Accelerators sulphenamide

The Goodyear vulcanization process takes hours or even days to be produced. Accelerators can be added to reduce the vulcanization time. Accelerators are derived from aniline and other amines, and the most efficient are the mercaptoben-zothiazoles, guanidines, dithiocarbamates, and thiurams (Fig. 32). Sulphenamides can also be used as accelerators for rubber vulcanization. A major change in the sulphur vulcanization was the substitution of lead oxide by zinc oxide. Zinc oxide is an activator of the accelerator system, and the amount generally added in rubber formulations is 3 to 5 phr. Fatty acids (mainly stearic acid) are also added to avoid low curing rates. Today, the cross-linking of any unsaturated rubber can be accomplished in minutes by heating rubber with sulphur, zinc oxide, a fatty acid and the appropriate accelerator. 

Abbreviation for cyclohexylbenzothiazole sulphenamide, the first of the sulphenamide range of delayed action accelerators. 

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

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. 

Benzothiazole sulphenamide accelerators are suitable for semi-efficient and efficient vulcanisation systems. 

Addition of bis-(3-triethoxysilylpropyl)-tetrasulphide plus accelerator and sulphur can counter loss of crosslinking. Accelerator systems which respond to this antireversion agent are the thiazoles and the sulphenamides. Thiurams do not respond. For cure state equilibrium to be maintained the proportions of the three constituents (sulphur, accelerator and antireversion agent) are adjusted to give a constant modulus. 

TV-Cyclohexylthiophthal i m idc (CTP) functions as an effective retarder of vulcanisation for accelerators in the sulphenamide classes. It produces scorch retardation without effect on compound modulus. It is not effective, however, in other classes of vulcanisation systems, notably those based on thiazoles, thiurams and dithiocarbamates. 

Kodama and co-workers [58] have reported TG-DSC curves for the analysis of the interaction between vulcanisation accelerators (tetramethylthiuram disulphide, dibenzothiazolyl disulphide, diphenylguanidine and N-cyclohexyl-2-benzothiazolyl-sulphenamide) and fillers (carbon black, white carbon, hard clay and CaC03). The initial melting point (MP) of the accelerators was largely influenced by the fillers. The higher the surface activity of the filler is, the lower and wider the melting range becomes. 

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. 

Accelerating agents which are usually metal oxides (MgO, PbO) or organic substances such as thiazoles, mercaptobenzthiazoles (MET) or sulphenamides. Activators are required to make the organic accelerators function effectively. These can typically be zinc oxide and stearic acid. Stearic acid also acts as a lubricant, softener and plasticiser. 

A good example of the competitiveness between chlorine and peroxygen oxidants is the preparation of rubber accelerators such as sulphenamides. Sulphenamides are prepared by the oxidative coupling of a mercaptan with an amine (Fig. 1). 

According to some authors, the ZnO and the stearic acid react with each other within the rubber compound during the vulcanization process and generate zinc stearate. The effect of zinc stearate as an activator for black filled SBR compounds with the sulphenamide accelerator TBBS has already been studied [52]. The authors of this work did not cite any other references on the topic. They examined the Zn stearate as an activator of the sulfur... 

Garreta E. Agullo N. Bonos S. The Role of the Activator during the Vulcanization of Natural Rubber using Sulphenamide Accelerator Type. Kaut. Gummi Kunstst., 2002, vol. 55, Jf 3, 82-91. 

Like disulphide formation, the coupling of thiols and primary or secondary amines is of great industrial importance in the manufacture of rubber vulcanisation accelerators, the products being sulphenamides. 

Accelerators guanidines, thiazoles. sulphenamides, dithiocarbamates, thiuram sulphides, xanthates, aldehydeamines retarders phthalic anhydride, N-nitroso diphenylamine activators zinc oxide/stearic acid... 

A strong bond is only formed with sulphur-vulcanised compounds. Additionally these compounds need to have a high sulphur level (4 phr) and a certain type of accelerator, i.e., delayed-action sulphenamides. Systems containing lower sulphur levels, semi-... 

It has been demonstrated previously that such additions can increase the strength of rubber-brass adhesion considerably. In this research it was established that polysulphides are only weak crosslinking agents for unsaturated rubber by themselves. In the presence of sulphenamide accelerators, such as OBTS, polysulphides, in amounts of 0.5 - 1 phr, activate the sulphur vulcanisation. However, the reversion process (crosslink breakdown) is not accelerated. A favourable effect on the physicomechanical properties of the vulcanisate was also reported. 

It was postulated that the delay was due to a reaction between polythiobenzthiazoles and the accelerator in preference to a reaction between the polybenzthiazoles and the rubber which formed crosslinks. Hence in the first stage the sulphenamide fulfilled the function of an inhibitor but in doing so formed species which catalyzed subsequent reactions leading to cross-linking and which were able to proceed once the initial accelerator had almost completely disappeared. 

Whilst butyl rubber may be vulcanized using the conventional sulphur-based systems used with diene rubbers the low degree of unsaturation requires that a much more active accelerator system be used. For this reason the powerful thiuram and thiocarbamate accelerators are generally preferred to the more conventional thiazole and sulphenamide types. As may be expected, both the rate and extent of reaction depend on the degree of unsaturation. 

In the presence of sulphenamide accelerators little difference is observed between ENR and NR. Similar types of crosslink, mono-, di- and poly-sulphidic, are produced and their ratio varies with the sulphur/accelerator ratio as with other highly unsaturated polymers. 

ENR possesses fewer double bonds than NR and therefore would be expected to be more resistant to oxidation. However, the oven air ageing of a conventionally cured ENR vulcanizate (S, 2-5 sul-phenamide accelerator, 0 5 phr) was found to be poor. A rapid hardening occurred on air ageing. This oxidative hardening is not an intrinsic property of ENR since when peroxide and efficient vulcanizing systems (S, 0 3 sulphenamide, 2 4 TMTD, 1 6 phr) were used their ageing characteristics were observed to be similar to those of the corresponding NR vulcanizates (Fig. 16). 

Hilton, A. S. and Altenau, A. G., Mass spectrometric identification of 2-mercaptobenzthiazole sulphenamide accelerators in rubber vulcanis-ates , 103rd Mtg Rubber Div., ACS, Detroit, May 1973, Paper 22. 

The influence of polymers and additives on the service life of non-tread tyre components is discussed on the basis of results obtained from studies of inner liner, belt and sidewall compounds. The effects of the bromine content of bromobutyl rubbers on the performance of inner hners, and of sulphenamide accelerators on the adhesion of NR belt compounds to brass coated steel cords were investigated. The mechanical properties and ageing and ozone resistance of black sidewall compounds consisting of NR blends with neodymium catalysed polybutadiene protected with different antioxidants and antiozonants were also evaluated. 5 refs. 

Hilton and Altenau and Hayes and Altenau used mass spectrometry to qualitatively identify volatile antioxidants in sheet samples of synthetic styrene-butadiene rubbers and rubber type vulcanizates. They extracted the polymer with acetone in a Sohxlet apparatus, removed excess solvent and dissolved the residue in benzene. Substances identified and determined by this procedure include N-phenyl-fi-napthylamine, 6-dodecyl-2,2,4-trimethyl 1,2-dihydroquinolines, trisnonyl-phenyl-phosphite, isobutylene - bisphenol A reaction product, 2-mercaptobenzothiazole sulphen-amide (accelerator) N-cyclohexyl-2-benzothiazole sulphenamide, N-tert-butyl-2-benzo-thiazole sulphenamide, 2-(4-morpolinothio) benzothiazole, 2-(2,6-dimethyl-morphal-inothio) benzothiazole, N,N -diisopropyl 2-benzothiazoles, 2-mercaptobenzo-thiazole and N,N -dicyclohexyl-2-benzothiazole sulphamide. 

Sulphur systems. Conventional cure systems for most current, practical, tyre-related and mechanical goods formulations consist of zinc oxide, plus sulphur or sulphur-donors, accelerated with sulphenamides or benzothiazoles. These types of accelerator function initially as retarders but ultimately produce very high states of cure. MBT (mercaptobenzothiazole) is an exception in that it will scorch bromobutyl stocks, but it can be used... 

From the practical standpoint, two minor alterations in cure system should be considered if the cure characteristics of a synthetic polyisoprene need to be altered to match exactly that of a natural rubber compound. A secondary accelerator (e.g. 0T-0-2phr of TMTD) may be added to a sulphur/sulphenamide system to reduce time to optimum cure. An increase of between 5 and 15 %, pro rata, in both sulphur and accelerator will improve the degree of cure, as indicated by maximum torque value on a Monsanto rheometer. 

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