, but it did not melt. Nor did hanging the charred material outside overnight in the cold Massachusetts winter cause it to shatter. It remained pliable. In a later test, Goodyear saw that along the edge of the charred rubber was a border that was perfectly cured. His happy accident would quickly revolutionize the rubber industry.
In chemical terms, what Goodyear had managed to do was to link together the long, linear chains of molecules in rubber. Rubber is derived from the sap of the rubber tree Hevea braziliensis. When natural rubber is heated with sulfur, the sulfur forms cross-links between the chains that are like a bridge, or the rungs of a ladder. The more sulfur is added, the greater the degree of cross-linking. In natural rubber, the chainlike molecules can slip past one another, or around each other, which is what causes the rubber to melt when it gets warm, and to break apart when it gets cold. If car tires were made of natural rubber, the friction of the road surface acting on them would reduce them to useless glop. But the cross-links act like anchors to prevent slippage. They are also what allows rubber to return to normal after it has been stretched (a property called elasticity). A rubber band, which is only moderately cross-linked, is elastic. A car tire, which is extensively crosslinked, is hard and bouncy rather than elastic.
Although Goodyear now knew that heat and sulfur changed the properties of rubber in a dramatic way, he had no idea how much heat he needed to apply or for how long. Many months of personal hardship passed, but in the end he came up with a formula that guaranteed uniform results. Overnight, what Goodyear called "vegetable leather" and "elastic metal" because of its durable properties became a useful commodity. It was stretchable, tough, waterproof, and could be used to stick things together. Above all, it was moldable, which made it ideally suited to mass manufacturing. Used first to make the ruffled fronts then fashionable in men's shirts, vulcanized rubber was soon shaped into other items of clothing, harnesses, bottle stoppers, frames for photographic plates, cigarette holders, and rubber dental plates. Consumption of rubber increased from 38 tons in 1825 to 8,000 tons in 1870.
Solid rubber tires, kinder to roads and to grasslands, appeared in 1867 for use in steam road vehicles, and in 1869 for bicycles. Rubber belting was used as conveyors to handle seeds and grain, and then minerals and ores, and to drive machinery and vehicles. With the discovery of the incandescent electric lamp, electricity would need to be distributed, stimulating demand for insulated cables and wiring.
But vulcanized rubber was not without disadvantages. It had to be gathered by hand, and prices were kept high worldwide by a small cartel of rubber "barons." Moreover, the material was not corrosion-resistant, which made it vulnerable as an insulator for submarine cables. Only once vulcanized rubber began to be used in machinery and particularly in automobile tires did the modern rubber industry become a reality. So effective was Goodyear's formula that, despite some technical improvements, the vulcanization process has changed very little since his day.
An appealing feature of Goodyear's recipe for cured rubber was its simplicity. Unfortunately, it also made the formula very easy to copy. Goodyear patented his invention in the United States, but had no money left to file for British patent protection. He proposed a British-American joint venture to the firm of Charles Macintosh & Co., but his agent's handling of the matter was maladroit. Consequently, four years after Goodyear's own discovery, Thomas Hancock, the managing director, reverse-engineered some samples the agent had left behind and promptly filed a British patent himself, only weeks before Goodyear got around to filing his own patent. It was Hancock who, on the suggestion of a friend, named the process vulcanization, after Vulcan, the ancient Roman god of fire.
Goodyear spent the rest of his life embroiled in patent suits—he prosecuted 32 infringement cases all the way to the Supreme Court—at one time hiring Daniel Webster at $15,000 for two days' work to defend him. At the Great Exhibition of 1851, he borrowed heavily to underwrite a Vulcanite Court, every part of which, including furniture, musical instruments, and six-foot-diameter balloons filled with hydrogen, was fashioned from vulcanized rubber. Six million people visited his exhibit.
Goodyear's life was laced with irony. Jailed in Paris for 16 days in 1855 for nonpayment of debts, he received the Cross of the Legion of Honor from French emperor Napoleon III while in prison (his son brought the medal to his cell). By 1860 an industry founded on his rubber patents was employing 60,000 people and making over $8 million a year; yet Goodyear died $200,000 in debt. At one time or another he pawned his children's schoolbooks and his wife's jewelry to pay bills. His autobiography netted him more money than he ever made from his 60 patents. His vision was unabashedly monomaniacal, though curiously enough, some of the ideas Goodyear had for uses of rubber that must have appeared madcap a century ago enjoy application today, including packaging for food, rubber paint, car springs, wheelbarrow tires, water beds, inflatable life rafts, and frog-man suits. Had he been able to, he would have used rubber to remake the world. And in a way, he did. Vulcanized rubber paved the way to synthetic materials.
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Goodyear, Charles. Gum-Elastic and Its Varieties, with a Detailed Account of Its Applications and Uses, and of the Discovery of Vulcanization. New Haven: Pub. for the author, 1853.
Kauffman, George G. "Charles Goodyear—Inventor of Vulcanisation." Education in Chemistry (November 1989): 167-170.
"Charles Goodyear and the Strange Story of Rubber." http://www.goodyear.com/us/corporate/strange.html