Accelerator 2-mercaptobenzothiazole

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

One such contaminant associated with sulphur-based vulcanisation systems is the organic accelerator 2-mercaptobenzothiazole (2-MCBT) and associated derivatives. In 1981 (Petersen et al., 1981) the presence of 2-(2-hydroxyethylmercapto) benzothiazole (HEB) was detected in the contents of a disposable hypodermic syringe. It was identified that the extractant was a reaction product formed between a 2-MCBT derivative and ethylene oxide used for sterilisation. Subsequently the oxidation product of HEB, 2-(carboxymethylthio)benzothiazole (CMB), was detected in the serum of premature babies receiving prolonged intravenous therapy (Meek and Pettit, 1985). So-called modem vulcanisation systems do not use sulphur as the cross-linking agent nor use 2-MCBT or derivatives, and are consequently free from this particular problem. These new vulcanisation systems show a considerable reduction in aqueous extractable matter and are often described as having low water extractables. 

Accelerators Mercaptobenzothiazole dithiocarbomates Fast accelerator, low temperature curing... 

The object of our study was acrylonitrile-butadiene rubber PERBUNAN 2845 F (LANXESS), acrylonitrile content 28%. Two types of carbon black were used Colour Black FW 200 (Evonik Degussa GMbH) and FEF N550 (Evonik Degussa GMbH). The elastomer was crosslinked by sulphur vulcanization system. The following compounds were used as accelerators mercaptobenzothiazole (MBT) and... 

Cyclohexylamine condensed with mercaptobenzothiazole produces the large volume moderated mbber accelerator JV-cyclohexyl-2-henzothiazolesulfenamide (41) [95-33-0] (see Rubber compounding). DCHA similady is used in piepaiing... 

The optimum modulus occurs at about a 2 1 weight ratio of OTOS to OBTS. Similar optimums have been observed with other accelerator combinations. The examples shown in Figure 4 are calculated from regression equations developed from designed experiments in a black-filled natural mbber compound. On a molar basis, the synergistic accelerator complex appears to consist of two dithiocarbamate ligands and one mercaptobenzothiazole moiety, as shown in stmcture (15) (14). 

The thiophthalimide (CTP) and sulfenamide classes of retarders differ from the organic acid types by thek abiUty to retard scorch (onset of vulcanization) without significantly affecting cure rate or performance properties. Much has been pubUshed on the mechanism of CTP retardation. It functions particularly well with sulfenamide-accelerated diene polymers, typically those used in the the industry. During the initial stages of vulcanization, sulfenamides decompose to form mercaptobenzothiazole (MBT) and an amine. The MBT formed reacts with additional sulfenamide to complete the vulcanization process. If the MBT initially formed is removed as soon as it forms, vulcanization does not occur. It is the role of CTP to remove MBT as it forms. The retardation effect is linear with CTP concentration and allows for excellent control of scorch behavior. 

Rubber base adhesives can be used without cross-linking. When necessary, essentially all the cross-linking agents normally used in the vulcanization of natural rubber can be used to cross-link elastomers with internal double carbon-carbon bonds. A common system, which requires heat to work, is the combination of sulphur with accelerators (zinc stearate, mercaptobenzothiazole). The use of a sulphur-based cross-linking system with zinc dibutyldithiocarbamate and/or zinc mercaptobenzothiazole allows curing at room temperature. If the formulation is very active, a two-part adhesive is used (sulphur and accelerator are placed in two separate components of the adhesive and mixed just before application). 

Vulcanizing latex adhesives are used in the manufacture of textiles, rugs and carpets. The vulcanizing ingredients are sulphur, zinc oxide and accelerators (for example, zinc dibutyldithiocarbamate and zinc mercaptobenzothiazole to produce vulcanization at room temperature). 

All compositions contain EPDM, 100 phr zinc oxide, 5 phr stearic acid, 1 phr antioxidant, 1 phr 2-mercaptobenzothiazole (accelerator), 1.5 phr tetramethyl thiuram disulfide (accelerator), 1 phr and sulfur, 1.5 phr. 

Ostromow [328] has described the use of conductometry for the analysis of extracts from elastomers and rubbers, such as the determination of various vulcanisation accelerations dithiocarbamates, thiurams (tetramethylthiuramdisulfide, tetramethylthiurammono-sulfide), 2-mercaptobenzothiazole, diphenylguanidine... 

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 further complicating factor with rubber compounds is that some compounding ingredients, e g., 2-mercaptobenzothiazole, will accelerate and increase the sulphur blooming. 

Type IV reactions are due to chemicals added during manufacture of NRL, which include accelerators, antioxidants, antiozo-nants, emulsifiers, stabilizers, extenders, colorants, retarders, stiffeners, and biocides. Accelerators primarily control the rate, uniformity, and completeness of vulcanization. The most common accelerators include thiurams, carbamates, and mercaptobenzothiazoles. These chemicals are covered in detail in their specific monographs in this volume. 

Captax (Structure 15.21) is used to the extent of 1% with hevea rubber and accounts for the major part of the over 30,000 t of accelerators used annually in the United States. Other accelerators widely used include 2-mercaptobenzothiazole sulfenamide (Santocure Structure 15.22), used for the vulcanization of SBR dithiocarbamates and thiuram disulfides. Thiuram disulfide (Structure 15.23) is a member of a group called ultra-accelerators, which allow the curing of rubber at moderate temperatures and may be used in the absence of sulfur. 

The mechanism of vulcanization by XVI involves the initial formation of 2,2 -dithio-bisbenzothiazole (XVII) via cleavage of XVI to 2-mercaptobenzothiazole followed by oxidative coupling. 2,2 -Dithiobisbenzothiazole reacts with sulfur to form the accelerator... 

The second important class of accelerators are zinc dialkyldithiocarbamates (XXI). These are more active with faster vulcanization rates than the 2-mercaptobenzothiazole sulfena-mides. Also, activators are not usually needed since the zinc is incorporated into the accelerator molecule. Tetralkylthiuram disulfides (XXII) in combination with activators S... 

Tellurium dimethylthiocarbamate in combination with mercaptobenzothiazole, with or without tetramethylthiuram disulfide, is the fastest known accelerator for butyl mbber. It is used extensively in butyl tubes for buses and similar vehicles and in other butyl applications (see Elastomers, synthetic Rubber, natural). 

In the case of sulfenamide accelerators, the inhibitor appears to function by reacting with 2-mercaptobenzothiazole (77MI11506) so suppressing the catalytic pathway (equation 11). This is illustrated by the reaction between 2-mercaptobenzothiazole and IV-cyclo-hexylthiophthalimide (39), one of the most effective PVIs currently in use (equation 12) (73MI11500). It is likely that the reaction between the PVI and amines (equation 13) also makes a contribution to the mechanism of inhibition (77MI11506). 

The chemistry of the vulcanization of rubber is complex. The reaction of rubber with sulfur is markedly expedited by substances called accelerators, of which those commonly known as mercaptobenzothiazole and tetramethyl-thiuram disulfide are examples ... 

Electroless copper solutions contain copper salts and a reducing agent, such as formaldehyde the preparations for industrial use contain also stabilizers like 2-mercaptobenzothiazole, to prevent decomposition other than on activated areas of the workpiece, and accelerators like ethylenediamine-tetra-acetic acid—which increase the rate at which metal is deposited. Formulating such solutions requires achieving a balance between stability on the one hand and speedy deposition on the other. 

After inactivation treatment, the catalyst is removed, and phenolic antioxydants and other stabilizers are added. Cross-linking curing is realized on unsaturated pendant groups. Peroxides are avoided because they cause chain scission and therefore systems with sulfur as cross-linker and zinc oxide, 2-mercaptobenzothiazole and tetramethylthiuram monosulfide as accelerators are used. 

Barnes et al developed an LC-MS method to identify vulcanisation agents and their breakdown products in food and drink samples. A large sample of 236 retail foodstuffs were analysed for the presence of 2-mercaptobenzothiazole (MBT) and its breakdown product mercapto-benzothiazole (MB). The accelerators 2-mercaptobenzothiazyl (MBTS) and A-cyclohexyl-2-benzothiazole sulphenamide (CBS), which are commonly used in food contact rubbers, were also looked for. MBT and MB are also known to be breakdown products of these two compounds. The detection limit for these species was found to depend on the food product type and ranged from 0.005-0.043 mg/kg. No MBT, MB, MBTS or CBS were detected in any of the samples above these levels. 

Accelerators are chemical compounds that iacrease the rate of cure and improve the physical properties of the compound. As a class, they are as important as the vulcanising agent itself Without the accelerator, curing requires hours or even days to achieve acceptable levels. Aldehyde amines, thiocarbamates, thiuram sulfides, guanidines, and thiasoles are all classified as accelerators. By far, the most widely used are the thiazoles, represented by mercaptobenzothiazole (MBT and benzothiazyl disulfide (MBTS). 

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