Tetramethylthiuram disulfide vulcanization of extracted rubber. I. Introduction and compounding

J of Applied Polymer Sci

1995

SYNOPSISExchange reactions between tetramethylthiuram disulfide, 2-mercaptobenzothiazole, and sulfur were studied by heating powdered mixes to vulcanization temperatures at a programmed rate in a DSC. The reaction was stopped at points along the thermal curve and the mixture was analyzed by HPLC. On dissolution, even unheated samples undergo a sulfide exchange reaction leading to a mixed accelerator, while polysulfides of the thiuram and mixed accelerator form in low concentrations. On heating, higher concentrations of these polysulfides are formed, particularly in the presence of elemental sulfur. Dimethyldithiocarbamic acid, formed in the exchange, influences the product spectrum if it remains trapped in the DSC pan. Tetramethylthiourea is formed only at elevated temperatures when dimethylamine, a degradation product of the acid, is trapped in the DSC pan. A series of reactions is proposed to explain the product spectrum obtained under different conditions. 0

Section: T U Td-mbtmentioning

confidence: 98%

Tetramethylthiuram disulfide and 2‐mercaptobenzothiazole as binary accelerators in sulfur vulcanization. I. Exchange reactions between the accelerators and sulfur in the absence of rubber

Giuliani

J of Applied Polymer Sci

1995

“…xss + xssx + xs + xs3x xss + xs3x + xs + xs4x (2) Their source of XSS radicals did not involve the unsymmetrical homolysis of TMTD. Instead, they suggested that XSS radicals were produced during the formation of TMTU.…”

Section: Current Mechanisms For Tmtp Formationmentioning

confidence: 99%

A study of the rate of formation of polysulfides of tetramethylthiuram disulfide

Geyser

J of Applied Polymer Sci

1995

SYNOPSISThe rate of formation of tetramethylthiuram polysulfides (TMTP), that play an important role in vulcanization, was studied. After a short induction period (< 30 s), tetramethylthiuram disulfide (TMTD) and TMTD-sulfur mixes, heated to 130-150°C in the absence of rubber, rapidly form a series of TMTPs. The concentrations of TMTPs of lower sulfur rank increase most rapidly, indicating that sulfur atoms are added to the accelerator sequentially. The incorporation of sulfur molecules to give TMTPs, which subsequently desulfurate, does not occur. Equilibrium concentrations of the various TMTPs are achieved in about 2 min. Little tetramethylthiourea is formed below 200°C. Tetramethylthiuram monosulfide (TMTM) is stable, but TMTM-sulfur mixes form TMTPs. A mechanism is proposed to account for the large amount of TMTM formed on heating TMTD in the absence of sulfur and the correspondingly higher TMTP concentrations in the presence of sulfur. 0 1995 John Wiley & Sons, Inc.

“…In accelerated sulfur vulcanization, the addition of ZnO to formulations is recognized as being important for attaining good physical properties in vulcanizates 1, 2. Stearic acid is commonly added as a coactivator for ZnO.…”

Section: Introductionmentioning

confidence: 99%

Effect of carboxylic acids on 2-bisbenzothiazole-2,2?-disulfide- and tetramethylthiuram disulfide-accelerated sulfur vulcanization. IV. Vulcanization of polyisoprene compounds with ZnO

Shelver

1999

J. Appl. Polym. Sci.

ABSTRACT:The effect of benzoic and stearic acids on 2-bisbenzothiazole-2,2Ј-disulfide (MBTS)-and tetramethylthiuram disulfide (TMTD)-accelerated sulfur vulcanization of polyisoprene compounds, containing ZnO, was studied at 150°C. In the presence of ZnO, the acids are rapidly converted to their zinc salts that, unlike the acids, do not attack accelerator polysulfides and, instead, promote vulcanization. The addition of accelerator polysulfides to the chain is not affected by zinc salts, but the rate of crosslinking of pendent groups is facilitated. In MBTS vulcanization, the promotion of crosslinking reactions reduces the number of pendent groups involved in cyclization reactions and higher crosslink densities are attained. In TMTD compounds, crosslink densities are increased on addition of ZnO and of ZnO/carboxylic acids. A mechanism is suggested to account for the promotion of crosslinking by the zinc salts. Bis(2-mercaptobenzothiazolo)zinc(II) and bis(dimethyldithiocarbamato)zinc(II) can act similarly to zinc benzoate or stearate to promote the crosslinking of pendent groups, but are less efficient. With benzoic acid, a limited attack by zinc benzoate on TMTP leads to a slightly lower increase in crosslink density than is achieved with the addition of ZnO alone.