ACCELERATORS

                      ACCLERATORS  

SELECTION CRITERIA FOR ACCELERATORS

•              Time delay of vulcanisation  initiation.
•            Speed of the vulcanisation after it is initiated.
•              Extent of the vulcanisation.
•              Type of cross linking that is formed.
•       Other factors such as green stock storage stability, bloom tendency etc., are also  important.

The principal chemical class of accelerators in commercial use today is discussed below. These compounds are typically classified as primary or secondary accelerators, 

Classification of Some Accelerators

Primary	Thiazoles	MBT
		MBTS
	Sulfenamides	CBS
		TBBS
		MBS
		DIBS
	Guanidines	DPG
		DOTG
Secondary	Thiurams	TETD
		TMTM
		TMTD
	Dithiocarbamates	ZBDC
		ZMDC
	Dithiophosphates	ZBDP

                 Comparison of Accelerator Types 

Accelerated  Type	Cure rate	Cross link	Acryronyms
None	Very slow	Very long
Aldehyde Amine	Slow	Very long
Guanidines	Medium	Medium Long	DGP, DOTG
Thiazoles	Semi-fast	Medium	MBT, MBTS
Sulfenamides	Fast delayed action	Shorter Medium	CBS – TBBS MBS – DIBS
Dithiophosphates	Fast	Short Medium	ZBDP
Thiurams	Very fast	Short	TMTD – TMTM,   TETD
Dithiocarbamates	Very fast	Short	ZMDC - ZBDC

Efficient Vulcanisation (E.V.) Systems – Vulcanizates, with predominantly mono and disulfide cross links, show excellent retention of properties on aging. The term “efficient” refers to a more efficient use of sulfur. E.V. Systems are developed by total replacement of sulfur by a sulfur donor or by use of very high ratios of accelerator to sulfur.

Semi-E.V. Systems – Vulcanizates using partial replacement of sulfur by a sulfur donor or by a moderate adjustment in the sulfur/accelerator ratios are widely used because they represent a good balance between aging, reversion, and fatigue resistance.

 

Physical Properties of Rubber Compounds Cured with Different Accelerator Systems

Property	Conv.	S-EV	EV
Tensile	Best	¬	Lower
Fatigue	Best	¬	Worst
Reversion	Worst	®	Best
Aging	Worst	®	Best

Conventional systems not only loose physical properties when over-cured, but they also tend to age more rapidly than semi-E.V’s after being over-cured.

Organic Vulcanisation Accelerators

Mercapto-accelerators
2-Mercaptobenzothiazole	MBT
Zinc-2-mercaptobenzothiazole	ZMBT
Dibenzothiazyl disulfide	MBTS

Sulfenamide-accelerators
N-cyclohexyl-2-benzothiazylsulfenamide	CBS
N-tert-buty-2-benzothiazylsulfenamide	TBBS
N.N’-dicyclohexyl-2-benzothiazylsulfenamide	DCBS
Thiuram  accelerators
Tetramethylthiuram disulfide	TMTD
Tetramethylthiuram  monosulfide	TMTM
Tetraethylthiuram disulfide	TETD
Dimethyldiphenylthiuram  disulfide	MPTD
Dipentamethylenethiuram  tetrasulfide	DPTT
Dithiocarbamate  accelerators
Zinc dimethyldithiocarbamate	ZDMC
Zinc diethyldithiocarbamate	ZDEC
Zinc dibutyldithiocarbamate	ZDBC
Zinc  pentamethylenedithiocarbamate	Z5MC
Zinc  ethylphenyldithiocarbamate	ZEPC
Zinc  dibenzyldithiocarbamate	ZBEC
Piperidine  pentamethylenedithiocarbamate	PPC
Sodium  dimethyldithiocarbamate	NaDMC
Sodium dibutyldithiocarbamate	NaDBC
Selenium  dimethyldithiocarbamate	SeDMC
Tellurium dimethyldithiocarbamate	TeDMC
Lead  dimethyldithiocarbamate	PbDMC
Cadmium dimethyldithiocarbamate	CdDMC
Cadmium pentamethylenedithiocarbamate	Cd5MC
Copper dimethyldithiocarbamate	CuDMC
Copper dibutyldithiocarbamate	CuDBC
Bismuth  dimethyldithiocarbamate	BiDMC
Dithiocarbamylsulfenamide
N-oxydiethylenedithiocarbamyl-N’-oxydiethylene    Sulfenamide	OTOS
Xanthate  Accelerators Zinc isopropylxanthate ZIX Zinc butylxanthate ZBX Sodium isopropylxanthate NaIX Guanidine Accelerators Diphenylguanidine DPG Di-o-tolylguanidine DOTG o-Tolylbiguanidine OTBG Amine Accelerators Butyraldehydeaniline BAA Tricrotonylidenetetramine TCT Hexamethylenetetramine HEXA Polyethylenepolyamines PEP Cyclohexylethylamine CEA Dibutylamine DBA Thiourea Accelerators N.N’-ethylenethiourea    (=2-mercaptoimidaxoline) ETU N.N’-diphenylthiourea (=thiocarbanilide) DPTU N.N’-diethylthiourea DETU Dithiophosphate  Accelerators Zinc dibutyldithiophosphate ZDBP Copper diisopropyldithiophosphate CuIDP Sulfur Donors 2-Benzothiazole-N-morpholyldisulfide MBSS Dimorpholine  disulfide DTDM Vulcanisation Retarders Cyclohexylthiophthalimide CTP Phthalic anhydride PTA Benzoic acid BES Salicylic acid SCS N-nitrosodiphenylamine NDPA