Vulcanisation of rubber

Like sulphur, selenium has been used in the vulcanisation of rubber. It is also used in photoelectric cells. 

In Ancient Egypt mummies were wrapped in cloth dipped in a solution of bitumen in oil of lavender which was known variously as Syrian Asphalt or Bitumen of Judea. On exposure to light the product hardened and became insoluble. It would appear that this process involved the action of chemical cross-linking, which in modem times became of great importance in the vulcanisation of rubber and the production of thermosetting plastics. It was also the study of this process that led Niepce to produce the first permanent photograph and to the development of lithography (see Chapter 14). 

In the vulcanisation of rubber products, aftercure is the amount of cure received after the termination of the cure proper, e.g., the cure effect resulting from the heat remaining in the product after removal from the mould or autoclave. The term is also applied to the continuation of the curing effect that results from exposure of the article to heat in use, or from accelerated ageing. See Post Cure. 

A pressure vessel constructed of steel, used for the vulcanisation of rubber products by the open steam method. The autoclave may be horizontal (vulcanisation of footwear, cables, hose), or vertical and fitted with a hydraulic ram (e.g., moulding pneumatic tyres). 

A solid or hollow metal pole used in the assembly or vulcanising of rubber products, e.g., the assembly of hand-built hose. 

Vulcanisation of rubber products carried out in a daylight press. 

Apphed to a high polymer which undergoes a chemical change when it is subjected to heat, after which its shape cannot be changed by the application of further heat and pressure. Although vulcanisation of rubber is a thermosetting process the term is usually applied to plastics . See Thermoplastic. 

Sulphur vulcanisation of rubber is catalysed by the presence of alkali materials. This activation of the vulcanisation system can result in unwanted short scorch times. The addition of weak acids to the rubber compound results in retardation of the crosslinking mechanism. The common materials used for retardation are... 

Continuous vulcanisation of rubber based products such as thin conveyor belting, flooring and similar can be achieved using a large rotating heated drum. Pressure is exerted to the product by means of a continuous stainless steel belt which presses the sheet to the surface of the drum. The belt is also heated from its reverse side to give optimum heat transfer to the vulcanising rubber. 

Vulcanisation of rubber Natural rubber becomes soft at high temperature (>335 K) and brittle at low temperatures (<283 K) and shows high water absorption capacity, it Is soluble in non-polar solvents and Is non-resistant to attack by oxidising agents. To improve upon these physical properties, a process of vulcanisation is carried out. This process consists of heating a mixture of raw rubber with sulphur and an appropriate additive at a temperature range between 373 K to 415 K. On vulcanisation, sulphur forms cross links at the reactive sites of double bonds and thus the rubber gets stiffened. 

It is also useful in the rapid vulcanisation of rubber, eg, in the preparation of thin rubber goods by coating molds or fabrics with mbber latex. Rubber... 

Nitrogen sulphide acts slowly on the acids of the paraffin series. In the case of acetic acid there is an evolution of sulphur dioxide, and sulphur and ammonium sulphate are obtained, as well as small quantities of free nitrogen. Considerable quantities of acetamide and diacetamide are also formed.7 The sulphide is indifferent towards primary and secondary bases of the aromatic scries and towards all tertiary bases.8 Nitrogen sulphide has been claimed to assist the vulcanisation of rubber. 

Carbon disulphide reacts additively with primary and secondary aliphatic amines to form alkylammonium salts of alkyldithiocarbamic acids. The products obtained with dimethylamine, diethylamine and piperidine, also certain derivatives of these products, are manufactured on a large scale for use as accelerators in the vulcanisation of rubber. With aromatic amines the disulphide reacts with elimination of hydrogen sulphide and formation of substituted thio-ureas, e.g. thiocarbanilide. 

Attempts to use selenium either in place of or in conjunction with sulphur in the vulcanisation of rubber do not appear to be completely successful,2 although it is claimed that rubber vulcanised with sulphur and selenium in the presence of an organic accelerator exhibits enhanced rigidity and resistance to abrasion.3 The incorporation of powdered selenium in ordinary rubber for vulcanisation by sulphur is said to provide crystalline selenium nuclei which induce the internal crystallisation of any superfluous sulphur and so prevent the undesirable surface crystallisation (or bloom ). The effect is attributed to the isomor-plious character of selenium and sulphur. 

Tabun Petrol additives, hydraulic fluids, insecticides, flame retardants, pharmaceuticals, detergents, pesticides, missile fuels, vulcanisation of rubber, extraction of gold and silver from ores. 

Solid raw materials have to be transferred into a fluid or plastic state, which is, nearly always, attained by heating (in exceptional cases by solution). In the fluid state the material is shaped, after which the resulting shape is fixed by cooling (thermoplasts), or by a chemical reaction (curing of thermosets, vulcanisation of rubbers). 

Vulcanisation of rubbers can be carried out as a separate process after shaping. Shaping can take place at relatively low temperatures since the unvulcanised rubber has an outspoken plastic nature. It is still solid enough to be transferred from the mould to a separate vulcanisation chamber, in which, at a much higher temperature, e.g. by steam, the vulcanisation is achieved. 

Silicone rubber compounds can be molded, extruded and calendered. The vulcanisation of rubber compounds occurs in two stages 1) in a press or steam boiler at high pressure and 120-150 °C 2) by thermostatic control at atmospheric pressure and 200-250 °C. 

Network polymers are formed either if tri-functional or even tetra-functional monomers are present during the polymerisation reaction or by cross linking of high molecular weight polymers, like vulcanisation of rubber. 

Modifications that are performed on starch can be compared to the modifications that are performed on other polymers, e.g. the vulcanisation of rubber. Similarly, starch is treated chemically to give greater stability to heat and shear. 

The vulcanisation of rubber sheet by radiation—instead of using sulphur in the manufacture of tyres— is being used commercially by several tyre companies. 

The cellulose xanthate is converted into rayon on acidification. Thiocarbanilide, S=C (NH.CgH5)2, results when CSg is passed into boiling aniline. It is used in the manufacture of dyes and pharmaceuticals, and in the vulcanisation of rubber. 

In the presence of bases, mild thiolation of organic compounds by treatment with sulfur provides an efficient route to organosulfur compounds. The reaction with alkenes is of great industrial importance in the vulcanisation of rubber. Many common reactions of... 

Accelerators, e.g. zinc oxide and fatty acids, increase the rate of vulcanisation of rubber by sulfur and they reduce the amount of sulfur required from 10% to <3%. Certain sulfur-donating accelerators, like thiuram disulfides (1) and mercaptobenzothiazole (2), will effect vulcanisation without added sulfur to yield products with greatly enhanced ageing properties.1... 

Charles Goodyear [1], an American scientist, worked with gutta-percha, a gum from natural tropical trees, and Thomas Hancock, a British scientist who simultaneously and independently developed a process for the vulcanisation of rubber (1839) by reacting it with sulphur and heat, are credited with the first deliberate attempt to chemically modify a natural polymer to produce a moulding material. Gutta-percha was used to protect and insulate the first submarine telegraph cables. The combined and independent efforts of these men helped to lay the foundation for the manufacture of synthetic materials using chemistry. 

At one time the main uses of sulphur were in the manufacture of gunpowder and of sulphuric acid. Nowadays its use for these purposes is more restricted. Sulphur is used in the manufacture of carbon disulphide, ultramarine, vermilion and numerous other compounds. Vulcanisation of rubber may be effected with sulphur. Enormous quantities are converted to bisulphites for treating wood pulp in the manufacture of paper. Sulphur is employed as a preventive of the growth of fungus on vines, and mould on hops it is burnt in the oast house to improve the flavour of the hops it is used as a disinfectant, a familiar form being sulphur candles . 

Thermoplastic polymers can easily be melted and moulded into flexible shapes. The rigidity and strength of the product can be improved by cross-linking between the polymer chains. One of the first deliberate cross-linking processes was the vulcanisation of rubber, which is used in car tyre manufacture. The process transforms sticky, soft rubber into a hard, flexible material. 

H. Willshaw, Moulding and vulcanisation of rubber articles, Proceedings of the Chemical Engineering Group (Society of Chemical Industry), 8 (1926), 111-121. The Bristol Instrument Company claimed to have introduced process cycle controllers in 1923, specifically with tyre moulding machines in mind (Bristol Company catalogue 1603, 1932). The illustration in Willshaw makes no mention of the Bristol... 

Sometimes curing agents, antioxidants and accelerators can interact, creating new toxic chemicals e.g., when guanidine accelerators are used during the vulcanisation of rubber with sulfur with phenylene diamine-based antioxidants, aromatic amines and isothiocyanates can be produced, both of which are suspected carcinogenic agents [11]. 

Compounds that form by the reaction of nitrosating agents with amines, usually produced during vulcanisation of rubbers. Although there is no direct evidence for their carcinogenic effects, they are considered as suspected agents. 

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