INDUSTRIAL A N D ENGIXEERING CHEMISTRY
April, 1924
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TABLEI1 (Base mixing: 700 rubber, 300 sulfur) Tensile Strength Ultimate Elongation Kg./Sq. Cm. Per cent 40 Min. 45 Min. 40 Min. 45 Min. Mineral Rubber-Sulfur-Rubber Volumes Mineral Rubber to 100
36 1
COh’CLUSIONS
1-There is a critical point in the process of vulcanization of hard rubber, and if the curing is interrupted previous to this point a flexible, leathery material is produced. If the curing is continued beyond this point, a sharp increase in breaking strength and corresponding reduction in ultimate elongation occur together with the hardening of the rubber-a specific case showing an increase from 500 pounds per square inch to 5500 pounds per square inch in the 10minutes near the critical point. 2-As the proportion of sulfur is increased, a point is Resin-Sulfur-Rubber Volumis Resin reached where further increase in sulfur no longer causes to 100 Volumes an increase in breaking strength, but an actual weakening Rubber due to dilution occurs. 3-Under the vulcanizing conditions described, materials of the mineral rubber type can be used with advantage up t o about 7.5 volumes, when a weakening of the compound occurs. 4-Lime and magnesia, which possess accelerating propTable I11 shows the influence of magnesium oxide and lime in :t base mixing of 700 parts of rubber and 300 parts erties in soft-cured rubber, also decrease the time required of sulfur. by weight. The quantities used of these two in- to harden the compound and increase the breaking strength organic rtccelerators are small, but as large as is common in when used in small quantities. 5-Resin may be used to actual advantage up to about soft rubber goods, and the figures show a decided hardening effect wjth the introduction of these materials and answer 5 volumes. 6-Tire reclaim of the grade described, in quantities up to 6 the question as to whether hard rubber compounds are influenced by inorganic accelerators. The graphs (Plate 111) volumes, causes a large increase in breaking strength and decrease in ultimate elongation, and in larger quantities reduces shown bring out this point more clearly. the breaking strength and increases the ultimate elongation. TABLE I11
Volumes MgO
(Base mixinn: 700 rubber, 300 sulfur) Tensile-Strength Ultimate Elongation Kg./Sq. Cm. Per cent 40 Min. 46 Min. 40 Min. 45 Min. Magnesium Oxide-Suljuv-Rubber
to 100 Volumes
Rubber 0.0 0.42 0.83 2.08 3.11
121.8 281.0 310.6 338.7 415.9
Volumes Lime
237.8 368.0 381.0 469.0 486.2 Lime-Su1.f~-Rubber
77.0 16.0 30.0 17.0 7.0
31.0 3.0 6.0 3.0 4.0
77.0 25.0 8.0 7.0 6.0
31.0 9.0 7.0 5.0 4.9
to 100 Volumes
Rubber 0.0
0 1 2 4
5s 16 91 37
121.8 288.2 350.0 468.4 485.3
237.7 386.1 430.1 451.7 450.2
Table IV and Plate IV show the influence of tire reclaim. A small quantity of reclaim acts as a hardening agent, as shown hy the increase in breaking strength and decrease in elongation. Increasing the quantity used, however, causes a softening of the specimens cured under like conditions, probably due to the rubber in the reclaim which does not have sufficient sulfur available to harden it. T A R L EIV-TIRE RECLAIM-SULFUR-RUBBER (Base mixing: 700 rubber, 300 sulfur) Volumes Reclaim Tensile Strength Ultimate Elongation Kg./Sq. Cm. Per cent t o 100 Volumes Rul~ber 40 Min. 45 Min. 40 Min. 45 Min. 0 0 121.8 237.8 77.0 31.0 5.11 372.8 480.4 7.3 4.5 10 22 335.2 428.2 16.9 7.5 20 44 329 4 404.9 35.4 8.8 40 88 221.8 289.8 68.9 57.2
A coniparison of the results obtained shows that lime and magnesia act much more rapidly than asphalt and resin and may be properly considered accelerators or hardening agents. Lime seems to be slightly more active than magnesia. Asphalt and resin may be considered as plastic diluents, their hardening effect within the limits considered being due to their bulk. Tire reclaim contains sufficient basic materials to act ab an accelerator when used in small proportion. Large quantities bring so much additional rubber that there is an insufficient quantity of sulfur in the base mix to produce hard rubber.
ACKNOWLEDGMENT The writer wishes to acknowledge his indebtedness t o W. H. Moore, who supervised the testing, and D. D. Kright, who assisted witb the graphs.
Nichols Medal Award Charles A. Kraus, director of research a t Clark University, Worcester, Mass., was awarded the seventeenth impression of William H. Nichols Medal of the New York Section of the AMERICANCHEMICALSOCIETY in recognition of his splendid researches on the properties of nonaqueous solutions. The medal was presented by Marston T. Bogert a t the regular March meeting of the New York Section on March 7, 1924. The Nichols Medal was founded in 1902 through the gift of William H. Nichols, and is awarded annually by a jury of the New York Section to that investigator whose contribution, published in the journals of the AXERICANCHEMICAL SOCIETY, shall have been judged of outstanding merit. It has been awarded to E. B. Voorhees, C. L. Parsons, M. T. Bogert, M. B. Bishop, W. H. Walker, W. A. Noyes and H. C. P. Weber, L. H. Baekeland, M. A. Rosanoff and C. W. Easley, Charles James, Moses Gomberg, Irving Langmuir (twice), C. S. Hudson, T. B. Johnson, G. N. Lewis, and Thomas Midgley, Jr. F. G. Cottrell, director of the Fixed h’itrogen Research Laboratory of the Department of Agriculture, following the introductory remarks of Clarke E. Davis, chairman of the New York Section, spoke interestingly of the personal side of the medalist, calling attention to his intense love of research, his interest in unusual phenomena and his method of coordinating everything to the end which he has in view. Perhaps the most important point brought out by Dr. Cottrell was the joy to be had from research in pure science which is often overlooked by chemists in these days of intense commercialism. Dr. Kraus has contributed fifty-four journal articles, two books, and twenty patents to the literature, as a result of his many researches in the field of liquid ammonia solutions and related problems. After fitting remarks of presentaten by Dr. Bogert, Dr. Kraus delivered his medal address on The Theory of Radicals as Applied to Modern Chemistry.” After reviewing the changes in the conception of chemical combination from the time of Berzelius, he discussed the theory of radicals in the light of modern investigation, showing that radicals could be placed in an electromotive series similar in all respects to that of the elements. His investigations of the complex alkyl tin radicals and their properties in liquid ammonia solutions formed the basis Tor the discussion, which will later be published in full in the Journal of the American Chemical Society, where most of his previous work has appeared.
