Did You Know?In 1839, American inventor, Charles Goodyear, discovered a way to improve the properties of natural rubber and make it stronger and more usable. He called the process vulcanization. It revolutionized the rubber industry.
Natural rubber is an elastomer (elastic hydrocarbon polymer), that is made from latex, which is a milky colloid obtained from many plants. An elastomer is a substance which can undergo much more elastic deformation under stress than most materials and still retain its previous size without any deformation. The commercial source of natural rubber is the native Brazilian plant, Hevea brasiliensis, which belongs to the family, Euphorbiaceae. Some other plants from which natural rubber is made are gutta-percha, rubber fig, Panama rubber tree, common dandelion and Russian dandelion. Natural rubber has been in commercial use since the early 20th century. Natural rubber occupies an important place in the market due to its large number of applications. Some of its applications include making tires used on racing cars, trucks, buses, and airplanes.
Synthetic rubbers are made in chemical plants by polymerization of monomers into polymers. They are artificially produced. Some of the most important synthetic rubbers are butadiene, styrene-butadiene, neoprene/ polychloroprene, polysulfide rubbers, nitrile, butyl rubber, and silicone. They have various applications and varying chemical and mechanical properties. Many synthetic rubbers have been developed during the 20th century. Some of them are used in place of natural rubber due to their properties. Typical applications include power transformers, wet-suits, laptop sleeves, orthopedic braces, electrical insulation, automotive fan belts, vehicle tires, shoe soles, pencil erasers, birthday balloons, adhesives, protective gloves, conveyor belts, flexible toys, tubing, mats, rubber bands, paint, hoses, gaskets, and floor tiles.
♦ Synthetic rubbers are made by the polymerization of different petroleum-based substances known as monomers. Some examples include styrene-butadiene rubber (SBR) which is produced from copolymerization of styrene and butadiene, butyl rubber (IIR), a synthetic rubber derived from copolymerizing isobutylene with isoprene, nitrile rubber (NBR), an oil-resistant synthetic rubber produced from a copolymer of acrylonitrile and butadiene, and neoprene that is produced by the polymerization of chloroprene.
♦ Natural rubber is made from latex, which is mostly extracted from the sap of the plant, Hevea brasiliensis. An incision is made into the tree bark, the latex is collected in a cup or pot, then filtered, washed, and made to react with an acid to make the particles of rubber solidify and form a mass. The rubber is then pressed into slabs and dried. It is then given for the next stages of production in the industry to make it refined.
♦ Synthetic rubbers are more resistant to oil, certain chemicals and oxygen, have better aging and weathering characteristics, and good resilience over a wider temperature range.
♦ Natural rubber has good wear resistance, high elasticity, high resilience, and tensile strength. It has a good dynamic performance and low level of damping. However, it ages with time and has poor chemical, oil, and ozone resistance. It has poor resistance to elevated temperatures.
♦ Styrene butadiene, one of the cheaper general-purpose synthetic rubbers has inferior physical strength, resilience, and low-temperature properties. However, its aging properties and abrasion resistance are better than those of natural rubber. Unlike natural rubber, it hardens with time instead of softening.
♦ Natural rubber has good physical strength, resilience, and low-temperature properties, but inferior abrasion resistance and aging properties compared to those of styrene butadiene. Compared to nitrile, its low-temperature properties are inferior.
♦ Nitrile has better oil resistance, low-temperature flexibility, abrasion resistance and resilience compared to that of natural rubber. It also has low gas permeability.
♦ Natural rubber has inferior oil resistance and resilience compared to that of nitrile. However, it has better physical strength.
♦ Ethylene Propylene Diene Monomer (EPDM), Neoprene/polychloroprene and some other synthetic rubbers have excellent heat resistance, oil resistance, ozone and weather resistance, polar fluids resistance, and better aging and chemical resistance. Also, physical properties and low-temperature resistance is good. It has low flammability and gas permeability. EPDM can be combined with other compounds to give excellent electrical resistance.
♦ Natural rubber has poor resistance to ozone, polar fluids, and chemicals. It is swollen and weakened by hydrocarbon oils and is degraded by oxygen and ozone as it ages.
Natural rubber has an important position in the market due to its applications. However, synthetic rubber is used in place of natural rubber in many cases, particularly when improved material properties are necessary.
♦ Silicone Rubbers have excellent electrical properties and great resistance to weathering and ozone attack. Physical properties are retained at higher temperatures. They are more expensive than most other rubbers.
♦ Natural rubbers have poor electrical properties and low resistance to weathering and ozone attack. They have better physical properties.