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.

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.

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.

Vulcanization of Elastomers. 28. Vulcanization of Natural and Synthetic Rubbers with Sulfur in the Absence of Accelerators. I

1960 ◽  
Vol 33 (4) ◽  
pp. 1051-1061
Author(s):  
Elisabeth Echte ◽  
Walter Scheele ◽  
Sigrun Sonnenberg
Keyword(s):  
Activation Energy ◽  
Natural Rubber ◽  
Zero Order ◽  
Sulfur Concentration ◽  
Kcal Mole ◽  
Sulfur Solubility ◽  
Temperature Relation ◽  
Sulfur Vulcanization ◽  
Rate Relationship ◽  
Kinetics Of

Abstract The decrease of sulfur concentration in the reaction of sulfur with natural rubber was studied. The following was found : 1. Sulfur decrease follows the 0.6th order law independent of temperature as long as the sulfur is dissolved in the gum (temperature!). From the rate-temperature relation, an activation energy of 35 kcal/mole is calculated. 2. In an investigation of the kinetics of sulfur concentration at constant temperature but increasing starting concentration, the following two cases can be differentiated : a) As long as the sulfur is soluble in the gum, sulfur decrease still follows the 0.6th order, possibly due to autocatalysis ; the linear relationship between starting rate and starting concentration shows that the process is 1st order with respect to the concentration; this may be the consequence of a thermal, rate determining cleavage of the S8 ring. b) As the sulfur at higher concentration is only incompletely soluble in the gum, conversion curves with points of inflection are found ; this becomes more pronounced at higher concentration. At the start of the reaction one finds an autocatalytic sulfur decrease basically of zero order; in the latter part of the reaction after passing the point of inflection a 0.6th order is observed, as in the range of complete sulfur solubility. 3. A discrepancy between the time law and the concentration-rate relationship is found in pure as well as accelerated sulfur vulcanization ; these conditions are compared and discussed.

Extraction and identification of fillers and pigments from pyrolyzed rubber and tire samples

1996 ◽  
Vol 54 ◽  
pp. 174-175
Author(s):  
P. Sadhukhan ◽  
J. B. Zimmerman
Keyword(s):  
Zinc Oxide ◽  
Electron Microscope ◽  
Carbon Black ◽  
Natural Rubber ◽  
Transmission Electron Microscope ◽  
Rolling Resistance ◽  
Synthetic Polymers ◽  
Nitrogen Atmosphere ◽  
Transmission Electron ◽  
Curing Agents

Rubber stocks, specially tires, are composed of natural rubber and synthetic polymers and also of several compounding ingredients, such as carbon black, silica, zinc oxide etc. These are generally mixed and vulcanized with additional curing agents, mainly organic in nature, to achieve certain “designing properties” including wear, traction, rolling resistance and handling of tires. Considerable importance is, therefore, attached both by the manufacturers and their competitors to be able to extract, identify and characterize various types of fillers and pigments. Several analytical procedures have been in use to extract, preferentially, these fillers and pigments and subsequently identify and characterize them under a transmission electron microscope.Rubber stocks and tire sections are subjected to heat under nitrogen atmosphere to 550°C for one hour and then cooled under nitrogen to remove polymers, leaving behind carbon black, silica and zinc oxide and 650°C to eliminate carbon blacks, leaving only silica and zinc oxide.

Coactivation of Delayed-Action Vulcanization. Part I. Polymeric, Nonmigratory Cure Coactivators for Accelerated Sulfur Vulcanization

1989 ◽  
Vol 62 (5) ◽  
pp. 957-972
Author(s):  
A. Y. Coran ◽  
F. Ignatz-Hoover ◽  
L. H. Davis
Keyword(s):  
Molecular Weight ◽  
Minimum Loss ◽  
Synthetic Rubber ◽  
Curing Characteristics ◽  
Sulfur Vulcanization ◽  
Delayed Action ◽  
Very High ◽  
Rubber Article

Abstract Rubbery vinylpyridine-butadiene copolymers, containing 20–65% by weight of vinylpyridine monomer units, are effective coactivators of vulcanization for TBBS-accelerated sulfur-vulcanized SBR. In addition to emulsion SBR, the new co-activator has been evaluated in copositions of solution SBR, BR, NR, and various blends. The co-activator is active in all of the compositions which contain butadiene-derived synthetic rubber. This includes blends such as SBR/BR, solution-SBR/BR, SBR/NR, BR/NR, SBR/BR/NR, etc. There is little or no activity in which NR is the only polymer. The most efficacious copolymers contain between 30 and 60% 2-vinylpyridine. The incorporation of such a copolymer into an unvulcanized butadiene-derived rubber mix can give a substantial increase in the rate of crosslink formation with only a minimum loss of scorch resistance. Since the polymeric coactivators are very high in molecular weight, it can be at least tentatively concluded that they will not migrate from one component stock to another in a built-up multi-stock rubber article, either before or during vulcanization. Since the curing characteristics of a vinylpyridine-copolymer-containing TBBS-accelerated stock can be similar to those of TBBS-accelerated NR, it might be concluded that the new additives will solve some of the problems in balancing the cures of adjacent NR and SBR stocks in a multicomponent cured rubber article.

Evaluation of natural and epoxidized vegetable oil in elastomeric compositions for tread rubber

2021 ◽  
pp. 009524432110386
Author(s):  
Camila Taliotto Scarton ◽  
Nayrim Brizuela Guerra ◽  
Marcelo Giovanela ◽  
Suélen Moresco ◽  
Janaina da Silva Crespo
Keyword(s):  
Mechanical Properties ◽  
Stearic Acid ◽  
Natural Rubber ◽  
Soybean Oil ◽  
Vegetable Oil ◽  
Epoxidized Soybean Oil ◽  
Natural State ◽  
Vegetable Soybean ◽  
Tire Industry ◽  
Petroleum Derivatives

In the tire industry, the incorporation of natural origin oils in the development of elastomeric formulations has been one of the alternatives to reduce the use of petroleum derivatives, with a high content of toxic compounds. In this work, soybean vegetable oil was investigated as a lubricant and co-activator in sulfur-vulcanized natural rubber compounds. The soybean oil was used in its natural state and chemically modified by the epoxy ring’s introduction in its structure. In an internal mixer a standard formulation of natural rubber, five formulations replacing a conventional aromatic oil and stearic acid by vegetable oil, and a formulation without an activation system were prepared. The natural and epoxidized soybean oil was characterized chemically, and the elastomeric compositions were evaluated by mechanical and rheological analysis. The mechanical properties showed satisfactory results when vegetable soybean oil was used as a lubricant and could be a substitute for conventional aromatic oils, thus guaranteeing reduction of aromatic polycyclic content in the formulations. The crosslink degree and the rheological characteristics of the samples prepared with vegetable soybean oil were similar to the natural rubber standard sample. The formulations without the zinc oxide and stearic acid evidenced the need for activators in the vulcanization reaction, as they presented properties below standard. We verified that the epoxidized soybean oil, even when promoting better dispersion of the fillers, interfered in the crosslink formation, and consequently there was a decrease in the mechanical properties of these formulations. Finally, we indicated vegetable soybean oil as a substitute for aromatic oil and stearic acid, in the elastomeric compositions used to manufacture treads.

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