Vulcanisation Process

Although the elastomer phase is essentially in particulate form, the tensile strength of the blend can be increased five-fold by increasing the cross-link density from zero to that conventionally used in vulcanisation processes, whilst tension set may be reduced by over two-thirds. Since the thermoplastic polyolefin phase may be completely extracted by boiling decalin or xylene, there is apparently no covalent chemical bonding of elastomer and thermoplastic phases. 

Facilitate pre-vulcanisation processing, increase softness, extensibility and flexibility of the vulcanised end-product. The rubber processing industry consumes large quantities of materials which have a plasticising function complex mixtures (paraffinic, naphthenic, aromatic) of mineral hydrocarbon additives, used with the large tonnage natural and synthetic hydrocarbon rubbers, are termed process oils. Because of the complexity of these products, precise chemical definition is usually not attempted. If the inclusion of an oil results in cost reduction it is functioning as an extender. The term plasticiser is commonly reserved for synthetic liquids used with the polar synthetic rubber. 

Any method of vulcanising rubber products which proceeds without interruption from start to finish as compared to the method of vulcanising separate batches of products or sections of a product. Continuous vulcanisation processes include the cold curing of proofed cloth, the vulcanisation of belting and flooring, of cables and certain extruded products by either the Liquid Curing Medium, Fluid Bed, Microwave, or Hot Air techniques. 

Zinc stearate is formed during the vulcanisation process with sulphur accelerated compounds, but the addition of zinc stearate alone as replacement for stearic acid and zinc oxide does not produce... 

A survey is made of French and European Union legislation relating to hazardous chemicals in the workplace, and particular attention is paid to regulations concerning exposure to chemicals in the rubber industiy. The carcinogenicity of nitrosamines formed during vulcanisation processes is examined, and methods used in their detection are discussed. 2 refs. 

In 1839, vulcanisation process was discovered by Charles Goodyear. In this process, the milled rubber is mixed with sulphur and then introduced in a mould and heated to 150°C for a few hours. The time and temperature of vulcanisation can be decreased by adding certain catalysts called accelerators. They generally contain nitrogen, sulphur or both. 

On heating a chemical reaction took place between the rubber and sulphur which resulted in production of tough elastic rubber that retained its moulded shape. Natural rubber is plastic in nature while vulcanised rubber is elastic. This vulcanisation process led to a rapid development of rubber industry. 

Accelerators are added to thermosets and rubbers to speed-up the curing or vulcanisation process to such an extent that an end product can be formed under optimal conditions. 

Variations in cross-link density may arise from spatial variations in the rubber formulation, although short-scale variations are often smoothed by component diffusion during the vulcanisation process. Differences on the mm scale can lead to interfacial structures like those depicted in Figures 7.16 and 7.17. Another source of variations in cross-link density on the mm scale is the curing process in combination with the sample geometry. Heat is supplied to the sample for a certain time and after vulcanisation is removed from the sample in a certain time. Near the heat source vulcanisation sets in first, and near the heat sink it sets in last. Depending on how the heat is supplied to and withdrawn from the object, complicated time-dependent temperature profiles are established in the sample. 

Dicumyl peroxide vulcanisation of high-cis BR and NR samples at different peroxide levels were investigated by solid-state 13C NMR [42], As the peroxide level increased, decreased signal intensity and peak broadening was observed in the main chain peaks in both BR and NR due to decreased segmental motion. In addition, cis-trans isomerisation was observed during the vulcanisation process in both rubbers. New peaks at 35 and 44 ppm were observed in the BR spectra while peaks at 14.9, 21.4, 30.6, 37.5, and 45.0... 

The second phenomenon due to carbon black on a proposed scheme based on the vulcanisation process shown in Figure 9.12. During the vulcanisation process, the reactions (1) and (2), and (3) and (4) form polysulfidic Ale and Bit, respectively. Considering the fact that Ale polysulfide reduces its sulfur rank to monosulfide and reaction (3) and (4) is the predominant process in the later stage of cure, the system may favour reaction (3) and (4) rather than (1) and (2) in the whole reaction scheme. BtSH is formed from the... 

From this chapter, it is clear that high resolution 13C NMR spectroscopy has made a large number of contributions to our knowledge of the structure of vulcanised crosslinked elastomers as well as the mechanism by which the vulcanisation process occurs. It is anticipated that further NMR measurements of these systems will continue to generate new structural and mechanistic information. 

High cis- 1,4-poly butadiene is manufactured on a large industrial scale and occupies a well-defined position in the elastomers market. It is employed mainly in the tyre industry, where it is blended with natural rubber and/or with styrene-butadiene rubber and applied in either sidewalls, threads or rims of tyres. It should be noted in this connection that natural rubber, in contrast to its synthetic counterpart, displays some physical properties that appear to be useful in the manufacture of tyres for heavy-duty machines. The fact is that some non-hydrocarbon substances appearing in natural rubber in small amounts (such as polypeptides) protect the high-dimensional tyre formed against collapsing prior to the vulcanisation process and thus enable a high-quality product to be obtained. 

Though nitric acid was not the cause of vulcanisation it enabled the first steps towards the process of manipulating rubber in this way. Since the nitric acid episode did not solve his problem of rubber stickiness successfully he made further trials and finally discovered true vulcanisation accidentally while boiling gum rubber with sulphur, when a lump of the sulphured gum fell on the stove. It remained for the vulcanisation process to be... 

The properties of elastic sulphur, pS, can be stabilised by adding a few percent of phosphorus. A vulcanisation process occurs in which cross-linking is produced via the P atoms, and as more phosphorus is added, the product becomes more brittle and finally vitreous when cross-linking is... 

Esters (and thioesters. Chapter 9) confer valuable anti-wear and corrosion inhibition properties when used as oil additives. Dialkyldithiophosphates (Chapter 9.10) can be used in vulcanisation processes to reduce staining of latex products. They remove metallic cations which otherwise can form intensely coloured complexes with the thiazole accelerators which are used. 

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