Organic accelerators

Mercaptobenzothiazoles. These compounds form the basis for the largest-volume organic accelerators. 2-Mercaptobenzothiazole (MBT)... 

The main producers of organic accelerators for mbber vulcanization are shown in Table 3. This table is not meant to be completely comprehensive, but rather to indicate the principal historical suppHers to the mbber industry. Most producers offer chemical equivalents in the largest-volume products. Within the range of smaHer-volume specialty accelerators, chemical equivalents become less common. Each producer may offer different products to achieve the same purpose of rapid cross-linking, resistance to thermal degradation, or other performance characteristics. Many offer proprietary blends of accelerators. 

Double-Bond Cure Sites. The effectiveness of this kind of reactive site is obvious. It allows vulcanization with conventional organic accelerators and sulfur-based curing systems, besides vulcanization by peroxides. Fast and controllable vulcanizations are expected so double-bond cure sites represent a chance to avoid post-curing. Furthermore, blending with other diene elastomers, such as nitrile mbber [9003-18-3] is gready faciUtated. 

Curing Systems. Polychloroprene can be cured with many combiaations of metallic oxides, organic accelerators, and retarders (114). The G family of polymers, containing residual thiuram disulfide, can be cured with metallic oxides alone, although certain properties, for example compression set, can be enhanced by addition of an organic accelerator. The W, T, and xanthate modified families require addition of an organic accelerator, often ia combination with a cure retarder, for practical cures. 

The organic accelerator most frequendy used is ethylene thiourea. However, concerns about the toxicity of this material have led to its use as a dispersion ia an iaert elastomer, or to replacement by other materials. 

The accelerated sulfur vulcanization of general-purpose diene rubbers (e.g., NR, styrene-butadiene rubber [SBR], and butadiene rubber [BR]) by sulfur in the presence of organic accelerators and other rubbers, which are vulcanized by closely related technology (e.g., ethylene-propylene-diene monomer [EPDM] mbber, butyl rubber [HR], halobutyl mbber [XIIR], nitrile rubber [NBR]) comprises more than 90% of all vulcanizations. 

Increase the rate of the cross-linking action with sulfur considerably allow for lower sulfur content to achieve optimum vulcanisate properties. Organic accelerators (e.g. thiuram, dithiocarbamate, etc.) are of major importance. In some cases it is necessary to retard the onset of vulcanisation to assure sufficient processing safety. The antioxidant 2-mercaptobenzimidazole (MBI) acts as a retarder for most accelerators. 

Fig. 6.1 The basic life cycle of organisms. N.B. Organic debris does NOT react fast with 02 of the environment, but H2S and Fe2+do. Organisms accelerate the organic reaction.

Abbreviation for the organic accelerator cyclohexylbenzothiazole sulphenamide, also abbreviated to CBS. 

Abbreviation for dibenzthiazyldisulphide, an organic accelerator of the thiazole class. 

An organic accelerator sold under a variety of trade names. It was first introduced in about 1920 and gained wide acceptance especially in tyre compounds due to its flat curing characteristics and the good age resistance it imparts to its vulcani sates. 

Organic accelerators of the thiazole class having delayed action and finding particular application in tyre compounds containing furnace blacks. Sulphenamides are manufactured from mercaptobenzothiazole by reaction with an amine, the nature of which determines the degree of delayed action. 

A term applied to a class of organic accelerators with a very fast and powerful accelerating action examples are the thiuram disulphides, dithiocarbamates and xanthates. See TMT, ZDC and ZIX. 

An activator in rubber compounds containing organic accelerators. In polychloroprene, zinc oxide is considered to be the accelerator rather than the activator. The use of zinc oxide as a reinforcing agent and as a white colouring agent is obsolescent. Zinc oxide is manufactured by either the French (or indirect) process or by the American (or direct) process. It can be used as a filler to impart high thermal conductivity. 

Chemicals such as magnesium and lead oxides, calcium hydroxide, antimony tri- and pentasulphide can be used as boosters for organic accelerators for some products, such as thick walled large volume articles, e.g., rollers. 

N-Nitroso compounds occur in many operations in the rubber industry. Some nitrosamines (nitrosodiphenylamine, N-N-dinitrosopentamethylenetetramine, polymerized N-nitroso 2,2,4-trimethyl-l,2-dihydroquinoline and N-methyl-N-4-dinitroso aniline) are used as organic accelerators and antioxidants in the production of rubber and often the products are found to be contaminated with such compounds [19]. 

Activator. (1) An organic substance that makes possible the cross-linking, especially in vulcanization of rubber (2) a fatty acid that increases the effectiveness of acidic organic accelerators. 

Ren Shen is the deputy. It can strongly tonify the Qi of these organs, accelerate the Yin generation and therefore enhance the ability of Mai Men Dong. 

In addition to dicumyl peroxide (DCP), in two different batches zinc oxide (ZnO) or a conventional organic accelerator (ZDMC) were used. Figure 34 depicts the corresponding XRD pattern. In both cases, the peak positions are almost the same as that of the pure peroxide-cured vulcanizates. However, the intensity of the XRD pattern was significantly reduced in the case of ZDMC, and there is only a little effect of ZnO. Obviously, the sulfur-containing zinc salt influences and promotes dispersion and reorientation of the layered... 

Fig. 40 WAXD patterns of non-polar rubbers (a) and polar rubbers filled with 20 phr swollen clay (b). All the vulcanized rubbers contain some curing ingredients like organic accelerator, zinc oxide, etc...

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. 

Around 1850, S. Wetherill of the New Jersey Zinc Company perfected a roasting furnace in which a grate was charged with coal and then covered with a mixture of zinc ore and coal. The zinc was reduced by the partial combustion of the coal and reoxidized at the furnace exit (direct or American process). These furnaces were subsequently improved but are now no longer used. During the second half of the 19th century, the use of ZnO in rubber was introduced to reduce the time needed for vulcanization. The discovery of the first organic accelerators for vulcanization in 1906 added to the importance of ZnO, which acts as an activator in these materials. 

Accelerators are second in importance only to sulphur. Their function is to accelerate the normally slow rubber-sulphur reaction, increase the rate of vulcanization, and increase productivity. Accelerators are classified into two main classes by types, namely organic and inorganic. The inorganic accelerators such as lime, litharge and other lead compounds and magnesia were employed extensively before the introduction of organic accelerators. They are still used mainly to produce hard rubber or ebonite products. Litharge is used in rubberized fabrics, insulated wires and cables and shoe compounds as well as chemical resistant rubber products... 

Stearic acid is an activator of vulcanization, as is zinc oxide, both reacting to form zinc stearate, which enhances the activity of the organic accelerators. Zinc stearate is impractical to add directly to the rubber because its shppery, lubricating nature makes it difficult to mix in the batch (see... 

The discovery of the first organic accelerators for vulcanization in 1906 added to the importance of ZnO, which acts as an activator in these materials. 

In 1921, C. W. Bedford, at Rubber Services Laboratories Co., L. B. Sebrell, for Goodyear Tyre Rubber, both in the US, and Bruni and Romani at Pirelli, in Italy, developed mercaptobenzothiazole (MBT) (97) as an organic accelerator. In 1931, Bayer converted mercaptobenzothiazole into sulfenamides, that contain the grouping =CSNR2. These later became the most important class of accelerators. 

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