The Determination of Free Sulfur in Soft Vulcanized Rubber by a Volumetric Method

1932 ◽  
Vol 5 (3) ◽  
pp. 360-362 ◽  
Author(s):  
W. D. Guppy
Keyword(s):  
Hydrogen Sulfide ◽  
Sulfuric Acid ◽  
Organic Compounds ◽  
Subsequent Oxidation ◽  
Vulcanized Rubber ◽  
Elementary State ◽  
Previously Treated ◽  
Mineral Sulfides ◽  
Free Sulfur

Abstract The methods so far proposed for the determination of the free sulfur in vulcanized rubber depend upon the removal of the sulfur by extraction of the rubber with hot acetone, and subsequent oxidation to sulfuric acid of the sulfur in the extract. The extract is liable however to contain, in addition to sulfur in the elementary state, organic compounds containing sulfur derived from the rubber resins, accelerator, or antioxidant. In the subsequent oxidation this sulfur will be oxidized to sulfuric acid to an extent which depends on the method of oxidation used. In the present work, a method of analysis has been developed which is more rapid than the existing methods, and in which it is considered that the determination of the sulfur present in the elementary state is less likely to be affected by organic compounds containing sulfur. It has been found that when vulcanized rubber placed in contact with a metal, such as tin or aluminum, is boiled in hydrochloric acid, hydrogen sulfide is generated by the action of the nascent hydrogen produced. This reaction occurred with rubber which had been previously treated with acid alone to decompose metallic sulfides, but no hydrogen sulfide was obtained from rubber which had been previously extracted with acetone and was free from metallic sulfides. As these results showed that the reactions were not due to the presence of mineral sulfides, or of sulfur combined with the rubber, it was concluded that the hydrogen sulfide was formed by the reduction of the free sulfur.

The Determination of Free Sulfur by a Volumetric Method Part II

1933 ◽  
Vol 6 (4) ◽  
pp. 512-517
Author(s):  
W. D. Guppy
Keyword(s):  
Hydrogen Sulfide ◽  
Organic Compounds ◽  
Sulfur Compounds ◽  
Acetone Extract ◽  
Volumetric Method ◽  
Organic Sulfur Compounds ◽  
Vulcanized Rubber ◽  
Volumetric Determination ◽  
Free Sulfur

Abstract 1. The method previously described for the volumetric determination of free sulfur in vulcanized rubber has been compared with the older gravimetric methods in cases where other organic compounds containing sulfur are present in the vulcanizate. 2. The volumetric method gave lower results than the methods involving oxidation of the acetone extract in the case of vulcanized rubber containing aldehydeamine condensation products of thiouram disulfide compounds. This indicated that the sulfur combined with some organic compounds was not reduced by the reagents used. 3. The results with the accelerator tetraethylthiouram disulfide showed that in some cases part of the sulfur in organic compounds was reduced under the conditions of the reaction. 4. The acetone-soluble and the acetone-insoluble portions of brown substitute contain organic sulfur compounds. Part of the sulfur in these compounds was reduced to hydrogen sulfide by the action of nascent hydrogen. 5. The sulfur compounds present in white substitute were stable toward the reducing agents used in the estimation of free sulfur. 6. The sulfur compounds formed by the vulcanization of ebonite were in part reduced to hydrogen sulfide with tin and acid. Variations in the composition of the mixing and in the vulcanizing conditions altered the amount of these reducible compounds. 7. The volumetric method previously described cannot be used for the determination of the free sulfur in ebonite, brown substitute or in vulcanized rubber containing brown substitute. In the case of vulcanized rubber containing brown substitute or of ebonite the method can be used to determine the amount of sulfur in the acetone extract. 8. The volumetric method can be employed for the determination of the free sulfur in soft vulcanized rubber containing white substitute and in reclaimed rubber.

Analysis of Vulcanized Rubbers. Influence of Accelerators on the Determination of Free Sulfur by the Copper Spiral Method

1952 ◽  
Vol 25 (4) ◽  
pp. 956-958
Author(s):  
J. Mann
Keyword(s):  
Hydrogen Sulfide ◽  
Copper Sulfide ◽  
Acetone Extract ◽  
British Standard ◽  
Standard Methods ◽  
Vulcanized Rubber ◽  
Potential Source ◽  
Source Of Error ◽  
Free Sulfur

Abstract The copper spiral method is being inserted in a revised edition of the “British Standard Methods of Testing Vulcanized Rubber”, and this raises the question of what sulfur compounds react as “free” sulfur. In this method, “free” sulfur is considered to be that part of the sulfur which is present in the acetone extract and which reacts with a copper spiral, placed in the acetone during the extraction, with the production of copper sulfide, the amount of which can be estimated after its removal from the acetone. Since most accelerators contain sulfur, it is obvious that the presence of accelerators or accelerator fragments is a potential source of error. Fourteen accelerators of various types were therefore examined, and it was found that some react with copper, producing compounds which evolve hydrogen sulfide on treatment with hydrochloric acid.

Spectrophotometric Determination of Thiabendazole in Feeds

1965 ◽  
Vol 48 (2) ◽  
pp. 288-295
Author(s):  
C R Szalkowski ◽  
J Kanora
Keyword(s):  
Hydrogen Sulfide ◽  
Spectrophotometric Determination ◽  
Coefficient Of Variation ◽  
Zinc Dust ◽  
Improved Method ◽  
Subsequent Oxidation ◽  
Color Development ◽  
Thiazine Dye

Abstract An improved method has been developed for thiabendazole in feeds. Thiabendazole is extracted from the feed with 0.2N HCl in 50% methanol; interfering substances are removed by making the extract alkaline and extracting into chloroform. The thiabendazole is re-extracted with dilute HCl; the solution is reduced with zinc dust in the presence of p-phenylenediamine to form a hydrogen sulfide complex. After subsequent oxidation with ferric solution to form a thiazine dye, the dye is extracted into n-butanol and measured at 605 mμ. More than 30 commercial unmedicated cattle and swine feeds show an apparent thiabendazole content of 0.00006–0.00044%. Recoveries on feeds made to contain 0.0025–10.0% thiabendazole ranged from 97.6 to 106.6%, with a coefficient of variation of 2.44%. In studies of 30 other drugs added to feeds, only nithiazide, Enheptin, and sulfathiazole interfere. Many variables involved in the color development were studied. The method gives the most accurate and reproducible results on solutions containing 0.2–2.0 μg thiabendazole/ml.

Investigations of the Reversion of Vulcanized Rubber under Heat

1952 ◽  
Vol 25 (2) ◽  
pp. 241-250 ◽  
Author(s):  
Uma Shankar
Keyword(s):  
Free Energy ◽  
Hydrogen Sulfide ◽  
Methyl Iodide ◽  
Energy Of Activation ◽  
Cross Linking ◽  
Molar Free Energy ◽  
Vulcanized Rubber ◽  
Free Energy Of Activation ◽  
Equilibrium Swelling ◽  
Free Sulfur

Abstract (1) During reversion of a vulcanizate, the breakdown of cross-linkages, including those of polysulfides, predominates over any simultaneous reformation of cross-linkages. (2) The reverting modulus falls exponentially with time. (3) The calculated molar free energy of activation is 33.3 ± 1.7 kcal., irrespective of the temperature or the atmosphere of cure or the composition of the mix, and is sufficient to rupture an —S—S— bond. (4) The degree of cross-linking, estimated from the equilibrium swelling measurements in benzene, falls during reversion. (5) The exclusion of oxygen during curing does not prevent reversion if the temperature is high enough to supply the energy needed to break up the cross-linkages. (6) During reversion in nitrogen, hydrogen sulfide is freely evolved, and the C/H ratio rises above the value for C5H8. (7) Evidence for the formation and breakdown of polysulfides during reversion is provided by an increase in free sulfur and a decrease in combined sulfur during a given cure, and the methyl iodide reaction of the reverted vulcanizates.

The Polarographic Determination of Organic Accelerators of Vulcanization

1941 ◽  
Vol 14 (4) ◽  
pp. 914-919 ◽  
Author(s):  
Gerard Proske
Keyword(s):  
Double Bond ◽  
Organic Compounds ◽  
Analytical Determination ◽  
Polarographic Method ◽  
Rubber Industry ◽  
Vulcanized Rubber ◽  
Color Reactions ◽  
Analytical Utility ◽  
Kjeldahl Nitrogen

Abstract In spite of the great importance which vulcanization accelerators have attained in the rubber industry, there is still an almost complete lack of analytical methods, both for determining the accelerator contents of rubber mixtures and for identifying accelerators in vulcanized rubber. Apart from the wholly unsatisfactory and uncertain method of deciding the existence of organic accelerators in vulcanized rubber by a Kjeldahl nitrogen determination, there is little of value in the literature. Twiss and Martin have described a few qualitative reactions of accelerators. Recently Shimada described some color reactions of accelerators with cobalt oleate, but the analytical utility of these reactions is very doubtful. Of far more promise than these is the polarographic method, the value of which in the analytical determination of a series of important accelerators was proved in an investigation which will be described in the present paper. It had already been proved in earlier polarographic investigations that organic compounds containing nitrogen with a double bond can be reduced electrolytically, provided groups with a tendency to rupture are close to the double bond. Shikata and Tachi have shown this to be true of azobenzene, and Winkel and Proske of dimethylquinoxaline.

Determination of Free Sulfur in Stocks Cured with Sulfur Containing Accelerators

1962 ◽  
Vol 35 (2) ◽  
pp. 498-500
Author(s):  
E. P. Khehaskova ◽  
N. A. Okhapkina ◽  
V. N. Provorov
Keyword(s):  
Sodium Sulfite ◽  
Sodium Stearate ◽  
Cadmium Acetate ◽  
Strontium Nitrate ◽  
Vulcanized Rubber ◽  
Normal Method ◽  
Sulfur Containing ◽  
Sulfite Solution ◽  
Free Sulfur

Abstract For the determination of free sulfur in vulcanized rubber the normal method is the sulfite method, consisting of the heating of a sample of rubber with a solution of sodium sulfite. The free sulfur reacts with the sulfite, forming thiosulfate, which is determined by iodometric titration. The unreacted excess of sulfite is removed with formalin. The method gives good results in the analysis of stocks which do not contain sulfur-containing accelerators. In the presence of these accelerators the results are high: in some cases the method is quite inapplicable, as it is impossible to establish the endpoint of titration accurately. This may be explained by the circumstance that the accelerators and the products of their decomposition during vulcanization can pass into the solution of sodium sulfite and react further with the iodine. The method of determination of free sulfur proposed by Hardmann, consisting of the acetone extraction of the rubber in the presence of copper gauze, is protracted and complicated. A certain improvement in the sulfite method of Bolotnikov and Gurova was introduced in the ASTM method (1952). Sodium stearate is added to the sodium sulfite solution for better wetting of the rubber, and a certain amount of paraffin to prevent the formation of foam. After termination of heating the solution the stearic acid is precipitated with strontium nitrate and certain accelerators with cadmium acetate. For the majority of stocks this method gives correct results, but in a number of cases it is difficult to establish the end of titration at all.

The Influence of Temperature on the Evolution of Hydrogen Sulfide from Vulcanized Rubber

1933 ◽  
Vol 6 (1) ◽  
pp. 46-55 ◽  
Author(s):  
A. D. Cummings
Keyword(s):  
Hydrogen Sulfide ◽  
Electrical Properties ◽  
Constant Temperature ◽  
Sulfur Compounds ◽  
Vulcanized Rubber ◽  
Measurable Amount ◽  
Wide Range ◽  
Long Time ◽  
Influence Of Temperature On

Abstract This paper presents the results of measurements of the evolution of hydrogen sulfide from rubber-sulfur compounds heated at various temperatures. Determination of the amount of hydrogen sulfide produced under different conditions was used to measure the degree of decomposition of the rubber. Two types of experiments were carried out: (1) Samples of vulcanized rubber containing 8 to 32 per cent sulfur were heated for 8-hour intervals at 13 temperatures between 105° and 265° C., and (2) samples having sulfur contents of 4, 10, 18, and 32 per cent were maintained for about 200 hours at constant temperature, one set of specimens at 136° and another group at 220° C. These measurements of deterioration were undertaken in connection with an investigation on the electrical properties of vulcanized rubber at relatively high temperatures. During these experiments, samples of rubber-sulfur compounds had been subjected to a wide range of temperatures. Time of exposure to each temperature had been about eight hours. The purpose of the present work was to determine when the sulfur content of a specimen had changed sufficiently to affect its dielectric constant and power factor by a measurable amount. In order to approximate the conditions under which the electrical tests were made, it was necessary to determine the amount of decomposition when rubber vulcanized with 8 to 32 per cent sulfur was heated for successive intervals of eight hours each at temperatures changed in unequal steps from 105° to 265° C. To make this information more complete and to obtain additional data which could be compared with previous investigations, the work was extended to include determinations of the loss of hydrogen sulfide from vulcanized rubber heated for a long time at constant temperature. The electrical properties of the whole series of rubber-sulfur compounds is the subject of a separate investigation at this bureau, and will be reported in another paper.

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