Kinetics of Thiazole-Accelerated Sulfur Vulcanization of Natural Rubber

1963 ◽  
Vol 36 (3) ◽  
pp. 835-843 ◽  
Author(s):  
R. Russell ◽  
D. A. Smith ◽  
G. N. Welding
Keyword(s):  
Natural Rubber ◽  
Induction Period ◽  
Consistent Difference ◽  
Crosslinking Reaction ◽  
Equal Concentration ◽  
Network Chain ◽  
First Order ◽  
Sulfur Vulcanization ◽  
Cure Time ◽  
Long Time

Abstract Thiazole-accelerated sulfur vulcanization of natural rubber gum stocks has been investigated at temperatures from 110° to 140° C for times over the range 1 to 104 min. Swelling measurements on the vulcanizates were used to estimate the contribution of chemical reactions to the network chain density, (ρMc−1)chem which was plotted against cure time. The kinetic graphs show clearly an induction period (t0), then fast crosslinking, a slow limited degradation, and finally a “long-time” crosslinking reaction. Apart from the induction period, each of the kinetic graphs is satisfactorily represented by a rate equation assuming three independent additive reactions: first order crosslinking, first order partial degradation, and a long-time reaction assumed to be zero order. The method has been used to compare MBT and MBTS at equal concentration. One consistent difference is the increase of induction period with MBTS in place of MBT, accompanied by a somewhat greater increase of time of cure to maximum network density. Also the completed contributions (Xand Δ) from the initial crosslinking reaction and the degradation reaction, respectively, are greater with MBTS than with MBT. Over the temperature range studied there is no difference between MBT and MBTS in the activation energies for crosslinking, or for t0−1 or for the long-time reaction, but MBTS has a higher activation energy for degradation than MBT. With rising temperature of cure, Δ increases towards X with each accelerator.

Kinetics of Sulfur-Free Thiuram Vulcanization

1972 ◽  
Vol 45 (4) ◽  
pp. 945-954 ◽  
Author(s):  
Vratislav Ducháček
Keyword(s):  
Activation Energy ◽  
Induction Period ◽  
Rate Equation ◽  
Radical Reactions ◽  
Network Chain ◽  
First Order ◽  
Cure Time ◽  
Long Time ◽  
Partial Degradation ◽  
Kinetics Of

Abstract Sulfur-free thiuram vulcanization has been investigated at temperatures from 160° to 190° C over 0.5 to 600 min. Continuous measurements in a VUREMO curemeter were used to estimate the extent of crosslinking, which was plotted against cure time. Simultaneously the values of the network chain density were calculated from swelling measurements on the vulcanizates. The cure curves show clearly an induction period (ti), then fast crosslinking, a partial degradation, a “long-time” crosslinking, and finally a slow, limited degradation. Apart from the induction period, the kinetic graphs are satisfactory represented by a rate equation assuming three independent first-order reactions: fast crosslinking, degradation, and slow crosslinking. The rate equation contains seven kinetic parameters. Over the temperature range studied, there is no difference between the values of activation energy for fast crosslinking, for degradation, for slow crosslinking, and for ti−1. Due to the presence of thiourea, the values of the induction period, the rate constant, and the extent of slow crosslinking are decreased. Simultaneously the activation energies calculated from degradation and slow crosslinking are significantly increased. On the basis of the above results, the mechanism of the sulfur-free thiuram vulcanization, in which ionic and radical reactions take place, is discussed.

Vulcanization of Elastomers. 12. Perbunan with Thiuram Monosulfide and Sulfur. I

1959 ◽  
Vol 32 (1) ◽  
pp. 128-138 ◽  
Author(s):  
Walter Scheele ◽  
Horst-Eckart Toussaint
Keyword(s):  
Activation Energy ◽  
Natural Rubber ◽  
Temperature Dependence ◽  
Induction Period ◽  
Rate Constants ◽  
The Other ◽  
Tetramethylthiuram Disulfide ◽  
First Order ◽  
The One ◽  
Limiting Value

Abstract The vulcanization of Perbunan 2818 by tetramethylthiuram monsulfide plus sulfur (1 mole monosulfide per gram-atom S) was thoroughly studied. The following results were shown: The limiting value for dithiocarbamate formation is 66 mole per cent of the initial thiuram monosulfide, indicating a two-thirds transformation. The limiting value is practically independent of temperature. The formation of dithiocarbamate can be described as a reaction of the first order. The formation of dithiocarbamate is characterized by an induction period which grows longer with lowering of the temperature, and at 100° C it amounts to about 100 minutes. The rate constants for dithiocarbamate formation were calculated, and it was shown that they were practically the same as those for the vulcanization of Perbunan with tetramethylthiuram disulfide. The activation energies as derived from the temperature dependence of the rate constants for dithiocarbamate formation in the vulcanization of Perbunan by thiuram monosulfide plus sulfur on the one hand and with thiuram disulfide on the other, are only very slightly different and are practically the same as the activation energy for dithiocarbamate formation during the vulcanization of natural rubber with thiuram monosulfide plus sulfur. The results were thoroughly discussed in light of the present conceptions of the course of thiuram vulcanizations.

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.

EFFECT OF BENZOTHIAZOLOYLTHIAZOLES AS SECONDARY ACCELERATORS IN THE SULFUR VULCANIZATION OF NATURAL RUBBER

2011 ◽  
Vol 84 (1) ◽  
pp. 88-100 ◽  
Author(s):  
R. Reshmy ◽  
R. Nirmal ◽  
S. Prasanthkumar ◽  
K. Kurien Thomas ◽  
Molice Thomas ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Tensile Strength ◽  
Natural Rubber ◽  
Chemical Method ◽  
Binary Systems ◽  
Minimal Amount ◽  
Tetramethylthiuram Disulfide ◽  
Solvent Free Conditions ◽  
Sulfur Vulcanization ◽  
Cure Time

Abstract The vulcanization of natural rubber and a blend of natural rubber and reclaimed rubber by using binary accelerator systems containing a novel series of benzothiazoloylthiazole as secondary accelerator (SA) has been studied. These secondary accelerators were synthesized by a green chemical method under solvent-free conditions, by the irradiation of microwaves (180 W). The synergistic effect of the SA with N-Cyclohexyl-2-benzothiazolsulfenamide as primary accelerator was studied at 150 °C. These binary systems were effective in reducing the cure time and improving the rheometric and mechanical properties. These SAs were found to be effective in reducing the cure time with a minimal amount of 0.5 phr, but commercially available SAs such as thioureas and tetramethylthiuram disulfide were reported to show reduction in cure time only by increasing the amount of SA. Mechanical properties such as hardness, abrasion loss, tensile strength, percentage strain at break, and modulus at different elongations 100, 200, and 300% were evaluated and found to be immensely improved. The improved mechanical properties were also shown to be at par with crosslink densities (1/2Mc) of different mixes.

Effect of CMCS on Cure Characteristics of Natural Rubber

2011 ◽  
Vol 402 ◽  
pp. 606-609
Author(s):  
Yong Zhou Wang ◽  
Hong Hai Huang ◽  
Hong Xing Gui ◽  
Tao Chen ◽  
Fu Quan Zhang ◽  
...  
Keyword(s):  
Natural Rubber ◽  
Induction Period ◽  
Linear Dependence ◽  
Arrhenius Equation ◽  
Carboxymethyl Chitosan ◽  
Curing Temperature ◽  
Maximum Torque ◽  
Ammonia Water ◽  
Cure Characteristics ◽  
Cure Time

The effect of carboxymethyl chitosan (CMCS) as preservation on cure characteristics of nature rubber (NR) was studied, which compared with NR using ammonia water as preservative agent. The results showed that the induction period and optimum cure time of sample N (Ammonia water dosage is 0.15% of the mass of fresh latex), CMCS-1(CMCS dosage is 0.05% of the mass of fresh latex) and CMCS-2(CMCS dosage is 0.1% of the mass of fresh latex) were obviously decreased with the increasing of temperature, corresponding to Arrhenius equation perfectly. The maximum torque was linear dependence on curing temperature and decreased with the increasing of curing temperature. The relation of MH0 were as follows: N>CMCS-1>CMCS-2, respectively.

Structural Characterization of Vulcan-Izates. XII. Efficient Vulcanization Using a Sulfenamide-Thiuram Disulfide Accelerator System

1972 ◽  
Vol 45 (5) ◽  
pp. 1366-1371 ◽  
Author(s):  
D. S. Campbell
Keyword(s):  
Natural Rubber ◽  
Structural Characterization ◽  
High Ratio ◽  
Mixed System ◽  
Tetramethylthiuram Disulfide ◽  
Sulfur Vulcanization ◽  
Cure Time ◽  
Accelerator System ◽  
Cyclic Sulfide

Abstract Vulcanizates obtained from the sulfur vulcanization of natural rubber using a combination of the accelerators N-cyclohexyl-2-benzothiazole sulfenamide (CBS) and tetramethylthiuram disulfide (TMTD) have been analyzed in terms of the numbers of poly-, di-, and monosulfide crosslinks, network-bound accelerator residues, and cyclic sulfide chain modifications as a function of cure time. The vulcanization system produced mainly monosulfide crosslinks at optimum cure, although there were differences in detail between this mixed system and a previously reported efficient sulfur vulcanization (EV) system using a high ratio of CBS to sulfur.

Study on sulfur vulcanized natural rubber formulated with nitrosamine safe diisopropyl xanthogen polysulfide/tertiary butyl benzothiazole sulphenamide binary accelerator system

2020 ◽  
pp. 147776062097749
Author(s):  
IHK Samarasinghe ◽  
S Walpalage ◽  
DG Edirisinghe ◽  
SM Egodage
Keyword(s):  
Mechanical Properties ◽  
Natural Rubber ◽  
Strength Properties ◽  
Nitroso Compounds ◽  
Tertiary Butyl ◽  
Study Behavior ◽  
Cure Characteristics ◽  
Sulfur Vulcanization ◽  
Cure Time ◽  
Accelerator System

An outstanding interest on elimination of nitrosamine generation in traditional sulfur vulcanization systems has led to introduce nitrosamine safe accelerator/s to produce safe natural rubber (NR) vulcanizates. It is an effective way to prevent formation of carcinogenic N-nitroso compounds during manufacture of rubber products. In the present study, behavior of nitrosamine safe binary accelerator system consisting of diisopropyl xanthogen polysulfide (DIXP) with commonly used non-regulated accelerator N-tert-butyl-2-benzothiazole sulfenamide (TBBS) was investigated in efficient sulfur vulcanization of NR. Cure characteristics, physico-mechanical properties and crosslink density of vulcanizates prepared with different combinations of the accelerator system were evaluated and compared with those of individual accelerators. The study reveals that moduli and strength properties of the vulcanizate prepared with DIXP accelerator are inferior to those of the vulcanizate prepared with TBBS accelerator. Nevertheless, optimum cure time of the DIXP compounds is lower in comparison to TBBS compounds. Moreover, progressive replacement of DIXP with TBBS in the accelerator system showed a synergistic effect in regard to cure characteristics and physico-mechanical properties.

Structural Characterization of Vulcanizates Part X. Thiol-Disulfide Interchange for Cleaving Disulfide Crosslinks in Natural Rubber Vulcanizates

1970 ◽  
Vol 43 (2) ◽  
pp. 210-221 ◽  
Author(s):  
D. S. Campbell
Keyword(s):  
Natural Rubber ◽  
Exchange Reaction ◽  
Structural Characterization ◽  
Disulfide Exchange ◽  
Sulfur Vulcanization ◽  
Cure Time ◽  
Natural Rubber Vulcanizates

Abstract The thiol-disulfide exchange reaction is shown to be applicable to cleavage of disulfide crosslinks in accelerated sulfur vulcanizates of natural rubber. The reaction, in conjunction with the previously reported selective cleavage of polysulfide crosslinks, is used to determine the distribution of crosslink types for several accelerated sulfur vulcanization systems as a function of cure time. Discrepancies between the results and published results obtained using the reagent sodium di-n-butyl phosphite for disulfide crosslink cleavage are discussed.

scholarly journals Electric properties of olive oil under pressure

2021 ◽  
Author(s):  
L. T. Pawlicki ◽  
R. M. Siegoczyński ◽  
S. Ptasznik ◽  
K. Marszałek
Keyword(s):  
Molecular Structure ◽  
Phase Transition ◽  
Phase Diagram ◽  
Phase Transitions ◽  
Olive Oil ◽  
Material Parameters ◽  
First Order ◽  
Long Time ◽  
Capacitive Reactance ◽  
First Order Phase

AbstractThe main purpose of the experiment was a thermodynamic research with use of the electric methods chosen. The substance examined was olive oil. The paper presents the resistance, capacitive reactance, relative permittivity and resistivity of olive. Compression was applied with two mean velocities up to 450 MPa. The results were shown as functions of pressure and time and depicted on the impedance phase diagram. The three first order phase transitions have been detected. All the changes in material parameters were observed during phase transitions. The material parameters measured turned out to be the much more sensitive long-time phase transition factors than temperature. The values of material parameters and their dependence on pressure and time were compared with the molecular structure, arrangement of molecules and interactions between them. Knowledge about olive oil parameters change with pressure and its phase transitions is very important for olive oil production and conservation.

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