
Rubber



by Chris Woodford. Last updated: July 26, 2019. Think of rubber and you probably think of elastic bands, car tires, or pencil erasers. But this super-stretchy material actually finds its way into tens of thousands of different products—everything from rubber stamps and waterproof shoes to surfing wetsuits, swimming caps, and dishwasher hoses. Rubber, which has been commonly used for over 1000 years, once came entirely from natural sources; now rubber products are just as likely to be made artificially in chemical plants. That's largely because we can't produce enough natural rubber to meet all our needs. And that, in turn, is because rubber is so fantastically useful. Let's take a closer look at one of the world's most amazing materials! Photo: Half of the world's rubber is used to make vehicle tires—and at least half of them are wasted in landfills, burned in incinerators, or otherwise dumped. What is rubber? When people talk about "rubber", they don't usually specify what kind. There are many different kinds of rubber, but they all fall into two broad types: natural rubber (latex—grown from plants) and synthetic rubber (made artificially in a chemical plant or laboratory). Commercially, the most important synthetic rubbers are styrene butadiene (SBR), polyacrylics, and polyvinyl acetate (PVA); other kinds include polyvinyl chloride (PVC), polychloroprene (better known as neoprene), and various types of polyurethane. Although natural rubber and synthetic rubbers are similar in some ways, they're made by entirely different processes and chemically quite different. Natural rubber Photo: Rubber bands are a very familiar everyday use of latex rubber. Natural rubber is made from a runny, milky white liquid called latex that oozes from certain plants when you cut into them. (Common dandelions, for example, produce latex; if you snap off their stems, you can see the latex dripping out from them. In theory, there's no reason why we couldn't make rubber by growing dandelions, though we'd need an awful lot of them.) Although there are something like 200 plants in the world that produce latex, over 99 percent of the world's natural rubber is made from the latex that comes from a tree species called Hevea brasiliensis, widely known as the rubber tree. Photo: Guayule: one of many plants from which rubber can be made. Photo by Peggy Greb courtesy of US Department of Agriculture/Agricultural Research Service (USDA/ARS). This latex is about one third water and one third rubber particles held in a form known as a colloidal suspension. Natural rubber is a polymer of isoprene (also known as 2-methylbuta-1,3-diene) with the chemical formula (C5H8)n. To put it more simply, it's made of many thousands of basic C5H8 units (the monomer of isoprene) loosely joined to make long, tangled chains. These chains of molecules can be pulled apart and untangled fairly easily, but they spring straight back together if you release them—and that's what makes rubber elastic. Synthetic rubbers Synthetic rubbers are made in chemical plants using petrochemicals as their starting point. One of the first (and still one of the best known) is neoprene (the brand name for polychloroprene), made by reacting together acetylene and hydrochloric acid. Emulsion styrene-butadiene rubber (E-SBR), another synthetic rubber, is widely used for making vehicle tires. For the rest of this article, we'll concentrate mostly on natural rubber.

How is rubber made? Photo: In 1839, American inventor Charles Goodyear (1800–1860) developed the vulcanization (heat-treatment) process that makes rubber harder and more durable. He'd spent many years as a struggling inventor, trying desperately to turn rubber into a useful product, when he accidentally dropped some rubber on a hot stove and watched it "cook" itself into a much more useful form: the black, vulcanized material most of us know as rubber to this day. Despite developing one of the most useful materials of all time, Goodyear never made much money from his invention and died deeply in debt. Fortunately, his name lives on in the Goodyear tire company—and his superb contribution to materials technology has never been forgotten. Photo courtesy of US Library of Congress. It takes several quite distinct steps to make a product out of natural rubber. First, you have to gather your latex from the rubber trees using a traditional process called rubber tapping. That involves making a wide, V-shaped cut in the tree's bark. As the latex drips out, it's collected in a cup. The latex from many trees is then filtered, washed, and reacted with acid to make the particles of rubber coagulate (stick together). The rubber made this way is pressed into slabs or sheets and then dried, ready for the next stages of production. By itself, unprocessed rubber is not all that useful. It tends to be brittle when cold and smelly and sticky when it warms up. Further processes are used to turn it into a much more versatile material. The first one is known as mastication (a word we typically use to describe how animals chew food). Masticating machines "chew up" raw rubber using mechanical rollers and presses to make it softer, easier to work, and more sticky. After the rubber has been masticated, extra chemical ingredients are mixed in to improve its properties (for example, to make it more hardwearing). Next, the rubber is squashed into shape by rollers (a process called calendering) or squeezed through specially shaped holes to make hollow tubes (a process known as extrusion). Finally, the rubber is vulcanized (cooked): sulfur is added and the rubber is heated to about 140°C (280°F) in an autoclave (a kind of industrial pressure cooker). Photo: Vulcanized rubber is heated in a giant sealed "cooker" like this one, used for making earthmover tires, pictured at Firestone Tire Company in 1942. At that time, it was the biggest rubber vulcanizer in the world, standing some 2.5 stories high when opened wide. I've colored the people in the pictures red to give you an idea of the scale. Photos by Alfred T. Palmer courtesy of US Library of Congress. Where does rubber come from? As its name suggests, the rubber tree Hevea brasiliensis originally came from Brazil, from where it was introduced to such countries of the Far East as Malaysia, Indonesia, Burma, Cambodia, China, and Vietnam. During World War II, supplies of natural rubber from these nations were cut off just when there was a huge demand from the military—and that accelerated the development of synthetic rubbers, notably in Germany and the United States. Today, most natural rubber still comes from the Far East, while Russia and its former republics, France, Germany, and the United States are among the world's leading producers of synthetic rubber. The world's largest single source of latex rubber is the Harbel Rubber Plantation near Monrovia in Liberia, established in the 1920s and 1930s by the Firestone tire company.

How does vulcanization make rubber stronger? Artwork: Top: Natural, latex rubber is easy to pull apart because the long polymer molecules it contains (made from carbon and hydrogen atoms) are only weakly linked together. Bottom: When natural rubber is cooked with sulfur, the sulfur atoms form extra cross-links (shown here as yellow bars) "bolting" the molecules together and making them much harder to pull apart. This process is called vulcanization and it makes the strong, durable, black rubber we see on things like car tires. Rubber—the kind you get from a tree—starts off as white and runny latex. Even when it's set into a product, this latex-based, natural rubber is very squashy, pretty smelly, and not very useful. The kind of rubber you see in the world around you, in things like car and bicycle tires, is vulcanized: cooked with sulfur (and often other additives) to make it harder, stronger, and longer lasting. So what's the difference between raw, latex rubber and cooked, vulcanized rubber? In its natural state, the molecules in rubber are long chains that are tangled up and only weakly linked together. It's relatively easy to pull them apart—and that's why latex rubber is so stretchy and elastic. When latex is vulcanized, the added sulfur atoms help to form extra bonds between the rubber molecules, which are known as cross-links. These work a bit like the trusses you see on a bridge, tying the molecules together and making them much harder to pull apart.

What do we use rubber for? Photo: Three everyday uses of rubber. Top: A latex pencil eraser; Middle: the tough vulcanized rubber drive belt from a vacuum cleaner; Bottom: the waterproof rubber gasket that seals a washing machine door tight. The physical and chemical properties of a material dictate what we use it for. Even if you know absolutely nothing about the real-world uses of rubber, you can probably make some very good guesses. For example, everyone knows rubber is strong, stretchy, flexible (elastic), durable, and waterproof, so it's no surprise to find it used in things like waterproof clothes and wellington boots, sticking plasters, and adhesives. The most important use of rubber is in vehicle tires; about half of all the world's rubber ends up wrapped around the wheels of cars, bicycles, and trucks! You'll find rubber in the hard, black vulcanized outsides of tires and (where they have them) in their inner tubes and liners. The inner parts of tires are usually made from a slightly different, very flexible butyl rubber, which is highly impermeable to gases (traps them very effectively), so tires (generally) stay inflated for long periods of time. Photo: Swimming caps like this are made from soft and stretchy latex rubber. The fact that rubber can be made either soft or hard greatly increases the range of things we can use it for. Soft and stretchy latex is used in all kinds of everyday things, from pencil erasers, birthday balloons, and condoms to protective gloves, adhesives (such as sticky white PVA), and paints. Harder rubbers are needed for tougher applications like roofing membranes, waterproof butyl liners in garden ponds, and those rigid inflatable boats (RIBs) used by scuba divers. Because rubber is strong, flexible, and a very poor conductor of heat and electricity, it's often used as a strong, thin, jacketing material for electrical cables, fiber-optic cables, and heat pipes. But the range of applications is truly vast: you'll find it in everything from artificial hearts (in the rubber diaphragms that pump blood) to the waterproof gaskets that seal the doors on washing machines! Neoprene (polychloroprene) is best known as the heat-insulating, outer covering of wetsuits—but it has far more applications than most people are aware of. Medical supports of various kind use it because, tightly fitted, it compresses and warms injured bits of your body, promoting faster healing. Since it's flexible and waterproof, it's also widely used as a building material, for example, as a roof and floor sealant, and as a spongy absorber of sound and vibration in door and window linings. Although the world has a vast appetite for new rubber, we also produce a huge quantity of rubber waste, especially from discarded vehicle tires—and that's becoming an important raw material in its own right. According to the Rubber Manufacturers Association, the United States alone produced almost 270 million waste rubber vehicle tires in 2011, which is about a third of all the tires used worldwide. While some of these are retreaded and others are ground up to make a low-grade aggregate that can be used for the floors in things like children's playgrounds, over half of them are wasted (either burned as a fuel or buried in landfills). Rubber manufacturers have recently turned their attention to recycling tires in all kinds of new ways, making everything from mouse mats and sports bags to shoe soles and car components. Photo: Half of all rubber is used in vehicle tires, and hundreds of millions are wasted each year. I've made a very slight difference to the problem by buying this recycled rubber mouse mat, made from an old car tire. It's colored black because it's made from hard vulcanized rubber. A brief history of rubber 1000CE: Indians living in Central and South America have learned how to made waterproof clothes and shoes using latex from rubber trees. They call rubber trees "cahuchu" (crying wood), which is why the French still call rubber caoutchouc (pronounced "cow-chew") today.

(pronounced "cow-chew") today. 1731: During an expedition to South America, French explorer Charles Marie de La Condamine (1701–74) sends back samples of rubber to Europe, prompting intense scientific interest.

(1701–74) sends back samples of rubber to Europe, prompting intense scientific interest. 1770: The discoverer of oxygen, English scientist Joseph Priestley (1733–1804), finds he can use pieces of rubber to erase the marks made by pencil on paper. In England, erasers are still widely called "rubbers" today.

(1733–1804), finds he can use pieces of rubber to erase the marks made by pencil on paper. In England, erasers are still widely called "rubbers" today. 1791: Englishman Samuel Peal develops a method of waterproofing cloth with a rubber solution.

develops a method of waterproofing cloth with a rubber solution. 1818: Scottish medical student James Syme (1799–1870) uses rubber-coated cloth to make raincoats.

(1799–1870) uses rubber-coated cloth to make raincoats. 1823: Scotsman Charles Macintosh learns of Syme's discovery, refines it, and patents it, earning fame and fortune as the inventor of the rubberized, waterproof coat. Waterproof coats have been known as "Mackintoshes" (with a slight variation of spelling) ever since.

learns of Syme's discovery, refines it, and patents it, earning fame and fortune as the inventor of the rubberized, waterproof coat. Waterproof coats have been known as "Mackintoshes" (with a slight variation of spelling) ever since. 1829: English chemist and physicist Michael Faraday (1791–1867) analyzes samples of Hevea and works out that the chemical formula for isoprene-type rubber is C 5 H 8 .

(1791–1867) analyzes samples of Hevea and works out that the chemical formula for isoprene-type rubber is C H . 1839: American inventor Charles Goodyear (1800–1860) accidentally discovers how to vulcanize rubber after dropping a piece of the material (which has been treated with sulfur) onto a hot stove.

(1800–1860) accidentally discovers how to vulcanize rubber after dropping a piece of the material (which has been treated with sulfur) onto a hot stove. 1830s~1840s: Botanist Thomas Lobb discovers a rubbery substance called Gutta-percha ( Palaquium gutta ) in Malaysia; Dr William Montgomerie , a surgeon working in the same region, sends samples back to Britain in 1843. According to a contemporary account by William Dalton, it has "remarkable properties, vast utility, and application to scientific and ornamental purposes" in everything from "boots and shoes" to "prevention of toothache."

discovers a rubbery substance called Gutta-percha ( ) in Malaysia; , a surgeon working in the same region, sends samples back to Britain in 1843. According to a contemporary account by William Dalton, it has "remarkable properties, vast utility, and application to scientific and ornamental purposes" in everything from "boots and shoes" to "prevention of toothache." 1876: Intrepid English explorer Sir Henry Wickham (1846–1928) smuggles thousands of seeds from the rubber tree Hevea brasiliensis out of Brazil and back to England. The English grow the seeds at Kew Gardens just outside London and export them to various Asian countries, establishing the giant plantations that now supply much of the world's rubber.

(1846–1928) smuggles thousands of seeds from the rubber tree out of Brazil and back to England. The English grow the seeds at Kew Gardens just outside London and export them to various Asian countries, establishing the giant plantations that now supply much of the world's rubber. 1877: US rubber manufacturer Chapman Mitchell develops the first commercial process for recycling rubber from scratch.

develops the first commercial process for recycling rubber from scratch. 1882: John Boyd Dunlop (1840–1921) invents the pneumatic (air-filled) rubber tire. The development of gasoline-powered cars with rubber tires leads to a huge increase in the need for rubber.

(1840–1921) invents the pneumatic (air-filled) rubber tire. The development of gasoline-powered cars with rubber tires leads to a huge increase in the need for rubber. 1883: US chemist George Oenslager (1873–1956) develops a much faster way of vulcanizing rubber using chemicals called organic (carbon-based) accelerators.

(1873–1956) develops a much faster way of vulcanizing rubber using chemicals called organic (carbon-based) accelerators. 1906–12: Bayer , a German chemical company, develops methyl rubber (a polymer of methylisoprene). It becomes critically important to Germany during World War I when supplies of natural rubber are cut off, but falls out of fashion when better alternatives are eventually developed.

, a German chemical company, develops methyl rubber (a polymer of methylisoprene). It becomes critically important to Germany during World War I when supplies of natural rubber are cut off, but falls out of fashion when better alternatives are eventually developed. 1910: English Chemist S.S. Pickles becomes the first person to propose (correctly) that rubber consists of long chains of isoprene. Technically, Hevea has the chemical name cis-1,4-polyisoprene, while Gutta-percha is a variation known as trans-1,4-polyisoprene.

becomes the first person to propose (correctly) that rubber consists of long chains of isoprene. Technically, Hevea has the chemical name cis-1,4-polyisoprene, while Gutta-percha is a variation known as trans-1,4-polyisoprene. 1930: German chemical company IG Farben develops a type of general-purpose, synthetic rubber named Buna-S ("bu" from butadiene, "na" from the chemical symbol for sodium, and "S" for styrene). Technically, it's a copolymer of butadiene (75 percent) and styrene (25 percent), which is why it's now more generally known as styrene-butadiene or styrene-butadiene-rubber (SBR); it's also sold under tradenames such as Goodyear's Neolite®. Today, styrene-butadiene remains by far the world's most important synthetic rubber.

develops a type of general-purpose, synthetic rubber named Buna-S ("bu" from butadiene, "na" from the chemical symbol for sodium, and "S" for styrene). Technically, it's a copolymer of butadiene (75 percent) and styrene (25 percent), which is why it's now more generally known as styrene-butadiene or styrene-butadiene-rubber (SBR); it's also sold under tradenames such as Goodyear's Neolite®. Today, styrene-butadiene remains by far the world's most important synthetic rubber. 1930: A team of US chemists at the DuPont company, led by Wallace Carothers (1896–1937), develop a revolutionary synthetic rubber called polychloroprene and sold as neoprene. (Shortly afterward, the same group developed an even more revolutionary material: nylon.)

(1896–1937), develop a revolutionary synthetic rubber called polychloroprene and sold as neoprene. (Shortly afterward, the same group developed an even more revolutionary material: nylon.) 1940s: Synthetic rubbers are produced in the United States for the first time by companies such as Firestone, Goodyear, and Goodrich.





Please do NOT copy our articles onto blogs and other websites Articles from this website are registered at the US Copyright Office. Copying or otherwise using registered works without permission, removing this or other copyright notices, and/or infringing related rights could make you liable to severe civil or criminal penalties. Text copyright © Chris Woodford 2008, 2019. All rights reserved. Full copyright notice and terms of use. Neolite is a registered trademark of The Goodyear Tire & Rubber Company Corporation.

Follow us



Rate this page Please rate or give feedback on this page and I will make a donation to WaterAid.