Meanwhile, in 1834, Charles Goodyear bought a rubber life-preserver and later obtained a U.S. Government contract to make rubber mail bags. But he found that the rubber mail bags began to decompose quite rapidly. They became sticky when hot and stiff when cold. In 1840, after many experiments, he developed vulcanization by accident when he spilled a mixture of white lead, sulfur and rubber onto a hot stove. The resulting product was unaffected by hot or cold weather, and, when stretched, returned to its original form. It was also resistant to water and chemicals and did not conduct electricity.
He tried to sell the process to Macintosh, in 1842, but Hancock realized how it was made and duplicated the technique, coining the term 'Vulcanization' and quickly obtaining a British patent.
Goodyear finally obtained a U.S. patent in 1844 but, unfortunately, he died before he could profit from his discovery. The Goodyear company was named in his honour.
Vulcanization creates di- and polysulfide bonds between the long molecular chains, which limits the degrees of freedom and results in chains that tighten more quickly for a given strain, thereby increasing the elastic force constant and making the rubber harder and less extensible.
Latex or natural rubber, consists of polymers of the organic compound isoprene with minor impurities. The forms of polyisoprene that are used commercially are classified as elastomers. The final properties of the rubber depend on modifiers and fillers, such as carbon black to improve strength (especially in vehicle tires), peroxide or bisphenol, to improve resistance and elasticity and to slow deterioration, and whiting and factice (vulcanized unsaturated vegetable or animal oil). Rubber erasers may have as much as 4 times as much factice as rubber in their composition.
The first bicycle tire dates back to 1830 and in 1845, R.W. Thomson invented the pneumatic tire, the inner tube and even the textured tread for bicycles. In 1850 rubber was used for toys and, in 1889, in England, John Dunlop produced the first commercially successful bicycle tires. In 1895, in France, Édouard and André Michelin and, in 1900 England, John Dunlop, all developed pneumatic tires for automobiles.
The auto industry created a huge demand for rubber but two world wars proved the need for substitutes to supplement inadequate natural rubber supplies. In 1910, in Russian, scientists developed the first synthetic rubber, Polybutadiene. In 1930, Germans scientists produced commercial synthetic rubber called Buna-S (a Styrene Butadience Copolymer).
The United States government started a research and development project which developed Styrene Butadiene Rubber (SBR).In 1934, DuPont produced Neoprene (originally Duprene). During World War 2, German industry created an oil-resistant rubber called Buna-N or Perbunan and by the 1950's Butyl rubber was developed.
In the 1960's:- DuPont introduced Hypalon and Viton while Bayer produced Polyurethane, Shell created Isoprene rubber and Goodyear produced Natsyn or Polyisoprene Ethylene Propylene Terpolymer Rubber or EPDM.More recently, thermoplastic elastomers were invented. These materials behave like rubber, but soften like plastic when heated.
The term, vulcanization, traditionally referred to the treatment of natural rubber but it now includes the hardening of other (synthetic) rubbers including silicone rubber and chloroprene rubber (Neoprene) using metal oxides. Vulcanization, like the curing of other thermosetting polymers, is generally irreversible.
Natural rubber is both elastomer and a thermoplastic (softens when heated). When vulcanized, it is a thermoset (irreversibly hardens when cured). Most rubber in everyday use is vulcanized to a point where it has both properties. If heated and cooled, it is degraded but not destroyed.
Natural rubber provides good elasticity, while synthetic rubber has better resistance to oils, temperature, chemicals and ultraviolet light.
Rubber is used for:- car tires (originally solid and later pneumatic), hoses (for water and compressed air, chemical and medical tubing), lining pipework, storage tanks and railroad tank cars, conveyor belts and rollers (used in industry and printing presses), gaskets, matting and carpets, flooring, gloves (medical, household and industrial), condoms, toy balloons, adhesives, rubber bands, pencil erasers and dampeners (anti-vibration mounts) for the automotive industry and it is used in many sports in the form of balls and pucks.
It is used in telephones, radio sets, other electrical instruments and wiring because of its good electrical resistance. The coefficient of friction, high on dry surfaces and low on wet surfaces, makes it useful for power-transmission belting, for water-lubricated bearings in deep-well pumps and for windshield wipers.
Rubber fibres, also known as elastic, were used extensively in textiles until they were largely replaced by the synthetic rubber neoprene (a polymer of chloroprene and an elastomer fibre) and spandex or elastane, because of their superiority to rubber in both strength and durability.
World production of rubber in 2017 was over 28 million tons, about 60% of which was synthetic rubber derived from petroleum. About 70% of all natural rubber was produced in Thailand, Indonesia and Malaysia. Natural rubber is not cultivated widely in South America because of native predators like South American leaf blight.
Many other plants produce forms of latex rich in isoprene polymers, although most these are not as easily usable the Hevea brasiliensis (or Pará) rubber tree. Some plants produce other desirable materials, like gutta-percha (Palaquium gutta) and chicle from Manilkara species.
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Engineering
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