Sulfenamide Accelerated Sulfur Vulcanization of Natural Rubber in Presence and Absence of Dicumyl Peroxide

1970 ◽  
Vol 43 (6) ◽  
pp. 1311-1326 ◽  
Author(s):  
S. P. Manik ◽  
S. Banerjee
Keyword(s):  
Complex Formation ◽  
Stearic Acid ◽  
Natural Rubber ◽  
Methyl Iodide ◽  
Intermediate Complex ◽  
Radical Mechanism ◽  
Dicumyl Peroxide ◽  
Sulfur Vulcanization ◽  
Cross Links ◽  
Presence And Absence

Abstract Sulfuration by CBS acceleration both in presence and absence of ZnO and stearic acid with or without DCP has been studied in detail. It is observed that CBS increases the rate of DCP decomposition and decreases the crosslinking maxima due to DCP—ultimately leading to zero cross links with high amounts of CBS. In accordance with the observed sulfur decrease, free MBT formation, combined sulfur as MS etc., a predominantly radical mechanism has been presented, presumably not proceeding through intermediate complex formation. In mixes containing DCP together with sulfur, CBS, ZnO, and stearic acid crosslinks are found to be formed nearly additively, further confirmed by methyl iodide treatment of vulcanizates. Attempts have been made to interpret the results in terms of radical and polar mechanisms.

Effect of Sulfur and Dicumyl Peroxide on Vulcanization of Natural Rubber with Tetramethylthiuram Disulfide and Zinc Oxide

1970 ◽  
Vol 43 (6) ◽  
pp. 1294-1310 ◽  
Author(s):  
S. P. Manik ◽  
S. Banerjee
Keyword(s):  
Zinc Oxide ◽  
Stearic Acid ◽  
Natural Rubber ◽  
Reaction Mechanisms ◽  
Elemental Sulfur ◽  
Initial Rate ◽  
Dicumyl Peroxide ◽  
Tetramethylthiuram Disulfide ◽  
Sulfur Vulcanization ◽  
Salient Features

Abstract The salient features of both non-elemental sulfur vulcanization by TMTD and elemental sulfur vulcanization promoted by TMTD both in presence and absence of ZnO and stearic acid have been studied. TMTD increases the rate of DCP decomposition and lowers the crosslinking maxima due to DCP depending on its concentration. However, with higher amounts of TMTD the initial rate of crosslinking is increased with the increased amount of TMTD, while crosslinking maxima are still lowered due to reversion. ZnO or ZnO-stearic acid, however, seems to alter the entire course of the reaction. Both the crosslink formation and TMTD decomposition are much higher in presence of ZnO or ZnO-stearic acid, but stearic acid seems to have no effect. The reaction mechanisms for TMTD accelerated sulfuration in absence and presence of ZnO have also been studied.

Studies on MBT-Accelerated Sulfur Vulcanization of Natural Rubber Reinforced with Carbon Black

1974 ◽  
Vol 47 (2) ◽  
pp. 251-265 ◽  
Author(s):  
S. Bhoumick ◽  
S. Banerjee
Keyword(s):  
Free Radical ◽  
Carbon Black ◽  
Stearic Acid ◽  
Natural Rubber ◽  
Radical Mechanism ◽  
Free Radical Mechanism ◽  
Sulfur Vulcanization ◽  
Polar Mechanism

Abstract Studies have been made on the mechanism of MBT accelerated sulfur vulcanization of natural rubber containing semi-reinforcing carbon black as a filler. DCP has been used as an aid to distinguish between free radical and polar mechanism. Results indicate that sulfuration by MBT and sulfur proceed by a free radical mechanism but it becomes polar when ZnO and stearic acid are also present. Carbon black does not interfere in the sulfuration but it gives rise to additional crosslinks.

Vulcanization. Part I. Fate of Curing System during the Sulfur Vulcanization of Natural Rubber Accelerated by Benzothiazole Derivatives

1964 ◽  
Vol 37 (3) ◽  
pp. 635-649 ◽  
Author(s):  
R. H. Campbell ◽  
R. W. Wise
Keyword(s):  
Stearic Acid ◽  
Natural Rubber ◽  
Sulfur Concentration ◽  
Benzothiazole Derivatives ◽  
Sulfur Vulcanization ◽  
Curing Agents ◽  
Delayed Action

Abstract Several investigators have proposed mechanisms for the delayed action sulfur vulcanization of rubbers which postulate that a number of intermediate compounds containing fragments of the accelerator are formed during the vulcanization cycle. Although a number of workers have measured the change in initial accelerator and sulfur concentration in the rubber during vulcanization, none have identified and determined the intermediate compounds which appear to be formed during vulcanization. The purpose of this paper is to first confirm the existence of these intermediates and subsequently to identify and quantitatively follow their concentrations throughout the vulcanization cycle. In our initial studies we have limited our investigations to natural rubber cured with sulfur and accelerated with (i) MBT (2-mercaptobenzothiazole), (ii) (MBTS)[2,2′-dithiobisbenzothiazole)], and (iii) 2-(4-morpholinothio)benzothiazole. In order to reduce the complexity of the system, other normally used additional curing agents, notably ZnO and stearic acid, have been deleted.

Vulcanization. Part VII. Kinetics of Sulfur Vulcanization of Natural Rubber in Presence of Delayed-Action Accelerators

1965 ◽  
Vol 38 (1) ◽  
pp. 1-14 ◽  
Author(s):  
A. Y. Coran
Keyword(s):  
Positive Integer ◽  
Stearic Acid ◽  
Natural Rubber ◽  
Zinc Ion ◽  
Square Root ◽  
Reaction Products ◽  
Sulfur Concentration ◽  
Sulfur Vulcanization ◽  
Delayed Action ◽  
Kinetics Of

Abstract The scheme and treatment of the kinetics of scorch-delay vulcanization proposed in a previous paper were applied to natural rubber sulfur vulcanization accelerated by 2,2′-thiobisbenzothiazole (MBTS), 2-(N-cyclohexyl)benzothizaolesulfenamide (CBS), 2-(N-morpholinothio)benzothiazole (MOR), or 2-(N,N-diisopropyl)benzothiazolesulfenamide (DPBS). According to the scheme (see PDF for diagram) where the subscript x = a positive integer. The specific rates k1 and k2 and the ratiok4/k3′ were related to starting concentrations of accelerator, sulfur, and stearic acid. In general, an increase in stearic acid concentration or a decrease in accelerator concentration induces an increase in k1 or k4/k3′ but a decrease in k2. An exception to this is that, when the highly hindered sulfenamide DPBS is used as the accelerator, k1 does not change with changes in starting concentrations. It is interesting that k2 does not respond appreciably to changes in sulfur concentration when sulfenamides are used, unless the sulfur concentrations are extremely low. In contrast to this, k2 increases linearly with the square root of the sulfur concentration when MBTS is used. The changes in rates which occur with changes in the starting concentrations were attributed to the formation of chelates between zinc ion (brought into solution by stearic acid) and accelerator, intermediate reaction products, or crosslink precursors. The differences noted between the rates obtained with the three sulfenamides were attributed to differences in steric hindrance and stability.

The Theory of Vulcanization and the Action of Accelerators

1956 ◽  
Vol 29 (3) ◽  
pp. 917-932 ◽  
Author(s):  
B. Dogadkin ◽  
V. Selyukova ◽  
Z. Tarasova ◽  
A. Dobromyslova ◽  
M. Feldshtein ◽  
...  
Keyword(s):  
Molecular Weight ◽  
Kinetic Constant ◽  
Kinetic Curve ◽  
Large Degree ◽  
Radical Mechanism ◽  
Mobile Hydrogen ◽  
Sulfur Vulcanization ◽  
Methylene Groups ◽  
Cross Links ◽  
Spatial Formations

Abstract 1. Vulcanization of rubber by benzothiazolyl disulfide (without sulfur) is a radical process. The benzothiazolyl radicals formed during heat dissociation either are absorbed by a double bond or accept the mobile hydrogen of the α-methylene groups of the molecular chains of rubber. The polymer radicals formed thereby react with the other molecular chains, leading to combination of the molecules through the —C—C— bonds into spatial formations characteristic of the vulcanizate. 2. Kinetic curves were obtained which describe the conversion of benzothiazolyl disulfide into mercaptobenzothiazole and combination with rubber molecules. 3. Changes of viscosity and molecular weight during the vulcanization of rubber solutions were studied by light-scattering. It was established that the kinetic curve of viscosity has a minimum, while the molecular weight increases to three times its original value toward the end of the process. 4. The number of —C—C— cross-links in the vulcanizate was calculated from the swelling maximum and equilibrium modulus of elasticity. The data obtained indicate that, on the average, two and not more than five elementary acts of union of the molecular chains of rubber are necessary for each benzothiazolyl radical. 5. Experiments on stress relaxation at 130° established that the vulcanizate contains —C—C— cross-links between the molecular chains of rubber. 6. The isotopic exchange of a radioactive vulcanizate with the diffused benzothiazolyl disulfide demonstrates the existence of benzothiazolyl groups in the structure of the rubber. 7. A scheme of the elementary radical reactions between rubber and benzothiazolyl disulfide which lead to vulcanization is given. 8. The kinetics of vulcanization of rubber with sulfur in the presence of benzothiazolyl disulfide was studied. The combination of sulfur follows a monomolecular law and the kinetic constant depends linearly on the concentration of accelerator. 9. In the earliest stage of sulfur vulcanization, benzothiazolyl disulfide is converted into mercaptobenzothiazole, which is consumed as vulcanization proceeds. At the same time the rubber reacts with the benzothiazol radicals, which initiate polymerization processes with the formation of —C—C— links between the molecular chains of rubber. 10. The ratio between —C—C— bonds and sulfide bonds in a vulcanizate depends on the ratio between accelerator and sulfur. 11. As in the case of vulcanization with benzothiazolyl disulfide, in sulfur vulcanization in the presence of an accelerator, the reactions involving the α-methylene groups of the molecular chains are of considerable importance in structure formation. Thus vulcanization can not be regarded as a process which proceeds only at the double bonds of the rubber molecules. Activation of vulcanization by disulfides and sulfenamide accelerators is due to a large degree to reaction between these accelerators and the rubber. 12. A theory advanced in the present article together with experimental data reveal the radical mechanism of vulcanization and the action of accelerators, as well as the existence of polymerization phenomena during this process.

Vulcanization of natural rubber by dicumyl peroxide in the presence of sulphur

1973 ◽  
Vol 38 (2) ◽  
pp. 408-416 ◽  
Author(s):  
B. Bakule ◽  
J. Honskus ◽  
J. Nedbal ◽  
P. Zinburg
Keyword(s):  
Natural Rubber ◽  
Dicumyl Peroxide

Aging of Natural Rubber Vulcanizates in the Presence of Dithiocarbamates

1959 ◽  
Vol 32 (3) ◽  
pp. 739-747 ◽  
Author(s):  
J. R. Dunn ◽  
J. Scanlan
Keyword(s):  
Stress Relaxation ◽  
Natural Rubber ◽  
Protective Action ◽  
Dicumyl Peroxide ◽  
Vulcanized Rubber ◽  
Aging Properties ◽  
Photochemical Aging ◽  
Natural Rubber Vulcanizates

Abstract The thermal and photochemical aging of extracted dicumyl peroxide-, TMTD (sulfurless)- and santocure-vulcanized rubber, in presence of a number of metal and alkylammonium dithiocarbamates, has been investigated by measurements of stress relaxation. The dithiocarbamates have a considerable protective action upon the degradation of peroxide- and TMTD-vulcanizates, but they accelerate stress decay in santocure-accelerated vulcanizates. The reasons for this behavior are discussed. It is suggested that the excellent aging properties of unextracted TMTD vulcanizates are due to the presence of zinc dimethyldithiocarbamate formed during vulcanization.

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