Testing of plastics and rubber - Zwick - #5

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5 Short Designation Application sign examples NR Natural Rubber Medical gloves, latex, blending component for synthetic rubber SBR Styrene Butadiene Rubber All-purpose rubber, (originally “Buna – S”) tire industry CR Polychloropren Rubber Contact adhesives, conveyor belts, sealings, hoses IIR Isobutene-Isoprene Sealings, membranes, (Butyl) Rubber cable insulations EPDM Ethylene-Propylene- Roof and pond foils, Diene Monomer sealings in automotive industry NBR Nitrile Butadiene Oil and fuel resistant sealings, Rubber membranes, hoses SI/MQ/ Silicone Rubber Sealings for freezers, stoves, PMQ/ window and cabin sealings VMQ of airplanes. FPM Fluorocarbon Rubber Sealings, moulded parts, hoses with a high temperature and chemical resistance, belts PUR Polyurethane Foams Rubbers When the Spanish conquerors came to Mexico and South America in the beginning of the 16th century, they saw Indians playing with a strange bouncing ball. The Indians called the material of the ball « Ca hu chu » (crying tree). Today we call this Latex-tree Hervea brasiliensis. More than 200 years later, rubber was used in Europe as well. In 1770, the English minister Priestley was credited with the discovery of the use of rubber as an eraser. Finally, in the 19th century, people discovered the precious properties of rubber: its waterproofing and elasticity. Rubber mixed with turpentine oil was used to manufacture bags, hot-water bags and life buoys. In 1824 the first braces and suspenders were manufactured. The rain coats that were available at that time were hard as stone in winter and sticky in the summer. In 1844, Charles Goodyear patented his revolutionary discovery. For many years he had been experimenting with rubber, and one day, some rubber mixed with sulfur dropped onto a hot stove. During carbonization, the grey, raw rubber turned into a smooth and solid material with good properties. Goodyear had discovered the vulcanization process. At that time, the demand for rubber was exclusively covered by supplies from the Brazilian rain forest. Brazil held the monopoly and suspiciously watched that no seeds of the tree were taken to other countries. In 1876, the English adventurer Sir Wickham smuggled rubber seeds to London, and the resultant seedlings were sent to India where they could be planted on English plantations. In 1880, Asian rubber was sold on the world market for the first time. Today, the world economy gets 3.5 million tons a year from the plantations all over the world. Synthetic rubber As early as 1826 Michael Faraday discovered the chemical structure of rubber, and in 1909, the German chemist Fritz Hofmann was the first to patent the production process of synthetic rubber. After World War I, the patent was expropriated and the production was discontinued. In 1930, America began large-scale manufacture of synthetic rubber and – since they had lost their plantations due to Japan’s entry into war – they built up huge production capacities of 840,000 t by 1945. The rubber industry strongly depends on the availability of petroleum, and as a result about 70 % of the world requirements are manufactured synthetically. There are about 20 different types of synthetic rubber, many of them with special properties. Just as natural rubber, they consist of long molecule chains creating a convoluted network. For vulcanization, the chains are provided with cross-links. Classical example is the sulfur vulcanization of natural rubber. The number of cross-links determines the properties of rubber: soft rubber with a few links, hard rubber with many links. Overview of rubber