Determination of Free Sulfur in Vulcanized Rubber

1941 ◽  
Vol 14 (2) ◽  
pp. 520-524
Author(s):  
J. G. Mackay ◽  
C. H. J. Avons
Keyword(s):  
Barium Chloride ◽  
American Chemical Society ◽  
Chemical Society ◽  
Acetone Extract ◽  
Vulcanized Rubber ◽  
Factory Production ◽  
Usual Manner ◽  
Physical And Chemical ◽  
Free Sulfur

Abstract In a rubber laboratory controlling uniformity of factory production by physical and chemical testing, free sulfur is perhaps the most important determination. In this investigation recently described methods for determining free sulfur have been compared. A previous examination by one of the present authors of various methods of estimating free sulfur led to the adoption of a procedure comprising oxidation of the dried acetone extract by a mixture of nitric acid, perchloric acid and bromine, followed by evaporation with sodium chloride and hydrochloric acid before precipitation of sulfate in the usual manner with barium chloride. In the Avon laboratories considerable use has also been made of the method recommended by the Rubber Division of the American Chemical Society, in which bromine alone is used to oxidize the acetone extract, and the sulfate so produced is estimated gravimetrically as the barium salt. Both methods are accurate, but they are not sufficiently quick for effective factory control. Meantime there had been published several new methods of determining free sulfur which were claimed to be quicker than the older procedures. With the aim, therefore, of finding a rapid method more suited to the requirements of a control laboratory, the following methods have been compared. Methods 1 and 2 below were included as controls. As test-samples, 22 different general rubber products selected from factory production were used. Each product contained at least one sulfur-bearing ingredient in addition to the sulfur added to effect vulcanization.

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.

Determination of Free Sulfur in Vulcanized Rubber

1942 ◽  
Vol 15 (2) ◽  
pp. 376-377
Author(s):  
J. G. Mackay ◽  
C. H. J. Avons
Keyword(s):  
Nitric Acid ◽  
Hydrochloric Acid ◽  
Barium Sulfate ◽  
Barium Chloride ◽  
Acetone Extract ◽  
Volumetric Method ◽  
Watch Glass ◽  
Rubber Industry ◽  
Vulcanized Rubber

Abstract The following comments pertain to a paper of the above title by Mackay and Avons, published in Transactions of the Institution of the Rubber Industry, Vol. 16, pages 117–122, October 1940, and reprinted in Rubber Chemistry and Technology, Vol. 14, pages 520–524, April 1941. H. P. Stevens draws attention to the penultimate paragraph on p. 522 in which it is pointed out that the bromine method of oxidation is tedious and the reagent unhealthful, whereas perchloric acid may be dangerous. As a result of many years experience he is of the opinion that neither reagent is necessary. After adding nitric acid to the acetone extract in the flask, which should be covered with a watch glass, and when the reaction has subsided, about 0.5 gram of potassium chlorate is added and the mixture kept warm at 50 to 60° C. The top of a water oven is convenient; but the heating must be limited, as the yellow oxides of chlorine are rapidly driven off near 100°, and the liquid changes back from yellow to orange. The flask can be left to itself for an hour or two, but further addition of chlorate may be necessary to complete the oxidation. The contents are evaporated to dryness and taken up twice with concentrated hydrochloric acid preparatory to precipitation with barium chloride. A volumetric method may be preferable when a large number of routine tests have to be made, otherwise the final estimation can be made as barium sulfate.

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.

The Determination of Free Sulfur in Vulcanizates by a Polarographic Method

1952 ◽  
Vol 25 (1) ◽  
pp. 161-166 ◽  
Author(s):  
F. C. J. Poulton ◽  
L. Tarrant
Keyword(s):  
Quantitative Determination ◽  
Acetone Extract ◽  
Polarographic Method ◽  
The Common ◽  
Free Sulfur ◽  
Working Processes

Abstract The polarographic method offers a rapid and accurate means of determining the “true” free sulfur in vulcanizates. In the case of single estimations, the test takes approximately as long as the copper-spiral method, but for multiple or replicate testing it is much quicker. Since the determination is made directly on the acetone extract, it was necessary to examine at some length the possibility of interference from other ingredients of the extract. It is shown that most of the common accelerators and antioxidants are not likely to interfere, and promising methods of determining certain of these substances were revealed. Thus MBT, MBTS, TCA, A11, ONV, ZDC, TMT, TET, Ureka, and some of the Nonox series of antioxidants give regular Polarographic waves readily distinguishable from that of sulfur, and the development of working processes for their determination should not present any great difficulties. Other accelerators and antioxidants, notably ZIX, some Nonox antioxidants and Agerite White, while showing Polarographic activity, give poor curves in the pyridine electrolyte. No doubt in other base solutions the form of curve could be improved, and their quantitative determination would then follow.

A Short Note on the Tensile Testing of Rubber

1932 ◽  
Vol 5 (3) ◽  
pp. 351-355 ◽  
Author(s):  
M. Jones
Keyword(s):  
Tensile Strength ◽  
Tensile Testing ◽  
Short Note ◽  
American Chemical Society ◽  
Chemical Society ◽  
Ring Test ◽  
Stress Strain ◽  
Test Pieces ◽  
The One

Abstract The evaluation of rubber has centered largely around stress-strain phenomena, and the property of tensile strength is probably the one which has the most general application throughout the industry. Rubber exhibits stress-strain properties quite different from the majority of substances, and peculiar difficulties are introduced during the determination of tensile strength. Although tentative standards have recently been issued by the American Chemical Society, there is no evidence that these are being strictly adhered to, and there is still need for a more rigid standardization of tensile-testing methods. There are essentially two methods of tensile-testing: (1) Using dumb-bell test-pieces with a Bureau of Standards machine, or a Scott type of machine; and (2) Using ring test-pieces with a Schopper type of machine. It is generally supposed that higher tensile results are obtained by the former method. Recently, occasion has occurred to make a comparison between both types and to study the effect of certain factors upon each method.

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.

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