Kinetics of Accelerated Vulcanization—III N-Cyclohexyl-Benzothiazole-2-Sulfenamide Accelerated Sulfur Vulcanization of Rubbers

1969 ◽  
Vol 42 (5) ◽  
pp. 1366-1382 ◽  
Author(s):  
S. K. Bhatnagar ◽  
S. Banerjee
Keyword(s):  
Zinc Oxide ◽  
Stearic Acid ◽  
Zinc Sulfide ◽  
Cross Link ◽  
Influence Of Temperature ◽  
Sulfur Vulcanization ◽  
Preliminary Study ◽  
Kinetics Of ◽  
Link Formation ◽  
Insight Into

Abstract Sulfenamide type of accelerators are well known for their outstanding processing safety combined with ultra-strong accelerating activity resulting in superior quality vulcanizates. Sulfenamides derived from different amines afford varying degrees of scorch delay and accelerating activity. Since there is no unanimity on the chemistry involved in this type of accelerated vulcanization, a preliminary study has been carried out to gain some insight into the mechanistic scheme. The present paper contains reports on the effects of varying concentrations of N-cyclohexyl-benzothiazole-2-sulfenamide (CBS) on the rate of free sulfur decrease and cross-link formation as well as zinc sulfide formation—whenever it occurs—both in the absence and presence of zinc oxide and of zinc oxide and stearic acid. The influence of temperature has also been investigated.

The Influence of Activators on the Vulcanization Process. II. The Influence of Zinc Oxide on the Structure of Vulcanizates

1959 ◽  
Vol 32 (3) ◽  
pp. 780-784 ◽  
Author(s):  
J. Beniska ◽  
B. Dogadkin
Keyword(s):  
Zinc Oxide ◽  
Stearic Acid ◽  
Zinc Sulfide ◽  
Network Formation ◽  
Marked Influence ◽  
Sh Groups ◽  
The Individual ◽  
Kinetics Of ◽  
Vulcanization Process ◽  
Kinetics Of Swelling

Abstract The influence of zinc oxide and stearic acid on the structures of vulcanizates was traced in stocks with mercaptobenzothiazole by means of the kinetics of swelling. It was found that zinc oxide in the presence of stearic acid has a marked influence on the rate and degree of crosslinked network formation in vulcanizates. In the formation of crosslinks (sulfur bridges) a number of reactions participate: the direct combination of rubber molecules with biradicals of sulfur, during which polysulfide bonds are mainly formed; the oxidation of rubber mercaptans (-SH groups), which is followed by the formation of mono-sulfide, disulfide and polysulfide links; and the decomposition of polysulfide links, which is followed by the formation of new crosslinks with a smaller number of sulfur atoms per crosslink. Zinc oxide has a varying influence on the individual reactions : the first two are activated by it, and the last one is retarded by it, because it does not react with the polysulfide sulfur to form zinc sulfide.

Sulfur Vulcanization of Vinyl-Substituted Polysiloxanes

1957 ◽  
Vol 30 (2) ◽  
pp. 406-418
Author(s):  
K. E. Polmanteer ◽  
R. J. Koch
Keyword(s):  
Zinc Oxide ◽  
Stearic Acid ◽  
Calcium Oxide ◽  
Elemental Sulfur ◽  
Organic Polymers ◽  
Cross Link ◽  
Bivalent Metal ◽  
Organic Bases ◽  
Sulfur Vulcanization ◽  
Metal Dithiocarbamates

Abstract The vinyl content of the polysiloxane polymer affects the rate of vulcanization in such a way that the vulcanization time varies inversely with the vinyl concentration raised to a power less than 1. Furthermore, this power appears to be dependent upon the vinyl concentration, so that a stationary value cannot be quoted. Sulfur alone crosslinks only polysiloxane polymers of high vinyl content. A 4 mole per cent vinyl-containing polymer exhibited no vulcanization after 3 hours at 160° C with sulfur alone. Vulcanization times in the same range as those found with sulfur-vulcanizing organic polymers were obtained in this polysiloxane system by the proper choice of accelerators. Starting with the most active, compounds for accelerating or activating this vinyl-containing polysiloxane-sulfur system were: strong organic bases (TEPA), DPG, thiuram disulfides (TMTD), magnesium oxide, bivalent metal dithiocarbamates, thiazoles (MBT), weak organic bases (aniline), calcium oxide. Zinc oxide and litharge are inhibitors in this system to varying extents, depending on the accelerator present. Organic acids such as stearic acid inhibit vulcanization in this system. For recipes void of elemental sulfur, the following conclusions may be made: Accelerators that vulcanize vinyl-containing polysiloxanes without the aid of elemental sulfur follow very closely the list of compounds capable of vulcanizing organic polymers. (D.P.)c data indicated that two vinyl groups are involved in each cross link.

The Influence of Activators on the Vulcanization Process. I. The Influence of Zinc Oxide on the Rate of Combination of Sulfur with Rubber

1959 ◽  
Vol 32 (3) ◽  
pp. 774-779 ◽  
Author(s):  
J. Beniska ◽  
B. Dogadkin
Keyword(s):  
Zinc Oxide ◽  
Stearic Acid ◽  
Zinc Sulfide ◽  
Kinetics Of ◽  
Vulcanization Process

Abstract In this work the effect of zinc oxide and stearic acid on the kinetics of sulfur combination with rubber was traced, in stocks containing accelerators as well as in stocks without the latter. It was proved that ZnO does not increase the rate of sulfur combination in sodium catalyzed polybutadiene rubbers (SKB-25). On the contrary, in stocks with mercaptobenzothiazole, zinc oxide decreases the rate of sulfur combination. In vulcanizates ZnS is formed in the presence of ZnO. The largest amount of zinc sulfide is formed in stocks with phenyl-2-naphthylamine and with stearic acid.

The Action of Vulcanization Activators

1958 ◽  
Vol 31 (2) ◽  
pp. 329-342 ◽  
Author(s):  
B. Dogadkin ◽  
I. Beniska
Keyword(s):  
Zinc Oxide ◽  
Stearic Acid ◽  
Zinc Sulfide ◽  
Isotope Exchange ◽  
Thiol Group ◽  
Elementary Sulfur ◽  
Crosslinking Reaction ◽  
Butadiene Rubber ◽  
Zinc Compounds ◽  
Kinetics Of

Abstract 1. Zinc oxide and stearic acid do not affect the rate of addition of sulfur to rubber in the vulcanization of pure sodium butadiene rubber in mixtures without accelerators. 2. In mixtures containing diphenylguanidine as accelerator zinc oxide and stearic acid do not affect the rate of addition of sulfur to rubber. 3. In mixtures containing mercaptobenzothiazole zinc oxide retards and stearic acid accelerates the addition of sulfur to rubber. 4. In a similar manner zinc oxide suppresses and stearic acid activates isotope exchange between elementary sulfur and sulfur of the thiol group in mercaptobenzothiazole. 5. Zinc oxide and stearic acid in mixtures with mercaptobenzothiazole increase the rate and degree of crosslinking of the molecular chains of rubber; zinc oxide has the greater influence on the degree, while stearic acid has the greater influence on the rate, of the crosslinking reaction. 6. In mixtures with diphenylguanidine the influence of vulcanization activators on the degree and rate of crosslinking is considerably less pronounced than in mixtures with mercaptobenzothiazole. 7. The kinetics of zinc sulfide formation during vulcanization has been studied and it was established that ZnS is formed as the result of reactions of zinc oxide and zinc compounds with thiol and polysulfide groups in the rubber. Model substances have been used to demonstrate other possible routes for the formation of zinc sulfide during vulcanization. The effect of zinc oxide and stearic acid on the rate and degree of crosslinking is associated with participation of these compounds in such reactions. 8. Isotope exchange between radioactive sulfur in the vulcanizate and elementary sulfur was used to follow the formation and changes in the numbers of polysulfide linkages during the vulcanization process. The amount of sulfur participating in isotope exchange as vulcanization proceeds at first increases, passes through a maximum, and then decreases, which indicates a regrouping of the polysulfide linkages with an increase in their number and a decrease of the average number of sulfur atoms per linkage. Zinc oxide decreases the degree of isotope exchange between the vulcanizate and elementary sulfur at all stages of vulcanization. 9. Vulcanization activators, by favoring a decrease in the number of sulfur atoms in the sulfur bonds, increase the heat stability of the vulcanizates. This effect of the activators was demonstrated by kinetic data on stress relaxation in deformed vulcanizates at 126°. 10. The cleavage and regrouping of polysulfide linkages in the presence of zinc oxide and zinc compounds is accompanied by the combination of part of the sulfur as zinc sulfide, which leads to a decrease in the number of newly formed crosslinks. This effect of zinc oxide is manifested in vulcanization reversion effects and in changes of vulcanizate properties under thermomechanical influences. 11. From the above experimental data the general conclusion may be drawn that the fundamental role of vulcanization activators does not lie in their influence on the kinetics of the addition of sulfur to rubber, but rather in their influence on the nature of the vulcanization structures formed and on changes in them in the course of vulcanization.

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.

Hydrogen Passivation Kinetics of Si Nanocrystals in SiO2

2003 ◽  
Vol 770 ◽  
Author(s):  
Andrew R. Wilkinson ◽  
Robert G. Elliman
Keyword(s):  
Reaction Kinetics ◽  
Activation Energies ◽  
Hydrogen Passivation ◽  
Time Resolved ◽  
Luminescence Efficiency ◽  
Si Nanocrystals ◽  
Preliminary Study ◽  
Kinetics Of ◽  
Insight Into

AbstractHydrogen passivation of non-radiative defects increases the luminescence intensity from silicon nanocrystals. In this study, photoluminescence (PL) and time-resolved PL were used to investigate the chemical kinetics of the hydrogen passivation process. Isochronal and isothermal annealing sequences were used to determine the reaction kinetics for the absorption and desorption of hydrogen, using the generalised consistent simple thermal (GST) model proposed by Stesmans for Pb defects at planar Si/SiO2 interfaces. This included determination of the activation energies and rate constants for the forward and reverse reactions as well as the associated spread in activation energies. The reaction kinetics determined from such measurements were found to be in excellent agreement with those for the passivation of Pb defects at planar Si/SiO2 interfaces, suggesting the nanocrystal emission process is also limited by such defects. These results provide useful model data as well as insight into the processing conditions needed to achieve optimum passivation in H2. As an extension to the work, a preliminary study into passivation by atomic hydrogen was pursued via a post-metallization Al anneal (alneal). A considerable gain in luminescence efficiency was achieved over the previously optimised passivation in H2.

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 INFLUENCE OF TEMPERATURE ON THE KINETICS OF CHEMISORPTION OF HYDROGEN ON ZINC OXIDE

1959 ◽  
Vol 37 (11) ◽  
pp. 1916-1922 ◽  
Author(s):  
Manfred J. D. Low
Keyword(s):  
Zinc Oxide ◽  
Hydrogen Adsorption ◽  
Influence Of Temperature ◽  
Influence Of Temperature On ◽  
Elovich Equation ◽  
Temperature Ranges ◽  
Kinetics Of

The kinetics of hydrogen adsorption by ZnO have been measured at constant pressures of 403 mm Hg over temperatures from 0 °C to 257 °C. Two distinct consecutive kinetic stages occur at all temperatures, each stage being precisely expressed by the Elovich equation. The rates and extents of adsorption increase in the temperature ranges 0–80 °C and 110–200 °C and decrease in the range 80–110 °C. The change with temperature of the constants a and 1/α of the Elovich equation parallels changes in the amount adsorbed with temperature.

A New Postural Force Production Index to Assess Propulsion Effectiveness During Handcycling

2013 ◽  
Vol 29 (6) ◽  
pp. 798-803 ◽  
Author(s):  
Julien Jacquier-Bret ◽  
Arnaud Faupin ◽  
Nasser Rezzoug ◽  
Philippe Gorce
Keyword(s):  
Force Production ◽  
Movement Analysis ◽  
Joint Torques ◽  
Production Index ◽  
Effective Force ◽  
Generation Capacity ◽  
Preliminary Study ◽  
Kinetics Of ◽  
Kinematics And Kinetics ◽  
Insight Into

The aim of this study was to propose a new index called Postural Force Production Index (PFPI) for evaluating the force production during handcycling. For a given posture, it assesses the force generation capacity in all Cartesian directions by linking the joint configuration to the effective force applied on the handgrips. Its purpose is to give insight into the force pattern of handcycling users, and could be used as ergonomic index. The PFPI is based on the force ellipsoid, which belongs to the class of manipulability indices and represents the overall force production capabilities at the hand in all Cartesian directions from unit joint torques. The kinematics and kinetics of the arm were recorded during a 1-min exercise test on a handcycle at 70 revolutions per minute performed by one paraplegic expert in handcycling. The PFPI values were compared with the Fraction Effective Force (FEF), which is classically associated with the effectiveness of force application. The results showed a correspondence in the propulsion cycle between FEF peaks and the most favorable postures to produce a force tangential to the crank rotation (PFPI). This preliminary study opens a promising way to study patterns of force production in the framework of handcycling movement analysis.

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