Ultra-accelerator

Thiuram Sulfides. These compounds, (8) and (9), are an important class of accelerator. Thiurams are produced by the oxidation of sodium dithiocarbamates. The di- and polysulfides can donate one or more atoms of sulfur from their molecular stmcture for vulcanization. The use of these compounds at relatively high levels with litde or no elemental sulfur provides articles with improved heat resistance. The short-chain (methyl and ethyl) thiurams and dithiocarbamates ate priced 2/kg. Producers have introduced ultra-accelerators based on longer-chain and branched-chain amines that are less volatile and less toxic. This development is also motivated by a desire to rninirnize airborne nitrosamines. 

Typical recipes for an antioxidant dispersion and an ultra-accelerator dispersion are given below. The antioxidant recipe is for Aminox (Uniroyal, Inc.), alow temperature reaction product of diphenylamine and acetone. 

Although ultra accelerators or sulfur donors can be used together with primary accelerator (such as sulfenamide, TBBS) to improve cure rate as well as the heat resistance [16-18], their use is restricted because of the associated nitrosamine issue [19]. Accelerators derived from secondary amines, for example, MBS, TMTD, TETD, TMTM, and OTOS fall into this category. The combination of sulfenamide, such as CBS or TBBS, and a thiuram, such as TMTD or TETD, shows high-cure rates but suffers from the adverse effects on scorch resistance and vulcanizate dynamic property [20]. Additionally as previously mentioned, the use of TMTD or Tetraethylthiuram disulhde (TETD) or A-oxidiethylene dithiocarbamyl-A -oxidiethylene sulfenamide (OTOS) or 4,4 -Dithiodimorpholine (DTDM) is undesirable [21] due to concerns over carcinogenic nature of the A-nitrosamines formed from the parent amines. The solution to this originated by introduction of nitrosamine safe ultra accelerator such as TBzTD [22,23]. 

An ultra accelerator of particular apphcation in the manufacture of dipped latex products. 

Organic compounds having four alkyl groups attached to nitrogen. A quaternary ammonium salt is employed in reversing the electric charge on natural rubber latex quaternary ammonium dithiocarbamates are ultra-accelerators for rubber vulcanisation. 

Salts of the series of xanthic acids of the general formula ROCSSH. Certain xanthates such as ZIX are ultra accelerators for mbber. Cellulose xanthate is the intermediate product in the manufacture of viscose. See Viscose Rayon. Xanthogen Sulphide... 

An ultra accelerator too scorchy for use as the sole accelerator in dry rubber compounding, but popular in latex work. In dry rubber compounding it is a useful booster for thiazole type accelerators. In some low ammonia latices it is used as a preservative. 

An ultra accelerator capable of vulcanising at temperatures as low as 38 °C (100 °F). In mixtures with dithiocarbamate accelerators it is used for room temperature vulcanisation. 

Dithiocarbamates are generally classed as ultra accelerators. When used alone they suffer from poor processing safety, due to a very rapid vulcanisation speed. They are usually used in combination with slower acting accelerators, except in the latex industry where elevated processing temperatures are not encountered. 

Classed as ultra accelerators, xanthates are among the fastest of accelerators available to the rubber compounder. Their speed is such that they find only limited application in solid rubber product manufacture but they are used in low temperature curing of latex articles. 

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. 

Thin articles may be vulcanized by treatment with sulphur monochloride by dipping in a solution or exposure to its vapours. This process has been replaced by using ultra accelerators which are capable of curing at room temperature. 

In 1933, the Calco Chemical Company began the manufacture of 97 by reacting aniline, carbon disulfide and sulfur together at elevated pressure (Scheme 31), and late in 1936 introduced mercaptobenzothiazyl disulfide (MBTS) (98). Goodyear was the major customer. Zenite ultra-accelerators , incorporating zinc (99), that brought about vulcanization in a few minutes, were introduced by Calco in the late 1930s100. 

TBBS is used as a vulcanization accelerator in NR, SBR, BR and rubber blends. Normally used alone or with small quantities of ultra accelerators in tire compounds or other industrial rubber products. 

Use Accelerator for latex dispersions and cements, etc ultra-accelerator for lubricating oil additive. 

BDMC. [Henley] Bismuth dimethyl di-thiocatbamate ultra accelerator for SBR, butyl and natural rubbers. 

Bismate . [R.T. Vanderbilt] Bismuth dimethyldithiocarbamate ultra accelerator for rubbers. 

---