Accelerators

Organic compounds that accelerate sulfur vulcanization. They shorten cure time and determine crosslink density. Speed depends on the class: thiurams and dithiocarbamates are ultra-fast, sulfenamides are delayed-action, and thiazoles are medium-speed.

The accelerator determines both the speed of sulfur vulcanization and the structure of the crosslinks formed. Without an accelerator, sulfur vulcanization takes hours and gives a weak vulcanizate; with the right system, cure time drops to minutes.

Compounds usually use a primary and a secondary accelerator together. The primary accelerator (mostly a sulfenamide or thiazole) carries the main body of the cure. The secondary accelerator (thiuram, dithiocarbamate or guanidine) is added in a small amount and speeds up the system.

Three questions drive the selection: how much scorch safety is needed during processing, how fast the cure must be, and which rubber the product is made from. In markets with nitrosamine restrictions, the amine source is also a selection criterion.

Comparison

Class	Speed	Processing safety	Typical role	Examples
Sulfenamides	Fast (delayed onset)	High	Primary	CBS, TBBS, DCBS
Thiazoles	Medium	Medium	Primary	MBT, MBTS
Thiurams	Ultra-fast	Low	Secondary / sulfur donor	TMTD, TBzTD
Dithiocarbamates	Fastest	Very low	Secondary / latex	ZDEC, ZDBC, ZBEC
Guanidines	Slow	High	Secondary activator	DPG, DOTG
Thioureas	Fast (in CR)	Low	Chloroprene, ECO	ETU, DETU

Relative, qualitative comparison; varies with formulation and rubber type.

ThiazolesMedium-speed primary accelerators based on MBT and MBTS — 5 substances

SulfenamidesDelayed-action primary accelerators (CBS, TBBS, DCBS, NOBS) — 7 substances

ThiuramsUltra-fast accelerators and sulfur donors (TMTD, TETD, TBzTD, DPTT) — 9 substances

DithiocarbamatesThe fastest accelerator class (ZDBC, ZDEC, ZDMC) — 14 substances

GuanidinesMedium-slow secondary accelerators (DPG, DOTG) — 2 substances

ThioureasAccelerators for chloroprene (CR) and epichlorohydrin rubbers (ETU, DETU, DBTU, DPTU) — 4 substances

42 substances

N-(Cyclohexylthio)phthalimideCAS 17796-82-6

2-MercaptobenzothiazoleCAS 149-30-4

2,2'-Dithiobis(benzothiazole)CAS 120-78-5

2-(Morpholinodithio)benzothiazoleCAS 95-32-9

3-Methylthiazolidine-2-thioneCAS 1908-87-8

Zinc benzenesulfinateCAS 24308-84-7

N-Cyclohexyl-2-benzothiazolesulfenamideCAS 95-33-0

N-tert-Butyl-2-benzothiazolesulfenamideCAS 95-31-8

N,N-Dicyclohexyl-2-benzothiazolesulfenamideCAS 4979-32-2

N-Oxydiethylene-2-benzothiazolesulfenamideCAS 102-77-2

N-Oxydiethylenethiocarbamyl-N'-oxydiethylenesulfenamideCAS 13752-51-7

N-tert-Butyl-2-benzothiazolesulfenimideCAS 3741-80-8

N-Cyclohexyl-N-butyl-2-benzothiazolesulfenamideCAS 3264-02-6

Tetraethylthiuram disulfideCAS 97-77-8

Tetramethylthiuram disulfideCAS 137-26-8

Tetramethylthiuram monosulfideCAS 97-74-5

Tetrabutylthiuram disulfideCAS 1634-02-2

Tetrabenzylthiuram disulfideCAS 10591-85-2

Tetraisobutylthiuram disulfideCAS 3064-73-1

Tetraisobutylthiuram monosulfideCAS 204376-00-1

Dipentamethylenethiuram hexasulfideCAS 971-15-3

Dimethyldiphenylthiuram disulfideCAS to be verified

Zinc dibutyldithiocarbamateCAS 136-23-2

Zinc diethyldithiocarbamateCAS 14324-55-1

Zinc dimethyldithiocarbamateCAS 137-30-4

Zinc dibenzyldithiocarbamateCAS 14726-36-4

Zinc diisobutyldithiocarbamateCAS 36190-62-2

Zinc ethylphenyldithiocarbamateCAS 14634-93-6

Sodium dibutyldithiocarbamateCAS 136-30-1

Sodium dibenzyldithiocarbamateCAS 55310-46-8

Tellurium diethyldithiocarbamateCAS 20941-65-5

Copper dimethyldithiocarbamateCAS 137-29-1

Ferric dimethyldithiocarbamateCAS 14484-64-1

Bismuth dimethyldithiocarbamateCAS 21260-46-8

Lead diamyldithiocarbamateCAS 36501-84-5

Zinc dialkyldithiophosphateCAS 68649-42-3

1,3-DiphenylguanidineCAS 102-06-7

1,3-Di-o-tolylguanidineCAS 97-39-2

Ethylene thioureaCAS 96-45-7

N,N'-DiethylthioureaCAS 105-55-5

N,N'-DibutylthioureaCAS 109-46-6

N,N'-DiphenylthioureaCAS 102-08-9

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