344 



THE INDIA RUBBER WORLD 



[April 1, 1916. 



What the Rubber Chemists Are Doing. 



EXPERIMENTS IN VULCANIZATION. variation in the nitrogen content of the rubber after creping 



NITROGEN and the rate of vulcanization of rubber has been preparatory to the vulcanization process. It is small in the case 

 studied by J. Grantham, who presents his results in the of rapidly vulcanizing rubbers, and larger in that of the more 

 ■•.\gricultural Bulletin" of the Federated Malay States slowly vulcanizing ones. 

 (October, 1915). The investigation was conducted on several The low percentage of nitrogen in rubber prepared as un- 

 slices of smoked and unsmoked plantation rubbers representing smoked slab is attributed partly to loss in the gaseous form 

 conditions of standard practice in the preparation of rubber from during the superficial drying of the slab, and partly to the wash- 

 its latex. ing out of nitrogenous decomposition products when the slab 



Although there is a wide difference in rate of vulcanization is creped prior to vulcanization. 



between smoked slab and smoked sheet, no difference is notice- Since rapidly vulcanizing smoked slab rubber contains as 



able in the nitrogen content. Comparison of the unsmoked sheet high percentage of nitrogen as slowly vulcanizing sheets, the 



and unsmoked slab showed that low nitrogen is connected with actual loss of nitrogen cannot be the cause of rapidity of vul- 



rapidity of vulcanization. canization, although it would appear from the results of the 



These observations were confirmed by a second series of ex- unsmoked rubbers that rapidity of vulcanization and loss of 



periments which yielded the following results ; nitrogen are in some way associated. 



Percentage Optimum SYNTHETIC RUBBER AND SAWDUST. 



Type of Time of Vulcan- !„ ^ recent number of "Le Caoutchouc & la Gutta Percha." G. 



of Rubber. Nitrogen, ization in Hours. Noyer reviews the work of Harries and other investigators on 



Thick smoked slab 425 V/2 the relation between levulic acid and rubber, and the value of 



Thin smoked slab 398 1^ sawdust as a source of levulic acid. Harries has shown that 



Thick smoked sheet 400 2j4 the ozonide of rubber yields levulic acid by the action of water. 



Thin smoked sheet 416 3 N^ satisfactory source has yet been discovered that will yield 



Thick unsmoked slab 210 IVi levulic acid in abundant quantity and at low cost. The author 



Thin unsmoked slab 3^2 IJ^ considers it possible that an abundant cheap source of levulic 



Thick unsmoked' sheet 386 2^ a^ij j^^y ^^ fg^^d in sawdust, and that the alcohol to be de- 

 Thin unsmoked sheet 394 3 rived would pay the cost of treatment. It has been estimated 



All estimates were made on the crepe prepared prior to vul- 'hat a ton of sawdust will give by Simousen's method, dilute sul- 



canization. Again no relation can be traced between the nitrogen P'"'"*^ ^"'^ ^' 8 atmospheres, 250 kilos of levulic acid, 



content and rate of vulcanization in the smoked rubber, and the I' '= PO'^'"*^ ^^""^ '^^"'"^ ^""^ '° derive .soprene; conse- 



differences are probably experimental errors. The unsmoked 1"^"*'^ " ^i" f^-'-''^'^ ^ synthetic rubber identical with natural 



rubbers, however, show a regularly increasing percentage of '•"''ber, and not one with unknown properties, 



nitrogen, with a decreasing rapidity of vulcanization. The VULCANIZING EXPERIMENTS, 



increase is not regular, however, the difference in nitrogen per- ^aton and Grantham have shown (The India Rubber World, 



centage between the two unsmoked slabs being much the March, 1916, page 289) how a particular method, which 



greatest. normally produces a uniform rubber with a very slow rate of 



The loss of nitrogen in the unsmoked rubber is probably ^u^g ^^^ inferior mechanical properties, can be altered so that 



due to decomposition of the protein, and the rapidity of vul- ^ rapidly curing rubber may be obtained possessing considerably 



canization appears to be associated with this decomposition. As superior physical properties after vulcanization, equal in fact 



far as the author is aware this relation between rapidity of jo the best samples of First latex rubbers. This is accomplished 



cure and low nitrogen content has not been recorded before, ^y allowing the coagulum to remain for about ten days before 



probably on account of the predominance of smoked rubbers jj undergoes the usual procedure for conversion into block, 



and crepes on the market, in which the relation is not apparent. Experimental results show that the rate of cure increases till 



Smoking has the effect of preventing the loss of nitrogen. It the sixth day, after which little or no change takes place. It 



does not, however, prevent a slab rubber developing a rapid j^as been established that it is perfectly safe to crepe the slab 



rate of vulcanization since the smoked slab cures in V/2 hours, ^fter ten days, since the change causing maximum rate of cure 



Hence it cannot be the actual loss of nitrogen which produces jj effected during this period. Examination of several old sam- 



rapidity of vulcanization. . ^ pigs of slab rubber indicate that the substance causing this ac- 



Experiments to determine at what stage in the preparation ggleration in rate of cure does not apparently decrease, 

 of slab rubber the nitrogen is lost showed that a large loss 



occurs when the slab is creped previous to vulcanization. It DETERMINING PROTEINS IN RUBBER, 



also appeared that most of this nitrogen is in such a form in A convenient method for the separation of the nitrogenous 



unsmoked slab that it is lost in the gaseous form when heated bodies contained in rubber has been perfected by Spence and 



to 212 degrees F. Kratz. 



Other experiments were carried out with fresh coagulum. A solution of rubber in benzene, chloroform or toluene when 



These showed a large loss of nitrogen during the drying of treated with acid loses viscosity. The decrease may reduce 



the slab. This is accounted for partly by the loss in the serum the viscosity to that of the solvent. At the same time the in- 



which drains away, and partly by the loss in the gaseous form soluble nitrogenous compounds in the rubber are precipitated and 



due to decomposition. readily separated. The reaction is hastened by sunlight or heat. 



The author summarizes his results as follows : The method has been applied to determinations on plantation 



In smoked rubbers from the same latex the nitrogen content and hard cure Para rubber. The results appear to demonstrate 



is constant, although the rate of vulcanization varies consider- that the insoluble nitrogenous residue found in rubber is not 



ably between slab and sheet. Smoking appears to fix the nitrogen, pure protein, but a complex of protein and carbohydrate, prob- 



In unsmoked rubbers from the same latex there is considerable ably a gluco-protein. The work of Spence and Kratz indicates 



