Inorganic compounds, rubbers

Rubber is vulcanised by treatment with sulphur chloride or by heating with sulphur. In most cases, however, rubber articles are made, not of pure vulcanised rubber, but of the latter mixed with various other substances, organic and inorganic. The organic substances more commonly used are brown and white factis, fatty oils, oxidised oils, waxes, mineral oils, paraffin wax or ceresine, resin or resin oils, bitumens, tar, pitch, starch, and artificial dyes. Very many inorganic compounds may be added either as fillers or to give colour, e.g., talc, kaolin, asbestos, chalk, gypsum, lime. 

Next in importance is the polymerization of butadiene, if the use of sodium is ignored in the production of such inorganic compound as sodium cyanide, sodium peroxide, and titanium. Buna rubber, prepared by the sodium-catalyzed copolymerization of butadiene and styrene, was of considerable importance during World War II, especially in Germany. More recently, Morton s alfin catalyst has caught the attention of the rubber industry because of the exceptional quality of polybutadiene prepared by his techniques. 

In addition to the use of organic chemicals, rubbers can be devulcanized by means of inorganic compounds. Discarded tires and tire factory waste were devulcanized by desulfurization of suspended rubber vulcanizate crumb (10 to 30 mesh) in a solvent such as toluene, naphtha, benzene, cyclohexane, etc., in presence of sodium [44]. The alkali metal cleaves mono-, di-, and polysul-fidic crosslinks of the swollen and suspended vulcanized rubber crumb at around 300°C in absence of oxygen. However, this process may not be economical because the process involves swelling of the vulcanized rubber crumb in an organic solvent where the metallic sodium in molten condition should reach the sulfidic crosslink sites in the rubber crumb. Also, the solvent may cause pollution and be hazardous. A technology was also proposed to reclaim... 

Properties of vulcanized rubber can be further enhanced by the addition of certain organic substances (also known as accelerators) and certain inorganic compounds (also known as activators). Commonly used accelerators are tetramethyl thiouran disulfide and diphenylguanidine. Commonly used activators are oxides and salts of calcium, zinc and lead. To prevent the oxidation of rubber, a little amount (1-2%) of antioxidant such as hydroquinone monobenzyl ether, phenyl p-naphthylamine, etc. are added. ... 

Lead azide - Also used as a primary detonator, lead azide is a highly sensitive inorganic compound that is usually handled and stored under water in insulated rubber containers. It will explode after a fall of around six inches or in the presence of a static charge. A related compound, copper azide, is even more explosive and considered too sensitive to be used commercially. 

Inorganic fillers, such as silica, silicates, barium sulphate and calcium carbonate, are used extensively in plastics and rubbers and to be effective these are usually incorporated at a level well in excess of 5%. This means that they can easily be quantified by TGA. Other inorganic compounds are also used in most products, and these include zinc oxide (a common co-agent used in the cure system of rubbers) and titanium dioxide (a popular weight pigment). In contrast to fillers, these additives are usually only added at levels below 5% but, given that the detection limit of TGA is around 0.5%, they can still be detected and a reasonably accurate quantification performed. 

World production of I2 in 1992 approached 15 000 tonnes, the dominant producers being Japan 41%, Chile 40%, USA 10% and the former Soviet Union 9%. Crude iodine is packed in double polythene-lined fibre drums of 10-50-kg capacity. Resublimed iodine is transported in lined fibre drums (11.3 kg) or in bottles containing 0.11, 0.45 or 2.26 kg. The price of I2 has traditionally fluctuated wildly. Thus, because of acute over-supply in 1990 the price for I2 peaked at 22/kg in 1988, falling to 12/kg in 1990 and 9.50/kg in 1992. Unlike CI2 and Br2, iodine has no predominant commercial outlet. About 50% is incorporated into a wide variety of organic compounds and about 15% each is accounted for as resublimed iodine, KI, and other inorganics. The end uses include catalysts for synthetic rubber manufacture, animal- and fowl-feed supplements. 

There were essentially three reasons for this opposition. Firstly, many macromolecular compounds in solution behave as colloids. Hence they were assumed to be identical with the then known inorganic colloids. This in turn implied that they were not macromolecular at all, but were actually composed of small molecules bound together by ill-defined secondary forces. Such thinking led the German chemist C. D. Harries to pursue the search for the rubber molecule in the early years of the twentieth century. He used various mild degradations of natural rubber, which he believed would destroy the colloidal character of the material and yield its constituent molecules, which were assumed to be fairly small. He was, of course, unsuccessful. 

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