r44 



THE INDIA RUBBER WORLD 



JCLY 1, 1921 



ccntage et petrolatum in steam-jacketed kettles or in kettles over 

 a direct fire. ' 



Paraffine Wax. This can be had in a variety of "melting 

 points" between 50 degrees C. and 60 degrees C. (122 and 140 

 degrees F.). Its melting point will naturally depend upon the 

 amount of volatile oils it contains.. So we find that paraffine wax 

 which has been reheated several times gradually becomes harder, 

 owing to the fact that some of the volatile matter has been driven 

 off. This wa.\ has been in use for many years as a compounding 

 material and in many cases performed the work and accomplished 

 the results now obtained by the use of pitches. It filled the minute 

 interstices in the rubber dough and for that reason the products 

 which contained it withstood the action of air in a very satisfac- 

 tory manner. It has also been used for waxing the outer surfaces 

 of finished rubber products to protect them from the action of 

 air. This applies to steam packings as well as to auto tires. 

 Paraffine wax is also useful in compounds which must pass 

 through the tubing machine, as it acts as a lubricant and imparts 

 a fine surface finish to the extruded product. 



Ozokerite. The principal deposit of ozokerite occurs near 

 Boryslaw in Galicia, Austria. It consists essentially of paraffine 

 hydrocarbons. The color of the crude material varies from 

 yellow to black. The specific gravity varies from 0.850 to 0.890 

 and the melting point, according to Boverton Redwood, varies 

 from 130 to 160 degrees C. (266 to 320 degrees F.). Owing to 

 its specific gravity it may be freed from loose clinging mineral 

 matter by heating in water. Ceresin is merely refined ozokerite. 

 Two methods have been proposed for its preparation. The one 

 is to extract the crude ozokerite with gasoline, filter and then 

 distil oflf the gasohne. The other is to wash the crude ore with 

 sulphuric acid, as is done in the case of petroleum hydrocarbons. 



MoNTAN Wax is obtained in Saxony, Silesia and Germany by 

 extraction of the lignites with volatile solvents. Brown coal or 

 lignite is a mineral related to bituminous coal on the one hand 

 and wood on the other. Various substances have been extracted 

 from it by destructive distillation. Montan wax is one of these. 

 It has a specific gravity of about 0.950 and a melting point above 

 70 degrees C. (158 degrees F.). This material as well as ozo- 

 kerite has been used to a considerable extent in Europe, in 

 general for insulating compounds and in particular for com- 

 pounds used on rubber-covered wire. 



THE ACTION OF CERTAIN ORGANIC ACCELERA- 

 TORS IN THE VULCANIZATION OF RUBBER— IIP 

 By G. D. Kralz, A. H. Flower and B. J. Shapiro- 



IT has for some time been generally recognized that although 

 aniline is effective as an accelerator in the absence of zinc 

 oxide, diphenylthiourea functions but mildly in the absence of, 

 and strongly in the presence of this substance. Reference to this 

 effect has already been made indirectly in the literature several 

 times, and recently Twiss" has given curves for physical test re- 

 sults which demonstrate quite clearly the effectiveness of 

 diphenylthiourea as an accelerator in the presence of zinc oxide. 

 His statement that diphenylthiourea is practically inert in the 

 absence of zinc oxide is, however, not in accord with our findings. 



In a previous paper of this series' we have shown that in the 

 acceleration of the vulcanization of a rubber-sulphur mixture, 

 the activity of one molecular part of diphenylthiourea is less than 

 that of an equimolecular quantity of aniline, but equal to that of 

 one molecular part of aniline and one molecular part of phenyl 

 mustard oil. 



Our former experiments, however, were confined to the de- 

 termination of sulphur coefficients at one cure, only. In the pres- 

 ent instance, we desired to compare the relative effects of aniline 

 and diphenylthiourea over a series of cures, and to effect this com- 

 parison both by means o^ the sulphur coefficients and the physical 

 properties of the various mixtures and cures. Further, it was 



desired to compare mixtures which contained zinc oxide, as well 

 as the rubber-sulphur mixtures previously employed. 



Summarizing our results briefly, we found that, in a rubber- 

 sulphur mixture, the accelerating effect of aniline is considerably 

 greater than that of diphenylthiourea, when judged either by 

 sulphur cocflScients or on the basis of the physical properties of 

 the vulcanized mixtures. In mixtures which contained zinc oxide, 

 however, the reverse was found to be true, and diphenylthiourea 

 was more active than aniline when judged by either of the above 

 criteria. It was also evident that in the case of the mixtures 

 which contained zinc oxide, although the tensile strength of the 

 mixture which was accelerated by diphenylthiourea increased 

 more rapidly than in the case of the mixture accelerated by ani- 

 line, the same maximum tensile strength was attained by each. 

 The sulphur coeflficients at their respective maxima were prac- 

 tically identical. While the maximum tensile strength of the rub- 

 ber-sulphur mixture which was accelerated by aniline was the 

 same as that obtained when zinc oxide was present in the mix- 

 ture, it was attained only at a much higher sulphur coefficient. 

 Lastly, it was also found that the tensile strengths of the mixtures 

 that contained zinc oxide and which were accelerated by either 

 aniline or diphenylthiourea, particularly the latter, were increased 

 tremendously during the first part of the vulcanization, and at 

 very low sulphur coefficients. This would indicate the possibility 

 of certain substances (accelerators) increasing the physical prop- 

 erties of a vulcanized mixture without greatly affecting the sulphur 

 coeflScient. 



This point is of interest as it already has been noted by our- 

 selves,' Cranor,' and others, that with mixtures which contain 

 zinc oxide and a strong organic accelerator, the correct (or 

 optimum) cure is obtained at abnormally low sulphur coefficients 

 when compared with those obtained for unaccelerated mixtures. 

 No explanation has been offered for this phenomenon. Bedford 

 and Scott,' however, regard diphenylthiourea as the aniline salt 

 of phenyldithiocarbamic acid after H;S has been liberated. This- 

 salt is extremely unstable, owing to the weakly basic properties 

 of aniline, and in this respect, according to Krulla,* is unlike the 

 metallic salts of the same acid. In this connection, it is par- 

 ticularly pertinent to note that Bruni" has recently found the- 

 zinc salts of the mono and disubstituted dithiocarbamic acids 

 to be violent accelerators. It is quite possible, then, that such a 

 salt may be formed during the vulcanization process in mixtures- 

 which contain both diphenylthiourea and zinc oxide ;'° and that,, 

 irrespective of its action as an accelerator, the zinc portion of 

 such a salt may be responsible for the physical improvement im- 

 parted to the mixture. 



Our present results, moreover, particularly when interpreted 

 with the assistance of the excess sulphur coefficients obtained for 

 the various mixtures at different times of cure, show that when 

 aniline is employed as the accelerator in the presence of zinc oxide, 

 the effect of the latter substance is manifested almost entirely 

 in the physical properties of the mixture. When aniline is re- 

 placed by diphenylthiourea the reverse is true, and the activity 

 of the original substance as an accelerator is greatly increased 

 when measured by either the sulphur coefficients or physical 

 properties. In the latter instance, then, the zinc oxide most 

 probably either assists in the decomposition of the diphenylthiourea 



' Presented before the Rubber Division of the .American Chemical Society^ 

 Chicago, 111., September 6 to 10, 1920. 



- The Falls Rubber Co., CiivahiRa Falls, Ohio. 



= .Tournal of the Society of Chemical Industry, 39, 1920, 125t. 



* Journal of Industrial and Engineering Chemistry, 12, 1920, 317. 



"Jt.urnal of Industrial and Ensinecring Chemistry, 11, 19iy, 30; Cheimcali 

 & Metallurgical Engineering, 20, 1919, 418. 



•The India Rubber World, 61, 1919, 167. 



' Tournal of Industrial and Engineering Chemistry, 12, 1920, 31. 



» Uer., 46, 2669. 



» British patents Nos. 140.387 and 140,3^8. 



"The action of diphenylthiourea with zinc oxide is apparently sJmilai" 

 to the action of the natural accelerator with magnesium o.xide, afi,, pointed 

 out in a previous paper (Journal of Industrial and Engineering Chemistry, 

 ..12. 1920, 971). In bothi cases the oxide serves in a contributory capacity 

 rather than as a primary accelerator. It is obvious that no one oxide will" 

 activate all accelerators equally well. 



