Benzothiazole type accelerator

Frequently, mixtures of accelerators are used. Typically, a benzothiazole type is used with smaller amounts of a dithiocarbamate (thiuram) or an amine type. An effect of using a mixture of two different types of accelerators can be that each activates the other and better-than-expected crosslinking rates can be obtained. Mixing accelerators of the same type gives intermediate or average results. 

The chemical microstructures of cis-polyisoprene (HR) vulcanised with sulfur and N-t-butyl-2-benzothiazole sulfenamide (TBBS) accelerator were studied as a function of extent of cure and accelerator to sulfur ratio in the formulations by solid-state 13C NMR spectroscopy at 75.5 MHz [29]. Conventional (TBBS/Sulfur=0.75/2.38), semi-efficient (SEV=1.50/1.50) and efficient (EV=3.00/1.08) vulcanisation formulations were prepared, which were cured to different cure states according to the magnitude of increase in rheometer torque. The order and types of the sulfurisation products formed are constant in all the formulation systems with different accelerator to sulfur ratios. However, the amount of sulfurisation has been found to vary directly with the concentration of elemental sulfur. 

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. 

Thiurams and carbamates have most commonly been responsible for the type-IV reactions due to rubber gloves. Mercaptobenzothiazole was the first benzothiazole accelerator used in gloves, but other derivatives can also be used. The reports on sensitization to thiourea compounds from rubber gloves are few and, for the most part, involve gloves made of neoprene rubber which may also contain diphenyl-guanidine (Estlander et al. 1994a, 1995 Kanerva et al. 

Altenau and co-workers [26,27] used MS to identify quantitatively volatile antioxidants in 0.02-0.03 inch thick samples of synthetic styrene-butadiene rubbers and rubber-type vulcanisates. They extracted the polymer with acetone in a Soxhlet apparatus, removed excess solvent, and dissolved the residue in benzene. Substances identified and determined by this procedure include N-phenyl-P-napthylamine, 6-dodecyl-2,2,4-trimethyl-l,2-dihydroquinolines, trisnonylphenylphosphate, isobutylene-bisphenol, 2-mercaptobenzothiazole sulfenamide (accelerator), N-cyclohexyl-2-benzothiazole... 

The third mode of decomposition is only important in A-type monosulfides (and D-type from the diene model 5) and then only in the presence of catalysts. This is a simple elimination reaction, but its course is often obscured by secondary reactions of the primary products (equation Many accelerators and accelerator transformation products are catalysts for this decomposition. They include zinc benzothiazole-2-thiolate (ZMBT) and zinc dithiocarbamates and their amine complexes, as well as CBS, MBT and MBTS (which would normally not be present in quantity when monosulfide crosslinks are formed during the course of vulcanization). 

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... 

Two thiuram accelerators developed by Goodrich, Cure-rite IBM tetraisobutylthiuram monosulphide and Cure-rite IBT tetraisobutylthiuram disulphide, were evaluated along with other commercial thiurams as co-accelerators for benzothiazole sulphenamides in the vulcanisation of NR and SBR/polybutadiene tyre compounds. The effects of these thiurams on scorch safety and cure rates during vulcanisation and on the reversion resistance of vulcanisates were investigated, and differences in the types of sulphur crosslinks developed by the various thiurams were examined. 6 refs. 

Tetraisobutylthiuram monosulphide (TiBTM) was evaluated as a retarder and secondary accelerator for both N-t-butyl-2-benzothiazole sulphenamide and N-cyclohexyl-2-benzothiazole sulphenamide in SBR/ polybutadiene and NR compounds. TiBTM was also compared in these systems to the retarder N-cyclohexyl thiophthalimide (CTP) and the secondary accelerator tetramethylthiuram monosulphide (TMTM). When used at low levels with sulphenamide accelerators, TiBTM could extend the scorch time by 2-3 minutes and then increase the cure rate beyond that of the primary accelerator. The extent of these effects was influenced by the types of rubber and sulphenamide. At low levels TiBTM performed as an equivalent substitute for a CTP/... 

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