Vulcanization of Elastomers. 18. Vulcanization of Natural Rubber with Sulfur in the Presence of Mercaptobenzothiazole. III

1958 ◽  
Vol 31 (3) ◽  
pp. 548-558 ◽  
Author(s):  
Otto Lorenz ◽  
Elisabeth Echte
Keyword(s):  
Zinc Oxide ◽  
Natural Rubber ◽  
Zinc Stearate ◽  
Oxide Content ◽  
Square Root ◽  
Initial Concentration ◽  
Velocity Constant ◽  
Equilibrium Swelling ◽  
Kinetics Of ◽  
Limiting Value

Abstract The present work is concerned with the influence of the concentration of sulfur and the zinc oxide content on the kinetics of the vulcanization of natural rubber with sulfur in the presence of mercaptobenzothiazole, zinc stearate and zinc oxide. The following results were obtained. 1. The velocity constant of the sulfur decrease, kSI, is inversely proportional to the initial concentration of sulfur. 2. The velocity constant of the change with time of the reciprocal equilibrium swelling, kQI, is inversely proportional to the square root of the initial concentration of sulfur. 3. The limiting value of the reciprocal equilibrium swelling, 1/Q∞ (degree of crosslinking), at constant stearate content, is proportional to the square root of the initial concentration of sulfur. 4. The amount of accelerator consumed during vulcanization increases with increase in the initial amount of sulfur. The decrease in the accelerator is a first order reaction having approximately the same rate as the decrease of sulfur. 5. The velocity constants of the sulfur decrease and the change with time of the reciprocal equilibrium swelling are practically independent of the amount of zinc oxide. Other situations exist, of course, for compounds without zinc oxide. 6. Empirical equations were derived to express the dependence of the constants kSI, kQI and 1/Q∞ on the composition of the mixture.

The Vulcanization of Elastomers. VII. The Vulcanization of Natural Rubber with Thiuram Disulfides. Part IV

1957 ◽  
Vol 30 (1) ◽  
pp. 69-76 ◽  
Author(s):  
Walter Scheele ◽  
Peter Stange
Keyword(s):  
Zinc Oxide ◽  
Natural Rubber ◽  
Constant Temperature ◽  
Rate Constants ◽  
Experimental Error ◽  
Oxide Content ◽  
Oxide Crystals ◽  
Kinetics Of ◽  
Limiting Value

Abstract The present paper deals with the kinetics of the thiuram vulcanization at varying thiuram disulfide concentrations as well as with the influence of the zinc oxide content upon vulcanization at constant temperature (120° C). It was found : 1. The limiting value of dithiocarbamate formation of 66 mole per cent relative to the amount of thiuram disulfide used is—within wide limits—independent of the initial thiuram disulfide concentration. 2. At constant thiuram disulfide concentration the limiting value of dithiocarbamate formation is unchanged when the zinc oxide content is successively increased. 3. Changing the zinc oxide content while the thiuram disulfide concentration is kept constant exerts an influence on the kinetics of the decrease of thiuram as well as on the increase of dithiocarbamate. The rate constants of both reactions increase. 4. It is concluded from these results that in all probability vulcanization is initiated on the surface of the zinc oxide crystals. 5. Even in stocks containing as much as 40 g. zinc oxide per hundred g. of compounds, the limiting value of dithiocarbamate formation remains unchanged. This was verified by the analysis of vulcanizates after extremely long cure times. The average limiting value of two experiments after 24 hours of cure was 65 mole per cent which corresponds to a two-thirds reaction within the experimental error.

Studies on the Kinetics of Vulcanization of Rubber

1964 ◽  
Vol 37 (2) ◽  
pp. 557-562
Author(s):  
H. L. Taneja ◽  
S. Banerjee
Keyword(s):  
Zinc Oxide ◽  
Steady State ◽  
Natural Rubber ◽  
Square Root ◽  
Initiator Concentration ◽  
Appreciable Increase ◽  
Kinetics Of ◽  
Kinetics Of Vulcanization ◽  
Free Sulfur

Abstract The dependence of the rate of accelerated vulcanization of natural rubber (smoked sheet) on the concentration of mercaptobenzothiazole accelerator has been reported on in this paper. The rate of decrease of free sulfur at the steady state has been found to be proportional to the square root of the initiator concentration expressed as grams/100 grams of rubber. The rate has also been found to be enhanced by the addition of 1% of zinc oxide. Higher amounts of zinc oxide does not lead to a further appreciable increase in the rate.

The Vulcanization of Elastomers. 13. The Vulcanization of Natural Rubber with Sulfur in the Presence of Mercaptobenzothiazole. II

1958 ◽  
Vol 31 (1) ◽  
pp. 117-131 ◽  
Author(s):  
O. Lorenz ◽  
Elisabeth Echte
Keyword(s):  
Natural Rubber ◽  
Rate Constants ◽  
Zinc Stearate ◽  
Molar Ratio ◽  
Crosslinking Reaction ◽  
Square Root ◽  
Kcal Mole ◽  
First Order ◽  
Equilibrium Swelling ◽  
Rate Processes

Abstract The vulcanization of natural rubber with sulfur, using mercaptobenzothiazole as accelerator in the presence of zinc stearate, was investigated. The results were as follows: 1) When natural rubber is cured with sulfur in the presence of zinc oxide and mercaptobenzothiazole, as well as zinc stearate, one observes, with the first order diminution of sulfur concentration, an induction period that grows longer as the cure temperature falls. 2) For the disappearance of sulfur there is calculated, from the temperature dependence of the rate constants, an activation energy of 19.5 kcal/mole. This value is considerably smaller than that found for the mercaptobenzothiazole-accelerated sulfur cure when no zinc stearate is present. 3) The percentage loss in mercaptobenzothiazole during vulcanization is, in the presence of zinc stearate, independent of the temperature; there is a reaction, independent of the amount of stearate added of 5 molecules of S8 for each molecule of mercaptobenzothiazole. 4) The diminution in accelerator can also be explained as a first order reaction, and it becomes evident that disappearance of accelerator and sulfur are equivalent-rate processes. 5) The crosslinking, measured by the reciprocal equilibrium swelling, goes according to the first order, yet sulfur disappearance and the crosslinking reaction are not equal rate processes, which was always true in the absence of zinc stearate. In each case the crosslinking rate constants are greater than those for the decrease in sulfur. 6) For the activation energy of network formation, we calculated, from the temperature dependence of the rate constants of the reciprocal equilibrium swelling, 20.5 kcal/mole. 7) When the stearate content is constant, there is a linear relationship between kSI, the rate constant for sulfur diminution, and the given amount of mercaptobenzothiazole, up to an initial molar ratio of mercaptobenzothiazole: stearate = 4:1. Increases in accelerator proportion beyond this initial ratio cause no further rise in the rate constants. 8) The rate constants of the crosslinking reaction also increase with increasing proportion of mercaptobenzothiazole (stearate portion remaining constant), until the initial molar ratio of mercaptobenzothiazole:zinc stearate = 4:1 is reached. Nevertheless, the relationship is not linear. 9) There is a linear relationship between the amount of zinc stearate in the vulcanizate and the maximum sulfur-loss rate constants kSI (max). 10) The maximum rate constants of the network forming reaction kQI (max) are proportional to the square root of the stearate content. 11) The number of crosslinkage points formed is independent of the quantity of mercaptobenzothiazole, when the stearate content is constant. 12) The number of crosslinking points formed increases, however, along with increasing stearate content, and is proportional to the square root of the stearate content. The investigations will be continued.

Vulcanization of Elastomers. 14. Role of the Oxide in Vulcanization with Compounds of the Thiuram Series. I

1958 ◽  
Vol 31 (3) ◽  
pp. 539-547
Author(s):  
Walter Scheele ◽  
Horst-Eckart Toussaint ◽  
Peter Stange
Keyword(s):  
Zinc Oxide ◽  
Linear Functions ◽  
Practical Significance ◽  
Molar Ratio ◽  
Oxide Content ◽  
Velocity Constant ◽  
Mixing Ratios ◽  
Oxide Addition ◽  
Kinetics Of

Abstract The present paper is concerned with the influence of TETD concentration and of zinc oxide content upon the kinetics of the vulcanization of natural rubber and Perbunan 2818 with TETD. The following results were obtained for vulcanization at 120° C. 1. The velocity constants of TETD decrease and ZnDEDC formation are linear functions of the zinc oxide content at constant TETD concentrations. 2. If TETD and zinc oxide are present in constant molar mixing ratios, then the velocity constant of TETD decrease is independent of the amount of the mixture while that of ZnDEDC formation rises linearly with zinc oxide addition. 3. The velocity constant of TETD decrease diminishes with increasing TETD concentration when the zinc oxide content of the mixture is held constant. Under these conditions the velocity constant of ZnDEDC formation remains unchanged. 4. Everything shows that the velocity constant of ZnDEDC formation depends only on the zinc oxide content of the mixture while that of TETD decrease is dependent on the molar ratio of zinc oxide and TETD. 5. The relationships found are expressed mathematically, and the practical significance of the relationships is pointed out.

Vulcanization of Elastomers. 23. The Chemical Kinetics of Vulcanization Reactions and The Physical Properties of The Vulcanizates. I

1960 ◽  
Vol 33 (2) ◽  
pp. 335-341
Author(s):  
Walter Scheele ◽  
Karl-Heinz Hillmer
Keyword(s):  
Activation Energy ◽  
Physical Properties ◽  
Chemical Kinetics ◽  
Kcal Mole ◽  
First Order ◽  
Equilibrium Swelling ◽  
Kinetics Of ◽  
Kinetics Of Vulcanization ◽  
Limiting Value ◽  
Good Agreement

Abstract As a complement to earlier investigations, and in order to examine more closely the connection between the chemical kinetics and the changes with vulcanization time of the physical properties in the case of vulcanization reactions, we used thiuram vulcanizations as an example, and concerned ourselves with the dependence of stress values (moduli) at different degrees of elongation and different vulcanization temperatures. We found: 1. Stress values attain a limiting value, dependent on the degree of elongation, but independent of the vulcanization temperature at constant elongation. 2. The rise in stress values with the vulcanization time is characterized by an initial delay, which, however, is practically nonexistent at higher temperatures. 3. The kinetics of the increase in stress values with vulcanization time are both qualitatively and quantitatively in accord with the dependence of the reciprocal equilibrium swelling on the vulcanization time; both processes, after a retardation, go according to the first order law and at the same rate. 4. From the temperature dependence of the rate constants of reciprocal equilibrium swelling, as well as of the increase in stress, an activation energy of 22 kcal/mole can be calculated, in good agreement with the activation energy of dithiocarbamate formation in thiuram vulcanizations.

Vulcanization of Elastomers. 36. Vulcanization of Natural Rubber and Synthetic Rubbers with Sulfur in Absence of Accelerators. II

1964 ◽  
Vol 37 (4) ◽  
pp. 910-926 ◽  
Author(s):  
W. Scheele ◽  
H. Müller ◽  
W. Schulze
Keyword(s):  
Natural Rubber ◽  
Concentration Dependence ◽  
Good Description ◽  
Kcal Mole ◽  
First Order ◽  
Different Temperatures ◽  
In Cis ◽  
Kinetics Of ◽  
Limiting Value ◽  
Homolytic Dissociation

Abstract In continuation of earlier work with natural rubber, the kinetics of sulfur decrease were studied in certain synthetic rubbers for different temperatures and sulfur concentrations. At the same time the formation of polysulfide bound sulfur was studied, using as example the reaction of sulfur with natural rubber and synthetic rubbers. It was found that: 1) When the decrease in sulfur concentration is portrayed by curves which are convex to the time axis (Perbunan), the 0.6th order time-law is fulfilled, (as in the case of natural rubber independent of temperature and concentration. 2) In contrast, the concentration dependence of the rate at which sulfur decreases, both in Perbunan and cis 1,4-polybutadiene, denotes a first-order reaction in agreement with experience with natural rubber. 3) The activation energy of sulfur decrease has the same magnitude for all the elastomers investigated (34 to 36 kcal/mole). 4) The disagreement between the time law and the concentration dependence of the rate of sulfur disappearance encountered in all the experiments with 1,5-polyenes, is interpreted as indicating autocatalysis, which likewise explains the shape of the curves for sulfur disappearance. 5) Sulfur reacts considerably faster in natural rubber and Perbunan than in cis 1,4-polybutadiene; consequently a homolytic dissociation of the S8-ring cannot be rate-determining. 6) Polysulfide sulfur shows, in each case, a maximum with reaction time, and in completely reacted vulcanizates it tends toward a limiting value. An equation was found, which provides a good description of change with time of polysulfide concentration (natural rubber and cis 1,4-polybutadiene). 7) An explanation is given for the appearance of the polysulfide maximum; and how the reaction of sulfur with 1,5-polyenes can be represented, making use of all available results, is discussed.

Kinetics-Controllable Hetero-Precipitation Process on the Nanoscale Solid-Liquid Interface of Spherical Particles

2011 ◽  
Vol 688 ◽  
pp. 45-50
Author(s):  
Xiao Feng Wu ◽  
Yu Chao Liao ◽  
Ren Liang Yue ◽  
Yun Fa Chen
Keyword(s):  
Shell Thickness ◽  
Spherical Particles ◽  
Composite Particles ◽  
Precipitation Process ◽  
Square Root ◽  
Initial Concentration ◽  
First Order ◽  
Solid Liquid Interface ◽  
Solid Liquid ◽  
Kinetics Of

Based on the growth kinetics of the SiO2particles, we studied the kinetic hetero-precipitation process on the interface of polystyrene (PS) microscale particles. The nanoscale SiO2shell thickness increased with increasing time and was proportional to the square root of the initial concentration of TEOS precursor while governed by hetero-precipitation process. Moreover, the hetero-precipitation process followed the first-order growth mechanism of silica onto the surface of templating PS pariticles. Properly controlling the reagent concentrations could alleviate and even avoid, to a certain extent, aggregation among PS@SiO2particles that could otherwise have an adverse effect on the properties and applications of those composite particles and the corresponding SiO2hollow products.

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.

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